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EH Microsynth Adapter

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  • #1

    EH Microsynth Adapter

    Hi, I have an old Microsynth here which refuses to power up... I'm not sure of the age but it's in the old-style casing...

    I was told by my local music store that uses a 24v DC adapter. However, I tried powering it up using a bench supply with no luck.

    When I opened it I found that the PCB connections from the power input are marked AC / AC+ which then runs through what looks like a bridge rectifier? AC for sure...

    Can anyone tell me what the power source should be?

    The boards are marked:
    PC 7901 - 1C
    PC 7901 - 2C

    Steven
    Tags: None
  • #2
    Originally posted by kingsteven View Post
    Hi, I have an old Microsynth here which refuses to power up... I'm not sure of the age but it's in the old-style casing...
    I thought that the old ones had a built-in transformer with an ac cord.

    Yes, if it wires to a bridge then ac is for sure. Until you find more info, look at the filter caps attached to the bridge. What is the voltage rating of the caps? This will give you an idea as to what the power suppy should be, and then work backwards from there.

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    • #3
      24VAC according to the schematic, bass or guitar it's the same. Didn't you get the adapter with it?

      MPM

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      • #4
        Originally posted by martin manning View Post
        24VAC according to the schematic, bass or guitar it's the same. Didn't you get the adapter with it?
        Na, It belongs to a friend of mine and it hasn't been used in a few years because the power socket was damaged (which I replaced) - the adapter was misplaced sometime...

        0.5 Amp will be enough wont it?

        Originally posted by 52 Bill View Post
        This will give you an idea as to what the power suppy should be, and then work backwards from there.
        Don't have it with me right now, but I think the cap was 25 or 35v which would back up martin I guess

        Cheers guys.

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        • #5
          I don't know if this is helpful or not.

          I've owned a Bass Micro Synth for about 5 years.

          I'm holding it's power adapter in my hands at this moment.

          It's output is rated at 24vDC 100mA

          The sleeve is negative
          The center is positive

          best regards,
          mike

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          • #6
            I think the version you have can be found here http://files.muziq.be/schematics/eh_microsynth.pdf.

            It uses an internal 120VAC Primary/24VAC secondary transformer. You should be able to find one at signal transformer or Mouser. Look for the .085A rated panel mount transformer. It should be a direct fit, form, and function.

            Or, you can power it using and external 120VAC/24VAC wall wart.

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            • #7
              Cheers guys,

              For reference, it seems there's at least 4 Microsynth designs:
              110 VAC
              24 VAC
              24 VDC
              9 VDC (hammond enclosure version)

              Who knows why they've revised it so much? It seems it would be easy to convert the 24VAC version to DC (I tried applying +/-10VDC after the rectifier and it appears to be working fine).

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              • #8
                Originally posted by kingsteven View Post

                The boards are marked:
                PC 7901 - 1C
                PC 7901 - 2C

                Steven
                PC-7901 would make it an original vintage unit. With a power jack it could be either an American unit modified for AC adapter or a Canadian unit which was sold with an AC adapter.

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                • #9
                  When you say "AC adaptor" do you mean an adaptor that provides AC to the pedal for rectification onboard, or do you simply mean somethng you plug into the wall that provides DC itself?

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                  • #10
                    Originally posted by Mark Hammer View Post
                    When you say "AC adaptor" do you mean an adaptor that provides AC to the pedal for rectification onboard, or do you simply mean somethng you plug into the wall that provides DC itself?
                    I'm just referring to an external power supply. Technically, the vintage unit would use an AC adapter and the newer ones use a DC adapter.

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