your expert help needed by newbie here please

[Kurdt_01]

hi

I own a boss DS-1 and i am intrested in modding it out so i can control the Gain with an expression pedal as i like the sound of both full gain and low gain.

I was thinking about adding a small latching swith so i could turn the expression pedal imput on and off.

so,  signal in - to gain pot OR to jack socket and pedal (depending on switch) - signal out

can you please help

Maybe a step by step guide or even a schematic including the parts and supplies (I'm uk based)

Thanks a lot

Dave

[Mark Hammer]

I'm a little confused.  Do you want to be able to manipulate the gain in real time or are you simply interested in having a lower and higher gain preset, each with their own control?

The gain and distortion of the DS-1 is set via a pot used as a voltage divider, with one leg going to ground, and the other leg going between the output of the op-amp and another fixed resistor in the feedback loop.  It's one of those wonky TA7136 op-amps, so I'm not going to even hazard a guess as to what you'd want to stick in with that pot.

On the other hand, since ALL diode-based clippers (and this is, at its heart, really just a glorified MXR Distortion+/DOD 250) depend on cumulative gain prior to hitting the diodes, AND since this has a single transistor gain stage remarkably similar to the input stage on a Big Muff immediately preceding the TA7136, it is safe to say that the amount of clipping is a result of the overall gain produced jointly by the single transistor stage and the TA7136.  That means you can vary overall gain by tweaking the one OR the other.  IN this case,, tweaking the transistor gain is likely to be the easier task of the two.  More importantly, I get the sense from the assorted caps in the TA7136 stage, that this particular stage is designed to provide some sort of tonal/bandwidth adjustment as gain is increased, and you probably don't want to tinker with that too much...at least not at this point.

How would you tweak stage-gain?  Don't ask me, I'm not a transistor guy.  But I gather it would involve either the 22R resistor between emitter and ground of Q2 or the 10k resistor between collector and V+ on the same device.  Either of these could be changed to have either a series resistor shunted or a parallel value added and by so doing switch "gain range", which would then be fine tuned by the pre-existing drive/dist pot.

Make sense?