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From: steve@pro-hindugods.cts.com (Steve Fenwick)
Newsgroups: comp.sys.apple2
Subject: Re: GS digitizing sounds
Message-ID: <1992May01.040028.20174@crash.cts.com>
Date: 1 May 92 04:00:28 GMT
Sender: news@crash.cts.com
Organization: Crash TimeSharing, El Cajon, CA
Lines: 28

In <1992Apr30.024719.6357@visual.spk.wa.us>
tkolstee@visual.spk.wa.us (Tony Kolstee) writes:

>I also have a question on the mod that I did.  When I hook the wires up to
>the SPEAKER port on my amplifier and put up the Oscilliscope (sp?) screen,
>the sound wave centers around the bottom.  If I blast the volume and then
>bring it back down, the wave centers in the middle, and it works okay.
>Why is this?  And how come if I connect my speakers to the amp at the same
>time the wave stays at the bottom no matter what I do?  Could this be an
>impedence problem?

I _had_ that EXACT same problem.  It is a grounding problem.  The Line and
Mic outputs of most equipment has a lower reference voltage for the audio
waveform signal.  To fix this, you need to run it through any op-amp I.C.,
and have a potentiometer going to ground from the inverting input to adjust
the waveform level.  Make sure you have a relatively large value capacitor on
the output, because I noticed that with small values, the waveform starts to
'drift' down, I don't know why, though.  I used an LM324, but any op-amp
should work.

Hope this helped!

Steve


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