JP-2C Channel 1 Volume Fluctuation

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Bottle Rocket
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JP-2C Channel 1 Volume Fluctuation

Post by lifeson2112 » Sun Jun 23, 2019 8:36 pm

Greetings! First post, and I'm sorry for no sappy introduction, but I have two young kids running around and barely have time to string two sentences together without being interrupted. I recently picked up a used JP-2C, and everything is great except that on Channel 2, the volume goes up every now and then, even to the point where when I turn the MV down on the amp, it doesn't work. I don't have the owners manual, and am just wondering if any users out there could assist in diagnosing this issue. On Channel 1 and 3, there is no problem.

I guess it's also worth mentioning the foot pedal cable is not working properly, either. Lot of 'blinking' lights and so forth.

Is this a customer service issue? I'm in the NYC area, so it's a ways away from LA.

Thanks for any input.

Mark IV
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Re: JP-2C Channel 1 Volume Fluctuation

Post by eudaimonia02912 » Sat Jul 06, 2019 9:30 pm

They happened to me. Bad tube. I think it was v3.

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Re: JP-2C Channel 1 Volume Fluctuation

Post by smd24fan » Mon Jul 22, 2019 7:02 pm

Just stumbled upon this post. I'm seeing volume swells in the clean channel on my JP-2C. I'm wondering if I might have a tube issue as well. Never had the problem with either of my dirty channels, just the clean. It's fairly pronounced too, goes from manageable volume to pretty loud.
Mesa Boogie JP-2C Head
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Re: JP-2C Channel 1 Volume Fluctuation

Post by bandit2013 » Sat Aug 03, 2019 9:29 am

Wow, never expected to be reading this.... So far I have had no issues after I replaced some of the original tubes that were in the amp. Still have mesa 12AX7 and power tubes. Had a recurring static issue but that was power tube related.

As for the OP, if the midi controller is going bonkers, double check that the footswitch is plugged into the footswitch jack on both ends of the cable, Note that the midi cable for the footswitch is a seven pin type. Yes, the 5 pin midi cable will also fit into the footswitch jack as I tried that but the footswitch cable will not fit into the midi-in/out jacks. Also, confirm you have the channel set to 0. If you are using a midi input from another device, you cannot use the footswitch as there will be a conflict between the midi controller and the footswitch as well as change in channel to anything but 0.

As for volume swells, hard to say exactly what is causing that. It could be preamp tube issue or power tube issue or something going on with the channel master for the clean channel. If it was preamp tube issue, I would think the change in tone from clean to distorted may also be apparent, not always the case with preamp tubes though. May be a crappy heater in a preamp tube or crack in the glass/leak.

I would definitely contact Mesa with your concern.

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