Bypass switch popping

[aflynt]

Hello.

I'm in the process of adding status indicator leds to 5 effects pedals, some DIY and some commercial. I'm using Cliff 3PDT switches and 8mm LEDs of various color from Pedal Parts Plus and the 3PDT wiring boards from Smallbear Electronics. I've wired up 4 of them and they are all basically functional (effect switches and led lights up) but 3 of them pop to varying degrees when switched now. The offending units are a Rangemaster clone, a Tubescreamer clone and a modified RAT II. I also did an MXR Phase 90 which doesn't pop at all.

The LED and switching circuitry is basically the same on all with the exception of different current limiting resistor values for the different color leds. The smallbear board grounds the effects input when bypassed and has a space for the current limiting resistor post led. The led is wired +9v -> +LED- -> Board -> Resistor (except for the Rangemaster which is positive ground). The resistor is only in the signal path when the led is grounded (on).

I've ensured there is no DC voltage present between input jack and ground and between output jack and ground with the effect engaged. I've also tried clipping in a 1 meg pulldown resistor between board input and ground and board output and ground. The pulldown helped eliminate about 90% of the pop on the Rangemaster between board output and ground, but the RAT and the Tube Screamer were un-helped.

For the Tube Screamer, I've experimented with the AMZ LED delay filter with no success. I'm using a 47uf cap, a 10 k and a 820 ohm resistor. I tried hooking it up two different ways since I read somewhere that the wiring diagram was wrong. I tried it with the cap negative going directly to ground and also with the cap negative being switched to ground (soldered to the same lug as the LED negative leg). With the cap negative wired directly to ground the LED flashes super bright when switched on. With the cap ground wired to the switch the LED doesn't flash when turned on but instead gradually fades away when switched off.

Any ideas for other things to try?

-Aaron

[amptramp]

If you suspect the LED circuitry, remove the LEDs and see if the same popping happens.

The original tube screamer used logic switching rather than true bypass and this provided a gradual on through the transistor as shown in the schematic:

http://generalguitargadgets.com/diagrams/ts-808.jpg

The 1 megohm resistor in series with the base of the LED switching transistor provides a slower switching time due to the Miller capacitance from collector to base slowing the switching.  If the LED's are the problem, perhaps slow switching via a transistor with a time constant at the base would eliminate the pop and the excessive LED current when powered by an electrolytic capacitor.  This can be done even with true bypass.

[aflynt]

If the LED's are the problem, perhaps slow switching via a transistor with a time constant at the base would eliminate the pop and the excessive LED current when powered by an electrolytic capacitor.

This is what I have implemented that isn't working:

http://www.muzique.com/lab/led.htm

I think it's supposed to do something similar to what you describe using an RC filter slow the current surge from the LED lighting. It just doesn't seem to be helping with the pop.