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