Metropoulos Forum

I'm no electronics whiz, so maybe this makes no sense.

I was wondering if something I did to a couple of guitars could also work with amps. I lined the body cavity of those guitars with copper tape. The adhesive on the tape conducts electricity quite well. Doing that and grounding the lining had a significant impact on reducing noise that was going to my pickups.

I think that some of the power wiring in an amp also generates a similar type of interference, resulting in noise when picked up in other components. Mostly that wiring is against the side or bottom of the amp chassis to keep it away from everything where possible. What if you taped that wiring down to the chassis with the copper tape, lengthwise to cover the wire? Would the copper tape shield some of the interference and ground it to the chassis through the conductive adhesive?

Yes, you would have to be careful to keep it away from solder joints or anything else that isn't insulated. But you could do that and still cover up the majority of that wiring. And it would be pretty easy. I suppose you could even tack it down with a little solder in case you don't trust the adhesive over time.

Thanks!

Night Owl

That wouldn't work at all. You see, the chassis is connected to the circuit as ground, so either way, it's already integrated into the amp. I suppose maybe shielding certain sections of the circuit (wires, etc) with sleeving would help reduce noise... but most of that has already been accounted for on the logs of many other people's build. The only thing that I would recommend is proper soldering technique and not exposing too much unshielded wire, as well as the twisting of wire carrying AC voltages (which is common sense).

Yes, proper lead dress, using shielded cable where needed and just generally good building technique should give you a quiet amp.
But, it's good you are thinking ahead.

Don't forget, you should usually have a shield for the chassis on the floor of the head cabinet.
Most of the time this is simply a thin gauge piece of sheet metal that the chassis sits on when bolted down.

So in a way, that completes the shielding of the components.
Sort of like a Faraday cage.
Look that one up, it's a neat topic.

It will work in terms of getting induction reduced between components actually within the amp. You could, for instance, use it on your power tube grid wires to shield them from the NFB wire.

The downside, though, is an increase in capacitance which is usually manifested as a loss of highs or 'sparkle'.

Local shielding is a good technique, if applied properly. It's no different conceptually to using shielded wiring to V1, or to using a shield can around specific components (take a look at the screening plate on the right-hand side in Larry's amp that he was discussing recently: http://www.larry-amplification.de/galle ... nside2.jpg" onclick="window.open(this.href);return false;).

I agree with the previous posts that good technique should get you the most of the way toward quiet operation. Although it seems like shielding as I described, and probably using shielded wiring, would help, it might impact the tone by losing some highs - not good.

Perhaps a better general approach to reducing internal noise is to have the shielding further away from the noise source - in this case the AC wires. If the shielding were further away, I think the capacitance effect would be less. If you had a large diameter shielding, that would probably be an improvement. Or something like a metal partition between the power section/wires of the amp and the signal section might be effective. I suppose that is the approach taken in the picture you referenced. That would probably require some layout changes to really be practical. If I were designing an amp, maybe that would be an option. But in building one of these specific designs from kits, it probably won't be very feasible. I'll look it over though. I wonder what distance between the wire and shielding would be necessary to reduce the capacitance effect?