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adding a dual power supply for my naim preamp

Discussion in 'd.i.y.' started by KiwiMike, Sep 28, 2020.

  1. KiwiMike

    KiwiMike Member

    Hi there ,
    just wondering if this attached drawing of my planned power supply is worth considering ?
    My transformer does not have a dual 25v 0 25v winding, only dual 0 25v

    thanks for any guidance[​IMG]
  2. graham-r

    graham-r pfm Member

    Absolutely a good idea, i'm in the process of doing exactly that with a NAC62 - using a separate +24v supply for each channel, for this I am currently modifying my kiCAD PSU design to use two LM317's or LT1086CT's (instead of LM317/337).

    I think some people have split the supply into 4 x 24v, but I don't know too much about that.

    There is always this page for some Naim info - you may have seen it already.
  3. Dowser

    Dowser Learning to bodge again..

    Centre tap provides better results though...IME :)
  4. KiwiMike

    KiwiMike Member

    My transformer doesnt have dual 25v 0 25v
    So how would 2 identical transformers go?
    Im finding it difficuilt to source a dual 25 0 25.
  5. graham-r

    graham-r pfm Member

    A 25v transformer will give about 35v rectified off load, which is more headroom than you need for a 24v supply.

    A 22-0-22v will give about 31v, more than enough to do the job.
  6. martin clark

    martin clark pinko bodger

  7. KiwiMike

    KiwiMike Member

    Thanks but now theres too many options,
    Im a little overwelmed,
    Would having 2 identical 25 0 25 transformers work? Or having the 2 rails
    Parallel with 1 transformer.
  8. graham-r

    graham-r pfm Member

    Complete overkill, keep it simple - a single dual secondary transformer is all you will need for this

    The Hicap pre-amp output are 2 x 24v @ 300mA each - a 22v transformer (see post above) with dual secondaries at 15VA (as a minimum) is more than enough.

    I am going to use a 22v Nuvotem PCB transformer (70055, 70065, or 70075) - like this.

    There is also this that may interest you

    I don't know where you are so these components may not be available.
  9. Dowser

    Dowser Learning to bodge again..

    Complete overkill is a good thing IME - my Naim PSU started with a single transformer. Adding a second and using Centre tap with half wave increased sound quality. Sure, you don’t need to...but it sounds better IME. Thread must still be here in DIY somewhere when I was building a PSU for my NAC 62 many years ago.

    I would use 2 transformers :)
  10. graham-r

    graham-r pfm Member

    Overkill just increases cost and bulk, I don't know much about the Hicap - the transformer looks pretty big - but it may have a number of secondary windings, either way the back of a Hiap states 2 x 24v @ 300mA each. I believe Naim.

    "half wave increased sound quality" - are you sure ?

    Half wave rectification will increase ripple considerably !
  11. Dowser

    Dowser Learning to bodge again..

    Ugh - full wave then? I forget the terminology :)

    But adding a 2nd dual secondary transformer, using Centre tap as earth return and only 2 diode junctions sounded better than 2 bridge rectifiers on a single dual secondary transformer. Pretty wasteful of transformer windings, of course.

    I try and dig out my original posts on the topic later
  12. graham-r

    graham-r pfm Member

    To help minimise switching noise you could try some byv27-200 diodes (or similar) - maybe with snubber caps and even some resistors - as above in the picture.
  13. KiwiMike

    KiwiMike Member

    Hey thanks for the ideas, i will start looking for parts asap, the transformer i have at the moment is a 0 - 25vac 0 - 025vac (4 wires)
    @15VA so i will get another one and try the twin transformer method.
  14. Brennus

    Brennus pfm Member

    The gold standard in Naim power supplies appears to be Ryan Sound Labs. Kit uses a 120 va dual secondary 25v transformer with dual regulators and a common earth AFAIK. So I would say a single transformer would be fine.
    Mynamemynaim and graham-r like this.

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