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Converting NAP200 to monoblocks

Discussion in 'd.i.y.' started by rontoolsie, Oct 16, 2020.

  1. rontoolsie

    rontoolsie pfm Member

    So a friend of mine is running a pair of non-DR 200s, using one per channel in the pseudomonoblock mode.
    He is about to get the recapped as they are quite old at this point.
    I started thinking if this may be a good opportunity to take them into a true-monoblock configuration.

    I THINK there are separate transformer windings per channel....if this is the case, would it be possible to double them up on the used channel? If so, does that mean that the voltages in the windings need to be carefully trimmed (and if so, to what tolerance to each other?)

    I think disconnecting the internal preamp supply may also be a good idea as he is using a 252, and does not need the 200s to provide a +24 out.

    Or maybe just junk the internal power supply and replace it with a Mini-cap6 or something??

    There is some je ne sais quoi quality about the non-regulated amps that seems to be lacking in the (?over)regulated amps. A cardinal example is the 160 vs the 250 for instance.
     
  2. cubeasic

    cubeasic pfm Member

    The paralleling of secondaries is common practice on smaller transformers like Block Print transformers. As long as the secondaries have the same VA rating and impedance the basic requirements are met.
    The phases of the secondaries should be identified or measured beforehand because they should not be connected the wrong way. -> result would be a short.

    I would also be interested in experiences when paralleling low resistance secondaries for poweramps, I am planning a similar project right now.
     
    rontoolsie likes this.
  3. david ellwood

    david ellwood Kirabosi Kognoscente

    Make much more sense to go active
     
    Mynamemynaim likes this.
  4. DaveMc64

    DaveMc64 pfm Member

    When I monoblocked my 180s I used the power supply from the removed channel to separately power the front low current half of the circuit. You obviously have to modify the pcb which, as the 200 is all on one board, would destroy any intrinsic resale value.
     
    rontoolsie likes this.
  5. rontoolsie

    rontoolsie pfm Member

    Agreed that is conventional wisdom. But the speakers have a near bespoke crossover design with a transfer function that is not the generic 3-rd order that Linn/Naim x/o use. It would take a lot of extra componentry to do an activ crossover in the analog domain to meet the needed transfer function. Digital crossovers are much more flexible, but usually are let down by cheapish components and weedy power supplies.
     
  6. Brennus

    Brennus pfm Member

    I would speak to Les W. Take his advice. Mini-cap6 and Qudos if they can be installed in the 200 may represent better vfm than a service.
     
  7. DaveMc64

    DaveMc64 pfm Member

    When you get to the point where the only things left are the case and the transformer, you might as well sell the 200 unadulterated and buy a new case and transformer as well.
     
    Stuart Frazer and Snufkin like this.
  8. say it as it is

    say it as it is pfm Member

    When I priced upgrade to my 180 it worked out the same as buying a used amp with mods already done it custom build
     
  9. Gervais Cote

    Gervais Cote Predator

    Hummmm........
    If I was to mono something, I would grab two little Naim NAP 110 and make them sing and rock !
    Many kits and tricks available to help you out.
    Easy to convert back to their original configuration if needed as well.
     
  10. Jo Sharp

    Jo Sharp Pulls on doors marked push

    I have 2 mono 110s with Avondale NCC200 boards driving the tweeters on active speakers - they are lovely. I can't imagine an NAP 200, even with doubled -up power supply, beating them.

    But in reply to Ron's question, you can pair up the transformer secondaries quite easily by detaching the leads from one side and re-connecting to the other channel's pins. Might be easier to leave the transformer secondaries in place, and pair up the output from the PSU caps to give you double the uF - that would mean cutting some tracks on the PCB I suspect to isolate the unused amp channel.

    As the NAP 200 amps are fashioned all on one PCB, it is not an easy job to install NCC200s - you have to strip everything out less the transformer and install *cap boards along with the NCC boards.
     
    Gervais Cote likes this.
  11. MJS

    MJS Technical Tinkerer

    Witch Hat have done exactly that for a couple of customers already. A new cap board was designed to fit behind the Phoenix amp boards. It's effectively dual mono, the only common 0v point being at the DIN socket.
     
    rontoolsie likes this.
  12. Jo Sharp

    Jo Sharp Pulls on doors marked push

    And I bet it sounds very good....
     
  13. rontoolsie

    rontoolsie pfm Member

    I have been in touch with Les...I am expecting some interesting modules to arrive at some point.
     
    Brennus and RichardH like this.
  14. Jo Sharp

    Jo Sharp Pulls on doors marked push

    Hopefully the Qudos versions.....
     

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