Dual 505 update
 

On Thu, 26 Feb 2015 20:09:31 +0000, Sumatriptan wrote:

On 16/02/2015 14:04, Sumatriptan wrote:
Yesterday, I got a Dual 505 on Ebay for £77.

Hi all,

More from a born again vinyl user..

When the tt arrived it was packed in the original Dual packing which
would have been fine, except the transit screws were not tightened and
the counterweight was left attached to the tone arm for transit. The 505
counterweight has a plastic stem, unlike later 505-x models. Sure
enough, it was broken and the weight was rattling around in the package.

The sender agreed to compensate me for purchase of a replacement if I
could locate one. A few messages at the Vinyl Engine forum resulted in
this:

http://www.dualfred.de/

Alfred and his wife who run this shop in Munich have a large stock of
apparently new Dual and Thorens turntable parts. I saw the exact part I
needed on their website. It took a week to arrive and the brand new
boxed part is labeled 'Original Dual Zubehor'

As I don't have a fully functional preamp and the main point of this
exercise is to get some/all of my collection digitised I decided to
obtain a Behringer phono-USB UFO202 interface to quickly get up and
running.

I haven't done a proper setup yet apart from tracking weight adjustment
to try out the tt for basic operation. All seems well so far, after a
listen via Audacity...except for one issue. There is significant mains
hum which I haven't tried to fix yet.

And that's where I'm at.


Now you have to look at the earth wiring.
There are almost certainly 4 wires to the cartridge, via headshell
connectors. When they leave the arm at the bottom, 2 of the wires become
L and R signals and the others become signal grounds. Note that none of
them must be connected to the chassis in any way whatsoever! The signal
grounds are only earthed in the amplifier.

Wire colours are probably:
Blue - outside - left channel ground
white - pin - left channel signal
Red - pin - right channel signal
Green - outside - right channel ground
To clean the connectors on the headshell try the eraser on a pencil.

The chassis *should* have a connection to mains earth for safety reasons
and that's all. This is sometimes via a separate wire to a screw terminal
on the preamp or amplifier.

Have fun... :)

Dual 505 update
 

Thanks all for comments.

Trevor, as per one of your suggestions...The biggest source of hum was
right channel RCA plug with screen intermittent O/C. Fixed that and
replaced both with gold plated versions while I was at it.

Java, I *like* a challenge so am happy to to chase hum. This tt has a 2
core mains lead, as expected, with the earthing being provided by a
earth wire connected to the pre-amp. Also, a continuity check showed
that the tone arm *is* isolated from the tt body, although a temporary
connection to it made no difference to the hum level.

Mick..thnks for cartridge wiring details, actually 5 wires including the
black earth wire from the tt metalwork to the headshell via the tone arm.

The hum level is now slight but perceptible at normal listening levels
in this room. Here's some figures from Audacity with record input set to
max for this test and tt connected to the phono-usb unit.

TT mains off, hum/noise RMS -60 dB
TT mains on, hum/noise RMS around -55 dB but varies a lot, see below.
Test track used at -20 dB RMS -6 dB peaks (not worried about headroom
for testing)
Motor on/off made no change.
Tone arm position gives no change.

Moving tt position in this office/workshop gave large, up to 15 dB,
changes in hum/noise. Maybe due to lots of mains wiring underfloor as
well as trailing extension leads to PCs etc. So...

I moved the tt to an acoustically and electrically quieter room and
tried it with my Pioneer amp (I had forgotten all about it in my earlier
posts). Result...hum not audible to me at normal listening levels.

Looks like my efforts will be aimed at finding somewhere in my office
that is electrically quiet for recording to PC. Or perhaps the problem
is with my phono-USB unit. Or the tt earthing which is getting to it via
UPS/power conditioning/PC chassis.

Comments please?

Dual 505 update
 

In article , Sumatriptan
wrote:

TT mains off, hum/noise RMS -60 dB TT mains on, hum/noise RMS around
-55 dB but varies a lot, see below. Test track used at -20 dB RMS -6 dB
peaks (not worried about headroom for testing) Motor on/off made no
change. Tone arm position gives no change.

Moving tt position in this office/workshop gave large, up to 15 dB,
changes in hum/noise. Maybe due to lots of mains wiring underfloor as
well as trailing extension leads to PCs etc. So...

Interesting that tone arm position had no effect but moving the entire unit
did. Did the move require changing the mains socket used?

Here I can measure changes in hum+noise level as the arm is moved, but I
can't compare that with what you get as I don't know the details of your
'test track'. The hum here is inaudible, though, regardless of where I play
the recordings or if I use speakers or headphones. cf below.

I moved the tt to an acoustically and electrically quieter room and
tried it with my Pioneer amp (I had forgotten all about it in my earlier
posts). Result...hum not audible to me at normal listening levels.

A complication is that how audible 'hum' may be will depend on more than
its simple measured level at the amp.

A) Depends on the room acoustics, speakers, etc. One room setup may make it
higher in level at the listener's ears than another.

B) Is the hum pure 50Hz? Or does it have a lot of harmonics? That can make
a big difference to audibility.

Check the spectrum of the 'hum' and the above. Otherwise there might be a
risk that you make recordings with the hum level 'sounding low' but then
hear it when you play the results back elsewhere.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

Hi Jim,


Interesting that tone arm position had no effect but moving the entire unit
did. Did the move require changing the mains socket used?


No, this was from a socket shared with the PC it was tried horizontally
and vertically within the radius of the 1.5M mains lead. Changing
sockets resulted in somewhat worse hum.

Here I can measure changes in hum+noise level as the arm is moved, but I
can't compare that with what you get as I don't know the details of your
'test track'. The hum here is inaudible, though, regardless of where I play
the recordings or if I use speakers or headphones. cf below.


Test track was from an acoustic guitar album from the 1980's to get a
ballpark volume setting.


not audible to me at normal listening levels.

A complication is that how audible 'hum' may be will depend on more than
its simple measured level at the amp.


I appreciate that.

A) Depends on the room acoustics, speakers, etc. One room setup may make it
higher in level at the listener's ears than another.


Agreed, all of the above were different. I'm just trying to determine
how big a problem it is for me and how much time/effort I should spend
on chasing it. All ultimately subjective :-)


B) Is the hum pure 50Hz? Or does it have a lot of harmonics? That can make
a big difference to audibility.


It is harmonic rich although the main component is 50Hz.


Check the spectrum of the 'hum' and the above.

Picture = 1000 words, see he

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

Notes
1) The spectrum was obtained before I normalised the audio track to
examine the waveform.

2) Hum is with mains on at tt, motor off, tonearm in resting position.

3) As explained, I can reduce the Audacity measured RMS hum level to
around -55dB in this room by repositioning...moving it around while
looking at the levels.



Otherwise there might be a
risk that you make recordings with the hum level 'sounding low' but then
hear it when you play the results back elsewhere.


I'm in no rush...I'll be making test recordings and trying them on other
systems before I spend too much effort on the 'real thing'.

Dual 505 update
 

On Wed, 04 Mar 2015 19:09:58 +0000, Sumatriptan
wrote:

Mick..thnks for cartridge wiring details, actually 5 wires including the
black earth wire from the tt metalwork to the headshell via the tone arm.

If you are prepared to lose the right to return the unit, I would say
detach that black lead from the TT metalwork and take it out the back
to the amp earth. Can you simply unscrew it, or would it be a matter
of cutting the connection? The former gives you some possibility of a
reversible test without losing the ability to return it, as long as
you're careful not to leave marks on the screw.

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

Notes
1) The spectrum was obtained before I normalised the audio track to
examine the waveform.

2) Hum is with mains on at tt, motor off, tonearm in resting position.

3) As explained, I can reduce the Audacity measured RMS hum level to
around -55dB in this room by repositioning...moving it around while
looking at the levels.

Wow, that's real dirty! I'm no expert at electronics, and would
always bow to the greater experience of those in this ng such as Jim,
but this suggests to me that this is not just a straightforward earth
loop problem.

