A simple lesson in troubleshooting

[Mark Hammer]

I perfed up the bitcrusher circuit from Experimentalists Anonymous.  You can also find it as the Horndog on Madbean.  Not "full featured" but it does the trick.  Over the course of several days' testing, I just could not get it to work.

So today , I decided to systematically test AC voltage at the input and outputs of each op-amp.  All was AOK, except for the output stage.  I had used a quad op-amp that was sitting in the parts drawer.  Could there be something wrong with that 4th op-amp?  Stuck another identifiably new one in the socket and Bob's your uncle.  One of the 4 op-amps was fried.  From what, I don't know, but I put the old one back in the drawer - not before marking off the pins of the bad stage with a paint pen.

You don't have to have fancy equipment to troubleshoot circuits.  Sometimes, all you need is a meter that can register meaningful AC voltages, and a sense of where on the circuit you ought to be seeing something of reasonable amplitude when you strum the guitar.  OP-amp outputs is usually a pretty good place to start.

BTW, I used a 1M Frequency pot and found that more than good enough.  As one rotates the pot, you get the sense that the circuit would REALLY love some sort of modulation of Frequency rate, whether by LFO, envelope, or expression-pedal.

[Electron Tornado]

You don't have to have fancy equipment to troubleshoot circuits.  Sometimes, all you need is a meter that can register meaningful AC voltages, and a sense of where on the circuit you ought to be seeing something of reasonable amplitude when you strum the guitar.  OP-amp outputs is usually a pretty good place to start.

What he said ^^^^


If you do add an LFO or expression pedal, please post a video or audio file.

[iainpunk]

i find 9/10 debugging situations are resolved after breaking out the audio probe. recently, i was fooled tho, one singal path that DID work had problems when audio probing (squeal and gating), but not when it was in normal use, while the other signal path was working properly when probing, but did some heavy motor-boating when not probing.
i ended up adding a 100n cap and a 100k resistor from that opamp output to ground to simulate the probe, and it keeps the circuit in check. (commission build; parallel overdrive and fuzz, mixed using some filtering.)

cheers