Bypass popping...again

[the monroe transfer]

Sorry to post such a seemingly-common question, but I haven't found an answer in the forums that seemed to work.

Just built a Tremulus Lune that's working fine, with the only problem being that the DPDT switch makes a colossal bang when turning the effect on and off.  Interestingly, it's very loud when there's a jack in the input socket, and when that's disconnected it's only the next switch push that makes a bang- it's silent after that.

I'm using a regulated 9V DC power supply, layout from here (http://www.tonepad.com/getFile.asp?id=84) and the 'offboard wiring 2" from here: http://www.tonepad.com/getFile.asp?id=76

Following RG's recommendations in another thread, I've measured the voltages at the tip of the input and output sockets with no jacks in either...

Effect on-  2.5mV input, 2.56V output (yes, volts, not mV)
Effect bypassed- input 0.03mv output 0.02mv

So, people much cleverer than I...what the hell have I done here?

[Paul Marossy]

Did you try a "pulldown resistor"?

[R.G.]

Effect on-  2.5mV input, 2.56V output (yes, volts, not mV)

The most likely explanation is that your output capacitor is backwards (if it's electrolytic) or shorted.

[the monroe transfer]

Man, you're good.  Yep, sure enough, having checked everything twice, the damned capacitor was in backwards. 

That's another one to add to the embarrassment pile...

But- aren't pulldown resistors part of the circuit already?  The 1M resistors going to ground near the signal In and Out are 'pulldown resistors', no?

[timehawk]

Yeah sounds like they would be.  But not all circuits have them in there design.

[R.G.]

Man, you're good.  Yep, sure enough, having checked everything twice, the damned capacitor was in backwards. 

That's another one to add to the embarrassment pile...

But- aren't pulldown resistors part of the circuit already?  The 1M resistors going to ground near the signal In and Out are 'pulldown resistors', no?

Don't let it bother you. Checking anything more than twice gets diminishing returns, as you are likely to see everything as correct the more often you look at it. Happens to you, me, everyone.

Pulldown resistors cannot cope with the low resistance of a backwards electro cap, which may only measure a few hundred or thousand ohms. the roughly-megohm pulldowns are there to cope with the tens-to-hundreds-of-megohms leakage of a properly oriented cap. Too much current overwhelms them.

[Paul Marossy]

Cool, glad you figured that out!