JCM1 Issue

50th anniversary amps JTM1, JMP1, JCM1, DSL1, JVM1, 1962LE

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Linster
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JCM1 Issue

Postby Linster » 01 Jun 2016, 13:28

I have a JCM1 Head and Combo along with a JMP1 and a JTM1


Both JCM1 amps seem to make noise when cut on without the guitar plugged in where the others are mostly dead quiet. Like the input is not grounded.
Now my JCM1 combo is acting very weird, when plugged in like there is an issue with the input jack.
Any suggestions on what to look for?

Thanks
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surfnorthwest
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Re: JCM1 Issue

Postby surfnorthwest » 01 Jun 2016, 13:44

Could be you have a micophonic tube, that would be the first thing I would check.
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GuitarBuilder
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Re: JCM1 Issue

Postby GuitarBuilder » 04 Jun 2016, 07:14

Linster wrote:I have a JCM1 Head and Combo along with a JMP1 and a JTM1


Both JCM1 amps seem to make noise when cut on without the guitar plugged in where the others are mostly dead quiet. Like the input is not grounded.
Now my JCM1 combo is acting very weird, when plugged in like there is an issue with the input jack.
Any suggestions on what to look for?

Thanks
Can you describe the noise? Is it an AC hum or a hiss? Does the Boost button make it worse?

You can test the input jack by creating a shorting plug (tip and sleeve shorted).
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Linster
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Re: JCM1 Issue

Postby Linster » 05 Jun 2016, 04:59

I changed all the tubes, it is definitely an input jack issue. Seems like when you remove the cord, the input of the tube does not make contact to ground to silence the input. You can pull the cord out a couple times and it will go to normal. I may need to replace the input jack but plan to check the connections first.
Marshall 1987X/Sourmash 2/12 G12M Heritage - JTM45RI/1960AHW 4/12 - Class 5/C110
JTM1C/JTM1 Offset/JMP1C/JCM1C/Anderton/Marshall CS JTM145/JVM1/JCM20001
Fender 1965 Deluxe Reverb/1965 Pro Reverb/1965 Princeton Reverb/1965 Vibrolux Reverb
Fender Deluxe Reverb ll/Concert/Twin Reverb ll
Gibson Les Paul Studio/Gibson Les Paul Studio/Fender Deluxe Ash Stratocaster HSS/Fender Select Stratacaster
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