Treble bypass test box

[stallik]

After making a switchable guitar volume Stompbox and playing with treble bypass for its volume pot, it occurred to me that being able to instantly compare the difference between the current guitar roll off tone with that of an alternative setup is very educational. For years I've followed convention and have been happy with the results but I'm now aware that there can be a substantial and rewarding difference between different setups.

So, I've started putting together a test box with a range of caps on one rotary switch and resistors on another which are introduced between terminals 1&2 of the pot. Duplicated to work with 250k & 500k pots, it becomes easy to choose the ideal combinations for a particular guitar and playing style while all the time being able to compare with the current settings. It's a bit like a resistor decade box I suppose and it's probably been done before but I've never come across one.

So far, I've only got a limited range of possibilities but it's already proving very useful - and informing me that my preferences for clean and distorted settings are quite different.

[EATyourGuitar]

how are you going to do consistent loading if you can just plug this box into any amp? is the input impedance of the amp you used for the test known or unkown?

[stallik]

Not sure I understand the question. The box goes after the guitar as a temporary replacement for the volume pot. I check out the effects of some combinations and if I find one I prefer, I wire those components into the guitar and the box goes back into the drawer. It just saves me repeatedly taking the scratchplate off and allows me to rapidly compare different values with what I've currently got. Nothing special but better than guessing.

[GibsonGM]

I personally don't think you'll notice much due to the changing load of different amps, all things being equal.  Good question tho. 

Most (all?) amps are going to have high enough input Z to not be much of a factor here...

[EATyourGuitar]

I thought it was to test the last volume pot on a pedal. that is something I would like to see. if you are doing this to find the right guitar volume pot then I would ask a different question. do you wire your pickups directly to the output jack of the guitar before doing the test with the box? there could be a parallel shunt if you run a volume after a volume. this changes the test. when you put the volume pot in the guitar and remove the box, there is only one shunt so it could be different than how the test was done. I hope you are using a low capacitance cable of less than 3ft to do these tests. I use mogami or evidence audio which is cheaper than mogami if you work for a distributor that has spools of it.