My suspicions would now rest on the deck or the PC's PSU. It would be
useful to know:

1) Is the deck powered by a wall-wart or an inline unit and
low-voltage DC actually coming into the deck, or is it mains coming in
and its motor works directly off it? If the former, I'd suspect the
PSU.

2) What sort of PC is it? A desktop, or a laptop powered by a
wall-wart or inline unit as described for the deck? If the latter, I
had some weird my experiences comparing between using a laptop's
inline PSU and powered via its docking station, and would again
suspect the PSU:

"... I got the normal PSU for the laptop, and removed the
docking station. Big, big hum! Replaced the docking station. Back
to normal. Removed it again. Big, big hum! Replaced it again. Back
to normal.

I conclude that the DS has a decent PSU, while that supplied for the
laptop is crap."

If you want or need to read all of the original very long post
covering a wide range of points about digitising analogue sound
sources, including some concerning hum that I've already mentioned in
these recent posts in reply to you, the original post is he

Java Jive: ROT: PC Audio Recording & Playback (was: Holst and a
Headache), 6/12/11
https://groups.google.com/d/msg/uk.t...k/a7R64KmusM8J
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before closing time of 30/03/2015 23:59:

http://epetitions.direct.gov.uk/petitions/71556
================================================== =======
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Dual 505 update
 

If you are prepared to lose the right to return the unit, I would say
detach that black lead from the TT metalwork and take it out the back
to the amp earth.


Yes, that is on my list. Might try it disconnected completely as well.

Can you simply unscrew it, or would it be a matter
of cutting the connection?


Probably be an unsoldering job, but that's fine.


Wow, that's real dirty! I'm no expert at electronics, and would
always bow to the greater experience of those in this ng such as Jim,
but this suggests to me that this is not just a straightforward earth
loop problem.


Most are higher order harmonics of 50Hz mains but some change in level
and frequency over periods of seconds and minutes.

My suspicions would now rest on the deck or the PC's PSU. It would be
useful to know:


What do you mean by the 'deck'? The interface between tt and PC is a
single unit containing pre-amp and RIAA eq. and a ADC followed by a USB
interface. It is powered via the USB from the PC.

With tt input disconnected from the pre-amp front end, hum/noise is too
low to be measurable using Audacity. S/N ratio is given in the specs as
89 dB @1 kHz

1) Is the deck powered by a wall-wart or an inline unit and
low-voltage DC actually coming into the deck, or is it mains coming in
and its motor works directly off it? If the former, I'd suspect the
PSU.


Motor is mains. If this mains supply is disconnected the hum level falls
by about 5 dB


2) What sort of PC is it? A desktop, or a laptop powered by a
wall-wart or inline unit as described for the deck?


Desktop powered by mains.


Java Jive: ROT: PC Audio Recording & Playback (was: Holst and a
Headache), 6/12/11
https://groups.google.com/d/msg/uk.t...k/a7R64KmusM8J


I just had a quick skim and your mention of laptops reminded me that I
do have a laptop available that I could try on battery power.

I am aware of the headshell contact issues with this turntable so will
be looking at that when I get more time to play.

Dual 505 update
 

On Thu, 05 Mar 2015 00:55:31 +0000, Sumatriptan
wrote:

What do you mean by the 'deck'?

I meant how is the deck powered, by mains AC, or low-voltage DC from a
wall-wart or inlne PSU block, but you've answered that below.

The interface between tt and PC is a
single unit containing pre-amp and RIAA eq. and a ADC followed by a USB
interface. It is powered via the USB from the PC.

With tt input disconnected from the pre-amp front end, hum/noise is too
low to be measurable using Audacity. S/N ratio is given in the specs as
89 dB @1 kHz

So, that would seem to make it the actual deck then - nothing else
seems to fit the facts.

1) Is the deck powered by a wall-wart or an inline unit and
low-voltage DC actually coming into the deck, or is it mains coming in
and its motor works directly off it? If the former, I'd suspect the
PSU.


Motor is mains. If this mains supply is disconnected the hum level falls
by about 5 dB

Do you mean actually pulling the plug out of the wall, or just
switching off, which might leave the deck still attached to neutral?
(I can't remember for sure whether power-points have double-pole
switches, but I think not.)

That also suggests that the hum may have two, or more, sources, and by
doing that you are fixing a less important one.

2) What sort of PC is it? A desktop, or a laptop powered by a
wall-wart or inline unit as described for the deck?

Desktop powered by mains.

Wouldn't have expected problems with that, though ISTR that Jim thinks
PC PSUs are noisy, electrically-speaking. Nevertheless I've digitised
stuff via a SB Live soundcard on a standard, homebuilt PC without any
difficulty. However, thinking about it, that may mostly have been
using an optical input, as described in the previously linked post, or
another of around that time, and that of course wouldn't hum!

Java Jive: ROT: PC Audio Recording & Playback (was: Holst and a
Headache), 6/12/11
https://groups.google.com/d/msg/uk.t...k/a7R64KmusM8J


I just had a quick skim and your mention of laptops reminded me that I
do have a laptop available that I could try on battery power.

Certainly worth a try.

I am aware of the headshell contact issues with this turntable so will
be looking at that when I get more time to play.

Good luck.
--
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UK Residents: If you feel can possibly support it
please sign the following ePetition
before closing time of 30/03/2015 23:59:

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================================================== =======
Please always reply to ng as the email in this post's
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Dual 505 update
 

On 4/03/2015 3:57 AM, Sumatriptan wrote:
Thanks all for comments.

Trevor, as per one of your suggestions...The biggest source of hum was
right channel RCA plug with screen intermittent O/C. Fixed that and
replaced both with gold plated versions while I was at it.

Java, I *like* a challenge so am happy to to chase hum. This tt has a 2
core mains lead, as expected, with the earthing being provided by a
earth wire connected to the pre-amp. Also, a continuity check showed
that the tone arm *is* isolated from the tt body, although a temporary
connection to it made no difference to the hum level.

Mick..thnks for cartridge wiring details, actually 5 wires including the
black earth wire from the tt metalwork to the headshell via the tone arm.

The hum level is now slight but perceptible at normal listening levels
in this room. Here's some figures from Audacity with record input set to
max for this test and tt connected to the phono-usb unit.

TT mains off, hum/noise RMS -60 dB
TT mains on, hum/noise RMS around -55 dB but varies a lot, see below.
Test track used at -20 dB RMS -6 dB peaks (not worried about headroom
for testing)
Motor on/off made no change.
Tone arm position gives no change.

Moving tt position in this office/workshop gave large, up to 15 dB,
changes in hum/noise. Maybe due to lots of mains wiring underfloor as
well as trailing extension leads to PCs etc. So...

I moved the tt to an acoustically and electrically quieter room and
tried it with my Pioneer amp (I had forgotten all about it in my earlier
posts). Result...hum not audible to me at normal listening levels.

Looks like my efforts will be aimed at finding somewhere in my office
that is electrically quiet for recording to PC. Or perhaps the problem
is with my phono-USB unit. Or the tt earthing which is getting to it via
UPS/power conditioning/PC chassis.

Comments please?

**Brand and model of cartridge would be helpful.


--
Trevor Wilson
www.rageaudio.com.au

---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

Dual 505 update
 

In article , Java Jive
wrote:
On Wed, 04 Mar 2015 19:09:58 +0000, Sumatriptan
wrote:

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

Notes 1) The spectrum was obtained before I normalised the audio track
to examine the waveform.

2) Hum is with mains on at tt, motor off, tonearm in resting position.

3) As explained, I can reduce the Audacity measured RMS hum level to
around -55dB in this room by repositioning...moving it around while
looking at the levels.

Wow, that's real dirty! I'm no expert at electronics, and would always
bow to the greater experience of those in this ng such as Jim, but this
suggests to me that this is not just a straightforward earth loop
problem.

Yes, it certainly doesn't look like a neat 50Hz physical loop!


My suspicions would now rest on the deck or the PC's PSU.

Mine tend to be that the cartridge or its wiring are picking up stray
magnetic fields from currents elsewhere. i.e. that the coils in the
cartridge and its wiring are having currents inducted from nearby mains
wirings. This tends to be supported by finding that moving things around
alters the hum. But I don't know enough about the deck, etc, and can't
experiment from here.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

In article , Sumatriptan
wrote:


Most are higher order harmonics of 50Hz mains but some change in level
and frequency over periods of seconds and minutes.

