This is the Maestro Filter/Sample & Hold project from JD Sleep’s site. The second foot switch (the one on the left) is for switching between Filter and Sample & Hold. The on/off status indicator is a bicolor LED, green for Filter, red for Sample & Hold. In addition to including all of Tonda’s mods, I added a couple of others. Here are my layout and PCB transfer files.
I used a MAX1044 chip, as described by R.G. at GEOFX, to make a bipolar (+/- 9V) supply that can be powered from a 9VDC wall wart or a single 9V battery. It’s a nice, easy way to deal with 9V bipolar power requirements. But, in this pedal, the battery option is more of a novelty than a practical option. This circuit draws something like ~38mA. So, I’m not even sure if a battery would even get you through one gig. No big deal, tho. I’m planning to use the wall wart, exclusively.
The other mod that I added was a wet/dry balance control. For bass players, this a nice mod to do on any pedal. And, it’s especially easy to do on this pedal. If you check out the schematic on JD Sleep’s site, you’ll notice that it includes a non-true bypass option (the switch at the output jack). Just replace that switch with a linear taper pot (wire the center lug to the output, one wiper to the C2/R4 junction, the other wiper to the C4/R14 junction). I used a 500Kb pot, but other values would probably work, too.
As for that ‘noise’ transistor in the S&H section, I think I’ve settled on an NTE123AP (same as 2N222A). But, I also got reasonably nice randomness with NTE161, 2N5308, 2N3392, and MPSA13. It took me some time to get those on-board trimmers set just right, too. R27 seems especially touchy. I’m still thinking about replacing it with a multi-turn. The 12K resistor on the copper side of the board is only there because I didn’t have a 10K trimmer handy, so I used a 47K instead.