I just finished a Frost Drive build. I'll post some pix in the Build Reports forum over the weekend.
I corresponded with Peter Rutter. He has some residual stock, but the C10K duals he has are 9mm and won't fit the pad pattern on the Frost PCB.
Here's the thing about the MID pot... rev audio (C taper) is the wrong taper for this circuit because the MID pot is wired backwards. CCW rotation makes the frequency of the mid hump go up; CW rotation makes it go down. As designed, the MID pot does not space the tuning out evenly, the top half of the rotation makes essentially no change in the tuning and the bottom half is too sensitive, especially near zero. See the simulation results below. Actual operation agrees. Two options:
1) Use an A10K dual, they're much easier to find. The rotation will still be backwards, but the tuning will be spread evenly.
2) This is the one I chose. Use a C taper pot and wire it backwards. If you want smooth tuning and normal rotation (CW makes the frequencies go up), that's what you have to do. It's actually pretty easy. Tie pin 1 on each gang of the pot together. No need to connect pin 1 to the board. Tie both pins 2 together and connect them to one of the pin 2 pads on the board, doesn't matter which. Connect each of the pin 3 terminals on the pot to the pin 1 terminals on the board, separately. If you think this sounds crazy, take a look at the schematic and you'll see why it works. We still have the problem of obtaining a C10K dual. I solved it this way: C100K duals with solder lugs are available from Pedal Parts Plus. There is nothing magic about 10K pots. Any reasonable value could be used as long as C3, C4, R4 & R5 are scaled accordingly. I made the pot resistance 10x bigger, so the impedances of the other 4 parts had to scale up by 10x as well. That means R4 & R5 are now 10K, C3 is 4.7nF and C4 is 12nF. Note that the PCB silkscreen and the schematic both have typos for C3. The BOM is correct (47nF). You can find the VFE Ice Scream schematic on MadBean's website. It has the same reverse rotation / wrong taper issue, but it does have the correct value for C3.
I used A1M for the DRIVE pot, it works fine. B1M will make the bottom end of the range too sensitive.
Mid Boost tuning (as designed). Each curve represents setting the MID pot to 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10.
View attachment 1672
Mid Boost tuning, corrected.
View attachment 1673
Here's a pic of how I wired the MID pot.
View attachment 1678