Hi Andy,
Thanks for your kind reply. Let me please put all this in context. I built an Alembic Bass preamp (essentially a Fender Showman preamp) some time ago. Then I put it in a stomp box. The project was largely based on this:
The sound was great both in front of the amp as well as in the FX loop. Then I stumbled upon the STM800 (a JCM800 preamp in a box) and I built it with several mods suggested mainly by member Abbey Road d'Enfer (which I still thank infinitely for his patience and wisdom). The thread is here in case you want to check it out: https://groupdiy.com/index.php?topic=70561.0
The STM800 schematic is here:
The short version is, I got back to the original STM800 stomp box project for several reasons, but the "JTM45 version". This is the schematic:
Then I added to that schem the Matchless Hot Box Clean Channel from here:
And ended up with this (some mistakes are now corrected like plate resistor on V1-A):
After building it I will probaby want to try adding LED clipping distortion somewhere, but as PRR said, I need to solder first and listen to what comes out
My previous question was to see if I could spare duplicating things but as you said that's not a good idea since I'd loose the ground reference when switching.
Regarding your other thoughts, which I appreciate, I am a passionate hobbyist aswell
Actually I'm a sound engineer and guitar player and I build things on my free time trying to understand the magic of electronics
andyfromdenver said:
I was just sort of thinking, maybe use 220k plate resistors on the first stage and 2.2k cathode resistors then you can at least parallel onto those to mess with different bias configurations.
V1-A seems to have that configuration. You can see it on the now corrected schematic. Or do you mean another stage?
andyfromdenver said:
Only last thought is do you need the exit coupling cap?
Actually that was going to be another 2 questions I have:
- Should I place the switch after the exit coupling cap BEFORE the Master pot?
- Do I really need the last cap? The cap is present on the original STM800 schem, and on very the first box I built (the AB273 modded circuit) that's why I kept it, but do I need it?
Thanks a lot for your time and help
Greetings
Sono