I'm new to Servo Controlled turntables, Is some speed variance normal?

CheeseofBorg

User Serviceable Parts
I recently acquired a Kenwood KD-5066 DD servo controlled turntable, and have been noticing a very slight variation in its speed. I will dial in the exact speed via the stroboscope, but over the course of a record the speed will shift ever so slightly and the stroboscope will slowly begin creeping forward or backwards. :no:
The variance is far less than what I can sonicly detect, however I like many of you can get very obsessive about this sort of thing. Is this behavior normal for a servo controlled turntable?

Also, I notice a detector arm (presumably for speed) that is meant to be triggered by a pin on the bottom of the platter, however the pin never actually triggers the detecting arm, instead passing it slightly. It is not used by any of the automatic functions and I suspect that the motor may be slightly misaligned causing the pin to miss the detector. Could this be a cause of my speed issues if they are in fact an issue?
 
Your drift may improve if you clean the pots. And it may not. With some servo DDs, there's drift, but it's the exception rather than the rule. Could be caused by something being out of spec in the circuit. The KD-5066 was a rather early DD motor design, no ICs or Hall elements that I can see on the schematic.

The service manual is here (you have to create an acct if you don't have one on VE). It's a great scan with voltages clearly marked, so you can check them if you're handy with a DMM. If you're trying to find an out-of-spec component, that might help you narrow it down.

Speed drift (if pitch increases over time) could also be lube in the motor, but I seem to recall that motor looks tricky to take apart.

You might just have to learn to live with it.

BTW -- the metal pin under the platter and the white nylon arm are for the auto-return function.
 
The kind that aren't quartz locked can drift somewhat as they warm up.


The trip may need to be cleaned and lubed. The grease often gets sticky and makes those functions foul up.
 
IMO it's just temperature drift. It can be designed out of a non-quartz locked circuit, but most probably suffer from a small amount. If you leave the table running for a while does it diminish or go away? If so, I wouldn't mess with it.
 
I think the speed adjustment pots are just dirty.
Is it Quartz locked?

I cleaned and lubed both sets of pots last night with no significant improvement. It is NOT Quartz Locked. I have tried running it for a long time to rule out temperature and it seems to help, however I am still confused at the seemingly useless detection arm.
 
I'd have to look at the drive and power supply circuits to be sure, but sometimes problems like this can be cause by aging electrolytic capacitors. Also, if there are any VD1212s in there, get them out.
 
In my experience, all servo locked non-quartz DDs vary a little, all the time. You can tweak it hot, cold or in between, it will still drift a tiny bit. The strobe only highlights the issue- if there was no strobe, you'd never know.

If you want to see drift, put a stroboscope on a belt drive- they wander all over the shop. Most belt drive aficionados are blissfully unaware of the speed drift in their megabuck TTs because the manufacturers weren't so silly as to put a stroboscope on the platter.
 
I'd have to look at the drive and power supply circuits to be sure, but sometimes problems like this can be cause by aging electrolytic capacitors. Also, if there are any VD1212s in there, get them out.

I work at radioshack (college job) and I will see if we have the proper caps in stock somewhere.
 
I work at radioshack (college job) and I will see if we have the proper caps in stock somewhere.

Most likely you won't. Mouser or Digi-Key is where you'll need to order them from to get everything. Even if your store has some of them, I'd get better caps, either Nichicon or Panasonic. The power supply probably needs attention more than the rest of it, but it's easier to just do them all at once.
 
Most likely you won't. Mouser or Digi-Key is where you'll need to order them from to get everything. Even if your store has some of them, I'd get better caps, either Nichicon or Panasonic. The power supply probably needs attention more than the rest of it, but it's easier to just do them all at once.

I did go to Mouser for my reciver's caps, but I was not sure that was recommended for a turntables. Can anyone offer any more input on the detector arm?
 
In my experience, all servo locked non-quartz DDs vary a little, all the time. You can tweak it hot, cold or in between, it will still drift a tiny bit. The strobe only highlights the issue- if there was no strobe, you'd never know.

If you want to see drift, put a stroboscope on a belt drive- they wander all over the shop. Most belt drive aficionados are blissfully unaware of the speed drift in their megabuck TTs because >>>the manufacturers weren't so silly as to put a stroboscope on the platter.<<<


Well, I guess Sony was silly then--cause they sure put one on their high end belt drive TTS-3000 and 3000A tables. I have both. They are servo controlled and do drift ever so slightly but only for the first minute or so...then stable.
 

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If you want to see drift, put a stroboscope on a belt drive- they wander all over the shop. Most belt drive aficionados are blissfully unaware of the speed drift in their megabuck TTs because the manufacturers weren't so silly as to put a stroboscope on the platter.

Maybe you were being a bit sarcastic, but IMO you hit it spot on - putting a strobo on a platter rim where it's always visible is just annoying. For broadcasting etc. it makes sense, but for home listening not so, I don't need to know if the speed is < 0.1% too slow or too fast, because I won't hear it anyway. So it just becomes one more thing to needlessly obsess over and one that is hard to ignore because those orange lights grab your attention.

With a servo controlled DC-motor, putting a strobo which uses the line frequency is not only annoying, but stupid, because you'll never know if any possible drift you see is because of small variances in line frequency or actual speed drift.

None of my belt drives with AC motors drift at all compared to the line frequency they lock on, but if line frequency fluctuates I will be blissfully unware of it since the strobo disk depens on it as well :) Where I live line frequency is very stable though, and I did a lot of timed runs at one point when I was servicing my Thorens.
 
I said 'most', we all have plenty of BD decks with strobes too, but 'most' high end BDs do not have strobes.

The Sonys certainly are a solid seat-of-the-pants deck though. Amazing for 1968 - 47 years old and still running...

[/U]

Well, I guess Sony was silly then--cause they sure put one on their high end belt drive TTS-3000 and 3000A tables. I have both. They are servo controlled and do drift ever so slightly but only for the first minute or so...then stable.
 
In my experience, all servo locked non-quartz DDs vary a little, all the time. You can tweak it hot, cold or in between, it will still drift a tiny bit. The strobe only highlights the issue- if there was no strobe, you'd never know.

If you want to see drift, put a stroboscope on a belt drive- they wander all over the shop. Most belt drive aficionados are blissfully unaware of the speed drift in their megabuck TTs because the manufacturers weren't so silly as to put a stroboscope on the platter.

I've been aware of inherent belt drive speed problems and thus was delighted when one of our members developed a practical solution for them.

Sent from my SM-N900V using Tapatalk
 
IMO it's just temperature drift. It can be designed out of a non-quartz locked circuit, but most probably suffer from a small amount. If you leave the table running for a while does it diminish or go away? If so, I wouldn't mess with it.

Well I did some testing, and it appears that it does stay steady after about 5-10 minutes of use. I have calibrated it to "perfect speed" while it is warmed up and playing a record.
 
The instructions for my Technics say that variations in line frequency can cause variations in the strobe light flicker. So it could be that you don't have precisely 60 Hz, or that it varies by a tiny amount, and you're seeing that variation. But the TT motor itself uses DC, so it isn't affected by fluctuations in frequency -- or so they claim.

Now, I have two TTs of the same model, and the strobe dots on one of them wander a tiny bit whereas the other one doesn't seem to. I have no idea why one does it and not the other, but it doesn't bother me. I can't hear any difference if there is one, which I seriously doubt there is.

So it just becomes one more thing to needlessly obsess over

+1 to that.
 
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