Boss DF-2 modification questions

[bside2234]

So I have five of these things now. Thought I'd try to mod one of them but have a few questions. The distortion on it is ok. Not great. Anyway, I was thinking of trying to disconnect the distortion part of the circuit and put in a simple overdrive or fuzz circuit in it's place. Something that would fit in the battery compartment most likely. I'm just not too sure where the distortion actually begins and ends or if this is even possible.

I'm guessing the output is either lug 2 of the Level pot or C14. Not really sure where the input would be. R3? The switching connecting to C17 is kind of confusing me as to where the input is.

Any help would be greatly appreciated.

Here is the schematic:

[Taylor]

The way I read it (sideways), the guitar signal and the PLL signal are mixed at C3 and both go through the distortion. The distortion is an opamp into clippers to ground, ala DS-1. The fundamental detector BTW is the same from the OC2.

If you wanted to change the distortion to a TS-style overdrive, you could remove the diodes to ground and add them back in parallel with the dist pot, which is controlling gain of the opamp stage just like you would see in a TS.

If you wanted to add an entire fuzz circuit, I guess I'd take out everything between c10 and c8 and insert your fuzz. This will keep the opamp setup as a booster, which I personally like in front of fuzz.

[bside2234]

Cool. Well I guess my overall plan is to disconnect the distortion part, solder an input and output wire to the board, run these wires to a breadboard and try different circuits until I find something that works well and sounds good. I was going to try this as C3 and C14 but the switching connecting at Q3 was confusing me and making me think this might not work.

[Mark Hammer]

There's too much to bugger up in there, and too great a resale value on this pedal.  I would suggest simply trying to eke out a little more distortion from the existing design.

You can do that by adding a little more juice to the gain stage built around IC 1a, which gets clipped by the diodes.
Presently it is set for a gain of 54x (which is generally not enough for serious fuzz, but I gather there is an earlier gain stage provided by Q2 that multiplies the gain in IC 1a).  If yo can identify the solder pads for R17 on the copper side, simply tack on a resistor between those two pads, of any value between, say, 10k and 2k2, to increase the gain and get more buzz on.

For me, that would be the least disruptive, invasive, and risky mod.  And its dead easy to do, so do it, give a listen, and decide if you like it.  Note as well that the tone control is the traditional Big Muff type, so all of the rules for modding those apply in this instance.  If you wanted a big midscoop so that the bottom and sizzle stood out more, that would be the easy way to go.

[bside2234]

Thanks Mark. I'm not too worried about resale value on the one I want to mod. It hardly has any paint left on it, the knobs aren't original and the bottom rubber is gone. It looks like it was dragged behind a car on the freeway for 100 miles. The other 4 I have are in really good shape so I'm keeping them stock. I'm not worried about buggering it up at all either. I'm really good at soldering.  I kind of just want to find an input and output point where I can disconnect the distortion, hook up some wires to my breadboard and play around trying different circuits in there with the feedback.