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

--
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