AC line purity and vinyl sound quality

[dazzdax]

Hi fellow audiophiles, many turntables are nowadays equiped with an external motor unit. This motor unit is often of the AC synchronous type with a dedicated transformer/regulator. I wonder why any form of AC line stabilization/regulation could affect the sound of the vinyl playback system. Would the use of an isolation transformer also have this effect on sound? If that is the case, then it is a bit hocus pocus to me.

Chris

[Uncle Ants]

AC motors are a simple, clever and cheap solution to getting a constant speed as the motor is effectively locked to the frequency of the mains - 50Hz here and 60Hz in the States and other parts of the world.

Quite clever BUT the mains frequency does sometimes drift from its nominal frequency, in theory making your turntable run a tad fast or slow - though in practice not by a whole lot. Also although AC mains is supposed to be a sine wave, it often isn't and the resultant hash can produce motor noise.

Hence Products like The Heed Orbit, Pro-Ject Speedbox, Linn Lingo and the NAS Wave Mechanic, which regenerate a 50Hz (or 60Hz) signal as a perfect sine wave and in the first three cases also offer puch button speed change by generating 67.5 Hz AC to take the motor up to 45 on the 33.3 spindle.

Just how effective this is, is to a large extent dependent on how crappy your mains is in the first place and how well your deck is isolated from motor noise.

Mains conditioning can allegedly have negative as well as positive effects on the amplification side of things, but shouldn't affect your TT. Depends on how well implemented it is I reckon.

Hope that helps.

[bauzace50]

Wonderfully expressed, UncleAnts. A bit further, I have the VPI SDS, which is a sophisticated sine-wave generator feeding from the mains. It processes the mains electricity and gives out a pure sine wave. Additionally, it can change speeds between 33 and 45, and can vary the speed in increments of hundredths of the assigned sine-wave frequency. Additionally, it senses when the motor is up to speed, and lowers the voltage fed into the motor, to an appropriate value, to lower motor noise.
ONE IMPORTANT DISTINCTION related to this specific type of processor: it is intended for turntable motors which derive their running speed from the electricity's frequency value (50 Hz, 60 Hz, etc)...I understand they are called INDUCTION MOTORS. However, other types of turntable motors, such as direct drive, etc. do not derive their running speed from elctricity's frequency.
It seems that the electricity reaching my home is pretty good quality, since the ONLY difference I notice with/without the processor, is an obvious motor acoustic hum (airborne, NOT induced into the cartridge signal), which is eliminated with the processor, when it automatically lowers the voltage. The convenience features won me over, with the speed shifting and speed fine-tuning made possible.
I am happy with the processor, and it is not inexpensive by any means.

[dazzdax]

Hi Uncle Ants and Beauzace, I understand that a stable 50 or 60 Hz sine wave could have a laudatory effect on the speed stability and hence on the final sound. What is not entirely clear to me is why this would give a sense of "blacker background" according to some. This finding is comparable to the effect a good interconnect shielding can have or pure AC line on the power supply of an amplifier, mainly due to rejection of high frequency noise. Why would motor and speed stability also alter the signal in such a way? A turntable is a mechanical device and a motor unit is mechanically decoupled from the rest of the plinth and should in principle not alter audio signal itself, which is an electrical phenomenon. I hope it does not sound to ignorant to you.


Chris

[bastlnut]

hi Chris, all,

take a look at this thread, power conditioning:
http://vinylengine.com/phpBB2/viewtopic.php?t=3406
it does make a difference, a big one.

regards,
bastlnut

[Uncle Ants]

A turntable is a mechanical device and a motor unit is mechanically decoupled from the rest of the plinth and should in principle not alter audio signal itself, which is an electrical phenomenon. I hope it does not sound to ignorant to you.

No, not ignorant at all, but I think the answer is right there. In theory the motor is mechanically decoupled from the plinth and in top notch tts in practice it is. If a clean sine wave results in less motor noise and any motor noise finds its way back into the plinth directly or into the platter via its belt (or idler wheel I guess) as a result of a dirty sine wave, then that's definitely going to impact background noise.

I'm currently using a Heed Orbit on a NAS Spacedeck ... and the impact on the sound quality is either negligable or non existent ie. I can't really hear it (I use it purely for the convenience of push button speed change).

But the NAS has superb speed stability to start with due to a high mass platter and has an exceptionally quiet motor, as its a very low torque design which doesn't need stepping down when up to speed as it won't get to speed without manually pushing it. Its also completely separate from the plinth. So there's very little background noise to start with.

On a deck with a much lighter platter and the usual motor on the plinth design running the same voltage at speed as used to get it there, a bigger difference will theoretically be more apparent. I've experimented with this on a Rega P2 (with the Heed) and a Pro-Ject Debut (with their budget speedbox) and it would seem to be the case in practice too. BUT its a question of where the money is best spent.

[bauzace50]

Hello again. One other thing came up this week, when my friend loaned me his AR XA turntable. My friend had commented previously that MY turntable was running slow. Of course, he was accustomed to hearing his system.
This week I placed a strobe disc on the AR, and found it running about 1% FAST! Then, I connected it to the SDS and adjusted it until the AR speed was correct.
This is just another source of a difference. A turntable that runs slower than your reference will seem "darker". This is different from obtaining lower motor noise, but is one additional benefit.

