I've just completed my first amp build and could use a little help: I need to troubleshoot a hum/hiss when a bypass cap is removed from the circuit (i.e. using a switch, intended to reduce gain); and This is prototype, and I'm looking to check some possible design improvements with people who actually known what they're doing before doing a final version. Any help is much appreciated! The amp: It's deluxe micro using Rob Robinette's design, with a couple of simple mods (passive fx loop, switched bypass caps). Apart from the above hum/hiss when switching out one of the bypass caps, the amp sounds amazing. The suspect part of the circuit: I have put two bypass caps on switches so they can be removed to reduce gain (using this layout for labelling, the V1B and V2 bypass caps are on switches). This was mostly as an experiment to see what switching them out would do to the sound. Re moving V1B from the circuit works as intended, less gain and no noise. Removing V2 from the circuit introduces a noticeable hum/hiss, and it's unaffected by any other variables. I have pictured the part of the circuit that switches out the V2 bypass cap. Question 1: Do you know what the noise could be and how I could fix it? Could it be: the V2 cathode resistor got fried when soldering? the long runs of wire to/from the switch be introducing noise (note the noise didn't change when I forced the wires into different routes)? that the V2 bypass cap can't be removed, or not without other changes? Design improvements: Full disclosure, this is my first amp build and was intended to be a prototype before building the final version. You are guaranteed to see issues! While the above is the only issue I can hear, please do tell me what else can be improved for the final version. I have a few specific ideas myself... Question 2: Are these worthy design improvements, and can you suggest any others? shortening and running more wires against the chassis with conductive copper tape - my theory is this will shield longer runs and reduce potential for noise; using eyelets instead of turrets - turrets look good but man are they hard to solder without melting everything else; no more screw terminals - I did it in case components were faulty or I made a mistake, but I'm unsure if these actually have any downsides; and using a solid state rectifier - while I love the look of a tube, they are expensive and I suspect this amp is not big enough to get any sag out of the rectifier tube.