I´ve just built this last pdf layout using a bc550b for silicon transistor and for germanium, tried russians mp21a/gt108v. Both of them sounded nice with differences in texture and gain.
I just tried 9v power, but I´m planning making a voltage switch. I´m thinking on using 18v instead of 24, as some people stated in this forum, (and on tgp as well),that it worked better.
I´m trying to understand the gain switch. I used a 3 positions on-off-on switch, so now I´ve basically have a medium/low/high gain switch.
it seemed that the 470ohms resistor sets the gain for the medium gain position, because the high gain position just sends q2 emitter to the 68ohm resistor and straight to ground. So if we put a trimmer in place of the 470 resistor, we should be setting just the low gain mode, right?
Anyway, so to my understanding, the only way of adding a second trimmer for the high gain mode using my layout would imply a more complicated switching network, right?
And just out of curiosity. I seemed to understand that johnk´s schematics has not only a couple of caps with inverted polarity, but a different q1 emitter network that leads me to understand that that one could have even more gain than the layout I used. Anyone has experience with johnk´s schematics build?
Finally I went for a bc549b and a mp21a.
Liked better powered with 18v.
Peach guitars layout has some similarities with johnks layout. Shared C3 C6 and C9 cap values but C3/C6 polarity are inverted like in Ciaran schematics.
Johnk's omited Q2 emiter 5.6k resistor to ground. Tried it on my build, but it went farty and it just didn't sound right, so back to where it was.
Changing C3/C6 polarities is a matter of taste. I changed C6 polarity and left C3 alone.
Placing a link where 68r resistor just gave a little more gain as I suspected.
This is by far the most dinamic overdrive I've built with difference.
Normally a good dinamic overdrive cleans up well, but always retain the pedal sound character. This one leaves your guitar tone intact when played soft and just breaks on a very beautiful vintage way with lots of harmonics when played hard.