Imagine you have a high impedance ground to the amp, the amp is powered on and stable, and it is drawing a given curent. There is a stable, low-voltage level at the input to the amp (the empeg is paused). You now press and release the brake pedal. When you release, you get an inductive EMF in the power line (a small one, since it's only a light bulb or two). The amp should allow the spike to pass if it's got on board RF supression, but the high impedance earth return means that the earth voltage rises with the spike in the power line. Relative to the input level, that is a step voltage seen at the input stage of the amplifier. If you have high gain on the amp, POP. I would get the guy at the shop to look at the earth point voltage of your amp, compare it to the DC ground for the amp (if they need to be seperate) and then have a look at what it does when you release the brake pedal. You will need a high impedance scope to do this.


One of the few remaining Mk1 owners... #00015