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K&K Audio / Lundahl Transformers

Sanity Check / Stax Headphone Amp.

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I have a tentative design for a Stax Headphone amp based on the Amity.
My main question was with the "output" transformer.
Would a LL1671 PP be a good choice for this application, or would either the LL1635 or LL1660 be more appropriate? I am looking at several output tubes, EL84, 2A3, etc.
FYI, If you aren't familiar with electrostatic headphones, they present a 120 pf load and require a high voltage drive. John Broskie targeted 250 V peak to peak in his headphone article. I was thinking of a design target of 450V p-p for dynamic headroom.
Thanks in advance;
Doug
"Its not a rip-off, its an homage."

Follow Ups:

Re: Sanity Check / Stax Headphone Amp. - KevinC 07:12:06 02/01/06 (1)
Yes, you could use the LL1671/PP with tubes like EL84 and 2A3. With a nominal 1+1:1+1 connection, 450vP-P is readily achievable at midband. I'm afraid that the choice of tube will have a substantial influence on the ability of the amplifier to "drive" the capacitance, though, at higher frequencies.
The other two transformers are not optimal. The LL1635, when gapped for 5mA of imbalance, simply doesn't have the primary inductance for the drive levels you want to achieve at low frequencies and is marginal for the required DC bias current through the primary, as is the LL1660.

Kevin Carter
K&K Audio
www.kandkaudio.com
- Re: Sanity Check / Stax Headphone Amp. - DougLockwood 19:09:17 02/02/06 (0)
  Thank you. That was exactly what I was looking for.
  Doug
  For reference:
  This link, http://www.tubecad.com/november99/page3.html
  details the drive issues with this design.
  - http://www.tubecad.com/november99/page3.html (Open in New Window)

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