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Which transformers are the best choice for a dual mono amp?

Discussion in 'd.i.y.' started by Luca, Dec 8, 2020.

  1. JimmyB

    JimmyB pfm Member

    Sorry to butt in but @James Evans are you running the VBE front end from the same 35v transformer as the back-end?

    I've done similar as all I had was 35-0-35v transformers but I thought it was suggested that running from something like 42-0-42v to the front end was the preference?

    Fancy getting some 40 or 42v transformers to try a front end voltage increase.​
     
    Last edited: Dec 10, 2020
  2. James Evans

    James Evans Bedroom Bodger

    Front end is running off 50-0-50 transformer from Les with the output voltage set on the vbe using zeners (can't remember off hand what the output is set at). I have previously not bothered with the zeners and just used a slightly higher voltage transformer for the front end than output stage and just let the dropout over the vbe set the voltage.
     
    JimmyB likes this.
  3. 337alant

    337alant Negatively Biased

    I have used the Torriods from Canterbury windings and I think they are excellent , as James stated they have the electrostatic screen between the primary and secondary windings and an external Goss band to reduce the radiated field and a potted centre.
    In my mono block NCC300s I use R-Core transformers and they are also excellent unfortunately they are not that easy to get hold now, I got mine from the Group Buy organised by TimH here on PFM.
    I see that a company calles JamesTransformers is advertising but I have no experience of them ?, maybe ask for a quote
    http://jamestransformer.com/en/transformer/index.html
    Alan
     
    Last edited: Dec 10, 2020
    Garrard 401 and Luca like this.
  4. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    A transformers a transformer... simple as... Any old transformer will do just fine. It's something I never even consider in all my work as it has no effect on anything.... other than radiated hum field, and then I'll almost always put the transformer in a separate case if hum field is critical.
     
  5. paulski

    paulski pfm Member

    That’s just plain nonsense.
     
    337alant likes this.
  6. Ian M

    Ian M pfm Member

    Comment from Avondale Audio.

    Classic comment from a prolific poster over in the Pink Fishery Pond:

    "A transformers a transformer... simple as... Any old transformer will do just fine. It's something I never even consider in all my work as it has no effect on anything.... other than radiated hum field, and then I'll almost always put the transformer in a separate case if hum field is critical."

    Here is a fellow who reckons to know his way about the industry and how wrong can he be.

    For many years, I used to conduct a simple experiment in front of visitors, some of them having not the slightest interest in HiFi. I would play a track at a certain level and once they'd heard it through, I would substitute an identically rated custom "C" Core transformer for the toroidal in the power amp and play the same track without changing anything else. The results always resulted in astonishment in that why should a transformer influence the sound so much .?

    I must do the same test again to see if the results are quite the same - I bet they are.
     
    john.luckins, Brennus and S-Man like this.
  7. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    People can't wait to advertise their zero knowledge of the subject as usual I see.
     
    Last edited by a moderator: Dec 11, 2020
    Shane2468 likes this.
  8. Jo Sharp

    Jo Sharp Pulls on doors marked push

    [Moderating] Ad hom removed. The DIY room thrives on respectful debate. Differences of opinions and/or experiences are part of that debate. Accusations of dishonesty are not. Accusations of someone having zero knowledge probably reflect more on the person making the accusation, rather than the target.
     
  9. John Phillips

    John Phillips pfm Member

    It seems seems to me there is a fundamental difference between the audiophile philosophy and the designer philosophy.

    If I observed the situation as above (with a system designer hat on, or as an occasional audio DIYer) I would be rather unhappy at an unexpected and undesirable outcome. I would think that either:
    • the specification I set out for the transformer was not sufficient to allow it to be substituted when required (e.g. to deal with supply chain problems); or
    • the amplifier design I had was not good enough to tolerate the substitution of a transformer that was equivalent according to the specification.
    However AFAICS the audiophile philosophy is that this sort of situation is both expected and desirable, to enable effective tweaking.
     
  10. sq225917

    sq225917 Bit of this, bit of that

    I'm in agreement, once you have sufficient voltage and amps available, and assuming decent psrr in the following circuit anymore is wasted.

    In always favour 1 traffo per channel though, I accept this is neurosis in 99% of cases however.
     
    martin clark and Luca like this.
  11. Luca

    Luca pfm Member

    Hi Si, to chose a single traffo with two secondaries 35-0-35 or two traffos with 2x35 is my first doubt. Is the extra money well spent by going with a couple?
     
