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Naim Pre amps power supply

Discussion in 'd.i.y.' started by Sid and Coke, Jan 12, 2004.

  1. Sid and Coke

    Sid and Coke and so the rebuild continues..

    Not really genned up on these amps. I know that The Naim pre amps have to be powered by an external PSU or a Naim Power amp. All of the PSU's that I've seen for sale ( s/h) seem to be fairly expensive, often many times more than the pre-amps themselves go for.
    Is there such a thing as a Pattern/Copy/Clone/DIY version of a PSU and are they very complicated/easy and expensive/affordable to make to make ?

    Something like a 32 or 32.5 looks to be interesting but the power requirements are putting me off a s/h purchase. If i was to go down this route it would be in a fairly cautionary manner and i probably wouldn't be able to afford an expensive Pre/Pwr/Psu combo straight away.

    I think I'm pretty capable of putting something together ( with plans and advice) but have no history of this brand as a user at all.
  2. coredump

    coredump Press <ALT-F4> to continue.

    Check this out:

    Neil McBride PSU.

    The concept shown here can be improved though using some more sophisticated regulation. Andy knows all about this :)

    Best regards,

  3. timH

    timH pfm Member

    transformer and caps and maybe rectifier diodes from Les, super regs from Andy, case up to you - could get in for under £250 maybe - trounce a hicap definitely - easy to make for sure - could send you a parts list and layout if you want

  4. VTA

    VTA pfm Member


    I am close to building a HiCap clone...... RichardH of these forums has built more than one PSU for his 32.5 and is finishing up one now that is built using boards from Avondale Audio. He will soon be posting an idiots guide to this project. This version is apparently the simplest to do as Avondale has done the tricky bit for you. Think boards are 18 pounds.

    hope your ok with me blurting this Richard :) I am excited to get started! :)

    If you get a 32, go for the 32.5 as this will accept a Hicap. Can be had for 150-175 pounds i think, and they sound great (even before you add a PSU)

    Also - if you are looking for a 32.5, you will need a power amp to go with it, and all but the most expensive (250 and up) have facility to power your 32.5 till you get the PSU together.

    Not sure what electronics you are using, but i am very hopefull you go for this, as if you have 1/10th the fun i have had listening to Naim gear you will be doing great.

  5. RichardH

    RichardH Bodging pleb

    Yes, I've just been messing with Les's TPR regulator boards, as I wanted to build an extra supply dirt cheap. His bare boards are around £6 each, and the parts are insignificant. I've also gone with a couple of those Avel Lindberg transformers he mentioned he had a while ago - again, cheapos.

    I've kept quiet so far because I've currently got some hum on it which I'm trying to fix.
    I had thought it was down to my poor installation of replacement parts on the phono boards it's powering, but running it from another supply shows that it's something to do with my power supply. Switching the power off on my new PSU kills the hum, and obviously I still get music while the caps discharge. FWIW I have the regulator boards up close to the phono boards, and the transistors, rectifiers and caps in a separate box. I assume the problem is likely to be upstream of the caps, and a change of rectifier didn't resolve anything, so it must either be the transfomers themselved, or maybe my wiring of the mains supply that's causing the problem. More later....

    Once I get chance, I'll report more on the TPRs themselves - in particular I can do a direct compare against a superreg rigged supply (I currently have a pair of DIYcaps with identical transformers, rectifiers and caps - one with superregs, one with a 317 based regulator).

    Sid - re diagrams etc, take a look at Andy's site - - in the projects section there is a schematic for laying the supply out, and should give you most of the info you need.
  6. VTA

    VTA pfm Member

    It took a LONG time for these images to load for me, but they do load. Just click, go make coffee and they should be there when u get back.

  7. mcai7et2

    mcai7et2 pfm Member

    Re: the hum problem, I had the same issue with the built in PSU in my power amp (Avondale NCC200s + SNAPS reg). It would hum at an annoying level. After fiddlng with the placement and routing of the ground and +ve wires from the regulator to the socket, the hum disappeared totally, the system is now silent when my ear is more than a couple of inches from the speaker.

    Might be worthwhile experimenting, especially make sure the ground and power lines run as close to each other as possible.

