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  • Farfisa Compact Duo Mk1 (non-effects)

    I've been doing some listening to Farfisa Compact Duos on youtube recently, and it confirmed something I noticed about my own Compact Duo during its restoration.

    I had a Compact Deluxe in my workshop at the same time, and I noticed that it sounded a lot better than my Compact Duo, which was frustrating after all the work I'd put into fixing the Duo. Specifically, my Duo Mk1 sounded thin in comparison.

    I started looking at the circuits, comparing the Duo Mk1, Mk2, and the Deluxe. My conclusion was that in the Duo Mk1, Farfisa screwed up and routed the output of the passive tone filters into a load impedance (the input of the PA-17 board) that's far too low and that interacts in a negative way with the passive filters. This results in the thin tone. I think the PA-17 was Farfisa's first solid-state preamp board and was a flawed design.

    The Compact Deluxe still used a tube preamp that has the high input impedance typical of tube preamps, so it did not suffer from this problem.

    The Mk2 version of the Duo has impedance buffers (emitter followers) at the inputs of the main audio output board (PA-31/1), providing the tone filters with a high input impedance that doesn't degrade their performance. PA-31/1 has five transistors compared to three on the Mk1's PA-17. Thus, PA-31/1 is the proof that Farfisa realized there was a problem and took steps to fix it.

    None of the Mk1 Duos I heard on youtube sounds "right" to my ear. On mine, I built and installed impedance buffers on small additional circuit boards. That transformed the sound and made it sound like a Farfisa is supposed to.
    I'm David. 'Dave' is someone else's name.

  • #2
    David I remember you mentioned this to me years ago and I had someone make me a replica circuit board PA31/1 for my MK1 Duo which rightfully improved the sound as you describe. Another modification I did was to add a discreet toggle switch underneath next to the bass output jack which defeated the 2' busbar so that instead of the mixture stop 2 2/3 - 2 you could use just 2 2/3' like the MK2 Duo. I was very pleased to find that two busbars were used for that stop. I believe the spare busbar was used for the percussion trigger on the MK2.

    I populated the PA31/1 circuit board myself and had to link the send and returns for tremolo and repeat functions and also fiddle with resistors on the input side to correct the signal level.


    Click image for larger version  Name:	farf_duo_pcb.jpg Views:	0 Size:	83.1 KB ID:	653292
    Last edited by Drawbar Dave; 03-25-2019, 01:01 PM.
    Hammond C3, M102, XB3, XB5
    Lowrey Heritage DSO-1, H25-3, Yamaha E70
    Farfisa Compact Duo Mk2, Vox Continental 300, Korg BX3 Mk1, Leslie 122, 145
    www.drawbardave.co.uk

    Comment


    • #3
      That's a nice board. You should have had a run of them done.

      And, yes, the 2' busbar is used for Percussion on the Effects version.

      I wonder how many Mk1 Duos there are compared to Mk2s. I know very little about Farfisa production numbers. I have a feeling there are 2 or 3 Mk2s for every Mk1 out there.

      The only thing I've seen done on a Mk2 that I can't do on my Mk1 and would like to is activate Tremolo on the lower manual only. I can't even do that on my Lowrey TBO.
      I'm David. 'Dave' is someone else's name.

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      • #4
        Interesting thread chaps. A Compact Duo with bass pedals is high on my want list. And with regard to split tremolo, the Lowrey DSO offered this feature (valve/tube precursor to the TBO) where you could have tremolo on either manual and add Main if need be. You can also engage a coupler to the lower manual and have Main and tremolo simultaneously (on the lower annual), but have the registrations sound independently from the Leslie and Main speakers.

        Regarding Farfisa production runs, this vid may shed a little light on numbers...

        https://www.youtube.com/watch?v=3bc9DfgbCEI

        rgds
        Lazlo

        Comment


        • #5
          Originally posted by David Anderson View Post
          That's a nice board. You should have had a run of them done.

          And, yes, the 2' busbar is used for Percussion on the Effects version.

          I wonder how many Mk1 Duos there are compared to Mk2s. I know very little about Farfisa production numbers. I have a feeling there are 2 or 3 Mk2s for every Mk1 out there.

          The only thing I've seen done on a Mk2 that I can't do on my Mk1 and would like to is activate Tremolo on the lower manual only. I can't even do that on my Lowrey TBO.
          When I was searching for a MK2 there seemed to be more MK1s around. Stupid as it may seem, I ended up importing my non working MK2 from Arizona. It was $300 plus the same again in shipping. I would have expected to pay £1000 GBP for one over here in the UK in non working condition. I wonder whether Farfisa didn't really start importing to the US until the MK2 was in production. I would love to know how long the MK1 was in production before the MK2 was released. I am guessing it was 1965-67 with the MK2 starting in 1968.
          Hammond C3, M102, XB3, XB5
          Lowrey Heritage DSO-1, H25-3, Yamaha E70
          Farfisa Compact Duo Mk2, Vox Continental 300, Korg BX3 Mk1, Leslie 122, 145
          www.drawbardave.co.uk

          Comment

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