My take on a Single Ended amp

Discussion in 'Tube Audio' started by kward, Jul 7, 2018.

  1. kward

    kward AK Subscriber Subscriber

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    Thanks Primo. Very good information. I'll look into those suggestions as I start to prototype mine.
     

     

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  2. primosounds

    primosounds SE KT120 w/ 6J5G drivers. LCLC ps + 2 x 5ar4 Subscriber

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    Te nada! El gusto es mio.
     
  3. Selmerdave

    Selmerdave Well-Known Member

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    Look for posts by Dr lowmu
     
  4. dowto1000

    dowto1000 Active Member

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    Hi,

    Good question. Personal Background.

    My first audio mentor was Robert W. Fulton, of Fulton Musical Industries . He was responsible for the FMI-80, FMI J-Modular, Premiere speakers ( 12HZ to 100 kHZ ) . I first met RWF in 1978, and in 1981, I built my first DHT amp, 2A3 P-P, from an AudioNote Kit for Audio and LP Reviewer Neil G. Levinson. In 1982, I decided to do my own design. The very first thing RWF told me was " to make all the chokes to the 2A3 Finals 20 Ohms or less, IF I can find them. " He also suggested two L/C sections in series, as being superior. A six chassis 700 pound monster evolved, 1982-1986 .....P-P-P 6B4Gs.

    Sadly, RWF died in 1988, and pre-internet, I corresponded with other amateur audio designers and DIYers, People like Art Loesch, Herb Reichert, JC Morrison, Jim Dowdy, and Dennis Fraker. I shared freely with them " 20 Ohms or less " on Ls.

    Reichert's Flesh and Blood 300B amp had my "only $8.00 surplus - priced potted 3 HY at 24 Ohms DCR choke ", as part of his final design in that Sound Practices magazine article.

    Dennis Fraker introduced me to a PhD EE - audiophile, who was head of the EE Department at the University of Alabama. Dr. Charles E. Halijac gave me a scholarly run down on DCRs in power supplies, and how conventional EE supply designs " by the book " were " outmoded and out-to-lunch ", something I already sorta knew, and it alluded to RWF's " 20 Ohms or less ".

    I think, in around 1998, Dennus Fraker, who was my brightest and best audio friend, and a " second audio mentor", developed his first Serious Stereo DC 2A3 SE audio amp. It used two 10 Ohm C-2708 Stancors, and two L/Cs, ....right up my alley. But Dennis' implementation was FAR FAR advanced, from just using Low DCR Chokes. He also BEAUTIFULLY devised a scheme where the chokes and the amount of capacitance, in uFs, was also low. This was HIS own LSES supply, totally unique in the history of audio. LSES stands for Low Stored Energy Supply.

    From Dennis' second year showing at RMAF / Denver, 2006, I attended those shows annually, to hear his SE 2A3 amp implementations, and anything else that sounded good to me, in audio. Fun. I applied his approach to my SE amps, and enjoyed unique results. When I A-Bed my SE 45 amp, with LSES, against, say, a local audio friend's Yamomoto A-08, my implementation put that Yamamoto SE 45 amp to TOTAL shame !! We both heard it instantly, we KNEW, and we were encouraged.

    I eventually wanted to share this supply , based on a MONO 45 or 2A3 amp, with good people on the Audio Asylum. There, I had mixed results. The " 100 year old textbook theory guys, " ALL of them never EVER hearing Dennis' amps at a RMAF show, wanted to criticise me for parting with their beloved theory of " critical inductance ". Two very very sharp EEs, Messers John L. Hasquin, and John Swenson, embraced the design concept, developed solid engineering theory to explain why it was so good, and developed their OWN version of LSES, called by Swenson, a FLYWHEEL. These two actually built a circuit and LISTENED to what they built...amazing !! If anyone wants to read their chronological AA Posts, I have them saved and can email them to you.

    I did try Swenson's Flywheel , ( which used Fraker's design concepts in different way ), and eventually, I personally went back to pure LSES, ala Dennis, - upon HEARING his RMAF exhibits annually, and have stayed there, and its been developed additionally, in subtle ways.

    So, ALL OF THE ABOVE, represents 37 years of my DIY audio life, dedicated to this subject ( 2018-1981) .

    In a separate post, I will address your questions, on HOW I would employ LSES in 2018, and what constitutes a good SE amp power supply, in my experience. This post, addressed my personal background for folks to comprehend.

    Have fun, I always do.

    'Am presently prototyping a SE two stage Direct Coupled 6AQ5 amp, ultralinear. That tube itself, deserves a great circuit implementation, IMHO.
     

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    Last edited: Jul 12, 2018
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  5. GordonW

    GordonW Speakerfixer Subscriber

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    My one qualm with the LSES idea, is that by using a low-value choke and low-value cap- you're creating a resonant circuit that's likely got a corner frequency within the audio band.

    I've heard tube amp power supplies with this issue- and my usual complaint, is reduced low bass energy and impact- and what bass is there, tended to be tubby and ill-defined. I've modified such designs, with additional capacitance and/or inductance- getting the resonant frequency below the audio band, and reducing the Q of the resonant circuit to a low enough level to not overshoot- and the bass has almost always improved.

    Incidentally- I HAVE heard Dennis Fraker's designs- at RMAF 2017. I actually directly compared his room, with another room, also using a monitor speaker based on the Altec 604, among other rooms I sought out, with tube amplification, anywhere I could find them. I thought Dennis' system (with the SE amps and Altec 604s) didn't have nearly the bass weight or definition of the other 604s, in fact. The sound in Dennis' room was sort of "thin", by comparison, to my ears.

    I didn't even know about his power supply designs at that time- but if they're designed in the way described above, the sound I heard actually makes more sense to me...

    Of course, I will admit- I'm more attuned and drawn to the bass authority, reach and clarity, generated by Kevin Hayes' VAC amps. It's hard for ANYTHING else to compete with that, IMHO... and that includes all other amp designs of all types, tube or solid state, that I've encountered, period...

    Regards,
    Gordon.
     

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