Roland JC 120- Got it back after 20 years!! I need a bit of help/advice....

[Wiseash2000]

Hey y'all... Its a long story but my Roland JC120 built in the early 80s disappeared after a gig and was recently returned after I saw it in a family members pic. Nice huh? This was my "go to" back in the day for that sweet,sweet clean/chorus. You know what I am talking about.

So, the good news is that it mostly works although, it seriously looks like it was dropped down the stairs and parts are missing. That's ok, it gives me a great project to work on.

Roland and others have been super helpful helping me replacing misc parts but the one item that I need help on is finding the Potentiometer for the Depth controll

That pot has no markings on it and was snapped off on the front so its useless (maybe it was replaced at some point?) Roland does not have the part and even though I have made some friends through them (shipped me items from Japan at no cost and they even gave me some free parts-pretty cool I thought!) they cannot tell me the spec or where to even get it.

I went to Potentiometers.com and after an hour or two they couldn't help. Other sources haven't helped. Even Ebay..

So, that brings me here. Seems like there are a lot of experts on here and any advice on where to get the exact one and or what the spec is I would appreciate it. Or...Maybe you know an expert on this amp that you could put me in touch with?

I am also looking for exact matching tolex and exact 80's type grill cloth. I have some sites that look pretty close but they are off. So... not to go to the "well" to much I thought I would ask while I am at it.

I have it torn down and I am resoldering/cleaning up etc.. I will post some before and afters when I am all done.

Hey thanks for the help!!

Chris

[nickb]

There are quite a few variations of the JC120 but I think the pot is a 10k linear see here for the '82 version

Remove it from the amp, take and post a few pictures. Then measure the resistance across the outer pair of terminals and finally again with the pot set halfway ( if you can move it) between an outer terminal and the middle (wiper) one and we can check.

[gtrplayr1976]

I think the one from 84 is 100KB.

[g1]

Nick, the schem. you linked shows 100KB for depth, but there are other versions that use 10KB like you said.
Here's one with 10KB depth pot:

[nickb]

Nick, the schem. you linked shows 100KB for depth, but there are other versions that use 10KB like you said.

Now that I've zoomed into it I can see that is indeed the case

Pull and measure and then there will be no doubt.

[gtrplayr1976]

Nick, the schem. you linked shows 100KB for depth, but there are other versions that use 10KB like you said.
Here's one with 10KB depth pot:

Yep I have two versions that show 10KB ,and one that shows 100KB.

[gbono]

Do you have the knob? What type of shaft - D, serrated, etc?

[Wiseash2000]

wow! I didnt expect such quick replys! Thanks guys.. Ok so, I did some more research its an 84 for sure.
Tell me if this sounds right..

100k Ohm 1 Gang Linear Panel Mount Potentiometer None 1 Turn Conductive Plastic 0.2W, 1/5W PC Pins

Trouble is, I don't know the proper length..thats if the above is correct...

[Wiseash2000]

...and its a split shaft thats Knurled

[g1]

100k Ohm 1 Gang Linear Panel Mount Potentiometer None 1 Turn Conductive Plastic 0.2W, 1/5W PC Pins

This sounds like something you found online.
You need to check the actual pot you have which should be marked either 10K or 100K, if it's not marked you need to measure with an ohm meter (between 2 outside legs with pot removed from circuit).

[J M Fahey]

84? ... Itīs probably the more modern IC driven 100k pot, the other one looks crude/dated by comparison.

But I suggest you follow the wiper track and see where it leads you;
* 100k resistor: 100k pot
* 27k resistor followed by a 10k one: 10k pot

In a nutshell: the pot value is related to the load it must feed.

[Wiseash2000]

Measured and its a 100k as suspected, thank you all for the help. Any idea how long it would be?

[nickb]

Measured and its a 100k as suspected, thank you all for the help. Any idea how long it would be?

There is only one way to do this: Remove it, grab a ruler and measure it. You have already removed it as asked in post #2 - right?