Removing POP from truebypass switching.

[served]

Hi.

I have been struggling to fight with pops in truebypass switching and so far some cases this has been impossible.
I don't know why, but it has something to do with the input, because if I ground the input directly to ground, it will not pop anymore.
The input Cap is not leaking, as I have tested some of them and used tested caps incase of a pop just to see what would it do with tested cap.

So it leaves to a switch maybe or something I am not familiar with. Maybe the circuit is not behaiving (it is using LM386N only), no buffers or anything.

This leed me to an idea that I remember seeing somewhere.

Why shoulnt we use a transistor that will short out the Input when the pedal is disengaged and its resistance would go to infinite when the pedal is engaged. In this case we would still keep it truebypass but instead of 1M resistor we would have more intelligent circuit.

Any ideas how to do it?
Has anyone already done it?
Any ideas about the POP. Its killing me!!!

[Kesh]

A few things to try

Put a high value resistor to ground at input. 1M5 or something.

If it's LED pop try http://www.muzique.com/lab/led.htm

[Mark Hammer]

Kesh is correct.  TWO major sources of switch popping:

1) "Free" end on an input or output capacitor.  Solved by having an input/output terminating resistor to bleed off stored charge of cap.

2) Sudden spike on the power line from an LED being turned on and drawing power.  Solved by either a) using a superbright  (>3000mcd) LED that can still be bright enough with a higher-resistance (>10-12k) current-limiting resistor (less current draw = less audible spike), or b) the "slow turn-on" strategy that Jack Orman shows.

Another source of switch popping that people rarely think about concerns the conversion of FET-switched pedals to "true bypass", and switching of true bypass pedals in line with them.  FET-switched and other e-switched pedals assume that the bypassing will be done within the pedal circuit, rather than around it.  So, they almost never include terminating resistors.  That will result in an audible thunk/pop when you first plug in, but all electronic on/off switching after you plug in will be done within the pedal circuit.  HOWEVER, if you stick a TB pedal in front of an e-switched pedal that has a "hanging" input cap, every time you stompswitch the TB pedal, you are momentarily disconnecting the input cap on the e-switched pedal, and then reconnecting it, thus mimicking what happens when you first plug your cable into one.  It is the e-switched pedal that is actually popping, but it is the preceding TB pedal that is causing it!  You can imagine that, after having used the e-switched pedal all this time, without EVER experiencing popping, it drives the user crazy in their pursuit of what they've done wrong with the TB pedal.  In fact, they haven't done ANYTHING wrong.  What they are experiencing is precisely what someone attempting to stray from the Microsoft universe experiences when trying to import or export a file: basic incompatibility between "universes".

[PRR]

> if I ground the input directly to ground, it will not pop anymore.

That "appears" to eliminate LED-pop and the box's own input cap.

Therefore you look at what is going IN to the box. Is it leaking DC? Put a meter on the patch-cord.

[served]

Hi.

Bypass wiring that I am using
http://img594.imageshack.us/img594/8776/wiring3pdt.jpg
Note that input is connected to ground when its bypassed.

So I will write down the things I have done.

1) Disconnected LED - still POP
2) Connected another 1M resistor for input cap (now its 500k, because there was one already) - Still pop
3) Effect PCB input straight to ground. - No POP (So I assume it is still the input that is causing this problem)
4) Additional non-leaking capacitor in series with the input cap (and 1M resistor to grount for the additional cap bleed) - Still POP
5) Output Cap bleed resistor 1M - Still POP.
6) Changed the switch - Still POP
7) Disconnected input ground if the pedal is bypassed. - Still POP.

The idea I had how to remove the pop was something like this.


So when the LED is not burning we have a zero resistance between Effect Input and ground.
If the LED is burning we have infinite resistance between Effect input and ground. In this case the shift can be delayed lets say 10ms. after the switch is pressed the resistance will change. Then if there is something gone bad then this method will ensure that there will be no POP no matter what is wrong with the circuit or switch.

And what we could penefit from this method also is that there is no additional resistor in parallel with the instrument. This should give us better results in some cases. So we can remove the bleed resistor completelly, for high-gain pedals it should give us some results.
I will measure the current that is moving after the switch is turned. Lets see what is going on there. I didn't get any readings though if I tried to measure the cap leakage.
Also it could be that there is something else wrong with the chain. Maybe my amps caps are leaking and there is voltage coming from my amp. I will find it out today.