    In my case the hum disappeared once the power was cut (I still got 2-3 seconds of music from the PSU caps).


  8. RichardH

    RichardH Bodging pleb

    Ed - that sounds exactly like what I'm getting. Wonder if it's partially because I have the regs a long way from the caps. I did have a brief jiggle around with the cables in the PSU box, but didn't notice any difference. More experimentation is needed, I think.
  9. Andrew L Weekes

    Andrew L Weekes Reverse Engineer

    if you have any pics you can send, I'd be happy to provide advice re: hum.

    You can do it in private, if you're embarrased at all ;)

    No.1 word at the moment though is loop / loop areas. Reading the text associated with the PFMOSCap wiring may give some ideas?

  10. RichardH

    RichardH Bodging pleb

    No, I'll get it all out in the open.... hopefully it will be enlightening for all!

    Couldn't be bothered with thumbnails, so here's links to three shots of the offending article.....

    DIYcap from above

    DIYcap side view (cap wiring)

    The DIYfix

    I'm fairly sure that the hum isn't being caused by the DIY prefix end, as running it from a different PSU (and therefore with regs at both ends) gave zero hum. And yes, it's a work in progress, so that's my excuse for the long singnal leads and tape on the PCB.
  11. VTA

    VTA pfm Member

    Richard, you stud, looks good. Hope the hum can be sorted.


    Why 2 transformer design instead of one HiCap sized one.

    Plastic Box? Could this be part of reason for hum.

    Did your daughter braid the wires (really nice job)



    oh, and also re Prefix - what are those other two boards in there besides the 323's???
  12. Richard Nichola

    Richard Nichola pfm Member

    I've had a look at what you've done and one thing worries me...

    You've appear to have unregulated DC (which will have some ripple and high frequency switching gunk left on it) running into your diyfix (which has very low level signals running down what looks like an unscreened cable). Maybe this is the problem..
  13. RichardH

    RichardH Bodging pleb


    First thing to remember is that this one is a cheapo special - it will probably end up powering the "non important" circuits in the 32.5 - buffer, etc.

    2 transformers because they're only a fiver each from Les, but only offer 1 x 24v (twin 12v secondaries), hence one needed for each channel. What would be really nice is a single 2 x centre tapped 24-0-24 jobby, but they're not an off the shelf thing.

    Plastic box - no, I don't think that's the reason. The main PSU is in an aluminium box (one of my DIY specials), and the DIYfix has worked without hum in it's current plastic box. This box is probably only temporary, anyway - cheapness, again.

    Braiding (sexist ;) ) - it was me - my daughter's too busy rockin' (actually it's not that neat.... but she was out at Rock School last night when this knitting was done ;) ).

    In the prefix, the extra boards are Les's regulator boards - I've located them there rather than the usual position of within the power supply because I'm hoping to remove the zener regulator circuit from the 323 boards, as it's apparently a large source of noise.

    As far as debugging the hum, I've tested the diyfix as it stands (i.e. with these regulator boards in place), using the same diySNAIC, but with another hicap, and there is no hum. This other hicap does have regulator boards, so there's another layer of regulation going on, but I don't think that will affect anything. I was also using this hicap with the 323s before I added the local regulation, and again no hum. So I'm pretty certain it's within the PSU that my problems lie.

    Richard - hmmm - I wonder. If that's the case, that would explain the reason that the other hicap was OK, as the DC input was regulated. It should be pointed out that the cable that connects to this carbuncle splits out right away into short screened signal leads going to the preamp, and a screened power lead that runs to the DIYcap, so the only unscreened area will be within the DIYfix itself, plus around the socket itself, which is probably more of a concern. Think I might try splitting the signal output from the power input, and screening the incoming power leads.
  14. markf

    markf pfm Member

    from the picture I don't see any decoupling caps on your
    24volt output, add some 10uf caps across Vcc and Gnd.
  15. RichardH

    RichardH Bodging pleb

    Do you mean the 24v output from the regs? They do have a decoupling cap on them - it might be masked by the lovely cabling :rolleyes: - it's nestled between the red and black bale that runs from the reg board to the 323s.
  16. markf

    markf pfm Member

    yes I meant the 24v out from the regs. I was expecting
    to see some de-couplers right at the reg output on the small vero board inside you PSU.
  17. RichardH

    RichardH Bodging pleb

    ahhh - that's the confusion - that veroboard thing is the rectifier (well, two actually - one for each channel).
  18. kptseng

    kptseng pfm Member

    Hi Richard,

    I do not see any heat sink on your retification board nor your regulator board, do they run hot?

