Where to use coax and why

[greiswig]

The "where" part of this question is pretty well documented for standard builds, although I'm less clear on the why. But...

In an unconventional implementation of something like the PAB, where you are partially lifting the ground on the drive pot, is it likely to be better to use a twisted pair of wires going from the relay to this secondary 50k pot, or should it be coax?

PS - while we're at it, any ideas why this type of relay switch would make popping sound *only* when there was signal present, but be absolutely silent when there isn't signal?

[selloutrr]

why - the shielding and extra rejection of RF and other interference on sensitive runs.

PS- have your tried shunting the tip of the relay to ground with a 1M resistor this quiets thumping FX pedals that switch hard.

[greiswig]

why - the shielding and extra rejection of RF and other interference on sensitive runs.

PS- have your tried shunting the tip of the relay to ground with a 1M resistor this quiets thumping FX pedals that switch hard.

So I guess the question is whether this is one of the "sensitive runs" or not. I figure that if I were switching ahead of the pot (the signal end), it would qualify. But that perhaps switching at the ground end of the pot would not? But perhaps raising the resistance to ground makes it sensitive... that's what I'm asking about.

As for shunting with a 1M resistor to ground, yes, I've tried...no effect. It has something to do with the signal itself, not with what I've encountered before as switching noise or a capacitor that has to have a discharge path when one end is disconnected.

[talbany]

PS - while we're at it, any ideas why this type of relay switch would make popping sound *only* when there was signal present, but be absolutely silent when there isn't signal?

The relay coil is basically a powerful inductor that you are switching on and off. When the current flow is cut off in an inductor, the magnetic field collapses, and produces a large voltage spike.If there is signal present you hear the pop..
Diode and capacitor across the relay coil (.1 film cap) can also help also make sure you have a 22-M across the relay contacts as well.
Also double check you DC voltages are matched..
You may also need to add more filtering if it's noisy when energized
(BTW) the brand of relay can also matter. Some relays are noisier than others.( smallest coil induced noise), and run at lowest currents... why putting them in a socket makes switching to different brands and types easier and find the quietest one for that amp

Hope This Helps

Tony

[greiswig]

Diode and capacitor across the relay coil (.1 film cap) can also help also make sure you have a 22-M across the relay contacts as well.
Also double check you DC voltages are matched..
You may also need to add more filtering if it's noisy when energized
(BTW) the brand of relay can also matter. Some relays are noisier than others.( smallest coil induced noise), and run at lowest currents... why putting them in a socket makes switching to different brands and types easier and find the quietest one for that amp

Hope This Helps

Tony

Tony, I already have a diode across the coil. Here's the funny thing: no signal through the switched circuit, no pop from switching. Very quiet. But as soon as you strike a note and then switch, there's a pop.

Also, Tony, since yours is one of the opinions I respect most here, do you have any input on my original question about the coax?

[talbany]

g
If what you are doing here is lifting the ground refrence of the drive pot to give the OD side more gain (If I have this right here) you will have quite a bit of signal here and real sensative to relay noise and pops.. If you were getting some gain noise after you implemented the mod then I would think the twisted pair/coax might help you there.. If the problem is only popping then I would suspect somewhere in the relay supply first..As far as why it's popping after you hit a note this is a good one.. I'll ask around..The only thing I can think of right off is to add a resistor 22m across the relay switches to relieve any stray capacitance that might have built?..I'll get back if get something..
Hope we can work it out!!

Tony

[greiswig]

Thanks, Tony. That's exactly how I'm trying to get a bit more gain. I currently have twisted pair going from the relay to the pot that controls the amount of "lift" above ground, but a single unshielded lead from the low side of the drive pot to the relay. Sounds like that might be an issue to look into, although it is still a real puzzle why it doesn't pop when there is no signal present if the coil unloading is what is causing it.

I'll post back if I find the solution...seems like the kind of esoteric thing that might be of value to someone besides me someday.

g
If what you are doing here is lifting the ground refrence of the drive pot to give the OD side more gain (If I have this right here) you will have quite a bit of signal here and real sensative to relay noise and pops.. If you were getting some gain noise after you implemented the mod then I would think the twisted pair/coax might help you there.. If the problem is only popping then I would suspect somewhere in the relay supply first..As far as why it's popping after you hit a note this is a good one.. I'll ask around..The only thing I can think of right off is to add a resistor 22m across the relay switches to relieve any stray capacitance that might have built?..I'll get back if get something..
Hope we can work it out!!

Tony

[talbany]

g
If it were me and I would want to pop in more gain in the OD side I would do a lift on the tail of the OD entrance trimmer with a fixed value or perhaps another pot on the back.. This way your manipulating the clean level signal and keep the runs relatively short and less likely to run into these relay and noise issues..As long as you keep the lift relatively small this IMO should work well..
Just a Suggestion

Tony

[Structo]

I know on my D'lite I went crazy with the coax.

The final go around I removed it from quite a few places.
Left it on the OD pots, left one on the master to the OD relay.

It really opened up the tone quite a bit.

[greiswig]

g
If it were me and I would want to pop in more gain in the OD side I would do a lift on the tail of the OD entrance trimmer

I thought about that, Tony, but it was easier to test the theory on the ground lug of the Drive pot. To my surprise, very little additional resistance makes a big difference there. I would expect the trimmer to be even more touchy! But maybe you're right, and I'd just need to use a lower value pot.

[greiswig]

(SNIP)
Also double check you DC voltages are matched..

Tony

Tony,

First off, I was wondering if you'd thought of any reason why this thing pops only when signal is present and is silent otherwise? Next, the quote above...I don't think I understand it. What DC voltages are we talking about here?

Thanks!