Again, that seems like the cartridge and its wiring are acting like a
pickup for EM fields around them.

Is it possible for you to try something like a 10 Ohm resistor in series
with the deck's ground wire to the amp? And if you have a spare headshell,
try that with its wires open and then connected to make shorts?

No idea if that will help, but its the kind of experiment I'd try to get
some more info to think about.



Motor is mains. If this mains supply is disconnected the hum level falls
by about 5 dB

By "disconnected" do you mean 'pull plug from wall socket' or 'using the
switch on the deck'? Do they give different results?

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

In article , Java Jive
wrote:
Wouldn't have expected problems with that, though ISTR that Jim thinks
PC PSUs are noisy, electrically-speaking. Nevertheless I've digitised
stuff via a SB Live soundcard on a standard, homebuilt PC without any
difficulty. However, thinking about it, that may mostly have been using
an optical input, as described in the previously linked post, or another
of around that time, and that of course wouldn't hum!

The problem is that its a matter of chance what kind of PSU you get in a
computer. Some may be OK, others may be a disaster.

I just got a new machine to use as an 'AV' box with my new HDTV. The
supplier who put it together for me tried the standard PSU that comes with
the main box. Found it produced so much crap that it stopped wired ethernet
working! Changed to a different external brick, no problems.

FWIW I routinely now use a computer to record from LP, etc, and it works
fine. I could probably get the noise and hum down, but in practice it rises
as soon as the stylus hits a real LP anyway! So no point in doing so. pun
alert!

I do use an external USB ADC, though.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

On 05/03/2015 03:02, Trevor Wilson wrote:
On 4/03/2015 3:57 AM, Sumatriptan wrote:
Thanks all for comments.

Trevor, as per one of your suggestions...The biggest source of hum was
right channel RCA plug with screen intermittent O/C. Fixed that and
replaced both with gold plated versions while I was at it.

Java, I *like* a challenge so am happy to to chase hum. This tt has a 2
core mains lead, as expected, with the earthing being provided by a
earth wire connected to the pre-amp. Also, a continuity check showed
that the tone arm *is* isolated from the tt body, although a temporary
connection to it made no difference to the hum level.

Mick..thnks for cartridge wiring details, actually 5 wires including the
black earth wire from the tt metalwork to the headshell via the tone arm.

The hum level is now slight but perceptible at normal listening levels
in this room. Here's some figures from Audacity with record input set to
max for this test and tt connected to the phono-usb unit.

TT mains off, hum/noise RMS -60 dB
TT mains on, hum/noise RMS around -55 dB but varies a lot, see below.
Test track used at -20 dB RMS -6 dB peaks (not worried about headroom
for testing)
Motor on/off made no change.
Tone arm position gives no change.

Moving tt position in this office/workshop gave large, up to 15 dB,
changes in hum/noise. Maybe due to lots of mains wiring underfloor as
well as trailing extension leads to PCs etc. So...

I moved the tt to an acoustically and electrically quieter room and
tried it with my Pioneer amp (I had forgotten all about it in my earlier
posts). Result...hum not audible to me at normal listening levels.

Looks like my efforts will be aimed at finding somewhere in my office
that is electrically quiet for recording to PC. Or perhaps the problem
is with my phono-USB unit. Or the tt earthing which is getting to it via
UPS/power conditioning/PC chassis.

Comments please?

**Brand and model of cartridge would be helpful.



Sorry, thought I had already said. M55E with Dual adapter.

Dual 505 update
 

So, that would seem to make it the actual deck then - nothing else
seems to fit the facts.


Could be, see below regarding laptop test.



Motor is mains. If this mains supply is disconnected the hum level falls
by about 5 dB

Do you mean actually pulling the plug out of the wall,


Yes, unplugging.



That also suggests that the hum may have two, or more, sources, and by
doing that you are fixing a less important one.



A reduction of 5 dB is worth looking for. Subjectively, it reduces hum
from perceptible to only just perceptible on quiet passages under my
listening conditions here.

I would imagine that there are often multiple hum sources and the object
is to reduce/eliminate enough of them so that what remains is not a
problem to the listener (me).


I just had a quick skim and your mention of laptops reminded me that I
do have a laptop available that I could try on battery power.

Certainly worth a try.


I tried it with my laptop. With laptop PSU plugged in Audacity gave
exactly the same hum levels as with the desktop.

With laptop PSU unplugged the hum drops by about 6 dB. This is almost
identical to the drop in level when I unplug the turntable mains supply
when connected to desktop. At this lower level the turntable sounds very
quiet. (In this room, with these speakers...etc etc.)

(BTW, I've been calling this 'hum' but with components up to and beyond
3 kHz I know hum/noise is a better description)

Above makes me think the problem is earth loop related but I can't see
how, yet. Would be interesting to isolate the tt motor supply with a 1:1
transformer to see if that 'breaks the loop'. I may have one around
somewhere, would be good if it had an isolating screen...


I am aware of the headshell contact issues with this turntable so will
be looking at that when I get more time to play.

Good luck.


I would have expected a headshell contact problem to result in erratic
and rapid signal level changes or discrepancies in hum between channels
etc. Still, something to check if all else fails.

Thanks for the ideas.

Dual 505 update
 

On 05/03/2015 09:40, Jim Lesurf wrote:
In article , Sumatriptan
wrote:


Most are higher order harmonics of 50Hz mains but some change in level
and frequency over periods of seconds and minutes.

Again, that seems like the cartridge and its wiring are acting like a
pickup for EM fields around them.

Is it possible for you to try something like a 10 Ohm resistor in series
with the deck's ground wire to the amp? And if you have a spare headshell,
try that with its wires open and then connected to make shorts?

No idea if that will help, but its the kind of experiment I'd try to get
some more info to think about.


Yes, what is suggestive of EM pickup is the preponderance of higher
order components. As you will know, EM coupling is dependent on frequency.

Haven't tried the 10 Ohm resistor yet but pursuing the wiring EMC idea
has given an interesting result. I wondered if it was movement of the
phono leads and USB cable rather than tt itself that causes the
hum/noise levels to change. Maybe they were acting as the pickup
antenna. The Behringer interface USB lead is almost 2M long so I tried
'shortening' it. Not physically! I just sort of scrumbled it up so it
formed a quite small EM antenna.

Result....the hum level dropped by 5 dB and is now very close to
satisfactory when listening. For me :-)

Removing the mains supply to the turntable gives a further 5 dB
reduction and there may be a second hum source. Doing this gives a RMS
hum/noise level below the -60 dB 'floor' of the Audacity level meters.
Not sure if I need to achieve this but will be fun trying.

I'll do some more tests later.



Motor is mains. If this mains supply is disconnected the hum level falls
by about 5 dB

By "disconnected" do you mean 'pull plug from wall socket' or 'using the
switch on the deck'? Do they give different results?


Unplugging and switching off give the sane result...a 5 dB reduction as
mentioned above.

Dual 505 update
 

In article , Sumatriptan
wrote:
On 05/03/2015 09:40, Jim Lesurf wrote:
In article , Sumatriptan
wrote:

Is it possible for you to try something like a 10 Ohm resistor in
series with the deck's ground wire to the amp? And if you have a spare
headshell, try that with its wires open and then connected to make
shorts?

No idea if that will help, but its the kind of experiment I'd try to
get some more info to think about.


Yes, what is suggestive of EM pickup is the preponderance of higher
order components. As you will know, EM coupling is dependent on
frequency.

Yes. As a rule of thumb at these low frequencies I tend to expect it to
'differentiate' the signal, so leading to a rise in sensitivity
proportional to frequency. The currents on mains systems (and to a lesser
extent, the voltages) tend to pick up a wild set of harmonics due to the
way other PSUs around the place react. Hence the fairly hairy result that
looks nothing like a 50Hz sinewave! Alas, that makes the result much more
audible than a pure 50Hz tone. :-/


Haven't tried the 10 Ohm resistor yet but pursuing the wiring EMC idea
has given an interesting result. I wondered if it was movement of the
phono leads and USB cable rather than tt itself that causes the
hum/noise levels to change. Maybe they were acting as the pickup
antenna. The Behringer interface USB lead is almost 2M long so I tried
'shortening' it. Not physically! I just sort of scrumbled it up so it
formed a quite small EM antenna.

