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MetroAmp JTM45 Kit Problems w/ video and pictures

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  • MetroAmp JTM45 Kit Problems w/ video and pictures

    Hi guy's long time listener first time caller,

    I wrapped up my Metro Themed JTM45 Build today and am having a problem. All of my voltages check out but when I plug a guitar in I get absolutely nothing no guitar output. All my voltages check out within reason with the voltage chart included in the MetroAmp JTM45 instructions. I have double and triple checked my wiring, I even lifted the PTP board out to check my under board connections. Through my numerous look through's I have only caught one mistake on my end (0.10uf mustard cap was hooked to pin 1&3 rather than 2&3 now fixed of course).



    I made a video to better help illustrate my problem (I just uploaded it to YouTube so it might take a little for them to process it)

    The video is somewhat out of sync (Droid X2 is a horrible smartphone btw) but it helps illustrate what I try to explain below

    But the main things I wanted to illustrate is:

    * When nothing plugged in the amp behaves as you would expect (very quiet but still the normal hiss when volume is rolled up ect)
    * When I was taking voltages of the amp it behaved as you would expect slight popping when probing for voltages as well as tapping V1 you can hear the slight normal microphonic)
    * When a guitar is plugged in this is when it gets interesting, the amp becomes noisy with absolutely no guitar output. (The guitar as well as cables are in working order tested on my 100w MetroAmp Plexi.) The noise can be controlled using the tone stack knobs touching the bare metal knobs can take away some of the nose. Rotating the knobs can generate a weird space like alien noise making the knobs even more sensitive, even coming close to the knobs will cause the amp to change noise.

    * Also could a bad mustard cap be responsible for these sorts of problems? I bought these from a eBay member in Greece, I have no idea how to test them ect.

    I'm open to any and all suggestions
    Here is my star grounding scheme from MetroAmp

    Here is my voltage chart

    Wall Voltage is 119.4 AC


    Youtube Link
    JTM45 Problem - YouTube







    Thanks guys
    Last edited by LJay942; 02-16-2012, 03:22 PM.

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      • #4
        Good looking build. I think you have mis-wired the input jacks. Plug in a guitar cable and ohm from the tip of the cable to pin 2 or 7 of the first 12AX7. The reading should be 68K or 34K depending on which jack you plug into.
        WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
        REMEMBER: Everybody knows that smokin' ain't allowed in school !

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        • #5
          I was thinking the same, that the you reversed the switch side and the input side. I went and looked at metro's instructions and step #9 shows the 1M res on the other side.

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          • #6
            Originally posted by loudthud View Post
            Good looking build. I think you have mis-wired the input jacks. Plug in a guitar cable and ohm from the tip of the cable to pin 2 or 7 of the first 12AX7. The reading should be 68K or 34K depending on which jack you plug into.
            Do you mean with or without a guitar plugged in?

            I plugged a guitar lead in then held a probe on the tip of the cable then probed to pin 2 and 7

            Here are my results

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            • #7
              I went ahead and took two quick pictures of my input jack wiring

              Input 1



              Input 2



              I hope you can see what I wired as my cameras macro setting leaves something to be desired.

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              • #8
                Originally posted by JHow View Post
                I was thinking the same, that the you reversed the switch side and the input side. I went and looked at metro's instructions and step #9 shows the 1M res on the other side.
                Great eyes!

                I went ahead and looked at a few pictures of my MetroAmp 100w Plexi build and they are indeed backwards!

                I really hope this is what the problem is!

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                • #9
                  To my looking at the jack in your picture, I think the 1M should be on the "spring" or "tip" side of the jack - opposite from what it looks like now.

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                  • #10
                    Originally posted by JHow View Post
                    To my looking at the jack in your picture, I think the 1M should be on the "spring" or "tip" side of the jack - opposite from what it looks like now.
                    You guys are great!

                    I checked a few pictures of my MetroAmp 100w Plexi and the MetroAmp instructions and you guys are 100% correct. Could this be the root of my problem?

                    On a side note, here is a picture of my 100w build this thing absolutely screams!

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                    • #11
                      Nice build. Very neat. That ought to wake up the neighbors!

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                      • #12
                        Originally posted by JHow View Post
                        Nice build. Very neat. That ought to wake up the neighbors!
                        The neighbors already love me, I just can't wait to get home and try switching the input jacks!

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                        • #13
                          If you do a side-by-side comparison with your 100w, it is the same hookup, that should work.

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                          • #14
                            Originally posted by JHow View Post
                            If you do a side-by-side comparison with your 100w, it is the same hookup, that should work.
                            I plan to do so tonight, I just hope this is my only error.

                            I figure since my voltages check out I'm half way there right?

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                            • #15
                              You guys are great!

                              The inputs were indeed wired wrong. Re-wired them and now there's nothing but pure sweet JTM45 tone!

                              Thanks again!

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