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Transformer for NCC220

Discussion in 'd.i.y.' started by say it as it is, Apr 17, 2021.

  1. say it as it is

    say it as it is pfm Member

    Ok been toying with the idea of putting the new boards in 2 mono cases. Have pretty much it all bar the transformers.

    Any recommendations for transformers for mono amps?

    For my stereo amp it was 33-0-33 (X2) as I have higher mains voltage about 250v.

    What size and make have you guys found best for mono amps?

    Other point with a smaller tx is a soft start still needed?

    Thanks
     
  2. Marra

    Marra pfm Member

    337alant likes this.
  3. mega lord

    mega lord Centre tapped

    No soft start required with smaller transformers.
     
    337alant likes this.
  4. Mike Hanson

    Mike Hanson Lovely!

    My last NCC220 QUDOS mono build used 330VA transformers, but I'm pretty sure you would be fine with less, given many stereo amps are 500VA.
     
  5. mega lord

    mega lord Centre tapped

    My amps (six monoblocs) run from the Avondale EI transformers that Les uses for the voyager front ends. Couldn't want for more, I prefer them to my CW 300VA toroids. My speakers are a very easy load though with passive line level crossover. Happy days :)
     
    337alant likes this.
  6. say it as it is

    say it as it is pfm Member


    The little 100VA 25-0-25 ones? I have them as TPX transformer didn't think I could use them for a power amp I have a couple laying about as well
     
  7. say it as it is

    say it as it is pfm Member

    Never seen O core before on paper look good at least.
    I know many speak highly of R core though.

    I have used AST from Les before and seem very nice, but also have a CW unit in a power supply that runs quiet as well.

    Food for thought stay with established format or try something new?
     
    337alant likes this.
  8. mega lord

    mega lord Centre tapped

    Yes those are the ones I use for my power amps. Don't tell anyone though cos my street cred will be gone. I don't use ncc though anymore and my speakers are a super easy load plus I have an averaged sized room and don't play loud. Give them a go and see how you like them. Don't blame me though if you don't like it. EI transformers have ALOT going for them.
     
    Last edited: Apr 18, 2021
  9. say it as it is

    say it as it is pfm Member

    Only concern is you have 6 amps so perhaps the lesser power works only feeding a bass/mid/tweeter ?
    As I be only using 1 amp per speaker unlike your 3 I presume?
     
  10. 337alant

    337alant Negatively Biased

    EI Transformers are said to have very good filtering of mains born interference but not so good performance on radiated field interference
    Toroidal transformers are said to have poor mains born interference rejection but very good radiated field interference performance.
    R Core transformers are said to have the majority of advantages of both of the above

    Alan
     
  11. mega lord

    mega lord Centre tapped

    Jez would tell you that all transformers sound the same :oops: I must be imaging it then :) but I am always drawn to EI over toroid in every different use (phono stage, cdp, TT motor, power amp. All my psu's are remote from their load (one metre) so the bigger stray field of the EI transformers is not a problem.
     
  12. say it as it is

    say it as it is pfm Member

    yes heard R core have benefits am sure a few years back Les W was singing their praises.

    the O core also seems interesting as space could be tight the dimensions might have a say in it
     
  13. say it as it is

    say it as it is pfm Member

    what design (if well made at least) would offer the lowest mechanical noise or hum?
     
  14. Marra

    Marra pfm Member

    I replaced a toroid from a well known maker which buzzed with an O core from James transformers which is totally silent and imho improved the sound of my amp.
    Probably opened a can of worms with that last comment though.
    I should add that the toroid was the only one of several that was noisy.
     
  15. say it as it is

    say it as it is pfm Member

    I have high mains voltage as high as 250Vac so what design works best and gives least noise in that environment?
     
  16. Marra

    Marra pfm Member

    If you are having one made you can spec all voltages. I always ask for 240v as like you the mains often sits above that although generally not as high as yours.
     
    quickie and 337alant like this.
  17. grahamdocman

    grahamdocman pfm Member

    I'm using AST 150VA 35 - 0 -35 transformers in my mono '110 NCC220' amps which I bought from Les after asking his advice. I recently tried them on a friends Isobariks and they drove them without any problem, much to mine and his surprise.

    They certainly were a quantum leap above his Naim 250 to such an extent that he's thinking of converting his 250 to a Voyager type QUDOS and doing away with the regulator boards.
    The move to "small Mono's" was well worth it, rather than driving both boards off one transformer and PSU, I expect this is why they perform so well.

    So unless you have a particularly difficult speaker load I wouldn't be too worried.
    My own speakers are Les' Revelation 2's, the 220 (QUDOS) '110's are more than enough to effortlessly drive those at high listening levels with the volume knob only half way around its travel.
    Room size 16ft x 13ft x 8ft
     
  18. say it as it is

    say it as it is pfm Member

    Hi yes I have 500Va AST from Les for my stereo amp its nice and quiet and certainly works! Its a toroidal

    Was not convinced that mono's offered much benefit but way things have worked out I have cases that look nice so why not.

    Your AST 150VA are they toroidal or laminate (EI) ?

    I was told you need at least 200VA per board, my 260Z had a 350VA fitted from new and definitely did not struggle for sure.
     
  19. grahamdocman

    grahamdocman pfm Member

    Mine are toroidal and no noise at all. I'm not sure where the "minimum" 200 VA per board came from, all I can say is that mine seem to work fine even into difficult loads such as my friend's 'Briks', Having said that, they are monoblocks.
    Additionally, the only remaining parts of my original Naim 110's are the shoebox cases, sledges and knob. I've replaced all the internal wiring too and used 6.3mm spade connectors.

    Transformer = AST 150VA from Les (this was the only size I could fit into my 110 shoebox), I think the original H&F were rated at 120VA and supplied both boards.
    PSU = Avondale Minicap 6
    Amp board = QUDOS (NCC220)
    NO PSU take off for preamp, that is supplied via HiCAP fitted with TPR4 module

    Hope this helps
     
    davidho and Stuart Frazer like this.
  20. say it as it is

    say it as it is pfm Member

    ah right might be more for the case size I have slightly larger case so a 300 or 350Va should fit just assessing what options are out there
     

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