IIRC you're using one of the UCA series - i.e. in the same series as the
one I tested and reported on at

http://www.audiomisc.co.uk/HFN/ADC/USBrecording.html

but I can't recall if you're using one that includes the RIAA.

If you're not already doing so, you may get better results by using a
dedicated RIAA preamp and having longer coax leads from its output to the
Behringer. This would keep the fields from the Behringer and computer
further away from the low level signals from cartridge to RIAA preamp.

A problem with using the RIAA in the Behringer is that you'd have to use
longer signal leads at low level to move the unit away, and so that may not
help - or make things worse! Better to keep low-level signal leads short,
the snag being if that also moves the source of interference closer! catch
22.

FWIW I did some more recordings here this morning so can give some values
for reference. Here I get about -72 to -74 dB hum+noise before the needle
drops onto the LP. This is with the 0dB RIAA reference level at about
-15dB. So the nominal level of hum+noise is in the ballpark of -60
dB(RIAA). However the hum is almost pure 50Hz and some of the value is
noise over a wide band as I'm using a 96k sample rate. In practice, the
noise goes up as soon as the needle finds the groove. Dominated by LF
rumbles for the best LPs as the system goes down to below 10Hz.

Here this is with the 'PC' next to the deck and the ADC just under it. But
the 'PC's power supply is a brick down on the floor.

FWIW The RIAA preamp I use does have a 10 Ohm lift resistor in the
grounding. I found this made a measureable improvement in hum in most
circumstances of normal use.

Ignore the hum values given in handbooks and reviews. They tend to use a
weighting filter and reference level that is, erm, 'kind' compared with a
straight measurement like the above.

FWIW2 I've just been doing some theory estimates of thermal noise for other
reasons. (Comparing MM with MC as a result of a daft assertion in a
magazine! Old campaigners can probably guess the source given that the
assertion showed 'innocence' of the physics of thermal noise. :-) ) So in
context this is an interesting comparison between ideal world and reality.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

On 05/03/2015 14:01, Jim Lesurf wrote:


IIRC you're using one of the UCA series - i.e. in the same series as the
one I tested and reported on at

http://www.audiomisc.co.uk/HFN/ADC/USBrecording.html


I'm using a Behringer UFO202. Looks almost identical to the ones in your
review.

but I can't recall if you're using one that includes the RIAA.


Yes, I am.

If you're not already doing so, you may get better results by using a
dedicated RIAA preamp and having longer coax leads from its output to the
Behringer. This would keep the fields from the Behringer and computer
further away from the low level signals from cartridge to RIAA preamp.

A problem with using the RIAA in the Behringer is that you'd have to use
longer signal leads at low level to move the unit away, and so that may not
help - or make things worse! Better to keep low-level signal leads short,
the snag being if that also moves the source of interference closer! catch
22.


That was something I hadn't considered when getting the UFO 202 but moot
point for now, see below.

FWIW I did some more recordings here this morning so can give some values
for reference. Here I get about -72 to -74 dB hum+noise before the needle
drops onto the LP. This is with the 0dB RIAA reference level at about
-15dB. So the nominal level of hum+noise is in the ballpark of -60
dB(RIAA).
However the hum is almost pure 50Hz and some of the value is
noise over a wide band as I'm using a 96k sample rate. In practice, the
noise goes up as soon as the needle finds the groove. Dominated by LF
rumbles for the best LPs as the system goes down to below 10Hz.

Here this is with the 'PC' next to the deck and the ADC just under it. But
the 'PC's power supply is a brick down on the floor.

FWIW The RIAA preamp I use does have a 10 Ohm lift resistor in the
grounding. I found this made a measureable improvement in hum in most
circumstances of normal use.


I tried a 10 Ohm resistor and it did give a small reduction of around 1
dB according to Audacity, so I will keep it. Every bit helps.

I also tried an (enormous 500VA) isolating transformer in the turntable
mains feed and this reduced the hum by quite a large amount.

Total reduction in hum from the 3 changes: ground lift, shielded
isolation transformer and electrically shortened turntable leads amounts
to around 10 dB overall reduction of the 50Hz component. The isolation
transformer contributed much larger reductions of the more troublesome
higher order harmonics and general hash. Some were eliminated entirely.
Compare the original he

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

With this:

http://www.nu-ware.com/Misc/Screenshots/Dual505B.png


FWIW2 I've just been doing some theory estimates of thermal noise for other
reasons. (Comparing MM with MC as a result of a daft assertion in a
magazine! Old campaigners can probably guess the source given that the
assertion showed 'innocence' of the physics of thermal noise. :-) ) So in
context this is an interesting comparison between ideal world and reality.


Reality wins out, every time :-)

My last tussle with thermal noise was modification of a ccd (not cmos)
camera for astronomical use. Peltier chips for refrigeration of the ccd,
image stacking to average out thermal noise etc. etc.

I'm happy with the Dual 505 hum level for now and will be moving on to a
workout of my test LP. No doubt I will be pestering you all with more
questions. Thank you so much all for your ideas and comments so far,
Jim, Java, Trevor, Mick.

Dual 505 update
 

On Wed, 04 Mar 2015 19:09:58 +0000, Sumatriptan
wrote:

Hi Jim,


Interesting that tone arm position had no effect but moving the entire unit
did. Did the move require changing the mains socket used?


No, this was from a socket shared with the PC it was tried horizontally
and vertically within the radius of the 1.5M mains lead. Changing
sockets resulted in somewhat worse hum.

Here I can measure changes in hum+noise level as the arm is moved, but I
can't compare that with what you get as I don't know the details of your
'test track'. The hum here is inaudible, though, regardless of where I play
the recordings or if I use speakers or headphones. cf below.


Test track was from an acoustic guitar album from the 1980's to get a
ballpark volume setting.


not audible to me at normal listening levels.

A complication is that how audible 'hum' may be will depend on more than
its simple measured level at the amp.


I appreciate that.

A) Depends on the room acoustics, speakers, etc. One room setup may make it
higher in level at the listener's ears than another.


Agreed, all of the above were different. I'm just trying to determine
how big a problem it is for me and how much time/effort I should spend
on chasing it. All ultimately subjective :-)


B) Is the hum pure 50Hz? Or does it have a lot of harmonics? That can make
a big difference to audibility.


It is harmonic rich although the main component is 50Hz.


Check the spectrum of the 'hum' and the above.

Picture = 1000 words, see he

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

Wow! That's impressively rich in HF harmonics which suggests the use
of an unscreened[1] transformer for powering the RIAA pre-amp[2]
allowing capacitive coupling of the higher frequency harmonics and
noise to dominate the mains hum interference.

The actual plot of the waveform bears absolutely no resemblence to
what I see via cheap 6v ac wallwart transformer used to supply a
nominal 1v level sampling of the mains via a simple resistive
attenuator for feeding into the line input of a laptop for comparitive
measurements between the real mains and a petrol generator I foolishly
thought would make a good IT kit standby supply a few years ago.

The resulting waveform in CoolEdit's window looked indistinguishable
from an oscilloscope's trace of its own mains derived 1v Pk2Pk
'calibration source' which quite clearly showed that the mains was far
from being a pure sinewave (essentially it looked like a sinewave with
the tops slightly but most definitely clipped with a slight downward
tilt to the 'flat tops' on the positive peaks and vice versa for the
negative peaks.

When I first observed this nearly two decades ago, I just assumed it
was an effect of the transformer. It was only much later when I
repeated the test with a SmartUPS2000 in line that I discovered this
was not so since the waveform of the UPS looked a perfect example of a
sinewave, except for some very low level sample switching artifacts
(around the 5KHz mark afaicr).


Notes
1) The spectrum was obtained before I normalised the audio track to
examine the waveform.

