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Peavey Classic 50 effects loop hum

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  • #1

    Peavey Classic 50 effects loop hum

    Just got this amp working again and prepping it for sale. One issue is that there is a bit of a hum, present on both channels, only control that changes it is MV. Hum gets noticeable when MV gets to 4, gets louder all the way until about 11, then quiets down some as the MV is dimed (or 12'ved, in the case of this amp). Found that a shorting cable in the effects loop jack pretty much gets rid of the problem. Cleaning the jacks didn't really help. Trying to figure out if this is just a switching jack problem or something with the MV (since the hum gets quieter when MV is essentially 0 ohm). Hope I don't have to replace the MV pot since this amp is a PITA to get the preamp board out.

    https://www.thetubestore.com/lib/the...-Schematic.pdf

    Anyone else ran into this?

    TIA,
    Greg
    Tags: None
  • #2
    Your Classic 50 has an FX loop?! Working on one now with a loud 60hz hum. No FX loop.

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    • #3
      Originally posted by lowell View Post
      Your Classic 50 has an FX loop?! Working on one now with a loud 60hz hum. No FX loop.
      On the one I had the effects loop was kind of hidden on the bottom edge of the chassis, near the footswitch jack. I don't know if there were other implementations or ones without a loop. Mine was one of the Chinese made ones with the big oval Peavey logo on the front. I did find that I had a lot of ripple on the 27V DC used for the effect loop buffer, but I ended up moving it along as a project for someone else to fix.

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      • #4
        The first Classic 50s had no loop. SOOOOO many people wanted one, PV came out with a kit to add one. The amp came out 30 years ago. A year later they came out with the FX loop kit.



        No, they no longer have them. Hey, after 30 years...

        PV Classic 50 FX loop mod.pdf
        Education is what you're left with after you have forgotten what you have learned.
        • Likes 1

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        • #5
          Originally posted by Enzo View Post
          The first Classic 50s had no loop. SOOOOO many people wanted one, PV came out with a kit to add one. The amp came out 30 years ago. A year later they came out with the FX loop kit.



          No, they no longer have them. Hey, after 30 years...

          [ATTACH]n944507[/ATTACH]
          That attachment link is not working.
          Originally posted by Enzo
          I have a sign in my shop that says, "Never think up reasons not to check something."


          ​

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          • #6
            I give up, I have no idea what I am doing wrong.
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              .. Click image for larger version Name: 9MFou.jpg Views: 217 Size: 135.1 KB ID: 944562
              soldering stuff that's broken, breaking stuff that works, Yeah!

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              • #8
                That is the schematic, but the whole file includes layouts and other data.
                Education is what you're left with after you have forgotten what you have learned.

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                • #9
                  Does this attachment work?
                  Attached Files
                  Originally posted by Enzo
                  I have a sign in my shop that says, "Never think up reasons not to check something."


                  ​

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                  • #10
                    yep it does for me.
                    nosaj
                    soldering stuff that's broken, breaking stuff that works, Yeah!
                    • Likes 1

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                    • #11
                      If the shorting cable gets rid of the problem, I'd be thinking there's something mechanical going on - either the switch contacts still have some resistance, the contact pressure is weak, or when the plugs are inserted there's a change in force that affects something - maybe a solder joint.

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                      • #12
                        Hey guys, just an FYI I no longer have the amp from my original post. Lowell has a non-effects loop amp with a hum.

                        Lowell, I would suggest starting a new thread and maybe we can help you fix it.
                        • Likes 2

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