  12. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If the accumulated knowledge of decades of scientific experimentation by countless engineers and the contents of every electronics text book are to count for less than "what some geezer believes his stereo sounds like" then I'm wasting my time.

    FWIW I was designing a power amp with around 0.0007% THD @20KHz before I logged back into pfm... I wonder what people who describe my professional opinion as "plain nonsense" were doing?

    Just buy the most expensive transformer with the most outrageous foo claims in the advertising... maybe Russ Andrews has some that give an inky blackness to the inter transient silences... they couldn't be wrong...
    I'm outa here....
     
    Shane2468 likes this.
  13. S-Man

    S-Man Kinkless Tetrode Admirer

    RA did do some totally OTT toroids many years ago. Seem to remember him saying that GOSS bands killed the dymanics.
     
  14. martin clark

    martin clark pinko bodger

    Or maybe such an approach reduced fizziness / HF noise feed-through inducing the kind of HF intermod brightness or (false) 'dynamics' that ..some expect to want/like/hear as 'more detail' - (the banal hangover of last 30+yrs of subjective magazine reviews, IMO: ultimate wood-for-the trees stuff).

    I dunno. I'm simple: so just tend to engineer/engender the best PSRR I can achieve after the raw supply, then assume if I don't like it, it's my fault.
     
    Luca likes this.
  15. JimmyB

    JimmyB pfm Member

    You sure that's a good idea? I'm pretty sure after years of hifi and reading mags that people actually prefer distortion.....it's the only conclusion I can come to when I see all the tweaks that make 'massive' improvement to their systems....

    My current amp uses five transformers. Effectively monoblocks in one case and the only real reason for five (one is on the k4700) is to run different voltages. Ideally I'd have got a single transformer wound to give me both outputs but I'm a cheapskate and it probably wouldn't have fitted in the case anyway.
     
  16. Jo Sharp

    Jo Sharp Pulls on doors marked push

    "If the accumulated knowledge of decades of scientific experimentation by countless engineers and the contents of every electronics text book are to count for less than "what some geezer believes his stereo sounds like" then I'm wasting my time."

    Not at all - it is the tone in which you make your argument that matters in this forum. Slagging people off or accusing them of being charlatans is not going to convince other members of your superior engineering knowledge. Explaining why you think you have a better answer in a polite fashion is usually more effective. If you want to flounce off, so be it; I'm sure the majority would prefer you to stay and learn from you.
     
  17. S-Man

    S-Man Kinkless Tetrode Admirer

    Goodness only knows what RA thinks.
    I remember meeting him at a hifi show about 20 years ago. He was playing some cream leather covered speakers at about 120dB. Sounded harsh to me, but maybe I mistook "dynamic" sound for harsh :confused:.
    To be honest, I don't think RA is a charlaton, just misguided.

    Any fervid cocksure should be treated with caution!
    (Including technical cocksures).
     
  18. Chops54

    Chops54 pfm Member


    Nowt wrong with being a cheapskate in these troubled times Jimmy, that's how I built my NCC300s. I bought the four main transformers from Airlink this time as I just didn't have the funds to go to Canterbury Windings. I had a used transformer in the spares box which was bob on for the protection boards.
    I usually go to Terry at Canterbury because he winds the transformer to suit my mains voltage which is always around 245V. When buying from Farnell or Airlink etc where their transformers all seem to have 230V primaries I have to calculate for a reduced secondary winding.
     
    Luca and 337alant like this.
  19. JimmyB

    JimmyB pfm Member

    Yes, mine sits at 248v so I'm always a bit nervous at switch on with 2 x115v primaries which is generally what I end up with.
    Another reason my Revox B250 is in mothballs until I built a bucker to feed it 220v...
     
  20. Chops54

    Chops54 pfm Member

    JimmyB, your post just reminded me that I recently built a bucking transformer for my JBL 6290 but with all the work going on at home I'd forgotten all about it. I used a 300VA toroid with a 25 volt secondary to get down to 220 volts. It's still on the bench in my workshop and just needs a few nuts and bolts in the casing to finish it off. Unfortunately I don't think I'll get it finished until after Christmas :(
     
    JimmyB likes this.

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