2) Hum is with mains on at tt, motor off, tonearm in resting position.

3) As explained, I can reduce the Audacity measured RMS hum level to
around -55dB in this room by repositioning...moving it around while
looking at the levels.



Otherwise there might be a
risk that you make recordings with the hum level 'sounding low' but then
hear it when you play the results back elsewhere.


I'm in no rush...I'll be making test recordings and trying them on other
systems before I spend too much effort on the 'real thing'.


[1] I'm referring to the inter-winding screen not a whole transformer
shield which would typically be either mu-metal or soft iron unless a
toroidal transformer is being used to make such magnetic screening
totally redundent as I well know from experience.

[2] I've assumed you're using an RIAA pre-amp of some sort in the TT
itself (quite honestly _the_ only place to do the RIAA
pre-amplification).

You'll have enough trouble competing against the millivolt or so of
mains hum at line levels even when the equalised cartridge signal is
safely boosted into the volts range in the hum loop free environment
of the confnes of the TT itself before it has to bully its way past
the hum loop afflicted line level interconnection to the main amp's
auxilliary input.

Unless you take extreme measures to eliminate hum loop noise, feeding
the cartidge output directly to the phono input of the main amp via a
yard or so of high quality screened cable often leaves you on a hiding
to nothing.

Mention of "high quality screened cable" reminds me of another
possible reason for the predominence of HF harmonics and other noise
in your test signal. Some, so called screened cable can have very poor
screening, in some cases just 3 or 4 strands spiral wrapped around the
signal wire, which makes them very prone to pick up electric fields
radiated by nearby (and sometimes, not so nearby) mains wiring around
the room. I'd certainly be examining the 'screened' cabling very
closely if I were in your current predicament (not forgetting that
phono plugs can fail to make a proper earth return connection in the
socket which can also produce the same symptoms).
--
J B Good

Dual 505 update
 

Johny B Good wrote:


Mention of "high quality screened cable" reminds me of another
possible reason for the predominence of HF harmonics and other noise
in your test signal. Some, so called screened cable can have very poor
screening, in some cases just 3 or 4 strands spiral wrapped around the
signal wire, which makes them very prone to pick up electric fields
radiated by nearby (and sometimes, not so nearby) mains wiring around
the room.


** Gotta back you up on that one.

Typical light gauge RCA leads from China have no screening at all - the insulated inner core simply runs parallel with bare copper strands up one side of the core.

The only thing they are good for is low impedance, line level signals with the proviso you never run them alongside speaker wires.

Plus, some of the heavy gauge RCA leads are little better, having only a thick outer cover and much the same inside as the light gauge ones.

I expect you will have to pay a fair old price to get decent quality, woven shield, low capacitance RCA leads that are suitable for connection of a MM or MC phono cartridge to an RIAA stage.

When repairing guitar amps, the leads to and from the Reverb Tank can need replacing and the cheap Chines ones are a disaster - producing loud buzzing hum and even high frequency oscillation if installed in the back of a combo amp.



..... Phil

Dual 505 update
 

In article , Sumatriptan
wrote:

I tried a 10 Ohm resistor and it did give a small reduction of around 1
dB according to Audacity, so I will keep it. Every bit helps.

I also tried an (enormous 500VA) isolating transformer in the turntable
mains feed and this reduced the hum by quite a large amount.

Total reduction in hum from the 3 changes: ground lift, shielded
isolation transformer and electrically shortened turntable leads amounts
to around 10 dB overall reduction of the 50Hz component. The isolation
transformer contributed much larger reductions of the more troublesome
higher order harmonics and general hash. Some were eliminated entirely.
Compare the original he

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

With this:

http://www.nu-ware.com/Misc/Screenshots/Dual505B.png

Interesting. What has struck me is how much your initial 'dirty' hum looks
a lot like the kind of pickup you can get simply by touching the probe of a
high impedance scope input.

I'm wondering if in Germany[1] the domestic mains system doesn't have the
UK's 'unbalanced' line-neutral. i.e. the 505 isn't designed to cope with a
situation where the line and neutral return both have non zero voltages but
with values that differ. I'm also wondering of you have a fair bit of 'dc'
on your mains. That can upset mains transformers that aren't well specified
and enhance hum harmonics.

Many years ago I went though a period where I and others at Armstrong took
home a wooden board and assorted transformers each night to try them out
and assess the *mechanical* buzz they made when presented with mains power
waveform/size/line-neutral imbalance, etc. They varies a lot from one
design to another, and from place to place and time to time. Alas, many
transformer makers seemed to have no interest in this. Ditto for good
sheilding.

cf comments in another posting.

Jim

[1] I'm assuming Dual is German, but my memory may be wrong here as I've
never used or owned one.

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

In article , Johny B Good
wrote:

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

Wow! That's impressively rich in HF harmonics which suggests the use
of an unscreened[1] transformer for powering the RIAA pre-amp[2]
allowing capacitive coupling of the higher frequency harmonics and
noise to dominate the mains hum interference.

Yes. It may also be that the transformer has a noticable external magnetic
field. I've come across mains transformers where you had to rotate the
transformer to find a 'minimum hum pickup' for nearby wires because of
external fields.



[2] I've assumed you're using an RIAA pre-amp of some sort in the TT
itself (quite honestly _the_ only place to do the RIAA
pre-amplification).

I think he's using the RIAA inside the Behringer - which is powered via the
5v line of its USB connection.

Which makes me wonder if it would also be wise to try using that via a
decent USB hub with its own external power. I've had problems with other
USB ADCs for such reasons. Not as bad as reported here, but then I only
used line level inputs not RIAA.

Echo the comments about choice of cable. But if changing this keep in mind
that the cable capacitance also matters for MM cartridges.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

In article ,
Phil Allison wrote:
Typical light gauge RCA leads from China have no screening at all - the
insulated inner core simply runs parallel with bare copper strands up
one side of the core.

The only thing they are good for is low impedance, line level signals
with the proviso you never run them alongside speaker wires.

Plus, some of the heavy gauge RCA leads are little better, having only a
thick outer cover and much the same inside as the light gauge ones.

I expect you will have to pay a fair old price to get decent quality,
woven shield, low capacitance RCA leads that are suitable for connection
of a MM or MC phono cartridge to an RIAA stage.

You're right there. And, of course, the only way to find out with moulded
on plugs is to cut one off.

Ages ago a bought 100 metres of good quality braided screen low
capacitance audio co-ax from RS. Even buying decent phono plugs, still
works out cheaper than buying ready made - and know what you're getting.

Standard impedance cartridges are just about the only thing on a Hi-Fi
were the connecting leads can make an audible difference, even under
normal circumstances.

--
*Why don't you ever see the headline "Psychic Wins Lottery"?

Dave Plowman London SW
To e-mail, change noise into sound.

Dual 505 update
 

On 06/03/2015 09:41, Jim Lesurf wrote:


Interesting. What has struck me is how much your initial 'dirty' hum looks
a lot like the kind of pickup you can get simply by touching the probe of a
high impedance scope input.


I think it is the same mechanism....pickup of stray fields from house
wiring etc.


I'm wondering if in Germany[1] the domestic mains system doesn't have the


Yes, Dual is German. They are still making turntables.

UK's 'unbalanced' line-neutral. i.e. the 505 isn't designed to cope with a
situation where the line and neutral return both have non zero voltages but
with values that differ. I'm also wondering of you have a fair bit of 'dc'
on your mains. That can upset mains transformers that aren't well specified
and enhance hum harmonics.


I just checked with a DC meter and it reads zero across the mains. What
is 'different' here is that the mains is via overhead line and is a PME
system. So the earth isn't a real earth, it is bonded to the neutral
conductor at the meter.

Dual 505 update
 

In article , Sumatriptan
wrote:
On 06/03/2015 09:41, Jim Lesurf wrote:


Interesting. What has struck me is how much your initial 'dirty' hum
looks a lot like the kind of pickup you can get simply by touching the
probe of a high impedance scope input.


I think it is the same mechanism....pickup of stray fields from house
wiring etc.

