[sdiy] percusion synth design and problems.

[harrybissell]

Hi Arun...

The LM386 amp is like walking around with a sign on your back that says
"Kick ME !!!".   It is almost sure to pick up radio and even the pros would
have a tough time...  Check out the device datasheet and make sure you are
using the AM noise reduction techniques... you might even be re-radiating the
noise to yourself....

National Semiconductor Audio/Radio Application Book (1980) says

AUDIO RECTIFICATION ELIMINATION TIPS
(or how come my phono detects AM ?)

a)  Reduce input impedance
b) Place capacitor to ground close to input pin or base (~10-300pF)
c) Use ceramic capacitors
d) Put ferrite bead on input lead close to device input
e) Use RF choke in series with input (~10uH)
f) Pray

H^) harry

Arun Bohm wrote:

> Hi, Was working on this here percusion synth idea and was wondering why,
> instead of damped oscillations, I was getting so much noise. Because I am a
> novice, I am used to making the mixing stage from manuals I got from radio
> shack(don't laugh, please) the amp I use is a utility amp using a 386 chip.
> The end result is all this RF transmission (I actually get some AM station)
> and a bunch of noise. What can I do to eliminate this problem? Any
> suggestions would be appreciated.
> arun_bohm at hotmail.com
>
> _________________________________________________________________