Can't Get Rid of Switch Pop

[DanD]

Quick Rundown:  Pedal is an combo AMZ Mosfet Booster(boost or buffered config)/Shaka 5.  One box, two stomp switches.  Both are Alpha DPDT and I used two Mil-Bypass circuits for LEDs.  I have spent the last couple days reading archives and trying all the tricks and tips I could find.  No dice!

A couple notes worth nothing:
1. All the input and output caps are either TRW or Sprauge Metallized Polypropelene - excess leakage should not be an issue.
2. I have 1 Meg pulldowns on the input and output caps of both circuits.
3. I am using new, cleaned mono jacks on input and out since I never use batteries.
4. Both circuits are on one protoboard with a +9v rail and gnd rail and no power or ground being brought in from elsewhere.
5. PCB, power jack, leds, & in/out jacks are star grounded to the input jack.
6. I use a self built power supply that's hospital clean and fully isolated.

Things I have done to try and narrow down the cause:
1.  Tried pulldown resistors all the way down to 1K to prove it was not a cap discharge problem.
2.  Removed the Mil Bypass circuits to take led current out of the equation - no difference at all.

3. Anything else anyone can suggest?

BTW other than the pops that are rendering this thing useless to me for gigs, I am in love with the pedal.  Both the mos-boost and Shaka are killer. 

[bioroids]

Hi!

How did you remove the Millenium Bypass?
Did you disconnect the cable that goes to the switch or just the led?

Luck

Miguel

[PharaohAmps]

Dan, I know how frustrating it is to have switch pop!  The "pop" is USUALLY the audible effect of a discharging coupling cap, and the pulldowns are designed to hold the cap low when the guitar isn't connected via the bypass switch.  There are other causes, but this is what I'd check for.  There are a few things you might try:

0.  DON'T assume anything is good.  I know you think that your caps are low leakage, but if you've spent days fixing this, then maybe you should re-think your assumptions.  Put the FX in bypass and measure voltage to ground on BOTH sides of each input and output cap.  I'd check the "outside" (other side of the cap from the fx circuit) on the mV range of your meter.  If you get anything over 50mV, replace the cap.  Try running from a battery, even if you don't use one normally.  I have "lifesavers" made up with a battery snap on one side and a 2.1mm ID coaxial power plug (Boss-size) on the other.  They're great for pedalboard power failures and testing stuff, cause you don't have to open up the pedal to change the battery, just run it from the external DC input.

1.  Where are your pulldowns with respect to your caps?  The input pulldown needs to be at the junction of the input and the cap, on the "outside" of the circuit, as it were.  The output pulldown should be after the output cap, at the junction of the output cap and the output wire leading to your stomp switch.

2.  Try wiring the DPDT switches WITHOUT using the Mill2 at all, but using one pole each for input and output.  That is to say, if the switch is seen as:

Code Select Expand


  jumper     input    fx input
     0             0           0
   ----------------------------
     0             0           0
  jumpter   output    fx output


Sometimes inexpensive stomp switches have some crosstalk between the poles, and the Mill2 wiring can cause this to become apparent.

3.  Use nice big filtering caps on each effect to the +ve rail.  I've seen a pedal make horrible popping sounds because a switch was changing the state of a bi-color LED, and the LED inrush was dipping the power supply rail just enough to carry through into the audio.  I'd go with probably a 47uf in parallel with a 0.1uf ceramic or poly cap near the main amplifying device of each circuit.  Those caps will help eliminiate power-related popping by keeping ripple off the supply rail.

4.  Try the pedal with just one effect wired to a stomp.  The Shaka 5 uses an opamp and a split power supply for it's "ground" in lieu of a bipolar supply, and so all the coupling caps into and out of the circuit are going to have almost 5V on them.  The AMZ booster is discrete mosfets, as I recall, and is a single-supply design.  There could be some interaction there, you never know.  Building on proto or perfboard might make your layout more receptinve to all kinds of noise, you never know.  I'd start with one effect at a time, and see if you can get it to pop by itself.  If neither pops by itself, but the combo makes noise, then the problem is in the parts common to each circuit.

5.  I've heard that some switches are noisier than others.  Try using a DPDT toggle switch and see if that helps.  I've also heard that some switches will become less noisy after several stomps, though I've never found this to be true with the switches I've used.  I have had pedals that would pop once when first switched and then been relatively quiet after that, as the caps "averaged out" and found their equillibrium points, but I usually have to replace those switches after a while anyway when one or both poles fail.

Good luck.
Matt Farrow

[DanD]

Thanks for the long reply.

Put the FX in bypass and measure voltage to ground on BOTH sides of each input and output cap.  I'd check the "outside" (other side of the cap from the fx circuit) on the mV range of your meter.  If you get anything over 50mV, replace the cap.

Forgot to mention previously that I checked this already.  The pulldown resistors are in the correct/typical locations.

Try wiring the DPDT switches WITHOUT using the Mill2 at all, but using one pole each for input and output.  That is to say, if the switch is seen as:

This is something I will try.  When I disconnected the Mil By, I removed Power and switch to the little boards I built, but I did not change the wiring to standard DPDT.

Use nice big filtering caps on each effect to the +ve rail.

There 200.1uF across the rail currently.  A large 100uf electrolytic at each effects power input and a 0.1uf next to the shaka's opamp.

I've heard that some switches are noisier than others.

I'll save this for last as it will involve a great deal of destruction to the protoboard and components.  I'm very meticulous with my layout so all of the components are clenched, formed, and clipped very specifically.  Many of the parts will be difficult to remove without needing to replace them with new.

I've heard that some switches are noisier than others.

I'm going to try this second.  I'll remove a 3PDT from another pedal see what happens.

Thanks for your help and wish me luck