Ok. That isn't an 'earth loop' in the way the term is normally used. This
kind of pickup can happen in systems with a single earth path. In effect,
your arm/deck wiring and the cartridge become a field-probe.

Ideally the metal arm and body of the deck would act as a shield to some
extent. Hence the use of a separate ground wire from the deck to do that
and keep any resulting currents away from the signal ground. But for that
to work you rely on the construction of the deck, arm, etc being
appropriate.

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

In article ,
Bob Latham wrote:
Standard impedance cartridges are just about the only thing on a Hi-Fi
were the connecting leads can make an audible difference, even under
normal circumstances.

OK, I'll bite.

Speaker cables are *often* audibly different from one another.

Yes, you could make a speaker cable which sounded different. But why would
you?

If you cannot here this I would give give very similar suggestions as to
someone who said (and many do) that they cannot tell the difference
between HD and SD tv.

Do they? Can't say I know anyone who can't see the difference between SD
and HD - provided it's an HD signal which is being transmitted.

God knows I should know better that to say this on this group but I can't
help it if you're all deaf or much more likely never tried it much, if at
all. After all, the theory says its not audible so why bother trying it.

Tin hat on, I'm ready.

The answer is simple. If you can reliably tell the difference between
adequately specified cables in a proper test, you'd have a point. But
no-one ever has been able to.

--
*You! Off my planet!

Dave Plowman London SW
To e-mail, change noise into sound.

Dual 505 update
 

In article , Dave Plowman (News)
wrote:
The answer is simple. If you can reliably tell the difference between
adequately specified cables in a proper test, you'd have a point. But
no-one ever has been able to.

That pretty much sums up my state of mind on this. For *decades* a large
cash 'prize' was on offer for trying in conditions that seemed perfectly
reasonable to me. The snag was that *none* of those saying the differences
were 'obvious', etc, would take the test. Not one. It was made clear that
it wasn't a 'bet' and they didn't have to pay anything if they couldn't
tell the cables apart in the test. So all they would have 'lost' would have
been some time and the risk of looking mistaken if they hadn't been able to
show they could tell a difference. But no triers at all. So no progress.

For some it might have been inconvenient to go and put in the time. But
that does get a bit shakey as the reason when so many made the claim but
*none* of them took the test. And if they "didn't care what others think",
why say the difference was so clear and obvious in the first place?

I'm still waiting, but I guess that by now the people who put up the cash
have wandered away and are doing something else because no-one would even
try.

I'm quite happy to accept others can hear things that pass me by. But
where's the beef?

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Dual 505 update
 

In article ,
Jim Lesurf wrote:
I'm quite happy to accept others can hear things that pass me by. But
where's the beef?

I'm happy to accept others may hear things differently too. But then you
get comments like 'you must be deaf if you can't hear the difference I
can'. In which case it should be easy to identify the 'better' cable
without seeing what is in use.

Of course having spent a lot of money on new cables - obviously expecting
them to be better otherwise why bother - its easy to convince yourself
there is a difference.

Seems the cash prize may still be on offer:-

http://gizmodo.com/305549/james-rand...les-are-better

--
*Why don't you ever see the headline "Psychic Wins Lottery"?

Dave Plowman London SW
To e-mail, change noise into sound.

Dual 505 update
 

On 06/03/2015 12:50, Jim Lesurf wrote:
In article , Sumatriptan
wrote:
On 06/03/2015 09:41, Jim Lesurf wrote:


Interesting. What has struck me is how much your initial 'dirty' hum
looks a lot like the kind of pickup you can get simply by touching the
probe of a high impedance scope input.


I think it is the same mechanism....pickup of stray fields from house
wiring etc.

Ok. That isn't an 'earth loop' in the way the term is normally used. This
kind of pickup can happen in systems with a single earth path. In effect,
your arm/deck wiring and the cartridge become a field-probe.

Ideally the metal arm and body of the deck would act as a shield to some
extent. Hence the use of a separate ground wire from the deck to do that
and keep any resulting currents away from the signal ground. But for that
to work you rely on the construction of the deck, arm, etc being
appropriate.


Understood. Perhaps this explains why adjusting positions of any
attached leads varies the hum level. I did some more adjustments of the
phono leads and the turntable mains lead and have achieved a setup where
audible hum is completely overwhelmed by surface noise as soon as stylus
contacts vinyl. Here's a pic:

http://www.nu-ware.com/Misc/Screenshots/Dual505C.png

Left spectrum is hum, motor running, stylus up.
Right spectrum is stylus down on lead-in before audio starts.
Waveform display normalised to -1.0 dB after spectrum analysis.


Being a pragmatic soul, I'll settle for that.

Dual 505 update
 

On Fri, 06 Mar 2015 09:48:36 +0000 (GMT), Jim Lesurf
wrote:

In article , Johny B Good
wrote:

http://www.nu-ware.com/Misc/Screenshots/Dual505A.png

Wow! That's impressively rich in HF harmonics which suggests the use
of an unscreened[1] transformer for powering the RIAA pre-amp[2]
allowing capacitive coupling of the higher frequency harmonics and
noise to dominate the mains hum interference.

Yes. It may also be that the transformer has a noticable external magnetic
field. I've come across mains transformers where you had to rotate the
transformer to find a 'minimum hum pickup' for nearby wires because of
external fields.



[2] I've assumed you're using an RIAA pre-amp of some sort in the TT
itself (quite honestly _the_ only place to do the RIAA
pre-amplification).

I think he's using the RIAA inside the Behringer - which is powered via the
5v line of its USB connection.

One possible workaround, using such an RIAA USB ADC, is to fit it
into the TT itself, along with a USB B socket and either locally
supply the 5v from an analogue PSU using a small toroidal mains
transformer or quality Mu-metal screened (with interwinding foil
shielding connected to the local ground return point of the amplifier)
or else a battery sourced 5v supply. You might actually get away with
using the 5v from the USB host but, since you already have a mains
feed for the TT motor, it's best to avoid use of the host supplied 5v
feed.


Which makes me wonder if it would also be wise to try using that via a
decent USB hub with its own external power. I've had problems with other
USB ADCs for such reasons. Not as bad as reported here, but then I only
used line level inputs not RIAA.

Echo the comments about choice of cable. But if changing this keep in mind
that the cable capacitance also matters for MM cartridges.


Surely, you must have meant Moving iron or variable reluctance
cartridges with a notional 47K ohms impedance where this does actually
matter rather than the very low impedance MM types, typically 10 to 30
ohm impedance, which even several hundred pF's worth won't disturb in
the slightest.
--
J B Good

Dual 505 update
 

Johny B Good wrote:


One possible workaround, using such an RIAA USB ADC, is to fit it
into the TT itself, along with a USB B socket and either locally
supply the 5v from an analogue PSU using a small toroidal mains
transformer or quality Mu-metal screened (with interwinding foil
shielding connected to the local ground return point of the amplifier)
or else a battery sourced 5v supply.


** There are no Mu-metal shielded mains transformers.
Normally, a copper strap around the outside suffices or a wrap made from transformer steel or simply a steel box.

Don't think Mu-metal can be used, as inrush surges and saturation of the core would likely cause the material to become magnetised.


Echo the comments about choice of cable. But if changing this keep in mind
that the cable capacitance also matters for MM cartridges.


Surely, you must have meant Moving iron or variable reluctance
cartridges with a notional 47K ohms impedance where this does actually
matter rather than the very low impedance MM types, typically 10 to 30
ohm impedance, which even several hundred pF's worth won't disturb in
the slightest.

** MM = moving magnet, the most common type of magnetic PU cartridge.

Most have about 500 to 700 ohms DC resistance, 0.5H of inductance and a recommended load of 47kohms in parallel with 250pF.

Moving coil ( MC ) cartridges have low resistances, generally from about 1ohm to 30ohms.



.... Phil

Dual 505 update
 

In article , Johny B Good
wrote:

Echo the comments about choice of cable. But if changing this keep in
mind that the cable capacitance also matters for MM cartridges.


Surely, you must have meant Moving iron or variable reluctance
cartridges with a notional 47K ohms impedance where this does actually
matter rather than the very low impedance MM types, typically 10 to 30
ohm impedance, which even several hundred pF's worth won't disturb in
the slightest.

