switching clicks in pedalboard problem - solved!! but why??

properly

I see what you're saying here Michael. So you would put the buffer in the pedalboard unit (which is separate from the fx units - these are 4 individual stompboxes mounted on top of the board and powered thru the AC adaptor inputs of the pedals by the board). So the suppply in the board would have to be dual, which it is not at the moment, but maybe with one of those charge pump type ICs, ad long as the caps there wouldn't cause a problem. Also, modifying the fx to a split supply is entirely out of the question. Aside from being horrendously complex (i.e., pretty much rebuilding the entire board for each fx unit), there isn't room for a spec of dust inside those things, let alone the circuitry that would be required to get a split supply happening.

The buffers idea is intersting tho.....

Thanks

Leakage currents exist in op amps too I'm afraid. The reason they were large was probably just because of the extremely high (ie; open circuit) impedance at those points. The multimeter wouldn't have loaded it down much either.

It would certainly help to have the outputs loaded, either by plugging in the destination or by adding redundant load resistors. But that's essentially what we're doing by putting resistors out the outer ends of the DC blocking caps though, and were having limited success.

I'd like to understand why X value resistor works better than Y value resistor in this case. As Tim Wescott alluded to when he said;

The bit that's never explained is HOW to determine what size resistors to use. Can anyone enlighten us on that?!!

niftydog

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Have you been to the

site? R.G. Keen talks about this in various articles there (never giving any specific values though). He suggests 1M-10M. Pretty wide range there. Maybe I'll try a resistor on the input to the pedalboard and see what happens. It's easy enough to try, since I can just put the resistor on the jack itself. Now, attaching one on the last pedal could be a bit tricky, since it will have to be inside the pedal itself....

I would like some better guidelines for this too, if any one has any thoughts. For instance, there must be a linmit to how small the resistor can be, which I assume would have something to do with the impedances that it is connecting to.

Thanks

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The article in particular at the Geofex site is under Tech Tips (at the side) and Why does my stompbox pop when I hit the bypass switch?

What do you know, I was pretty close in my assesement ;) You guys are talking about #1 and choosing the right resistor? If so I think guess it does have to do with the reactance?

since Z = R + I*X

if R = 0 then Z is purely reactive and there is a 90 degree phase shift

by choosing R large you make Z become more resistance and reduce the phase shift.

The phase shift is important because it can introduce clicks. I'm not quite sure of all the interactions that cause this but maybe the capacitances when the switch is on is different than when it is off and hence there is a phase change? Since R > 0, increasing R will only reduce this phase to 0 assuming X is "constant". R must be much larger than X for it to work though(although any R would be better.

Ofcourse to high of an R might cause problems too such as loading and stuff. If what I say above is basically whats going on then I would imagine that you use the largest R right where the clicks are barely impreciable and then double it(or maybe add an order of magnatude).

Anyways, just though I'd say that. I'm not sure if I'm talking about the same thing you are guys are or not.

Jon

Yup I have, but I'm revisiting it this morning. It still doesn't really explain how to choose the best sizes for your DC drain resistors though.

I think it's like this; When RG Keen recommends "100K to 4.7M" it's because 100K is the bare minimum impedance you want before you start loading the signal too much, and 4.7M is as high as you want to go because anything higher might not drain the DC effectively. (ie; too high might actually cause more problems than it solves, like when tempus fugit measured very high DC when the inputs/outputs were open circuited.)

The phase issue throws the cat among the pigeons though.

What Jon said makes sense, could it be that higher resistances are better for reducing phase shift, while lower resistances are better for draining DC? So picking somewhere in the middle and living with the compromise seems like the thing to do.

Tempus, in regard to #3 in RG's article, perhaps you should try grounding out the input lead so there's no signal, and see if that makes for softer clicks and pops? Maybe the noise getting into your signal path is the source of those sudden shifts in phase.

I dunno, just thinking out loud this morning...

niftydog

In another article of Keen's (can't remember which now) he talks about using a 1M-10M resistor for this purpose. I kind of figured 100K must be about as low as it could go, but it's nice to have some agreement there.

Tempus, in regard to #3 in RG's article, perhaps you should try

If I turn the volume on the guitar all the way down, it still clicks - this is the same as grounding the input lead isn't it? Also, these clicks are more noticeable now that the buffer amp is there. Of course, there is actually a gain of 2, so I guess I can see why that would be. Also, it didn't click with the volume turned down before the buffer was added.

In general, bleeder resistors on each side any kind of switch of 1M will kill most of this. For piezo inputs it should be 3M to 10M. For many other inputs, and almost all inter-stages (inter-fx), a mere 50k is sufficient (though often a 1M usually works just as well). For relative uncommon Low-Z inputs 50k is still sufficient, though little lower, say 10k should better (as low as 2k may be needed). There is trade-offs between draining leakage induced DC and added noise from the resistors themselves.

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 JosephKK
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