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JC-55 unwanted distortion, reduced clean headroom?

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  • JC-55 unwanted distortion, reduced clean headroom?

    No, I'm not talking about the undesirable built in distortion effect (joke at expense of notoriously bad built in distortion)

    With distortion off, I'm getting a distorted signal. I'm unsure if I've simply exhausted the normal clean headroom of the amp or if there is an issue causing a decrease in clean headroom.
    When I use "high" input the amp starts distorted a little over half way on the volume setting, depending the pickups I'm using (my tele has very low output pickups, the problem isn't just too hot of pickups). When I use input 2 (attenuated input), the amp starts to break up at 8ish volume with my tele and a little over halfway with a 90s Parker Fly.

    Can someone with experience with these amps tell me if this is normal or if I should be expected a clean signal at pretty much any setting?

    Many thanks,
    Jim

  • #2
    Hi Jim, and welcome to the forum.

    Hopefully someone who has one of these amps will chime in, but in the meantime I've taken a look at the schematic, which has signal levels marked. For an output of 24.5W per channel (14V RMS into 8 Ohms) the input level for High is 24mV and Low is 93mV with all controls at 10, reverb and chorus 0, distortion off.

    24mV is pretty sensitive - A Tele pickup will easily exceed that. I'm thinking you may just be out of headroom.

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    • #3
      Thanks a bunch! That makes sense. I hadn't thought to make that comparison; I learned something today. I appreciate it.

      Originally posted by Mick Bailey View Post
      Hi Jim, and welcome to the forum.

      Hopefully someone who has one of these amps will chime in, but in the meantime I've taken a look at the schematic, which has signal levels marked. For an output of 24.5W per channel (14V RMS into 8 Ohms) the input level for High is 24mV and Low is 93mV with all controls at 10, reverb and chorus 0, distortion off.

      24mV is pretty sensitive - A Tele pickup will easily exceed that. I'm thinking you may just be out of headroom.

      Comment

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