SET Asylum

RE: Nice OPT

24.27.41.140

Triode_Kingdom

A

In Reply to: RE: Nice OPT posted by Paul Joppa on January 04, 2024 at 22:47:51

I'll never build another high power (>5W) SET. I believe the performance limitations of available transformers render the goals of wide bandwidth, low bass performance and low distortion unattainable. Parafeed designs might overcome some of this, but then the signals are required to pass through large coupling caps. All things considered (including power supply idiosyncrasies), an ultimate amplifier should probably be based on push-pull class A triodes. I'm also not opposed to a few dB of feedback to help shore up damping factor.

Follow Ups:

RE: Nice OPT - Paul Joppa 07:37:56 01/05/24 (6)
If you are going for the ultimate performance, I agree. The most appealing approaches to me are either bi-amping (i.e. a subwoofer with separate amp) or parafeed with a high-power current source to replace the plate choke. Both have other, practical objections. No free lunch at the 3-star restaurant!
- One vote for bi-amping - Donald North 18:26:47 01/14/24 (0)
  Use SET for the vocal range upwards and push-pull for the deep bass.
- And then again, - Ian L 16:32:59 01/10/24 (4)
  TK,
  Out of interest in whether forms of feedback I hadn't tried were as unlovable as the ones I had, I built some circuits from articles by Frank Blohbaum (in Linear Audio Magazine, Volumes 6 and 8). I'd say his designs are very good and they do well with available transformers.
  
  The individual articles can be had as pdf's from Jan Didden , Linear Audio Mag's publisher.
  
  PJ
  I've been told parafeed sounds even better with a plate load resistor! : )
  - RE: And then again, - Triode_Kingdom 22:03:23 01/12/24 (3)
    At the risk of sounding immodest, I've been pleased with my own implementations of feedback in single-ended amps. It helps when the driver exhibits an abundance of headroom and good test equipment is available to tweak and vet the results. It has been my experience that optimization of the numbers can in fact coincide with good sound quality.
    - RE: And then again, - Ian L 11:04:19 01/17/24 (2)
      After an initial non-start with feedback as cathode degeneration (including cathode circuit use in RIAA filters) or global from the OT secondary (and those being the only forms I knew of at the time), I became interested again after reading some of Frank Blohbaum's ideas using 'nested' or local forms. Building some of his circuits confirmed there was positive potential there.
      
      By the way: He gets that abundance of headroom you mention by making a transconductance amplifier at the input stage with a triode and BJT for 'abundantly' high gain (≥1000X ! ).
      
      Any resistance to the subject of feedback I have now comes mostly from difficulty with the way it's talked about.
      No matter how hard I try, I can only see the oft reproduced Crowhurst block diagram for series feedback as a parallel arrangement of some sort, and no-one so far has been able to explain it in a way that I can translate back into thinking that would be useful in designing tube circuits.
      
      Last time at Barnes & Noble I scanned the shelves for "Feedback for Dummies" but apparently they were sold out. : )
      - RE: And then again, - Best audiotransformers 11:33:51 01/17/24 (1)
        
        In Reply to: RE: And then again, posted by Ian L on January 17, 2024 at 11:04:19
        
        What does your comment have to do with this topic?
        
        Edits: 01/17/24
        
        RE: And then again, - Ian L 18:01:44 01/17/24 (0)
        
        In Reply to: RE: And then again, posted by Best audiotransformers on January 17, 2024 at 11:33:51
        
        Well, it's on topic in as much as the general underlying theme of these forums is friendly discussion of our audio related interests.
        
        The OP (Original Poster/ Thread Starter) has to all intents and purposes abandoned this thread, leaving it open to the flow of discussion between those of us who have become acquainted with each other (or our monikers at least) over the years, much like the wandering flow of any friendly conversation.
        
        Because of the way the Asylum is set up (ie. not locking positions of posts in chronological order), the OP is always free to come and post again above this if he wants to steer some discussion back along the lines of his own original interest.
        
        Thanks

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