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1413Re: [dallasaudioclub] Aikido preamp

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  • Blair Chapman
    Jun 3, 2013
      Hi Rich,

      Have you tried to add 2-5K resistance to the output of the line stage or the grounded part of the pot? You could be making an oscillator at wide open. 

      I'd love to hear your design. Where are you? I'm in McKinney.


      On Jun 3, 2013, at 10:59 PM, "Rich Davis" <fly46davis@...> wrote:



      I built from scratch using a steel chassis and a power tranny I had on hand. Phonostage is a conventional dual triode with shund/shunt riaa filter interstage. Linestage is a common cathode dual triode with a little local neg feedback in the output. My goal was lots of headroom and a very low impedance output to swamp parasitic capacitances. Linestage is stunning with output impedance 2200 ohms at 400 cps going up to 8800 ohms at 20 cps, limited I think by the output cap. Phonostage is nice sounding but I've challenges chasing hum and a tendency to motorboat with both channels wide open. I used 5965s all the way around. My original idea was to use 5687s on the output, and I still might, but they are terrible current hogs.
      Audio Expressed is interested in the article if I ever finish it.
      Best regards,
      Rich Davis
      ----- Original Message -----
      Sent: Monday, June 03, 2013 12:06 PM
      Subject: Re: [dallasaudioclub] Aikido preamp


      It's a fine sounding preamp from what I've heard. Most of them using. 6DJ8/6922 varieties. 

      Several locals have built them. With all the tube combinations you can use, it's hard to say something as general as "is this a good preamp?" Because people use various tubes in each position. 


      On Jun 3, 2013, at 11:58 AM, "Robert Cham" <cham@...> wrote:


      Hi Mike,

      I've got a mostly built one that won't be finished anytime soon as
      I'm 2,000 miles away building our retirement house.

      I gutted a PAS 3 and installed two 9 pin mono boards and a PS 1
      board for separate regulation of each channel's power, after some
      metal work and clear plastic "Contact Paper" on the bottom plate as
      the spacing is a bit tight to the board traces. Separate regulation
      of channels has yielded improvement in crosstalk in SS preamps, so I
      thought that I'd try it in a hollow state one.

      Still to be done is the wiring of the selector switch and Alps volume
      control with Mogami snake cable stripped out of it's overall jacket,
      and the transformer chassis, which will connect to the PAS 3 through
      the already installed Cinch Jones connector. I'm making my own
      multi-conductor cable for the power interconnect by using heat
      shrink tubing over cable of various gauges, depending one whether
      it's for Plate or Filament power.

      I'm going to try using 6H30s for their low output impedance, as I
      want to try using Nelson Pass's passive low level crossover from an
      old Audio Amateur, which requires the ability to drive 5K loads.
      John Broskie doesn't like the sound of that tube, but we'll see what
      I think. The crossover will drive a pair of ST-70s, which will
      bi-amp the Maggie Tympani 1Cs. The phono preamp will continue to be
      the Transcendent Sound kit built unit, easily the most accurate and
      impressive sound stage presentation that I have ever heard.

      So, I still haven't heard an Aikido either, but I also have heard
      much good about them, and as an engineer, I really admire Broskie's
      work. The engineering on them is really solid.

      Bob Cham
      (presently in Virginia)

      >I just recently joined the group and I wanted to pose a question to
      >the group. I am thinking about building the Aikido preamp. I have
      >heard good things about this preamp. Has anyone in the group heard
      >the Aikido? I would love to hear your impressions.
      >Thanks all.

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