Thursday 3 July 2014

Guitar amp hiss. Roland Jazz Chorus 120 JC-120


This is my first electronics-related post.
As I said in the previews posts, I hope it will be useful for someone.
Please let me know in a comment if it does.

CAUTION!!!!  If you are not familiar with terms like high current, high voltage and other electrical phenomenon that could harm you, please let a professional do the job. You know, the electric shock could tickle you a little...till death.

Subject: ROLAND Jazz Chorus JC-120 guitar amplifier

Symptoms: The amp is working well, except there is a very big hiss (I hope you hear it in the video).
The owner told me that after a show where the amp performed very well, he transported it at home.
The noise appeared at the same time when it was turned on after the shipping.
Hmm ...transportation implies sometimes big vibration so I guess it could be a mechanical contact failure.

Problem solved: YES.
 Well, first  I did the wood stik test. What is this test about?
I opend the amplifire so I could see and touch the electronic parts inside the amp.
With the amp plugged in and turned on, I tapped the wood stick (or other nonconductive material) on every component  and at the same time, I listened for changes in sound from the loudspeaker.
Lucky me, when I hit one multiwire connector (depicted in the picture) the noise stopped right away.
So this is it. A bad connection because of shipping vibration.
After I ensured that the connection was good, the job was done.

Conclusion: First check for visual clues and then for mechanical connection failure with wood stick test.
The problems could be much more simple than they seem to be.
It would take much longer time to use DMM to find the problem.

Good luck!


  1. Thanks for suggest from Italy.
    I'm Young to Big a JC-50 that seems gas the same issue ,bit less evidente

  2. entonces... es solo conectar bien el multiwire?

  3. then... it's just connecting the cable well?

  4. See this mod explanation, it worked pretty well for me


Powered by Blogger.