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Octal EAR 834P phono preamp


During my visit to NYC earlier this summer, my buddy Ding loaned me his home-brewed octal version of the EAR 834P phono preamp using 3 x 6SL7 octal tubes. Powering the preamp is a General Radio 1201-B tube regulated power supply.


Ding is not into boutique parts. Instead, he used carbon film resistors, mylar coupling capacitors and electrolytic caps gathered from Hamfests and surplus stores. Proper grounding and parts placement ensured a very quiet phono stage.


Traditional tube phono stages like the classic Dyna PAS 3 and Marantz 7 employed active RIAA EQ networks inserted in the negative feedback loop from the final stage to the input stage. In the 834P, Tim de Paravicini used active RIAA EQ with a clever twist - the EQ network is fed from the cathode follower output back to the second stage only. IMO, the benefits of this topology are: a 1st stage unimpeded by negative feedback, low noise and low output impedance.

I've been enjoying this phono stage so much that I'm inspired to build my own version. Good job, Ding!

Comments

  1. Hi Joseph,

    Your report sounds rather interesting. Has Ding exactly copied the plain 834p schematic and just dropped in the 6SL7 to replace the 12AX7's? Or did he amend specific values?

    Kind Regards,

    Ernst

    ReplyDelete
    Replies
    1. Good question! He told me it was based on the original circuit but upon closer scrutiny the 2nd stage is direct coupled to the cathode follower and since he used a 6SL7 there, the cathode load is 120k.

      Delete
  2. Hi Joseph,

    Maybe Ding would like to share the cirquit diagram with the DIY community?

    All the best,
    Ernst

    ReplyDelete
    Replies
    1. The circuit Ding used looks very similar to this -http://usr.audioasylum.com/images/3/33813/834p_variation_2.jpg - instead of 12AX7 + 12AT7, he used 6SL7s in all positions.

      I will post a loktal version, stay tuned ;)

      JE

      Delete

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