Lead shield variations

[jeff12]

Just a question about shielding leads. Looking at pictures of a couple of builds on the forum I see what appears to be a hand wound coil of wire around the signal lead. Are there advantages to this method over standard braided shielded wire?
Of course other than being able to put parts inside the shield. Any special kind of wire or design requirements needed?

[Reeltarded]

Faraday principle!

I was considering using a fine steel mesh I found as a place to hide all the power from all the signal, just haven't gotten around to that yet. I wanted to ask a few questions myself. I believe that you can ground both ends to the chassis and since it isn't part of the circuit, no ground issue.

A coil can be added to an existing run somewhere to taste too. No loss on that run from the resistive nature of the shield on a multi pair.

Dave did it in his pcb RJ amp. Let's bug the crap out of him.

[Colossal]

Jeff,

Just my $0.02, but I have built amps using standard issue shielded coax and a shield coil approach. I have had issues with radio interference using either method in the absence of an input grid resistor (e.g. Trainwreck). With the PCB Express I just finished, I used the coil shield method but I used grid resistors (both 825R). There is no problem with RF; the amp is dead silent with the guitar's volume knob turned down. The reason I went with the coil approach this time around is that I wanted to use pure copper wire to move signal from the input jack to the grid, no shielding foil around the signal wire itself. The coil is grounded on one end, at the input jack ground. I can't say that there is any audible advantage (that I can yet quantify) to the shield coil approach over coax. Personally, I like the robustness of using hookup wire to move signal from the jack to the grid (I'm using teflon over pure copper, no tinning or plating) and I wanted there to be no influence (if any) due to shielding directly adjacent to the signal wire. Of course my hypothesis, if there is any, is probably negated by the fact that I'm transporting the guitar's signal via shielded wire From the aesthetic side, the shield coil is reminiscent of coiled instrument cables.

[jeff12]

Jeff,

Just my $0.02, but I have built amps using standard issue shielded coax and a shield coil approach. I have had issues with radio interference using either method in the absence of an input grid resistor (e.g. Trainwreck). With the PCB Express I just finished, I used the coil shield method but I used grid resistors (both 825R). There is no problem with RF; the amp is dead silent with the guitar's volume knob turned down. The reason I went with the coil approach this time around is that I wanted to use pure copper wire to move signal from the input jack to the grid, no shielding foil around the signal wire itself. The coil is grounded on one end, at the input jack ground. I can't say that there is any audible advantage (that I can yet quantify) to the shield coil approach over coax. Personally, I like the robustness of using hookup wire to move signal from the jack to the grid (I'm using teflon over pure copper, no tinning or plating) and I wanted there to be no influence (if any) due to shielding directly adjacent to the signal wire. Of course my hypothesis, if there is any, is probably negated by the fact that I'm transporting the guitar's signal via shielded wire From the aesthetic side, the shield coil is reminiscent of coiled instrument cables.

Thanks for the information, it has been a long time since electronics school and I don't remember seeing anything like that before in standard use. The coil caught my eye and does look very cool. Now if someone would design a guitar cord like it. I remember seeing a power cord at the Nashville amp show that was designed to make your amp sound better.
Very expensive, but it only came in a three foot or so length. Then you were to plug it into a standard extension cord? I may try your approach on my next build just cause it looks cool if nothing else

[Colossal]

Now if someone would design a guitar cord like it. I remember seeing a power cord at the Nashville amp show that was designed to make your amp sound better. Very expensive, but it only came in a three foot or so length. Then you were to plug it into a standard extension cord? I may try your approach on my next build just cause it looks cool if nothing else

For a cool coily cable, check out Lava Cable's Retro Coil:
http://www.lavacable.com/index.php?id=25

I may try your approach on my next build just cause it looks cool if nothing else

Yes, I like how it looks too! The Komet Amps guys used a faraday coil to shield the Fast/Gradual split plate load mod in the Concorde and K60 amps.

[Reeltarded]

I subbed just one run in from input to v1 and it sounds more open, like the amp did before cascading, but still cascaded. I still have over 9' to experiment with.

I bet the reso I have on a 15" (30 there and back hah) run will make the biggest difference. This amp has a resonance control just above the only input lol I still can't believe I get away with this murderous circuit bashing and have anything worthwhile.

Umm.. I stuck both ends to ground. No problem. Should I float one?

[jeff12]

I subbed just one run in from input to v1 and it sounds more open, like the amp did before cascading, but still cascaded. I still have over 9' to experiment with.

I bet the reso I have on a 15" (30 there and back hah) run will make the biggest difference. This amp has a resonance control just above the only input lol I still can't believe I get away with this murderous circuit bashing and have anything worthwhile.

Umm.. I stuck both ends to ground. No problem. Should I float one?

The common method to wire shielded cables is to ground only the source end of the shield to avoid ground loops. Funny how things work sometimes, even when the book says it shouldn't or won't.

[Reeltarded]

Today I cranked it loud and there was a little runaway squeal with this rig, so I put the shielded wire back and it's twice as bad, whereas before it was quiet.

I hate a mystery! LOL Never happy? Never happy!

Experiment #10,987,532. Fail! (me, not the principle)