Other Amps

JC 120 mod

1

Probably blasphemy around here but i picked up JC-120 head sans speakers and cab for $25 today. Reoldered one loose cap and cleaned the pots and whammo works perfectly. Always like the stereo possibilities of these amps as I run a RE-150 Space echo (separate dry and scho outputs) stereo into two amps. i just discovered that the non effects channel on this amp(I think an early 80s version) has it's own power amp that has a coax connecting it to the wet channel. then a 47k resistor (mixing resistor keeps the two inouts from interacting)and then a coax FROM the wet channel into this power amp (so the effects are stereo). This makes it so both channles go to both amps accessing the amps full sound and allowing the effects to be stereo.

So I disconnect the coax going from the non effects channel to the effects power amp and boom! I have a channel that only goes into the dry power amp. I plug into my space echo, run the dry sound into the chorus channel which feeds into both channels and then plug the echo into the no effects channel and it only comes out of one speaker! Stereo echo and chorus(when wanted) All I did was desolder one small connection. A neat mod for an older JC-120

2

For $25? Nah, that's not blasphemy. For a few bucks and a bit of bodging, you got yourself a clever device. Congrats!

3

Thanks! I'm pretty happy. I also just figured out to make the otherwise mono line out proper stereo too. Neato! Good for listening stereo through headphones via my board or late night recording of ideas

-there are two wires hooked to the hot on the ineout -For ease disconnect the one that comes from the effects channle board(pin 29)

-Attach it to an added 1/4" female jack (you'll need to drill a hole for the jack) with a 100 ohm resistor going from the hot pin to ground. Attach ground to...ground!

Done!

The lineout jack basically just sums the two channels with 47k mixing resistors but a common 100 ohm resistor to ground on the dry circuit board(keeps the level out reasonable), So when you separate them you need to add a 100 ohm resistor to ground on the new line out so the two channels are balanced

4

I got the little JC-22, new model, but find you lose a lot of the bass response when the chorus is on.

5

Great mod!

Even better deal you made. Good god, they do make heads only versions of JC-120s, and they usually go for 3-5 hundred.

I've had mine for 34 years . My son uses it every day. Great amps.

6

Gave it a good whirl tonight in rehearsal with the rockpop power trio I have with a couple of old friends. I used a 2 x 12 cab that had a couple of okay speakers in it. One new fender (special design) ex blues junior speaker(came with the head) and a similar powered (30-50 watts) Utah ceramic. It sound great. I like the chorus but not as much as I used to (25 years ago!) Too bad I couldn't rig it up with the two JBL D130s I have but then it would weight 1000 lbs and be a fridge!

I bet these amps would sound great with a pair of PA speakers


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