BACK OFF...passive control.

[deadastronaut]

this just gets more passively-puzzling....

[ashcat_lt]

Yup, that's exactly what it is, hence my comment about a different way. You're right about the pot, I've got a 2M2 (linear is all I had) and I do have to turn it down, + everything happens in a small part of the sweep. Nevertheless, once set, it works without popping.

I gues what I was trying to say is that what this does is completely dependent on what's driving it.  The source whatever is the top half of this divider.  Putting it after different things will make it behave completely differently.

It doesn't work as a tone control as there's no cap

Most of the action of the T pot in a passive guitar comes from the inductance of the pickup.  It doesn't need a cap to kill treble.  In fact, the cap is kind of there to stop the cutoff frequency from getting too as the resistance gets smaller.  This is exactly why input impedance matters - it's the R-to-ground in an LR low-pass.

So put a pedal between the guitar and this box (thought you were doing that) and instead of a series L we have a series C, and this is the R in an RC high-pass.

[anotherjim]

this just gets more passively-puzzling....

Passive Aggression. The worst kind to have to deal with. Maybe that's a name for the box?

Got a wild idea, that may not fix it, but might be a clue - ground your pot via a cap instead of wire, big enough to all pass - maybe 100nF.

I get what's being said about step change in impedance, but a JFET bypass is a great big step change, doesn't click if done right.

Because the bias via 1M in and out sides means there is negligible change in voltage when switching. That said, even 1mV before high gain could be an audible click.

[stallik]

Seems Ashkat was right (thanks)- my circuit was loosing treble. so...

Replicated deadastro's circuit without the LED. No Popping with distortion- at least I think there isn't. As I now have the full treble content, there is a slight raise in background noise which, combined with the click of the switch, could sound like a bit like a pop. However, if it was a real pop, I would have thought that it would have repeated if I used a delay pedal after it. It doesn't and I can't hear it at all while playing at a volume level high enough to drown out the switch click.

I'm using it straight after the guitar (strat with JB junior & a tele) into Spitfire with the wick turned up, PT80 delay then chasm reverb. Tried it with 2 different valve amps and both at the same time. Will try to rig something up with the recording out of the amp. May be enough to prove it one way or the other

[anotherjim]

I had a play with the original DA idea  on BB. It do click - but only when there's signal or hum present. Doesn't have to be much if there's a lot of gain after it. If it's absolutely silent, everything is ground and stays that way no matter what the switching does.

Can't help thinking, if it must be passive, then a volume pedal with an extra minimum volume control is the answer - rock between drive and backed-off.

[stallik]

I've recorded from the direct out of my amp and the switching is pop free.

[deadastronaut]

i just found the EHX SIGNAL PAD schemo...

it has a 220p to ground before going to the 1MA  pot...

the led has a 9v>>> 100uf to ground,  3.3k. >>>led...

[Rixen]

Well, caught in the act. Didn't have a foot switch handy, so tested with a snap action push button. There is just the scope, and a 1 M resistor across the contacts:



next I tried a microswitch:



..and yes, these pop when connected to an amp..

tried a momentary rocker (no 1M in this case, but switched the scope and probe over to x 1, so that's 1 M anyway:

Some observations during testing:

1- Switches which don't 'snap' don't seem to exhibit this behavior.

2- These spikes also occur on switch contacts that are not actually being switched, so it is not the make and break of the connection.

3- Noise is also generated if the body of the switch is hit with a screwdriver.

I'm going to stick my neck out and suggest that some (most ?) switch bodies have a dose of piezo electric effect in their plastic. I certainly have plenty of coax that is microphonic due to the type of insulation used, so why not switch bodies ?

[deadastronaut]

interesting, cool tests....

can you try a 220p to ground at input, as the ehx signal pad does..?

[duck_arse]

don't forget the spring holding something somewhere internal, metal on metal. if that jiggers w/ motion, it could rub disimmilarr metals together, like. maybe.

[samhay]

Rixen - what is the range on your scope / how big are those spikes?

[Rixen]

@DA - 220pF across the contacts with 1 M (scope input) load kills the spikes.
@samhay - the range is 200mV per division. Duration is short, scope is set to 100us per division

[samhay]

Wow - thanks.
What happens if you AC couple the switch? - I don't think it would take much leakage current to give you a spike like that across 1M.

[deadastronaut]

cheers rixen.

what about a 220pf  not across the lugs, but..at the in to ground...


in>>>>>>220p>>>>>>>>pot lug 3......
                  /
                 /


sorry for the crappy ACSII....

[Rixen]

@samhay - yep, tried that with a polyester cap, same result
@DA- because a scope is used, one of the switch lugs by default is ground.. I'll have a think about how to make it more like a typical guitar set up.

BTW, connecting switch lugs to an audio amp - I could hear screwdriver handle taps on the switch case through the speaker...

bit of further research (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20020044745.pdf) shows (some ?) polyamides (ie nylon) are piezoelectric.

..I guess guitar pickup selectors don't show this because they don't snap..

I was never able to completely clean up my TS808 clone, eliminating DC to the best of my ability.. guess I have an answer now. I see if I can fix it when I get it back from the guy I loaned it to... 

[samhay]

OK - cool. Thanks for checking.

[Ripthorn]

Because of the changing over of the contacts, the popping doesn't surprise me.  The reason a volume pedal works is that there is always that resistive path to ground that doesn't get interrupted.  Instead of switching the pot in/out with the true bypass, what if you always had a high resistance voltage divider (much like a pot always on) and you then switch in the pot as a variable resistor on the ground leg, thus instantaneously changing the resistance to ground, but not the entire signal path.  The small series resistance in the signal path might help keep pops from happening and it always has a signal path that doesn't get temporarily lifted while the contacts switch.  No idea if it would work, but seems like it would agree with a volume pedal concept more completely...

[MrStab]

i'm surprised no-one's mentioned using an optocoupler yet, with an RC on the LED line for delayed turn-on. i'm late to the party so it's probably an unhelpful suggestion, but it's there! take it or leave it! lol

Edit:

delayed

that's probably why no-one suggested it.

[Jdansti]

Also, he's trying to do make it work passive.

[MrStab]

Also, he's trying to do make it work passive.

ah, just saw the schem with a FET and assumed the wrong thing