Putting together a JMK board right now. I've added the Bass/treble boost switches from the Codtone site. I also decided to use a pot for the drive, instead of the switches. I decided to use a footswitch to jump it into the "Forbidden" zone.
The drive pot that replaces the switches is a 1K linear. Now, the switches, notwithstanding the forbidden setting, give you three resistances; 560R, 1.1K, and about 371R with the two in parallel. Using a 1K pot, I used a 330R resistor between lugs 2 and 3, and a 110R resistor on lug 1. The other end of the 110R resistor goes to the board, as does lug 3 of the pot. Sweeping the pot gives you all the resistances of the switches, with all the in between settings too. As for the forbidden mode, the switch will break the connection between lug 3 and the board of the new pot. In a pinch, you could use a switched 1K pot as well, using the switch to go into forbidden mode. I would however use a resistor instead of going wide open in forbidden mode, which is totally unruly. Maybe I'll try a 1M trimmer to try and find a resistance that will be "out there", but useful.
As for the diodes, I've tried a bunch of different types, including germaniums, but the best sounding ones are some NOS 1S1588 Japanese diodes that I bought a while back. Looking at some Expandora gutshots, the seem to look identical, right down to the blue bands.
The LM108's are great. I haven't got the Russian ones yet, but I really like the LM's so I soldered them in. An old 4558DV is sitting in a socket. I might swap in something else to try, but the DV is working quite nicely. A 5087 is the transistor of choice here.
The H11F1 is what I'm using, and seems to work fine. I must say though, I had to check the units I bought from Ebay, 3 out of the batch of 10 that I bought were defective (no resistance swing with varying voltages applied, just dead).
My initial testing has my ears drooling. From what I've read, there's a bit of a love/hate relationship with this circuit, but I absolutely LOVE it. With the Drive knob set just so, and a setting the Gain pot to the amount of distortion desired, this is one absolutely interactive beast with the guitar volume. Backing off the volume, it cleans right up, and I mean "right up". Very clean. I can maybe push it a tad into grind if I really dig in, but not a peep of dirt if so desired. Dial up the volume, and grind galore comes to life. Quite frankly, I'm so impressed, I just bought a 2000R version on Ebay, and I'm looking forward to looking at the guts of that one. Wish I could find the 2001 version schematic. The links over at the other place are broken, but from the small picture, it looks really different from the other versions.
