Roland jc-120

[Mikelib]

Hi guys,
I have a Roland jc-120 and am having a few problems with it. The chorus effect seems to be stuck on one setting and the knobs wont change the sound. The same knobs control the vibrato perfectly fine. Also when i turn up the reverb a buz starts to occur and increases with the amount of reverb added. Any help will b greatly appreciated. Cheers,Mike.

[Don Symes]

It sounds like the chorus/vibe switch - or the traces connected to it - may be having problems. Start by ohming out the switch contacts in each switch position (broken switch), then try touching up the solder joints at the switch and where those traces go. There are probably switching ICs involved in the signal routing, so you may wind up debugging those.

The reverb buzz - try some known-good cables with shields grounded at only one end. Try disconnecting the drive cable - buzz gone? - bad drive stage.
Buzz still there? - cables, recovery stage or tank - probability in that order.

Hope this helps!

[drasp]

Mikelib - any luck fixing this issue? My JC-120 seems to be having the same issue w/ the chorus controls.

[lobo_sito]

Hi, I have problem with the reverb of my jc-120, It doesn't work.

[deerhunter]

roland 120

I Bought the amp off eBay and it dose not have any knobs in the add it looked fine I've looked all over the enter-net and can't find any place to buy them if any body knows were I can get them pleas let me know it's a real nice amp with knobs it would be even better

[drasp]

There is a seller on eBay selling a set of knobs for the JC amps, also available direct from Roland @ ~$4.50ea. I think. . .

[edwardcooper]

Guess this thread is pretty old, but just thought I'd chime in:

My JC-120 just fell out of the trunk of my car and now it's reverb doesn't work at all - I know little about the internal workings of amps and was wondering if anyone has suggestions.

And in response to the question about the chorus:

The JC-120 has no settings for it's chorus effect, it's just on/off. The vibrato is adjustable by depth and rate, and you'll notice that the vibrato approaches the sound of the chorus when the rate and depth knobs are turned all the way up...


best
eddie

[Alex R]

These amps went through a lot of versions but if yours has the reverb tank 'made by beautiful girls' then...

Take out the chassis with the amp unplugged. The connections to the reverb tank are hard-wired into the tank - one green and one red. Trace them through inside the chassis and you will see that they join a board on the right of the chassis more or less side by side, splitting into two as they join the board. One of each of these split pairs is a screen and one the hot wire. Check the resistance between each hot wire and its screen. Should be a low resistance, much less than 1000 ohms. One is just a couple of ohms. If you get a high resistance for either, note which one and remove first the big heatsink and then the reverb tank, and check the two-wire internal connections that go to the little coils for continuity. Sometimes they break - that might have happened when you dropped it. In that case you can often mend the break carefully.

But if your reverb was not made by beautiful girls, someone else will have to help you.

[drasp]

+1 on what Alex said.

My JC-120 & JC-60 both have the WI made "beautiful girls" reverb tanks. The JC-60 wasn't working when I got it. Found the break inside & had to repair a VERY tiny black wire. Couldn't have been more than a few strands. Not the prettiest job, but it worked & the 'verb has been great ever since. I'm actually a big fan of these little 'Z' spring tanks - anyone know if they're the same as were used in the old Space Echo tape units? I know the RE-201 (and '301?) had spring reverb units arranged in a 'Z' pattern & the reverb on my RE-20 sounds a lot like the 'verb on my Jazz Chorus amps.

Also - thanks edwardcooper for pointing out what I learned in another thread here (after TONS of diagnostic work) - that the chorus has fixed speed & depth. I'm a knuckle head.

[edwardcooper]

great advice

Thanks alex/drasp,

Took me a while to get around to it, but I took my JC-120 apart tonight and, lo and behold, found that one of the wires inside the reverb tank had detached. I soldered it back into place and it actually works!

Of course, it took me like a half hour to figure out how to reattach the speakers...

thanks so much!

eddie

[teemuk]

The JC-120 has no settings for it's chorus effect, it's just on/off. The vibrato is adjustable by depth and rate, and you'll notice that the vibrato approaches the sound of the chorus when the rate and depth knobs are turned all the way up...

Cunningly, Roland simply changed the "Vibrato/Chorus" labels to "Manual/Fixed" in some JC-series models. IMO, they should have done the same update to all models within JC-series but maybe they feared that if they did that people would think that some features were removed.

[punX]

Hi, I own a vintage (possibly 1982) JC120 model. Does anyone here know what the small knob at the rear of the vintage JC120 is for (left of the Ext. speaker Outputs).

Thanks. x

[Fragger]

It`s not the fuse? (What I saw looking at pictures in this thread)

[punX]

no, it's not the fuse. it's a recessed knob between the fuse an the speaker outputs.

[Alex R]

Off the top of my head, it's likely to be the 'chorus focus' control. Affects the intensity of the focus a little. Try twiddling it.