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Re: Apple II preamplifier



Simon D. Williams wrote:
On Mon, 5 Dec 2005, Michael J. Mahon wrote:


Simon D. Williams wrote:

On Sun, 4 Dec 2005, Simon D. Williams wrote:



For reasons that probably should remain a mystery, I'm trying to
"cross-over" the cassette I/O ports on a pair of IIes... the immediate
problem is that the output is at line level and the input expects a much
higher level, so I need to amplify the signal. Is it possible to make a
very small amplifier to achieve this?


Forget that last sentence... obviously it's possible. The question should
be: how can it be done simply and cost-effectively?

If you'd rather buy the parts at Radio Shack than buy the
assembled unit, then you are looking for a microphone
pre-amplifier circuit.  Google should turn up dozens,


Indeed... Google is more helpful than I could possibly want -- didn't
realize there were so many variations on such a simple thing.


and you can take your pick--discrete transistors, IC op-amp,
single-voltage supply, split supply, etc.

Frankly, unless you really like to build things, buying a
pre-amp or mic-input mixer--or picking up a used cassette
recorder at Goodwill--is the simplest way to go.


Good point.

If you'd like to build one, here's a pretty good circuit
for a gain of 0-100 preamp.  For the Apple (or any non-
electret microphone), you can eliminate R1.  And C4 can
be dropped to 1mF or so to drive the Apple cassette input.

http://lwn.net/2000/features/xcircuit/micprebig.jpg

-michael

Music synthesis for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
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