Jet city JCA20H mod - can't find schematics or instructions

[vintagekiki]

Jet city JCA20H mod

What do you think about the diagram above?

[spunko]

[ATTACH=CONFIG]54413[/ATTACH]

Thank you very much, that is awesome!!

One question, adding those resistors (1M and 2M2) wouldn't change the behavior or sound of the amp even in the crunch/normal mode??

[vintagekiki]

One question, adding those resistors (1M and 2M2) wouldn't change the behavior or sound of the amp even in the crunch/normal mode??

Resistors 1M and 2M2 do not affect the sound in any one mode.
They generally serve to reduce the "click" that may possibly occur when switching SW1 from clean to crunch and vice versa.

[g1]

Resistors 1M and 2M2 do not affect the sound in any one mode.
They generally serve to reduce the "click" that may possibly occur when switching SW1 from clean to crunch and vice versa.

Why the change from 330K to 1M, is it so there is less attenuation on clean setting?

[vintagekiki]

Why the change from 330K to 1M, is it so there is less attenuation on clean setting?

The clean / crunch mode does not change the schematics JCA20H.
Only added SW1 (clean / crunch switch) and "anticlick" resistors 1M and 2M2 .
Resistors 1M and 2M2 do not participate in attenuation of the signal.
1M provides polarization of g1 (V1a), and 2M2 allows "emptying" C24 when SW1b is in clean mode.

[spunko]

Thank you very much for the help.
I tried vintage kiki diagram and so far so good.
I'll give you an update in a couple of days.

[spunko]

Hello friends.

An update to this thread. I tried J M Fahey in my first mod and it worked really well, but I ended up mixing it with another suggestion from another forum. (If you see my first diagrams) and the clean mod sounded really good, but when switched to gain/normal, and if you strum a chord, at the end of the trail the volume faded down and up again. This is the reason why I tried a different aproach with the suggestion I got from Dr. Olaf Krampe by email.
Whe I switched back to normal, no mods at all, the amp stil behabed with the fade down/up problem, and it turned out to be flux residiu on the PCB that I didn't clean.
Perhaps my first attemp would worked well if I had cleanned that flux residiu.

Well, I tried the second mod suggested by Dr. Olaf, and improved by vintagekiki, and it is working great. It sounds really good.
It drops the volumen quite a bit, but not that much to bother, and with the improved headroom, it sounds good and interesting. Like if its another amp.

It would be awesome if we could still keep this thread alive, improving or changing the mod.

*Edit:
This is how I hooked the mod to the switch.
Sorry vintage kiki for butchering your diagram.

[J M Fahey]

Oh, you can keep it alive , just test other options and post results.

Glad you found a solution you like