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From: wbrown@beva.bev.lbl.gov (Bill Brown)
Newsgroups: sci.electronics
Subject: Re: Adding speed control to cassette deck
Keywords: cassette tape deck speed pitch control
Message-ID: <3774@helios.ee.lbl.gov>
Date: 12 Sep 89 14:55:05 GMT
References: <2245@crdgw1.crd.ge.com>
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Reply-To: wlbrown@lbl.gov (Bill Brown)
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Organization: Lawrence Berkeley Laboratory, Berkeley
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In article <2245@crdgw1.crd.ge.com> mak@seneca.UUCP (Michael A. Kinstrey) writes:
>I want a half-speed cassette deck for practicing guitar
>I will be doing the mods to a CHEAP deck, walkman, or player.
>  ...
>I have an OK understanding of circuitry and electronics, and
>have done several small projects and modifications to boards.
>
>My questions:
>  1) Do the cheap walkman-type players and office-use tape players
>     (< $40) have the speed control monitor?
>
>  2) If not, is the job as easy as installing a pot to the motor?
>     If the speed monitor has to be bypassed, where is the best place?
>
I've adjusted the speed on two different "Walkman" (probably somebodys'
TM!) tape player/recorders.  They started playing at too high a speed, altho
(WARNING - EDITORIAL COMMENT) I'm not sure that was a bad thing given the
stuff my kids listen to.  Gets it over with quicker! (END OF COMMENT).
There was a pot on the p.c. board that adjusted the speed of the tape and
apparently just go crudded up and opened, opening the servo loop.  Twisting
it back and forth a couple of times cleaned up the contact and I was able
to adjust the speed.  I don't know what the range of adjustment was, but
even if it isn't enough you should be able to trace out the circuit and maybe
change a resistor value to get the range you want.

>  3) What kind of effect will the varying voltage and speed have on
>     the life of the motor? Dramatic or only slightly?
>
I'd be surprised if it made any noticable difference.
>  4) Do these type of motors only operate under a tight range of voltage?
>
I think that they are usually Perm. Magnet motors - they have a wide speed
range and fairly good speed regulation; that is for a given applied voltage
the speed if fairly constant over a modest range of torque.  Since they seem
to be driven by a servo of some sort (I'm not sure how they derive the,
feedback, hmmm gotta look into that) you should have no big problem.

						-bill
						wlbrown@lbl.gov

Disclaimer:  These opinions are my own and have nothing to do with the
    official policy or management of L.B.L, who probably couldn't care 
    less about employees who play with trains.