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Benefits of a speed controller

SteveJewels

SteveJewels

Well-Known Member
After going through a few iterations I have my speed controller working. It is not an off the shelf unit, it is assembled of commercial equipment that is readily available.

The sine wave source is an HP 33120A Arbitrary Waveform generator. This outputs a sine wave that is adjustable to 0.000001 Hz and with the high stability timebase will drift in frequency not more than 1 part per million per month.

The limitation of the 33120A is that the maximum output is 10 V pp, not enough to drive a turntable.

The task of increasing the voltage is performed by a Crown Com-Tech 400 which has a stated THD of 0.05%. The 200 or 210 would be adequate, this one happened to have an input module that would work and was not very expensive.

It is not a turnkey operation. You have to set the frequency of the 33120A and adjust the output while measuring to voltage.

But it works, and seems to work very well.

I have been reading quite a bit about turntables in the last few weeks. One of the inherent flaws is that the synchronous motor used in the VPI and other turntables, responds rather precisely to the frequency of the input power. If that is not stable the motor will faithfully vary with it.

That is, I believe, the intent of the Music Hall Cruise Control and SDS. To provide a stable input frequency for the motor to synch to.

So much for the technical.

I finally got my system (Steve's Speed Control Contraption?) working well enough to hook it up to the turntable and have a listen.

I was prepared to have to listen for quite a while to discern any improvement and for the possibility that there would be no improvement at all.

Only a short way into the first track the difference in the bass was obvious. Cleaner, clearer, and extended lower in frequency.

I have not listened to it all that much. I would like to know what sorts of improvements, if any, you perceive with your speed controller.

Please state what motor controller you are using or have listened to and what turntable.

In addition to learning what sorts of improvements there are to be had, perhaps some correlation of controller and turntable will appear.

Thanks,

Steve
 
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Nice.

Fortunately the TT I use convert to DC and use PLL and logic to assist with speed accuracy, regardless of the AC voltage and frequency.
 
I'm using a prototype controller by a 3rd party on my HW-19 MkIII, described in the VPI thread.


Sent from my SCH-I605 using Tapatalk
 
1TUFSS said:
Technics Quartz Direct Drive.

;)
Click to expand...


LOL! My thoughts exactly. :)

Even those low budget Technics belt drives of yesteryear (the ones that audiophools dismiss as "mid fi" and "consumer decks") had electronically-controlled speed.

No doubt that speed accuracy is the number one most important factor in turntable design and operation. You'd never guess it though looking at many of the mediocre turntables on today's market.

Kudos to the original poster for caring enough about performance and designing a speed controller.
 
It should be fairly straightforward to set up a scope to display a Lissajous figure of power company "60 Hz" and your system's output. Regardless of their initial phase relationship, the figure should be stationary when they're in sync, and dynamic when/if they're not. That would be an interesting YouTube vid to watch, for a few minutes...

Is your audio system's AC feed filtered to remove HF interference components, if any?

Chip
 
I myself use the VPI SDS.

Basically, I'm an "electronic dunce", but I have heard it said that line frequency in hertz is usually fairly stable, and accurate coming through the power lines. Of course I know if there was any fluctuation, this would play havoc with an AC Synchonous Motor.

One problem I note though, with belt driven tables like the VPI's, and others similar, is that they will often possess speed error. This is due to the variations of both Platter, and Drive Pulley Diameters, besides other factors.

Even when I changed Platters on my own HW-19 as an upgrade years ago, there was little difference in speed, the Table always ran slightly slow (according to a KAB Strobe Disc), and this always seemed to give the table a somewhat sluggish sound IMO. One shortcoming, was my Drive Pulley only had two Steps-Diameters, one for 33.3, and one for 45rpm.

Some of the later VPI Pulleys I understand had stepped Drive Pulleys, where one could perhaps get closer to proper speed, and my VPI SAMA has this feature, where once one fine tunes at the SAMA's Drive Pulley, I then found I needed to then correct less at the SDS Speed Controller.

Again, as I said, I am dumb electrically, but I had thought I once read about what "type" of electricity gets fed to such AC motors, by that I mean Square Wave, versus Sine Wave that one can have a detriment?
Mark
 
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Lately I have been using the Music Hall Cruise Control 2.0 on vintage Thorens and AR turntables with great success. Thing I like about the Cruise Control is the fine adjustment option, or pitch control. I also like, since the belt on the Thorens and ARs stay on the 45rpm portion of the pulley, at 33rpm, the noise level of the motor is significantly decreased.

