Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!ukma!tindle
From: tindle@ms.uky.edu (Ken Tindle)
Newsgroups: sci.electronics
Subject: DC motor noise in audio circuit
Summary: Audio circuit design resembles black magic!
Message-ID: <15857@s.ms.uky.edu>
Date: 24 Aug 90 02:25:23 GMT
Reply-To: tindle@ms.uky.edu (Ken Tindle)
Distribution: na
Organization: U of Kentucky, Mathematical Sciences
Lines: 28

I'm working on an audio project and have run into a nasty problem.

I'm using some cassette mechanisms with a circuit of my design in a
language learning system, and have magnetic coupling of noise to the
ground plane.

The motor is by necessity physically close to the circuit, and it is
definitely a case of magnetic coupling only (not direct conduction).
I can move the motor away to stop the noise, and it is being driven
by a supply voltage which is completely separate from the audio circuit
(there is a ground reserved only for the motors).  Problem is that there's
no way to permanently move the motor far enough away.

The motors have an integral speed control circuit, and it could be part
of the problem, too.

So how do manufacturers of portable cassette players keep this trash out
of the audio?  They don't *seem* to do anything special as regards the
motors themselves, so is there a black magic way to keep the power bus
clean?

I suspect there's no easy answer to this, in keeping with the ways of magic.

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INTERNET:tindle@ms.uky.edu | "Could you please continue the petty bickering?
BITNET: tindle@ukma.bitnet |  I find it most intriguing."   ---    Data, 
Ken Tindle - Lexington, KY |  Star Trek, The Next Generation, "Haven"
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