Guitar Effects Debugging Page
Copyright 2000 R.G. Keen. All rights reserved. Permission to
link but no permission for local copies or serving from any web site other than
Please note: This page was updated 8/5/00 and is getting pretty complete. There is
that is not yet sorted into place. A few links are still just stubs, but it does cover a lot of
situations. As always, additions and corrections are welcome.
- Assess your personal capabilities
- Have the right tools
- Getting brand new effects that you've built running for the first time
- Geriatric Effects - resuscitating the elderly stompbox
- Select the most obvious symptom:
- Has the effect ever worked? That is,
is it one you built new or is it one that is either commercial or that used
to work OK?
- Mechanical damage - broken case, broken
knobs, cracks, crunches, evidence of liquids poured in, etc.
- Completely dead - no sound whether bypassed
or not, no indicator lights (if the effect has them), nothing
- Sound only when bypassed, no sound at
all in the effects position
- No or
very little effect in the sound when the effect is engaged
- "Blatty" or gated sound
or sound only when you hit strings hard, or sound only as
the note decays away.
- Radio interference
- Distortion on effects that are not intended to distort
Almost always a bias problem. The DC voltage tests, transistor tests, or
opamp tests should show this one up.
- Testing Transistors in the circuit
If you think you have a dead transistor, try this.
- Testing Capacitors
Temporarily unsolder one lead, and measure the resistance with your
ohmmeter. It should read open circuit on the highest scale.
- Testing Resistors
Easy - measure them; however, the other stuff in the circuit may cause a
fake lower reading. To get an accurate measurement, you have to unsolder one
- Testing operational amplifiers (op-amps)
- Symptoms peculiar to particular types of effect
- Distortion pedals
- Delays of all kinds - flangers, chorus, echos, digital delays, etc.
- Spring reverbs