Inside a Roland JC 120

[Mincer]

Yeah, all other choruses (chorusi?) are a pale imitation to the original stereo idea of what chorus is...one plain signal on one side, with a delayed signal on the other, with the delay modulated with an LFO. It sounds absolutely huge.

 

[Securb]

Sad but when I used this amp in the 90's I got my chorus from my rack. I didn't have the footswitch for the amp.

 

[beaubrummels]

On Roland' site they said that : "While commonplace today, the chorus effect was actually first introduced to the world as part of this very amplifier."
(introduded in 1975)

My understanding is the onboard chorus of the Jazz 120 is literally the much-coveted BOSS CE-1 circuit.

 

[Chris Pile]

Yeah, all other choruses (chorusi?) are a pale imitation to the original stereo idea of what chorus is...one plain signal on one side, with a delayed signal on the other, with the delay modulated with an LFO. It sounds absolutely huge.

One pro player here in town (plays 5 nights a week even during The Time of Covid) used to have a pair of early 80's JC 120's for the gig - one on each side of the stage. Didn't matter what guitar he used, or the tune he played - he sounded magnificent. Last year he retired them and bought a pair of Katana 100's.... "They have all the sounds".... They are also lighter than JC's - but his gear doesn't move often. Plus, they are just as loud and as powerful. He doesn't need a big pedalboard anymore because the overdrive and distortion programs sound really good. I think all he uses now is a BOSS Wah / Volume.

 

[Securb]

My understanding is the onboard chorus of the Jazz 120 is literally the much-coveted BOSS CE-1 circuit.

One of the things I did not know in the 80s/90s so I was getting my chorus from my Digitech rack unit.

 

[Securb]

Daymn that amp was filthy. I know it looked clean inside but inside the jacks were disgusting. But now all the knobs, jacks and switches are dead silent

 

[Artie]

I think it has more to do with how they design and test. They targeted Jazz initially, so they tested with jazz boxes, which are quite dark, often using neck pickups solely. When it became clear other players were using the amp, they adjusted and began testing with a wider variety of guitars and situations. (I have a friend that has worked at the Roland headquarters in Hamamatsu and I've toured their facility, studio and test labs.)

That would've been cool. I wonder if the new "little" Jazz Chorus', (JC-22 & JC-40), match the classic JC-120 sound?

 

[Securb]

That would've been cool. I wonder if the new "little" Jazz Chorus', (JC-22 & JC-40), match the classic JC-120 sound?

They sound great. The only issue is what you would have with any 10-inch speaker or 6.5-inch speaker vs 12-inch speaker. The 12 has a certain bloom and fullness. Don't get me wrong they are both great amps but the 12s really project the chorus even more so with closed back cabs.

 

[aroldo]

Hello, I saw some pictures of you with a jazz chorus 120H. Do you have a photo of the wall where the board trails are? You put a photo of the top part of the board, I need a photo of the bottom part where the tracks are. I have the same one and mine burned and punctured the board where the 4 power transistors are connected. I really appreciate it if you can help me.

 

[Securb]

Unfortunately, I do not have a picture of the circuit board traces. I want to help you and would if it didn't require me to take my amp apart. Here are some schematics I hope can help

https://music-electronics-forum.com/filedata/fetch?id=811912

https://schematicheaven.net/newamps/roland_jazz_chorus.pdf

 

[idsnowdog]

If the IC's are socket mounted it would be interesting to replace the 4558s with NE5532s or another more modern op-amp. I have read where people have replaced IC's on Peavey Classic and MusicMan hybrids with good results.

 

[aroldo]

If you take a picture of the part under the sign where the trails are, I'll pay for your service and I really appreciate your help..
Thank you very much