And for mid-80s AR owners, two other pluses: 1) stops the motor pulsating when "off" and 2) no more belt switching to play 45s.
 
markd51 said:
Basically, I'm an "electronic dunce", but I have heard it said that line frequency in hertz is usually fairly stable, and accurate coming through the power lines. Of course I know if there was any fluctuation, this would play havoc with an AC Synchonous Motor.
Click to expand...
As I post this, mains power in Durham is sitting at 49.89 Hz. That deviation from 50 Hz might not sound like much, but it's still a shade over ten times higher than the speed deviation of a certain turntable a lot of people like to bash - and that's before the rest of the drive system comes into play (belts, dynamic resistances, platter inertia, etc, etc).

Long story short... electronic speed control is absolutely necessary for accurate reproduction.
 
1TUFSS said:
As I post this, mains power in Durham is sitting at 49.89 Hz. That deviation from 50 Hz might not sound like much, but it's still a shade over ten times higher than the speed deviation of a certain turntable a lot of people like to bash - and that's before the rest of the drive system comes into play (belts, dynamic resistances, platter inertia, etc, etc).

Long story short... electronic speed control is absolutely necessary for accurate reproduction.
Click to expand...


That amount of power frequency error is about five to ten times what we usually see here in the US.

Aside from that, I don't think we need to make this thread about Technics.
 
SteveJewels said:
Interesting. How does the tach sense the speed of the turntable?

What sort of improvements to you see?
Click to expand...

Other than the magnet I think an optical pick-up is optional for when the magnet isn't practical. Aside from assured speed, there is a confidence in the system to maintain loop-locked accurate speed while retaining the benefits of the BD system, thus pitch cannot vary short or long term. How much is psychological and how much is perceptual may depend to a certain extent on the individual user and their sensitivities and priorities tho' I think long term listening will out in the end in favor of having it on board for most users.
 
SteveJewels said:
Interesting. How does the tach sense the speed of the turntable?

What sort of improvements to you see?
Click to expand...

Since, like the developer, you seem a follow-thru kinda guy I'll share some background. He originally signed in here with a question on applying a tach system to a BD turntable as he was developing a precision speed controller and needed a way to monitor speed. I engaged him on the idea and made some suggestions which brought him to realize the two devices could be electronically coupled to correct rotation rate to an absolute precision standard. This is where the break-through came for something quite special as an advance over the free-running regenerative synchronous AC motor precision controller concept first commercialized in the Thorens TD-125 of 1972.
 
Chip Chester said:
It should be fairly straightforward to set up a scope to display a Lissajous figure of power company "60 Hz" and your system's output. Regardless of their initial phase relationship, the figure should be stationary when they're in sync, and dynamic when/if they're not. That would be an interesting YouTube vid to watch, for a few minutes...
Click to expand...

The Lissajous method of comparison is in my plans. I am attempting to obtain other controllers, MH and SDS, for comparison. I was to slow on the draw on a MH on BT last week.

I am not sure how precise the comparison would be. I used this method years ago to make a 0.000 Hz comparison. Nor am I sure how precise the comparison needs to be. At what level of frequency stability has the maximum discernible benefit been reached?

Chip Chester said:
Is your audio system's AC feed filtered to remove HF interference components, if any?

Chip
Click to expand...

Funny you should ask. I surveyed the input power requirements of my system yesterday with an eye toward using Crowns to power it.
 
quadtech said:
Pretty cool.

You could possibly get the Sander/Nigel speed controller board,
and use the 33120A sine wave generator instead of the
XR2206 daughter board to provide the 60hz to the chip amp driver board -

http://www.lencoheaven.net/forum/index.php?topic=13981.0
Click to expand...

As I was exploring a means to get the output of the Arb Gen up to 115 VAC I looked at transformers. IIRC they cause considerable harmonic distortion, on the order of 5% (could have been 0.5%) and their worst distortion is at the low frequencies.

I saw that and moved on. Unfortunately I did not save the reference.

The Crown amp has a stated THD of .05% and an amplifier has the least of its distortion at the lower frequencies where this will be operating.
 
Pio1980 said:
Since, like the developer, you seem a follow-thru kinda guy I'll share some background. He originally signed in here with a question on applying a tach system to a BD turntable as he was developing a precision speed controller and needed a way to monitor speed. I engaged him on the idea and made some suggestions which brought him to realize the two devices could be electronically coupled to correct rotation rate to an absolute precision standard. This is where the break-through came for something quite special as an advance over the free-running regenerative synchronous AC motor precision controller concept first commercialized in the Thorens TD-125 of 1972.
Click to expand...

Thanks! There is a wealth of good information there.

I am looking at rotary encoders to measure the speed and speed stability of the motor. The smallest granularity I can find is 5,000 pulses per rotation which on a motor that is turning at 10 revolutions per second is 50,000 pulses per second.

That would equate to 0.00002 Hz. Pretty good, but not quite the level I am looking for. It may do for a start though.
 
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