SOHA II thoughts?

Discussion in 'DIY' started by fraggler, Mar 20, 2019.

  1. fraggler

    fraggler A Happy & Busy Life

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    As part of a nice DIY score, I got a mostly built SOHA II board. As far as I can tell it is stuffed completely, but since the Cavalli website isn't up and the archived pages I can find are missing pictures, I'm not sure. Not sure how to test it without potentially blowing up some headphones.

    Anyone familiar with this amp think it is worth trying to test and finish? I have a WHAMMY, Vali 2, and MCTH on hand. Any ideas on where it might stand in comparison to those?

    I might have to try to bribe @dBel84 with some whiskey or something to get a few hours of his DIY time to help me out.
     
  2. shafel

    shafel New

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    Here are some documents I've managed to download before cavalli site went down.
    Regarding SQ, I like the vali(1) far better for most music and is ahead in most sound quality areas , excluding EDM, which i think is better on the SOHA since it has a very aggressive sound and a lot of bass impact.
     
  3. Cspirou

    Cspirou They call me Sparky

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    Use a resistor as a load and test if there is DC on the output. If there is no DC at any volume then you can start playing music at the lowest volume and ramp up slowly.

    Obviously a scope would be better if you have one.
     
  4. Cspirou

    Cspirou They call me Sparky

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  5. dBel84

    dBel84 Friend

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    it has a dc offset sensing circuit on the output which is linked to a relay - if the relay releases, headphones will be safe.

    no harm checking though.

    documents from @shafel are pretty much all you need to get going.

    I have a completed soha II that I still occasionally fire up and also have a board or 2 that are unpopulated. I liked this amp - it was the early evolution of hybrid heapdhone amp , the original SOHA ( simple opamp headphone amplifier ) used an opamp coupled to a tube front end, some people added monolithic buffers ( me included ) and then Alex developed this discrete output circuit to provide current drive for headphones while the tubes offered voltage gain. It played its part in the development of headphone amps as we know them today and remains a decent amp - you can try play with various BJT output pairs for different sound.

    ..dB
     
  6. dBel84

    dBel84 Friend

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    at my request, @fraggler left the amp with me after the small gathering recently

    The amp was pretty much assembled with a little case work to be finished off

    Most all voltages checked out - needed to bring the tail current in a little so that the tube conducted optimally. DC offset is 2mV

    [​IMG]

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    [​IMG]

    given the limited space and optimal set up as a single chassis amp , I used a Cannon Pro XLR for the mains hookup

    fired it up with headphones plugged in - there is a small amount of mains hum apparent which I will take a look at , but the music coming out is all good.

    ..dB
     
  7. fraggler

    fraggler A Happy & Busy Life

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    You went far above and beyond what I was hoping for. Thank you so much! Currently shopping for a transformer cover and a nice big knob.
     

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