[Uncle Ants]

Hello again. One other thing came up this week, when my friend loaned me his AR XA turntable. My friend had commented previously that MY turntable was running slow. Of course, he was accustomed to hearing his system.
This week I placed a strobe disc on the AR, and found it running about 1% FAST! Then, I connected it to the SDS and adjusted it until the AR speed was correct.
This is just another source of a difference. A turntable that runs slower than your reference will seem "darker". This is different from obtaining lower motor noise, but is one additional benefit.

Interesting thing about the use of strobes is that if you are using a mains driven light, and the motor/spindle is correctly calibrated for mains frequency, then if your mains is "running" fast or slow the strobe will always show correct speed even when it isn't (because the mains freq is off nominal) - because both the light and the deck are running at the same frequency. All it can really tell you is that the decks drive mech is correctly calibrated.

The corollary to this is that if your mains is "off" and you use a regenerating power supply then your deck is likely spot on but a strobe will incorrectly show it to be fast or slow. Only way to be sure is to use a battery powered, quartz locked strobe.

[LousyTourist]

From my experiences testing customers AC for noise and other issues, I can say that the frequency of the signal was ALWAYS dead-nut on. No matter how many dairy farms turned on their milking machines at the same time -- which impacted the AC in many other nasty ways -- the frequency was 60.00 cycles, day in and day out.

Again, from my experience back then, to clean up the AC was no small task. Any aftermarket box is doomed to failure IMHO. The only way to get REALLY clean power is to generate it yourself, free from the 'contributions' that other consumers put on it.

Typically customers would have an electrical engine that turned a flywheel. The normal, nasty AC drove the electric engine. The flywheel in turn (about the size of a car) would mechanically drive a generator, with absolutely no electrical connection between the outside power and the inside power.

THAT was clean power; any other non-isolated method has drawbacks that are a bit deep for casual conversation.

Having said all that, I know a fellow who swears by power cord upgrades; and the way he tells a 'good' one is to use it for his TT. This struck me as madness; where else would a PC have LESS impact than driving a motor that is electrically isolated (ideally) from the analog circuit?

But, being the gullible fool that I am, I replaced the thin, brown mains cable on my Thorens with a good quality (not crazy level) PC and was pleased with the difference. Pretty sure that it was all panacea effect though. I still can't figure how the motor's AC supply would make that kind of difference.

[Uncle Ants]

Interesting stuff. Here in the UK, it doesn't vary a whole lot. Just to give an idea, these guys measured the frequency over a week here:

http://www.picotech.com/experiments/mai ... sults.html

The graph of interest is this one:



Looking at this there were a couple of dips and peaks at around +/- 0.2 Hz. It generally stayed within 0.1Hz. The funny thing is the dips look to be at breakfast, 11ish and early evening ... tea time in other words

That only takes care of the speed mind. Wonky sine waves are another thing. Has to be pointed out though that regenerating a perfect 50Hz sine wave for a turntable drawing very little power is a very different thing to effective mains conditioning for something like a power amp.

PS. These guys took a look at the shape of the AC supply here:

http://www.acoustica.org.uk/other/mains_noise.html

and a graph:



Eeeeww!!

[Steerpike_jhb]

I have a 1970s digital clock by my bed. At night the 'hum' of the transformer is plainly audible. One might imagine you'd hear an unobtrusive 50Hz hum, which is true sometimes, but other times there are all kinds of odd 'noises' in there too - the 'audible' component of all the junk in the mains supply. Now if these odd noises leaked into a phono cartrige by one route or another I can well image the effect it might have on the sound.

[dazzdax]

"Now if these odd noises leaked into a phono cartrige by one route or another I can well image the effect it might have on the sound."

Steerpike: with an external motor unit, decoupled from the turntable plinth, how could a cartridge be able to pick up these odd noises?

Chris

[Uncle Ants]

"Now if these odd noises leaked into a phono cartrige by one route or another I can well image the effect it might have on the sound."

Steerpike: with an external motor unit, decoupled from the turntable plinth, how could a cartridge be able to pick up these odd noises?

Chris

If the external motor unit is truly decoupled from the turntable plinth it won't. No deck that I'm aware of is truly decoupled in that at the very least the drive belt is connected to the platter (with idler wheels and direct drives the connection is even more direct), though I reckon some are well designed enough that for all practical purposes they are as decoupled as you are going to get ... Unless someones invented a completely contact free drive system - magnetic drive mebbe - though I suspect that would present a whole raft of new engineering problems in itself.

PS. Maybe the point can be simply stated the route for this electrical noise to the cartridge is mechanical not electrical, via the motor. If the motor is maximally decoupled (as far as it can be) it is mitigated to the point where it isn't a problem, but in many designs it isn't mitigated to that point. In those systems a regenerating power supply is theoretically likely to lower background noise. (and experience using such supplies on budget designs backs up the theory)

[bastlnut]

hallo,

If the external motor unit is truly decoupled from the turntable plinth it won't. No deck that I'm aware of is truly decoupled in that at the very least the drive belt is connected to the platter (with idler wheels and direct drives the connection is even more direct), though I reckon some are well designed enough that for all practical purposes they are as decoupled as you are going to get ... Unless someones invented a completely contact free drive system - magnetic drive mebbe - though I suspect that would present a whole raft of new engineering problems in itself.

here is one:
http://www.ear-yoshino.com/news/news.asp?ID=104
even if the motor is isolated from the platter and all else, there is still the electrical feedback to the electronics that will effect the sound. the ground is connected to the masse/earth of the amp, the signal masse is also connected to this, thus the cartridge too. can you imagine what happens?

regards,
bastlnut