Adding bass pot/switch to Tubescreamer

TTBZ

So I was going to buy something new but then thought it must be possible to mod my existing pedal. I have a BYOC tubescreamer (either 808 or TS9, not sure which, how do I find out?) which I generally like for boosting apart from the bass rolloff sometimes. I want to add a control to adjust the rolloff frequency from stock to a fair bit beefier so I can dial in the right amount - ideally a pot but could do it on a switch if thats easier.

Seems like this is a common mod (change C3 to alter the rolloff frequency) but I can't seem to find a straightforward DIY guide for doing it on a pot or switch. Any tips? 

aord43

When I built my TS clone I added the fat bass mod here: http://www.muzique.com/lab/fatt.htm
I must say that I prefer it with the mod enabled, it's very thin without it. 

TTBZ

So with that mod the C2 capacitor is either stock or completely bypassed? I'd like to add some other options otherwise I can see it mudding up if it's too bassy. I don't really understand how the toggle switches work tbh - I can follow a simple diagram when wiring a guitar but proper schematics mean nothing to me! 

rico

Try looking at the fuzzdog manual for their TS. I built a TS808 with a three way switch to vary the bass cut so it’s defititely possible! 

aord43

I don't know the layout of your TS but if you can identify the capacitor in question, the simple version of the mod (which is what I did) is simply take a straightforward SPST toggle switch (one with just two terminals, either open or closed) and connect one terminal of the switch to each end of the capacitor. Closing the switch will bipass the capacitor to give you the bass response back. 

aord43

A slightly more complex mod could switch in a second capacitor in parallel with the original one to give an alternative bass response. 
I haven't tried it but going by the website I linked to, an 0.1uf capacitor should be a good value to try.
If you have a SPDT switch (one with three terminals) and with a centre off position, you can have three settings. 
Connect the centre terminal to one end of the original capacitor. Connect one of the other terminals to the other end of the capacitor. Connect the new capacitor between the two outside terminals.
Hopefully someone can correct me if I am wrong but that should give you three options. 
1. Completely bipassed - full bass response 
2.(centre off) original behaviour
3. New capacitor in parallel with the original, increased the value therefore extended bass response.
You might also want to try an 0.047uf new capacitor instead of 0.1uf. As I said, I haven't tried it and I am just going by the suggestions on the Web page I linked to. 

TTBZ

Edit. Ok will it work if I wire up a dpdt switch across the existing capacitor so I can have it stock in the centre position, then additional capacitors in parallel for varying levels of bass? Like so but with caps instead of resistors and with a cap across the pcb pads as well?

https://i.pinimg.com/originals/63/e1/f0/63e1f023e299fa9d3f709dc98934bb27.gif

aord43

TTBZ said:

Edit. Ok will it work if I wire up a dpdt switch across the existing capacitor so I can have it stock in the centre position, then additional capacitors in parallel for varying levels of bass? Like so but with caps instead of resistors and with a cap across the pcb pads as well?

https://i.pinimg.com/originals/63/e1/f0/63e1f023e299fa9d3f709dc98934bb27.gif

That looks like it will work to switch between two alternatives (assuming the resistors in the diagram are actually capacitors of different values).  My suggestion was to do it without removing the original from the PCB. Although you have said "in parallel" but your diagram will switch either A or B, with no option to have A + B in parallel.  Neither can your one be used with centre-off because the original is removed from the PCB and centre-off would have no capacitor there at all.
Edit: Just realised you said "a cap across the PCB pads as well" in which case yes, you would be adding the new ones in parallel, and centre-off would leave just the original in the circuit.