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Tip 2. What causes popping in amplifiers?
Have you ever noticed a pop when you change pick-ups, or turning on any true bypass effect switch? Most of the time, this can be explained by what is called a D.C. input offset. What does that mean?
It's basically when your amplifier input which should be sitting at 0 volts has drifted to a different level. When your guitar is plugged in and playing normally, the input is given a ground reference and everything works great, but when you break the circuit, even for a fraction of a second like selecting pickups, or with true bypass switching, that voltage drifts back up to a different level. The pop sound is when the circuit is reconnected and the voltage comes back down to ground with a THUD!
So what can be done about it?
There are a few things, so here's a few to try. Measure to see if it is on the input of the amp. Plug a normal guitar lead into the input and see if you can measure any DC voltage between tip and ground. If it reads anything other than zero that could be a big part of your problem. You may need to look at the valves or the filter caps in the amp.
On pedals you can use a pull down resistor on the switch so the there is always a reference to ground which helps enormously but be careful of the value, you don't want to effect the tone of the pedal. Most people use a 1 meg resistor with good results. The resistor goes from the output of the switch to ground.
HOWEVER, if there is leaking DC on the input of the amp you may find it very difficult to solve this problem even with a pull down resistor on pedal. If this is the case make sure you get a qualified tech to look at the amp.
