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Realistic MPA-20 PA amp

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  • Realistic MPA-20 PA amp

    Hi,

    Does anyone have a schematic for the Realistic MPA-20 PA amp? The one I have uses power transistors, not a chipamp.

    Thanks, Jeff

  • #2
    I don't have the schematic, but working MPA20s are on ebay and Reverb.com for $20-25 each.
    Education is what you're left with after you have forgotten what you have learned.

    Comment


    • #3
      Originally posted by Enzo View Post
      I don't have the schematic, but working MPA20s are on ebay and Reverb.com for $20-25 each.
      I picked this one up for 10 bucks at a local thrift shop. It works fine but shortly I will begin surgery to create some kind of Franken-amp. My guitar playing is not so good so a great deal of my fun is through seeing what kind of sound I can get out of repurposed stuff. Good to know about sources for more MPA20s because sometimes my tinkering makes the magic smoke come out...

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      • #4
        I don't know if you still need it, but I made a schematic of my own MPA-20 last year. The power transistors might be a bit different, since I've seen ones that have 2SB337's as well as ones with 2SB449's like mine.
        Click image for larger version

Name:	MPA-20 Power Amp.png
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        Click image for larger version

Name:	MPA-20 Power Supply.png
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        Click image for larger version

Name:	MPA-20 Pre-Amp.png
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ID:	846317

        Here's hoping that it actually uploads.

        -Cameron Jenkins

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        • #5
          Originally posted by camjenkins View Post
          I don't know if you still need it, but I made a schematic of my own MPA-20 last year. The power transistors might be a bit different, since I've seen ones that have 2SB337's as well as ones with 2SB449's like mine.
          [ATTACH=CONFIG]44731[/ATTACH]
          [ATTACH=CONFIG]44730[/ATTACH]
          [ATTACH=CONFIG]44732[/ATTACH]

          Here's hoping that it actually uploads.

          -Cameron Jenkins
          Awesome, this is perfect. Mine has the 2SB337s. So far all I have had to do is reattach the thermistors as they had come loose. Although it sounds ok I am going to pull a few caps and test them. Thanks so much!

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          • #6
            You're welcome. It feels weird to actually have a schematic that someone else needs. Some things that I think you should know: The power supply in this amp is kinda lousy and its voltage drops dramatically as you turn it up. Because of that, mine struggles to make even 14 watts of power. Also, it doesn't do very nice power amp distortion.

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