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QUDOS - the brilliant new amplifier boards from Avondale

Discussion in 'd.i.y.' started by misterc6, Jul 10, 2017.

  1. laverda

    laverda pfm Member

    Q1. So I have 15 or so MJ15003's HFE's all around 50-60ish and a couple of the 15004's having an HFE of 150ish...is there an issue being this far apart. Or do I just get 150HFE 15003's and match as close as poss..

    Q2. BD237 is available in 3 variants of HFE 3, 25 and 40.

    Which would be preferable in the QUDOS application.

    Sorry for the dumb questions...TIA

    Above Sorted now...but
    Last edited: Nov 10, 2017
  2. laverda

    laverda pfm Member

    NCC220 boards built and on the bench PSU -35 0 +35 perform and measure well at 40ma bias with a rock steady 15mv offset....all good.

    Now this is were I need some help..

    I'm (trying) to building a dual mono amp in a 5u chassis from HIFI2000.
    Without the amp boards connected to the PSU (minicap6) MUR460 diodes..6x10000x63v caps. Sometimes (lets say 5 out of 6 start ups are OK) but no 6 at switch on two diodes go pop (this has happened 4 times) with either a short or open circuit to the diodes either on the + or - rails.... not both rails. The first two pops took out the MJ1500x output device on the amp boards. There is nothing wrong with the minicap 6 boards or diodes....all checked and rechecked on every rebuild. With just the PSU (no amp boards connected) its the same story.

    Sometimes it will blow the IEC T4 fuse sometimes it does not. ??

    The transformer/s (500va) are giving 30-0-30 off an Avondale soft start...so looking at +&- 40v rails to the amp boards.

    Les, is at a loss (and has been very patient) I'm at a loss and another DIYer is at a loss...I have built at least 10 pairs of these amps and countless other PSUs including Class A and exotoica over 15 years for my projects, friends and family but never seen this....

    Any help much appriciated.....please
  3. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    Your MUR460 are only rated at 4A it could be the surge, although with the soft-start it would be unlikely but its the only thing I can think of.
    I use MBR2020s with no soft-start into 4x10000uF with no problems.


    Maybe a dry joint or a bad crimp on the transformer wires that makes connection after a while or intermittently.
  4. laverda

    laverda pfm Member

    Thanks for the input Pete,

    Yes, I did try an alternative PSU board which incorporates MBR20200's (my fav.) These are 10A devices and F*** me the + rail MBRs went pop too....errrrr.

    I'll be checking all wiring and crimps on the spades...
  5. misterc6

    misterc6 Wasted and wounded, it ain’t what the moon did

    I’m also at a loss other than suggesting you use higher current diodes.

    When you’ve sorted your power supply problems I’d advise turning the bias up quite a bit as this is where the NCC220s really start to sing. The NCC200 boards should be set to ~38mA into the positive; I run my NCC220s at 120mA and I remember Les telling me he was running his at 150mA.
  6. chiily

    chiily PFM Special Builder

    Could the soft start cct be faulty at all?

    Try the old elimination game, swap the transformer out, bypass the soft start cct.
  7. chiily

    chiily PFM Special Builder

    120mA, really? Oh...something new to try.
  8. laverda

    laverda pfm Member

    Yes, thats what its down to now...the elimination game. Ist the Soft Start is coming out and a re-check of all the spade crimps..
  9. Marra

    Marra pfm Member

    And the answers were?
  10. laverda

    laverda pfm Member

    So, the rectifier blow ups all sorted now. t'was a poor crimp spade connection on the 0v supply side of of the minicap6's.


    Up and running all be it a bit 'DIY', the NCC220's are sounding fantastic even though its early days....
  11. Marra

    Marra pfm Member

    Glad to see you got things sorted and that the amp is up and running. I took delivery of a pair of boards and a few components from LesW a short while ago. A winter project.
    Can you let me know the answers were to you question regarding the transistors, tia.
  12. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!

    I don't think you will have a problem with the outputs, the drivers can cause problems if they are too low gain, I had to seek out some BD139/140 with higher gain in my 135 clones, I couldn't set the quiescent current high enough with the standard ones, so get the highest gain DB237.

  13. laverda

    laverda pfm Member

    The MJ15003&4 'ideally' you would/could match as close as poss as they are both available in HFE of 150ish. I already had a load of 15003's so just sorted the highest HFE I could, which was 80ish for the 15003's and just dropped them in next to the 15004's of which where around HFE 150. There seems to be no detriment to the amp...I biased to 40ma and run them at this for a day or two...after I was happy all was well I upped the bias to 100ma (runs very very slightly warm)

    The BC237's (TR5) I had measured to a HFE of 20ish so just used those. One measured 7 from the same packet of 5 ?? but this seems not to be critical at all...as long as its strapped to the heat sink.

    I'm running 40v rails at present but will in time up this to 50v as I have the transformers sat in on a shelf. Then onto a PSU for the front end of the board RE the Voyager.

  14. Marra

    Marra pfm Member

    Thanks for that; much appreciated.
  15. chiily

    chiily PFM Special Builder

    Glad you got it sorted after such a wild goose chase.

    Those speakers are magnificent. Are there any build details for them?
  16. laverda

    laverda pfm Member

    Yes, I have a cad drawing of the plan I did some time ago. I'll get it pdf'ed and post it.
  17. russel

    russel ./_dazed_and_confused

    KSC2690A are a good transistor, higher Ft than BD139 and friends so care if you are swapping. All but free from RS


    KSA1220 is the complementary part.
  18. laverda

    laverda pfm Member

    An update to the ongoing NCC220 builds....This morning I dropped in the 350va 0-33 0-33 transformers I had on the shelf and moved from 40v rails 100ma bias to 50v rails and 150ma bias. This is now a class act amp in its simplest form. So much more control and sweet as you like. No hint of the Naim harshness...or even dare I say NC200.
  19. chiily

    chiily PFM Special Builder

    I'm going to have to buy a set of boards aren't I....
  20. Joe Hart

    Joe Hart pfm Member

    I wonder how easy these are to fit for those lower down on the diy audio amp side

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