direct drive speed control

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lenjack
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direct drive speed control

Post by lenjack » 19 Nov 2018 23:26

I'm curious about the pros and cons of servo vs quartz lock speed control on direct drive tables. Seems to m, that q lock would be a one time set it and forget it thing.

analogaudio
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Re: direct drive speed control

Post by analogaudio » 20 Nov 2018 00:02

Yes that is generally the case, the speed reference is a quartz crystal and these have pretty good long term stability.

Servo direct drive usually uses a R-C oscillator as a speed reference and speed stability long term is sometimes inferior to quartz lock. Variable speed adjustment for servo models often uses a simple analogue rotary pot and over long periods these can become contaminated and give rise to grossly unstable speeds. Sometimes the remedy is cleaning the pot inside, or sometimes simply rapid operation of the pot a few dozen times promotes self-cleaning.

The variable speed for quartz-lock models requires some kind of adjuster also and it is often an analogue pot. The change from fixed to variable speed sometimes over-rides the quartz-lock and the crystal-reference stability is temporarily lost.

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Re: direct drive speed control

Post by lenjack » 20 Nov 2018 00:14

As I thought...thanks. Barring contamination, can the servo type be considered to be extremely accurate?

Van_Isle
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Re: direct drive speed control

Post by Van_Isle » 21 Nov 2018 09:33

Servo can be very accurate yes.

The quartz lock tables can use IC's that are unobtainium now ... whereas servo control tend be all discrete components. Some 'future proofing' there

cafe latte
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Re: direct drive speed control

Post by cafe latte » 21 Nov 2018 13:46

Van_Isle wrote:
21 Nov 2018 09:33
Servo can be very accurate yes.

The quartz lock tables can use IC's that are unobtainium now ... whereas servo control tend be all discrete components. Some 'future proofing' there
Not true for Technics, the sl1200 are all obtainable as are the sp10's and sp10mk2's, and the unobtanium chip for other Technics models now has a very good alternative which is very available it is better too so no problem. Cant comment on other tables.
Chris

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Re: direct drive speed control

Post by Van_Isle » 21 Nov 2018 14:06

As I said, 'can'. Perhaps it should have been 'may'.

cafe latte
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Re: direct drive speed control

Post by cafe latte » 21 Nov 2018 14:10

Van_Isle wrote:
21 Nov 2018 14:06
As I said, 'can'. Perhaps it should have been 'may'.
Most often it is some Technics models that are supposed to have unobtanium chips which comes up often and they dont anymore so just sayin if this is what you meant it is not true as things have changed.
Chris

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