Early JC-120: chorus works, controls don't - help?

[drasp]

At least in some circuit revisions the chorus mode (if I remember right) disables both of the potentiometers (speed and depth) completely and replaces them with a constant resistance value or something. That’s just a basic “feature” of those amps. I believe it’s like that in all of them. The controls are not even supposed to work in chorus mode.

WHAT??!! If this is the case with my amp, then there is NO problem at all. The chorus sounds heavenly! I may have done a poor job of describing the problem in my original post - the only issue with the chorus on my amp is that when engaged the speed & depth controls don't function or change the chorus, it just "is". That said, it's heavenly, deep, lush, etc., I just assumed I should be able to control it in the same way as the vibrato. . . Any ideas on how I can confirm that my amp shouldn't have control over the chorus?

THANK YOU!!!

[teemuk]

Manual from 1996:
http://www.nuci.org/store/manuals/Ro...orus%20120.pdf

Quote: * Neither the speed nor depth of the Chorus effect can be changed.

---

I think it's been this way since day one.

[oc disorder]

Hey that would be a good one for April 1 drasp !

When in doubt read the manual...................................

[teemuk]

I think the problem is that there are so many JC-series amplifiers and so many revisions of them. Someone should make a fan site with compiled service info, manuals and model/revision information according to serial numbers. Those revisions are, by the way, stated in the form of JC-120-XX where the XX is a letter code that marks the revision. This thing should be found from the badge at the rear. Some of the revisions are very different from one another - and I don't just mean the addition of the FX loop. Most differences you can't see unless you sketch out the circuit or you're shown the circuit diagram.

Now, the basic JC-120 has a fixed chorus, like this:

The dial reads: “VIBRATO-OFF-CHORUS”. But without manual it is indeed quite impossible to realize that the controls affect the vibrato only and that the chorus settings are fixed. In some revisions the selector was a rocker switch instead. Like in this older specimen:


However, the chorus/vibrato thing in JC-120H (the head version) is a lot smarter:

(I think this labelling was also used in the JC-77). There's a “MANUAL-OFF-FIXED” rocker switch but no vibrato feature. ...Or is there? Now, what was originally vibrato mode is now the manual mode. The fixed mode is the ordinary fixed chorus mode. Did the operation change? No, just the labelling but it makes a lot more sense now. Those heads do have some real differences too, like a potentiometer to replace the bright switch and different kinds of jacks at the rear panel.

But anyway, someone should really make a dedicated site about these amps.

[drasp]

But anyway, someone should really make a dedicated site about these amps.

Well, I agree 100%. I'd like to help with a project like this, maybe even start the site. Just need to find more info. I've started threads on a number of forums (Haunting Mids, HCFX, here, etc.) to start compiling info & pictures on the JC amps. Thanks for posting the pictures you did - if you have any more, I'd love to see them! I'm also trying to find more gut-shots so if anyone has a JC amp of ANY version, please post up anything you've got!


I feel like a real goober for looking so hard to solve a problem that was actually a feature. . .

[jzr85j]

Hello all
I too am having a chorus related problem with a JC-120,
the vib.works fine but the chorus effect is inop with the toggle switch in chorus mode.This particular JC 120 uses the MN3007 BBD (bucket brigade device) and the MN3101 clock generator .I have been searching the internet for day's in hopes of finding the theory of how the circuit functions,where the circuit picks off the dry signal and where the dry and chorus signals mix.I have the schematic but I'm having a hard time figureing out the signal path.