I finally got around to replacing the wires from the potentiometer,
rheostat, input and speaker out all with shielded cable which worked -
99.9% of the noise is gone. The only noise left is a slight buzz which
goes away when my hand touches the guitar strings. (Which leads me to
question whether the guitar is properly grounded. Any advice on how to
ensure that it is?)

Anyway thanks to everyone for their replies, the shielded wire did the
trick.



On Jun 1, 6:20 am, charlie wrote:
Mad Scientist Jr wrote:
I am just plugging an electric guitar directly into the input. I don't
have the actual circuit here with me right now but the schematic is
here (see page 5):

http://makezine.com/09/crackerboxamp/

I believe the + of the input goes to a 0.01 uF capacitor, the - goes
to ground.

BTW can anyone explain how to add an XLR out (either balanced or
unbalanced) to directly connect the amp to a mixer or recorder?

SNIP

First of all, any sensitive amplifier needs to be build in a metal
box no bigger than is necessary. The box acts as a screen so you
have no need to use screen leads inside the box. The circuit you
have used has no RF decoupling at the input nor on the supply (the
100uf capacitor on the supply will not decouple very well at RF), I
would put a 10n ceramic capacitor across it and, for good measure, a
100n across that!

At the input I would put something like 1n to ground (if your input
is a guitar then the pickup will be low impedance so there won't be
any effect on it's output. I would also be tempted to put an RF
choke in series with the input.

If, as I suspect, you are picking up AM broadcasts coiling the input
cable a few times at the input won't have much effect.

These links may be useful:

http://www.rane.com/note151.html

http://www.benchmarkmedia.com/caig/html/caig06.html

Good luck!

Charlie.

--
M0WYMwww.radiowymsey.org