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It looks great.

Please forgive my ignorance. For a decal, in what order are things done? Drill first, apply decal?

I guess I am curious about the whole process. At this point I should be using the search function, I suppose.

I tried it, but I must have done something wrong. There was a lot of the effect signal even with the switch off. I am pretty sure I just matched the old DMM bypass.

I am not going to do a build report, but I figured I would post this here since I am in the mods area: It sounds great. However, I would definitely recommend the resistor changes to decrease the range of the modulation depth and speed. For the stock values, it can go so fast that it ceases to be modulation, and just adds noise. The depth is such that the control at noon is what I would consider the maximum for normal use. Also, it can be pretty difficult to get at the mod depth resistor after the surrounding components are in place.

Also, I wanted a very different control layout, and did end up with some LFO ticking at first, solved after moving wires around.

That should work. You could also just wire a 78L12 on the rotary switch for another position.

I am curious if anyone has built a Dirtbaby with a buffered bypass similar to the original DMM. I like the idea of ending my board with a buffer/volume even with the delay off. I know Howard Davis has publicly said he thinks the true bypass DMM was a bad idea.

Does the Dirtbaby have any trouble with matching on and off volumes in true bypass, given it has the trim resistor?

It looks like I just need to take switch the output off the blend pot before the 150 Ohm resistor and jumper some pads on the board.

I think I got it. With a center off SPDT, connect the middle lug to pin 3 of the depth knob as normal, connect the 2.2u capacitor as normal. Connect the 0.47u capacitor from the middle lug of the switch to pin 6 on IC3. In the spot where the 0.47u is supposed to go, put a jumper. You would then have 3 positions: shorted/defeated, 0.47u, and 2.67u.

Another PT2399 design, the Echo Base has pretty much the same LFO. That design has a switch to short out the feedback cap on I3B to turn off the modulation.

I was thinking about the same question. I ordered the dirtbaby this week, but have not built it. If I am reading this right, IC3A is a schmitt trigger, and IC3B is set up as an integrator. I think switching between the capacitors just gives different levels of integration on the pulse, so leaving it open would essentially make your modulation a big square wave, not what you are looking for.

I was considering getting a DPDT center off toggle, wiring one side to switch the caps, and one side so the center position opened the positive feedback between R34 and IC3 pin 3. I honestly don't know if this would work. Another option would be shorting the depth pot wiper to ground. I didn't take the time to figure out how to make this work.