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

http://epetitions.direct.gov.uk/petitions/71556
================================================== =======
Please always reply to ng as the email in this post's
header does not exist. Or use a contact address at:
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http://www.macfh.co.uk/Macfarlane/Macfarlane.html

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

---
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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