    I did a few DIY-Caps, almost identical to what Neil has on his page including the regulating stage (never have a chance to get the very much talked about ALW-SR).
    I started with no heat sink but find my 317s and 1086s running fairly hot when touch, so I added those clipped-on heat sink.
    For the last 3 I did, I have the 317s and 1086s bolted onto the aluminum casing.
    I've been using those matel case bridge rectifiers from IR (rating at least 12amp) and they are bolted onto the casing.

    One more thing, I spoke with a guy recently and he recommended atting an inductor in series between the +ve of 2 smoothing caps, claiming that that will reduce the frequency further which will give the dc a more linear supply, any comments?

    Hope you'll solve your hum soon.


  19. Andrew L Weekes

    Andrew L Weekes Reverse Engineer

    There's been some good advice so far, I'm impressed!

    Here's my 0.02p...


    I think the greatest problem may well be the unregulated DC you're feeding to the Prefix.

    A better solution may be to feed AC to the Prefix box and put the rectifiers / smoothing in there.

    Since this isn't practical some pre-regulation would be worthwhile, I feel. The problem is the AC from the transformer will be nominally a sine wave - with care in cabling / wiring the radiated field from this can be controlled quite readily, but the rectified / smoothed DC you are feeding, whilst it looks 'cleaner' will have ripple superimposed on the DC and due to the switching action of the rectifier diodes there will be greater high frequency content, ready to couple into the high-gain, easily upset, phono stage.

    The only real wiring mod I'd make in this box is to reduce the length of the two green wires from the RHS of the bridge ass'y, bend these a little sharper and reduce the length between these and the pink wires at the other side.

    Nothing major ;)


    The unscreened input wiring rings alarm bells here, adding some screened, low capacitance cable from BNC - board or, even a lightly twisted pair would work better, from BNC - board.

    If it were possible I would have put both phono board side-by-side and put the TPR's the other end of the box, assuming a DC regulated feed.

    Further to the internal wiring you have both input signal wiring and o/p signal wiring floating in space.

    Are there any 0V connections to the BNC's, I can't see them in the pic?

    The input signal from the cartridge is created in reference to the -ve of the cartridge, therefore all wiring at this point needs to be reference to the cartridge -ve.

    Simply put this means two closely-spaced parallel conductors running from BNC input to the board (co-ax / twisted pair/ cable tied harness).

    The same is true for the PSU to the boards, so again the PSU wiring from the board to the TPR's should consist of two closely spaced parallel conductors (as you've done). This also applies to the input to the TPR's. Two paralleled pairs should run from DIN to TPR boards (again this looks good as you've done it).

    Now what about the o/p?

    The phono board produces an output that's in reference to its 0V, but if we run another 0V from board - DIN we create an earth loop - you already have a 0V running from DIN - TPR - Phono stage, so the best solution is probably to run the more robust, low impedance output signal in a single wire, but route it alongside the existing 0V wiring from the PSU.

    A diagram would be easier, if I get chance I'll try and scribble something, but don't hold your breath ;)

    You may also wish to add an output resistor in series with the phono board output (at the DIN socket, preferably) to decouple the effects of cable capacitance from the phono stage, which may cause instability. Try 10-100R, this adds isolation so that the phono stage doesn't see any capacitance from the subsequent wiring, that could impact it's stability.

    Hope that helps.

  20. timH

    timH pfm Member

    I had a similar problem with my diy prefix. Mine is slightly different in that I've got the 323 boards under the plinth and no arm cable but similarly with a local Sreg fed smoothed but unregulated dc from an OSCAP. The output then goes to a line input on the pre (well actually its the phono input with a link across the pins on the main board)

    I had some hum at first which I cured by reconnecting the earth wire from the deck to the earth post on the pre.


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