Mad Scientist Jr wrote:
Did you use shielded wire to connect the controls and jacks?

Thanks for your reply...

No, just normal stranded wire. Is that where the most interference
would be leaking in?

I found shielding paint (see below) - would it help to paint the
inside of the project box with this?

http://www.lessemf.com/paint.html

SUPER SHIELD

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Super Shield A general purpose EMI/RFI shielding in a handy aerosol
spray for use on most substrates. Especially good for RF shielding
plastic electronics enclosures. Consists of a tough, durable acrylic
base pigmented with a high purity nickel flake. One to two mil coating
provides 40dB - 50dB shielding across a frequency range of 5 to
1800MHz. About 1600 in²/can coverage at 1.5 mil. Contains no CFC 'S,
NO HCFC'S, ozone friendly. 340g (12 oz) aerosol can. Dries to a dull
gray color. Click to see MSDS

* Surface Resistivity ~0.7 Ohm/sq
* Dry time: 10 minutes at room temperature
* Recoat time: 5 minutes
* Excellent adhesion to most plastics
* Tested as per IEEE Std. 299-1997
* Underwriters Laboratories Recognized File No.: E202609
* NO CFC 'S, NO HCFC'S, Ozone Friendly
* RoHS Compliant

Flammable aerosol, ships by ground only.

Super Shield (Cat. #A285) ....................................... $24.95
add to cart

It would probably be little help. And if you coat the box
with anything conductive, it won't help much unless you can
make a good electrical connection between the coating and
pin 4 of the chip. If you really want to try this, thin
brass shim stock cut and folded to fit the box, is probably
the best you can get, short of a copper or aluminum box. It
is also easily solderable to make the ground connection.

If this amp powered by a battery?

In this configuration, pin 2 is the most sensitive node, and
anything connected to it should be surrounded with shielding.

Pins 1 and 8 are also somewhat sensitive so if the gain pot
has a metal case, that case should also have a ground wire
run to pin 4 to shield the resistive element.

Pin 7 is less sensitive, and since this circuit connects
nothing to it, it is probably not involved in the noise.