This Epiphone EA-5RVT Emperor came into my shop with a general complaint that it didn’t sound right. The most obvious issue was when the reverb was switched off and the volume was down, turning up the reverb knob resulted in a distorted tone. I opened it up, and it look like someone tossed a bunch of filter caps in the air and wired them wherever they landed! Each capacitor had it’s own ground, tied only through the chassis.
It’s easy to assume that ground is ground is ground, so it doesn’t matter how they are connected. In reality, the rectifier pushes pulses of current through the filter caps into ground, 120 times every second. These pulses can approach 1 amp. 18 gauge copper wire has a resistance of 0.0016 per 3 inches. With this wire, 1 amp of current produces 1.6 millivolts of noise on the ground. This may not seem like a lot, but if your V1 tube stage uses this “ground” as a ground reference, but your input jack does not, this small voltage gets amplified right along with the guitar signal! To give you an idea of how much 1.6 millivolts really is, the Soldano Super Lead Overdrive needs only 0.4 millivolts to overdrive the lead channel!!
It’s important to remember that all wires have resistance, and ground is not always ground. Interestingly enough, my tech notes about the Silvertone tremolo are an example of exploited bad grounding in order to make the tremolo run. Proper grounding can make all the difference in the world!
JDP Amplifiers 