High output current 300B pre/phone amp

[erik2A3]

What a luxury to have time away from teaching for audio construction projects! With a strong preference for scratch building, kits, particularly those that do NOT use circuit boards, are always enjoyable. I have built many Transcendent Sound products over the last twenty years, including designs published in Glass Audio magazine (before TS Kits were even available.).

The latest from that company for me is one for which I have very high expectations. The "Masterpiece" as it's called, is a combination high output current preamp and headphone amplifier. I have built a number of line stages using the more common dual triodes in various output configurations -- cathode followers, SRPP, unity gain impedance buffers, etc. -- and while many sounded quite good (and a couple not so good), none comprehensively addressed an issue many of us encounter: the deleterious effects of pairing higher output impedance preamps with amplifiers that are connected via long runs of cable. Cable inductance, capacitance, and resistance are electrical characteristics which some cable companies don't address (at least overtly), and what the end user is often left with are flattering descriptions of speaker and line-level cables that are named after various species of snake or, perhaps, the names of famous composers or tall mountains -- all of which to me are essentially meaningless in terms of determining suitability with one's specific components.

The "Masterpiece" was designed to take advantage of the perceived sonic attributes of the 300B (which for me has become a favorite) and develop a linestage/headphone amp that can drive long ICs with ease, and/or be used as an extraordinarily high quality headphone amplifier that's compatible with large number of headphones.

I am not the designer of this circuit, so it would not be appropriate for me to share specifics of the circuit. Transcendent Sound is well known for its OTL amps (which as an owner I can tell you are (subjectively, of course) stunning with Klipsch Heritage horns, but this preamp is one product I think is going to be exemplary.

The chassis is completely pre-punched and machined (good for me since my Greenlees are getting old and dull), but the entire circuit is wired point-to-point. Those of you who know what you're looking at will be able to quickly determine that it does not use tube rectification for B+.

http://www.transcendentsound.com/Transcendent/Masterpiece.html

Hardware has been installed and basic power supply connections complete: I use my own wire of choice and in some cases make changes in terms of overall parts layout. One of the advantages of PTP wiring, in my view. I would not recommend this project for a first build. The Grounded Grid preamp would be a better choice.

Edited June 17, 2015 by erik2A3

[MyOwn]

eric2A3

This is my next Kit from Bruce, Hopefully next month I can pull the trigger. Currnetly have the GG with no Mods except mute circuit, and his SOB. What an awesome combination these provide to the music coming out the RF-7ii. Cant wait to get the "Masterpiece" in place of the GG.

 

Please let us know when you get yours up and running and your thoughts.

[erik2A3]

Hi, Steve

I can see how that would be a very nice setup! I have built several SEOTL amps (original version) as well as six T16s (and own examples of both of those), but I am completely unfamiliar with the sound of Bruce's current generation of OTLs. However, I have been following his work since the very early 90s, and find him to be an extremely original thinker and designer. I would think that the output impedance and damping characteristics of the SOB (acronym for Son Of Beast -- for those unfamiliar) would be particularly good with the RF7II.

Should be done with the MP in a few days -- I'm working on a few different amp projects at the same time. I will be using it with our La Scalas and Grado and Senheiser headphones.