First Watt F8 Power Amplifier

Discussion in 'Power Amps' started by beemerphile, Aug 26, 2020.

  1. beemerphile

    beemerphile Friend

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    I finally pony up for a First Watt J2 for my Susvara and the same week Good Old Nelson announces the F8. I don't think it changes my mind as the SE outputs on the Yggdrasil are gimped and the J2 is still the only First Watt amp with a balanced differential input. I've been a Nelson Pass fan since I acquired a first gen. Adcom GFA-555 in the late 1980's. I'd pretty well decided that I wanted to try another N. Pass amp before he hangs it up (without having to sell my house), but what drew me to the J2 was the simplicity of the circuit and the novelty of the power transistor. Turns out that the F8 is simpler still and retains the SemiSouth power JFET. Further to that, it is lower in distortion and purer in 2nd order harmonic content. I'd love to hear it..... or maybe I shouldn't.

    Coming in September 2020...

    http://www.firstwatt.com/pdf/prod_f8_man.pdf
     
  2. JeffYoung

    JeffYoung Friend

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    Yeah, it looks very interesting. But I already have a DIY J2, and neither one is up to the task of driving my Maggies in my main listening room.

    But at least now I know what to do with my spare set of SemiSouth JFETs. ;)
     
  3. Senorx12562

    Senorx12562 Case of the mondays

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    I cannot imagine that anyone who talks about what to do with their "spare set of SemiSouth JFETS" will ever be buying a commercially sold amplifier. Just a guess.
     
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  4. penguins

    penguins Friend, formerly known as fp627

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    No lie and somewhat embarassing - still haven't figured out which Nelson Pass amp I'd want to DIY (probably XA25 if I buy) after a year or so of debating this. Really need to figure out what I'm doing in this regard...
     
  5. beemerphile

    beemerphile Friend

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    With Nelson's low power designs, matching the amps to the power requirements of the speaker system is so much more important, and most likely the key consideration. If you have low impedance speakers, or speakers with a wide variation in impedance vs frequency, neither the J2 nor the F8 would rise to the top. The XA25 (or the F6?) would be better there. My planar HP's are high impedance (for a "speaker") and very nearly a uniform resistive load. As far as DIY, though he remains most gracious to the DIY crowd, he understandably wants to make a bit of money with a design before he passes it along to the DIY community. In that regard, the F8 may be a while in coming.

    Antoine de Saint-Exupery said “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. Albert Einstein's expression of the same truth is that "Everything should be made as simple as possible, but no simpler". I think both men have an adherent in Nelson Pass. Class A sounds like Truth, but it has some well known drawbacks. Designers have attacked the drawbacks of Class A for many years and often ended up with only a more complicated and less desirable amplifier to show for it. In rare instances, like the Class H Benchmark AHB2, they will succeed.

    First Watt J2 "Empty $4,000 box"...

    [​IMG]

    Benchmark AHB2 hyper-technical pièce de résistance...

    [​IMG]

    Hard to believe these two guys are trying to solve the same problem. At that point you have to determine whether the philosophy of the designer and the topology he chooses to employ are important to you. For me, it is. As an engineer, it has always been part of the experience for me. Some part of Nelson comes out in the music. His simple low power class A amps have sonic merit that to me is worth building a system around. I feel fortunate that it matches well with the Susvara which (like the HE-6 before it) I also believe is worth building a system around. Thinking about this a bit further, I guess some part of Fang Bian is in my music as well. He is not so warm and philosophical a character as Pass, but being a Dire Straits fan he must be an ok guy.
     
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  6. JeffYoung

    JeffYoung Friend

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    Here's what I'm working on now:

    progress2.JPG

    60-ish Class A watts per channel. Push/pull output stage similar to a F4, although it's switchable between vertical and lateral MOSFETs. I'm doing three front ends for it: a very simple BA-2 variant, an F5 variant, and a Hitachi variant (similar to the Pioneer M22).

    These are my first clean-sheet designs, so they might make smoke rather than music....
     
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  7. Senorx12562

    Senorx12562 Case of the mondays

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    Once again, respect, young Jeff.
     
  8. beemerphile

    beemerphile Friend

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    My guess is that it will play for several minutes after you turn it off.
     

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