Roland JC-120 Serial 410546

[tired eyes]

I'm working on this Jazz Chorus amp that has been severely modified by a previous owner, and I don't want to put any time into it without the schematic and PCB layout. It's a mid to late 70's model JC120, serial #410546. There are no opamps in the preamp section, and it uses 2N3773 power transistors. The closest schematic I can find is this one - http://www.freeinfosociety.com/elect...C120-JC160.pdf
However the wire / terminal labels are completely different on my amp. Rather than 2 digit numbers they are mostly letters - IN1, OP, etc. I need to first restore the original wiring between boards, so this information is essential.

I did search this board and google extensively and found 3 or 4 schematics that do not match my amp. Can anyone help me find the correct one?

Here are some pictures: Jazz Chorus - a set on Flickr

[Steve L]

I have the schematics and board layouts for that serial number, however it is way too big to attach here. (10M, entire service manual)
If you send me a PM with your email address I will send it to you.

Steve

[jasoncreek]

PLEASE send me schematic/layout too, Steve!

my email address is my username at hotmail.

I have THREE JC-120s now... could probably do more harm to this discussion than good, but I think I like the slightly newer-than-the-oldest one best (SN 340xxx). The newest one (made about 1999) stinks in comparison.

Nice option: try Peavey Black Widows in the JC-120. Unbelievable difference, and 100% delivery of power (no flopping about wildly at high volumes). Deafening and wonderful.

[jasoncreek]

tired eyes, you have the oldest one; strangely, the SN range is higher than the SN range for the JC-120 that succeeded it. does yours noisily "hiss out" the chorus/vibrato when your input signal decays out (i.e., when your guitar signal tapers off)? wish the chorus/vibrato would just stay on at all times, noise or not.

[Ghostrider]

Greetings everyone. This is my first crack at this kind of thing so here goes. After having read a minimum of about 200 threads about Roland JC amps, mostly dedicated to the JC-120, I've come to the conclusion that the JC-90 (which I own) is either extremely reliable and hence needs no space here or there are simply not many of them in use. I suspect the latter. Anyhow, my first request is the most obvious. Does anyone have a schematic? Not the two or three that I can find out there for the 120, but the actual JC-90 schematic. I'm sure there are some similarities, but I want to be safe. Second, what kind of speaker would be recommended for this amp. The stock 10's from Roland produce "farting", though not sure why or how to isolate without having additional speakers to swap out. I don't want to pull the trigger on a couple greenback's or something just to find out that the problem is in the amp. I experience this even with no pedals in front and clean settings and moderate volumes. And of course it's much worse when using a highly over driven stomp box. I may be making some huge assumptions here but bad speakers immediately comes to mind. Or at least that's my "worst case" scenario. If not then obviously I'll need proper schematics to get to the cause. Another reason I'm looking for schematics has to do with many of the reviews I've read on the JC amps. Seems a lot of people pass on this amp due to its perceived "lack" of distortion, apparently oblivious to the fact that "hello...McFly" it's a JAZZ CHOURS amp. In my opinion it's more akin to Mild Overdrive than Distortion. In any case, recently I was working on a stomp box mod of a Boss OD-1 pedal to give it a little more oomph and the mod involved changing the value of some of the components in the clipping circuit. So, with that in mind, does this amp utilize a similar circuit layout for it's "Distortion" effect? And if so what components would I have to swap and in what direction do I change the values to increase the amount of deliverable distortion? I know what some of you are saying right now, "why not use a pedal in the front"? I can and do. But I think I might enjoy a few raised eyebrows when switching on distortion sans effect pedals. Why this hasn't been done yet considering the plethora of digs on this feature is beyond me. Sounds like a challenge don't you? I have this nagging feeling that I've opened up a can of worms here but could do without the whole "get a tube amp" or "go with a pedal" reply's, which I'll undoubtedly get, and love a good joke as well as the next guy. But I would really like to do this if it's simply a matter of changing the value of a few discrete components in a small circuit. I think it may make this amp even that much better. I'll apologize now if this post is in the wrong place and beg your patience as I learn how this works.

[Jazz P Bass]

Whoa!!
One Paragraph.