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Another quandry Top Hat plexi clone

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  • #1

    Another quandry Top Hat plexi clone

    Customer brings me a Top Hat Emplexador plexi clone, says it doesn't sound right, uninspiring. I put it through the paces, everything works, tubes check out, although it was biased over 90%. Corrected that, voltages look OK, I am just not finding anything wrong with it. My shop speaker is a 300 watt Avatar bass cab with tweeter turned almost off, so granted it is not ideal, but it usually gets the point across well enough.

    Don't know what else to do in this case. Guy seems like a great guy, but I don't know his level of expertise. Could be all in his head, but I never like to suggest that. Could be his cabinet also, he didn't bring that to me. I never like these vague, "I don't know, it just doesn't sound as.... hmm, green as it used to" type of repairs.
    It's weird, because it WAS working fine.....
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  • #2
    It's in his head.

    I get at least a couple of those a month.

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    • #3
      Could also be his guitar. Coincidences happen. Maybe something else went wrong just about the time he was plugging into that amp. So maybe it's his guitar or his cabinet. But probably not, so...

      Check to see that Top Hat is using the correct impedance tap for the NFB loop. There may be too much NFB. Check to see if Top Hat decided to use 150k bias feed resistors. A lot of guys say it improves reliability and I wouldn't be surprised to see that value show up in a boutiquy build. Check to see if the plate voltage is consistent for the design (420-470). Hell, go ahead and check that the inputs are wired correctly and he's actually plugging into the high gain input/s.

      Ask him how he's using it? With an attenuator? Does it have a master volume? What kind? Is the customer actually familiar with such an amp, how to use it and what to expect? Otherwise...

      Ask him what it is he wants. I know you're a repair guy, but we do mods here. A lot of them. Is it not aggressive enough? Not enough LF or HF? Does he want more gain? There are all sorts of very simple mods for the plexi circuit to get more joy.
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "If you're not interested in opinions and the experience of others, why even start a thread?
      You can't just expect consent." Helmholtz

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      • #4
        Maybe his ears are shot from playing through a plexi clone?
        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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