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Helpful advice from Max Baars
In an Email sent to LevNet
From: Max Baars
To: "Mike"
Subject: Re: [Levnet] question about digital theremin from the univ.of Glasgow
Date: Sat, 08 Dec 2001 18:05:53 +0100
On Sat, 8 Dec 2001
17:23:30 +0100, you wrote:
>Hello,
>
>can anybody please help me to fix my digital theremin from the
univ. of Glasgow.
>My problem is to adjust all the potentiometers, when I adjust
the pitch the volume antenna
>is not responing well and vice versa.
>Further I can't seem to get a nice sine wave out of it, altough
it sounds
like a sine wave but then
>with a lot of noise into it. This is also exactly what I'll see when I
connect the output with a scope.
>
>Thank you, and I hope that there's someone able and willing to help
me......
>
>kind regards.
Hi.
I haven't build that theremin but here are some ideas that may
help:
Dit you decouple the ic's that are used as oscillators? You may need
to solder a 100nf capacitor accros the
power supply of each ic (thus
from VCC to gnd), as close to the ic as possible, to avoid unwanted
oscillations. It
might be wise to simply decouple all ic's to be safe.
If there are any unused gates, make shure their inputs are
either
grounded or connected to vcc.
Make shure the power supply is free of noise. Sometimes supplies with
the
standard 78xx regulator ic's tend to oscillate.
If you have done the above and still cant tune the volume and
pitch
sections separately, check their frequencies. Your volume oscillators
should be on a different frequency as your
pitch oscillators eg.
volume on 200 kHz and pitch on 600 kHz.
Still no luck? Make shure that all oscillators are
physically
separated as well as possible. Like avoid crossing and twisted wires.
Using logic circuits in there kind
of applications is possible but
sometimes you'll find that things dont work well, and then it
sometimes helps to try a
chip from a different brand.
Still no luck?
Try to disconnect the connections that join the different modules
of
the instrument together, than test each module separately and then
connect each module one at te time to another to
try to isolate where
the unwanted interaction comes from.
There is a FAQ for this theremin on the thereminworld
website, there
are some mods as well, perhaps the problems you have are adressed
there.
Got it right? Let us
know.
Max
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