Erm... Its normal to refer to moving iron or variable reluctance as 'MM' or
moving magnet as a class to distinguish them from MC or moving coil.

As Phil has pointed out MMs tend to have coil resistances much higher than
the "10 to 30" you state. I've just been doing some stats on this for
reasons I mentioned a while ago. And again as he says, the load capacitance
affects MMs and the makers tend to recommend values. (I've only found one
or two MC with recommended load capacitances. These being above 1 *micro*
Farad because their coil inductance is so small.)

FWIW since I did go though old reviews to collate values I can give some
results he

http://jcgl.orpheusweb.co.uk/temp/trans.png

shows the sensitivity and coil resistance (not the recommended loading)
of some MM and MC examples. It also shows the effect of using an x10 or
x20 voltage step-up transformer with the MCs.


Perhaps you're confusing the recommended *loading* with the actual
cartridge impedances, and saying MM when you mean MC?

Jim

--
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Dual 505 update
 

On 07/03/2015 01:58, Johny B Good wrote:

One possible workaround, using such an RIAA USB ADC, is to fit it
into the TT itself, along with a USB B socket and either locally
supply the 5v from an analogue PSU using a small toroidal mains
transformer or quality Mu-metal screened (with interwinding foil
shielding connected to the local ground return point of the amplifier)
or else a battery sourced 5v supply. You might actually get away with
using the 5v from the USB host but, since you already have a mains
feed for the TT motor, it's best to avoid use of the host supplied 5v
feed.


Makes sense, but I don't think it is the 5v USB feed causing the
problem. I'm now convinced it is stray field pickup due to the poor
quality, long phono leads. I tried 'shortening' the leads by wrapping
them into a small volume and the hum level reduced considerably. That
workaround plus the isolating transformer in the motor 50Hz feed has
given this result:

http://www.nu-ware.com/Misc/Screenshots/Dual505C.png

Left spectrum is motor running, stylus raised. Right spectrum is stylus
lowered into the lead-in groove. Hum is now considerably lower than
vinyl surface noise.

The waveform shows the (normalised to -1 dB) signal before/after the
stylus contacts the lead-in and before any audio is played.

I consider this to be good enough for my needs since I can't hear any
hum with this workaround, even at higher than normal listening levels.


Surely, you must have meant Moving iron or variable reluctance
cartridges with a notional 47K ohms impedance where this does actually
matter rather than the very low impedance MM types, typically 10 to 30
ohm impedance, which even several hundred pF's worth won't disturb in
the slightest.


See my reply to Phil.

Dual 505 update
 

On 07/03/2015 04:02, Phil Allison wrote:


** MM = moving magnet, the most common type of magnetic PU cartridge.

Most have about 500 to 700 ohms DC resistance, 0.5H of inductance and a recommended load of 47kohms in parallel with 250pF.

Moving coil ( MC ) cartridges have low resistances, generally from about 1ohm to 30ohms.


Spot on. Cartridge I'm using is MM, a M55E. According to Shure spec DC
resistance = 630 Ohms, inductance = 730 mH preferred load = 47k Ohms,
and about 400 pF

Which led me he
http://www.tnt-audio.com/sorgenti/lo...magnets_e.html

Dual 505 update
 

In article ,
Sumatriptan wrote:
I'm now convinced it is stray field pickup due to the poor
quality, long phono leads. I tried 'shortening' the leads by wrapping
them into a small volume and the hum level reduced considerably. That
workaround plus the isolating transformer in the motor 50Hz feed has
given this result:

If it's hum pickup in the cables, you can usually prove this by moving
them, and see if it changes.

--
*He who laughs last, thinks slowest.

Dave Plowman London SW
To e-mail, change noise into sound.

Dual 505 update
 

On Fri, 6 Mar 2015 20:02:38 -0800 (PST), Phil Allison
wrote:

Johny B Good wrote:


One possible workaround, using such an RIAA USB ADC, is to fit it
into the TT itself, along with a USB B socket and either locally
supply the 5v from an analogue PSU using a small toroidal mains
transformer or quality Mu-metal screened (with interwinding foil
shielding connected to the local ground return point of the amplifier)
or else a battery sourced 5v supply.


** There are no Mu-metal shielded mains transformers.
Normally, a copper strap around the outside suffices or a wrap made from transformer steel or simply a steel box.

Don't think Mu-metal can be used, as inrush surges and saturation of the core would likely cause the material to become magnetised.


Echo the comments about choice of cable. But if changing this keep in mind
that the cable capacitance also matters for MM cartridges.


Surely, you must have meant Moving iron or variable reluctance
cartridges with a notional 47K ohms impedance where this does actually
matter rather than the very low impedance MM types, typically 10 to 30
ohm impedance, which even several hundred pF's worth won't disturb in
the slightest.

** MM = moving magnet, the most common type of magnetic PU cartridge.

Most have about 500 to 700 ohms DC resistance, 0.5H of inductance and a recommended load of 47kohms in parallel with 250pF.

Moving coil ( MC ) cartridges have low resistances, generally from about 1ohm to 30ohms.



Drat! I misread (Gawd knows why!) MM as MC. Yeah, Moving Magnet is in
the same class as Moving Iron / variable reluctance which allows for a
stronger magnetic flux without trying to move a relatively heavy
magnet around, along with the luxury of static windings with enough
turns of wire to generate higher voltages into more sane load
impedances, notwithstanding the necessity to aim for a preferred
capacitive loading to help hold up the frequency response at the high
end by making use of the resulting high inductance of the pickup coil
windings to provide a rather damped LC parallel resonance voltage
magnification effect.

Modern MM carts using today's wonder rare earth Neodium magnets would
probably compete well against variable reluctance designs in terms of
both output sensitivity and transient response.

Apologies to Jim for picking up on an a non-error.

Obviously I was referring to MC types with my low impedance remarks.
I just misread MM as MC and failed to realise the error even when
typing the response. :-(
--
J B Good

Dual 505 update
 

On Sat, 07 Mar 2015 09:48:56 +0000 (GMT), Jim Lesurf
wrote:

In article , Johny B Good
wrote:

Echo the comments about choice of cable. But if changing this keep in
mind that the cable capacitance also matters for MM cartridges.


Surely, you must have meant Moving iron or variable reluctance
cartridges with a notional 47K ohms impedance where this does actually
matter rather than the very low impedance MM types, typically 10 to 30
ohm impedance, which even several hundred pF's worth won't disturb in
the slightest.

Erm... Its normal to refer to moving iron or variable reluctance as 'MM' or
moving magnet as a class to distinguish them from MC or moving coil.

As Phil has pointed out MMs tend to have coil resistances much higher than
the "10 to 30" you state. I've just been doing some stats on this for
reasons I mentioned a while ago. And again as he says, the load capacitance
affects MMs and the makers tend to recommend values. (I've only found one
or two MC with recommended load capacitances. These being above 1 *micro*
Farad because their coil inductance is so small.)

FWIW since I did go though old reviews to collate values I can give some
results he

http://jcgl.orpheusweb.co.uk/temp/trans.png

shows the sensitivity and coil resistance (not the recommended loading)
of some MM and MC examples. It also shows the effect of using an x10 or
x20 voltage step-up transformer with the MCs.


Perhaps you're confusing the recommended *loading* with the actual
cartridge impedances, and saying MM when you mean MC?

This last bit, conflating MM as MC (in my mind) as you may already
have seen in my previous reply to Phil's post[1], is the error I'm
totally guilty of. Once you translate my use of MM as MC, my post then
makes perfect sense (other than for the fact that it was a pointless
response to yours).

[1] In my embarassed response to the mistake so eloquently picked up
by Phil, I overlooked his remarks about transformer shielding.

Mu-metal shielding _is_ sometimes employed, not internally but as a
total shroud around the transformer to screen magnetically sensitive
components from the inevitable stray leakage flux of classic E&I (T&U)
cored designs.

