Superstitions and the Ghost in the Machine.

[Bill Mountain]

I've built the same circuit 4 times.  1, 2, & 4 came out swimmingly.  Number 3 on the other hand was super glitchy, noisy, but mostly disappointing.

I made some simple mods on No. 3 that were logically sound (swapped a few resistors) and should not have cause any sort of meltdown but the build failed anyway.  On No. 4 I went back to stock to guarantee it worked.  Now...I'm afraid to deviate from the "established" circuit for fear of it happening again.  It's possible I made a soldering or part selection mistake but two days of debugging turned up nothing!!!!!!

The issue is, is that the "established" circuit is a hodgepodge of ideas that I cobbled together as a proof of concept.  Now I want to refine it but I'm also afraid to mess with it.

Anyone have any superstitions against certain parts or mods because of unexplained circumstances?

[samhay]

Surely there is no harm in breadboarding the circuit with the mods. If it doesn't work, sequentially switch them back to the stock values until it works/identifies the problem.
If there is no problem, then yay.

[Phoenix]

Maybe if you post the circuit and the modifications you made to it in edition 3, someone here can help you identify why the changes you made caused problems despite your expectations?

[Bill Mountain]

Maybe if you post the circuit and the modifications you made to it in edition 3, someone here can help you identify why the changes you made caused problems despite your expectations?

Sure:

I moved R4 to R5 to hardwire the boost switch "On", I removed R23 and shorted the pads for the bypass switch to hardwire the EQ "On", and I increased R31 to 150k to get a little more output volume.

I replaced R6 with a pot to try out some different boost levels but I reverted back to the original value when the pedal didn't work right.  I tried the pot on build 4 but realized it wasn't necessary.

I also used 3.3M resistors for the 10M (R2 & R25) because I didn't have any.  I ran out and the supplier sent me 10k instead.  On build 4 I used 2.2M because I had plenty of them.

What I thought was the main culprit was increasing R31 but I am using a bipolar supply on the last stage so I should have had plenty of clean headroom.

The main issues with the build was that it was muffled sounding, the EQ knob didn't work right, and there was a loud squeal and ticking sound in most settings.

But...my main question was about superstitious habits you all might have developed due to experiences in previous builds.

[Bill Mountain]

Surely there is no harm in breadboarding the circuit with the mods. If it doesn't work, sequentially switch them back to the stock values until it works/identifies the problem.
If there is no problem, then yay.

True but I had vetted 99% of this build on a breadboard.  I thought I was safe making a few small changes.  Live and learn I guess.

[samhay]

Fair enough, as far as superstitious habits go: measure twice, then once more.

[Bill Mountain]

Fair enough, as far as superstitious habits go: measure twice, then once more.

This is a good idea.

One thing that I've started doing is that I hand write out the parts list every time I build.  Then I cross off each item only after I confirmed the correct value against the schematic, measured it, and placed it in the correct spot on the board.  It takes a while but most of my builds fire up immediately.

I also wire all the bypass circuitry first and confirm it works before I continue.  Sometimes I wait a day to make sure my mind isn't exhausted from all the prep work.

[Phoenix]

As far as superstitions go, I can't really think of any but one: I work mostly with tube amps, and on a handful of occasions I've had persistent crackling noise problems to repair that have turned out to be caused by a mica anode bypass cap. I've never been able to measure any leakage current or see any signs of physical damage or been able to provoke the examples to go open circuit or change in value or anything else that I could think of that would cause them to behave badly. Just seems that when these mica caps go noisy, the only way I've been able to confirm it is in circuit - not with any kind of measurement that I'm aware of. I also do not know of any established reason for the behavior I've seen exhibited. So I tend to avoid mica's whenever possible. It's getting easier to find plastic film caps in the low capacitance values and high voltages that used to be the domain of silver mica, so it's not really been a problem.