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Hello everyone,
My name is Juan, I'm part of a service center where we repair professional audio equipments. I'm having a pretty big trouble so I came here for help. Let me explain the situation.
We received a Roland Jazz Chorus JC90 for repair. It had noisy potentiometers due to dirt stuck inside. We opened them, cleaned them up properly, the noises were gone, problem solved. But then the client claimed that the amplifier started doing a noise that supposedly wasn't there when he first brought it in. We received it back and checked, and... there's the slightlest hiss, you literally have to put your ear against the speaker to hear it. It's very possible that the noise was there from the very beginning but we didn't pay attention since it wasn't declared as a fault and it's minimal. But the point is, the client use this amp in a recording studio and claims that it wasn't there before.
So we started researching, measuring, checking everything... the amplifier is perfect. Newer capacitors and checking different parts of the circuit made no change. And searching about it, all JC have hiss since they have a high gain preamplifier, we even borrowed a JC77 and a JC120 to compare and show the results, but since they weren't JC90, the owner didn't acknowledge the fact.
We turned to Roland, asked them for information on this. They discontinued the product so they no longer have any information on their database. They DELETED it. What the... so no refferences to measure and compare from factory to this amp.
Does anyone has a JC90 in good condition, or has measured the noise level of this amp, and could share with us this information?
I'll be waiting good news, thank you very much!
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02-28-2024 10:25 AM
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Roland JC hiss has been discussed over and over in this very forum and probably every other one.
Originally Posted by STAGEFIX
Compiling those threads and emailing them to the customer should help, but probably won't.
Some of the threads detail circuit mods to deal with it. I have no idea if they're effective and safe.
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That hiss was always there, it's part of the design. The JC series of amplifiers are infamous for it, in fact. What likely happened is (1) other noises were distracting from this noise floor, and (2) the customer is just paying more attention to the sound now than they normally had.
This isn't your fault, it's Roland's fault. And it's not really repairable, although there is a thread on this forum about mods to try to reduce the hiss.
A possible circuit mod solution for Roland Jazz Chorus hiss... current explorations
as far as I am concerned, the biggest problem with those amps is turning them on (I don't care for the sound of them even when they're operating optimally. To my ears it is a cold, hard sound.).
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Hiss usually disappears the moment a drummer hits their cymbal.
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