In this case, the flux levels are only a tiny fraction of that which
links the windings so doesn't represent a saturation risk to the
Mu-metal[2]. Although it can slightly mag up the Mu-metal or soft
steel often used as a cheaper substitute, this permanent magnetism
isn't a problem to nearby pickup coils (tape heads and phono
cartridges) which, in any case, is confined to the screening material
used, whether it be Mu-metal or soft steel.

Toroidal transformers otoh, so effectively confine their magnetic
flux, they don't normally require any such screening, not even when
placed inside the confines of an IBM 14 inch CRT monitor originally
designed for 120v mains in order to convert it to 240v mains. A feat
not possible with a conventional transformer even when placed outside
of said monitor if not a good 60 cms or more away as I discovered two
decades back.

[2] Is Mu-metal any worse than soft iron for self magnetisation? If
so, it seems a strange choice for the pole pieces of magnetic
replay/recording heads, especially since it has such poor wear
properties.
--
J B Good

Dual 505 update
 

On Sat, 07 Mar 2015 09:58:59 +0000, Sumatriptan
wrote:

On 07/03/2015 01:58, Johny B Good wrote:

One possible workaround, using such an RIAA USB ADC, is to fit it
into the TT itself, along with a USB B socket and either locally
supply the 5v from an analogue PSU using a small toroidal mains
transformer or quality Mu-metal screened (with interwinding foil
shielding connected to the local ground return point of the amplifier)
or else a battery sourced 5v supply. You might actually get away with
using the 5v from the USB host but, since you already have a mains
feed for the TT motor, it's best to avoid use of the host supplied 5v
feed.


Makes sense, but I don't think it is the 5v USB feed causing the
problem. I'm now convinced it is stray field pickup due to the poor
quality, long phono leads. I tried 'shortening' the leads by wrapping
them into a small volume and the hum level reduced considerably. That
workaround plus the isolating transformer in the motor 50Hz feed has
given this result:

I concur with your analysis on the source of the noise being a matter
of poor electric screening rather than hum loop problems. I only
suggested isolating the 5v USB power feed if the RIAA equalised ADC
were to be installed in the deck itself as a means of guarding against
the possibility of other computers with noisier supplies being used in
the future (after all, the deck will have an existing supply of mains
voltage by which to power a noise free analogue source of the required
5 volts).


http://www.nu-ware.com/Misc/Screenshots/Dual505C.png

Left spectrum is motor running, stylus raised. Right spectrum is stylus
lowered into the lead-in groove. Hum is now considerably lower than
vinyl surface noise.

The waveform shows the (normalised to -1 dB) signal before/after the
stylus contacts the lead-in and before any audio is played.

I consider this to be good enough for my needs since I can't hear any
hum with this workaround, even at higher than normal listening levels.

It looks like you've cracked the problem then. You'll probably just
need to rewire using quality cable and connectors to convert your
'workaround' solution into a permanent fix.



Surely, you must have meant Moving iron or variable reluctance
cartridges with a notional 47K ohms impedance where this does actually
matter rather than the very low impedance MM types, typically 10 to 30
ohm impedance, which even several hundred pF's worth won't disturb in
the slightest.


See my reply to Phil.

As I've already stated. I made a mistake in misreading MM as MC (with
apologies to Jim for picking up a non-mistake). Likewise apologies all
round to anyone thinking "This Granny needed to be taught how to suck
eggs."

I don't need egg sucking lessons so much as 'comprehension' and "not
misinterpreating what others type" lessons. :-( Gah!
--
J B Good

Dual 505 update
 

Johny B Good wrote:


[1] In my embarassed response to the mistake so eloquently picked up
by Phil, I overlooked his remarks about transformer shielding.

Mu-metal shielding _is_ sometimes employed, not internally but as a
total shroud around the transformer to screen magnetically sensitive
components from the inevitable stray leakage flux of classic E&I (T&U)
cored designs.


** Sometimes = extremely rarely, not in typical items of audio equipment and not available off the shelf. So your advice was pointless.


In this case, the flux levels are only a tiny fraction of that which
links the windings so doesn't represent a saturation risk to the
Mu-metal[2].

** Small ( like 5VA ) e-core transformers operate the core heavily into saturation - if you want a strong 50Hz AC field just pick up any plug-pak that uses one. Also, Mu-metal is ineffective at high flux levels while the other techniques I mentioned ( copper and steel bands) are very effective.


Toroidal transformers otoh, so effectively confine their magnetic
flux, they don't normally require any such screening, not even when
placed inside the confines of an IBM 14 inch CRT monitor originally
designed for 120v mains in order to convert it to 240v mains. A feat
not possible with a conventional transformer even when placed outside
of said monitor if not a good 60 cms or more away as I discovered two
decades back.

** Toroidals do have an external field and I often see steel bands wrapped around them to reduce it. These bands seem to be made from the same material as is used for the cores.

The magnitude of the field depends on the size of the transformer, any lack of symmetry in the windings - PLUS the level of magnetisation in the core. The biggest effect seems to be that toroidals are invariably run below core saturation while most e-cores are run well into core saturation.


[2] Is Mu-metal any worse than soft iron for self magnetisation? If
so, it seems a strange choice for the pole pieces of magnetic
replay/recording heads, especially since it has such poor wear
properties.

** Ever see a tape head demagnetiser ?

Every hi-fi shop sold them once.

I certainly do not want a large magnet anywhere near the mu-metal shield covering the tube inside my scope, as it would be a real bugger to demagnetise.


..... Phil


--
J B Good

Dual 505 update
 

On 07/03/2015 12:57, Johny B Good wrote:


It looks like you've cracked the problem then. You'll probably just
need to rewire using quality cable and connectors to convert your
'workaround' solution into a permanent fix.


I've now got to the stage of trying a test record and immediately found
several issues. The two most important are wiring errors resulting in
L-R reversal and a phase reversal on the left channel. In other words,
it's a pigs ear. Tone arm wire colours are correct so the errors must be
where they connect to the external phono leads. I could correct by
swapping cartridge connectors around but I may as well do it properly
and make the hum fix permanent at the same time.

Dual 505 update
 

As I said earlier, these days manufacturers take even less care with
vinyl than they do with other media sources.

CD technology could and should have given us a flat FR from near DC up
to 25kHz, easily covering the range of human hearing. Even going up
to 22kHz it still covers quite comfortably the range of older
listeners such as myself. So to all intents and purposes we could and
should be getting near perfect audio reproduction. But what do we
actually get? While there are some very good quality CDs available,
even of those recordings originally released on vinyl, there are also
too many examples where the sound has been ruined by over-processing.
As has been said many times before, the fault lies not in the
technology, but in the people who use it

It's sad that with each passing generation music in particular and
artistic endeavour in general seem to become less 'art' and more of a
commodity, to be bought, sold, resampled, even stolen.

On a lighter note, not even musical names are safe from this process.
I have come to realise that up here in Scotland, there's a flourishing
humorous line in 'resampled' names for bands, tunes, and songs:
Ceilidh Minogue
Def Shepherd
Red Hot Chilli Pipers
Top Of The Crops
Tradivarious
.... and close, but no cigar ...
Bah Hamburg Part II
The Band From Rockall
The Last Tango in Harris

I know there was another I particularly liked, but I can't remember it
now.

Cue a long off-topic subthread where everyone offers their own
suggestions ...

On Sun, 08 Mar 2015 11:34:47 +0000, Sumatriptan
wrote:

I've now got to the stage of trying a test record and immediately found
several issues. The two most important are wiring errors resulting in
L-R reversal and a phase reversal on the left channel. In other words,
it's a pigs ear.
--
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Dual 505 update
 

Java Jive wrote:


CD technology could and should have given us a flat FR from near DC up
to 25kHz, easily covering the range of human hearing. Even going up
to 22kHz it still covers quite comfortably the range of older
listeners such as myself.

** What a load of ********.

The CD format was designed to record and reproduce MUSIC with no audible loss of quality compared to the original signal.

The format will reproduce signals containing frequencies up to 20kHz with no change.

With MUSIC signal, extensive testing showed that no-body could hear components beyond that frequency.

That some young people can detect steady tones above 20kHz, when reproduced at a high enough level, is irrelevant.


.... Phil