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
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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