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Help with diode choice problem please

Discussion in 'd.i.y.' started by Mynamemynaim, Jul 21, 2021.

  1. russel

    russel ./_dazed_and_confused

  2. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

  3. torstoi

    torstoi pfm Member

    Guys, that's not necessary in my opinion.
    The thread has been very interesting so far, Jez has pulled out & I think we should just move on..?
     
    martin clark and jpk like this.
  4. russel

    russel ./_dazed_and_confused

  5. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Another question or two

    I've made a rectifier board with smoothing caps...No resistors or Inductors fitted at present

    I stuck a couple of probes on the output and (with the oscilloscope) on DC it showed a fairly nice trace (+ and - dc) with surprisingly little ripple ect (maybe 2mv)

    So I changed over to AC reading and saw the picture below
    [​IMG][/url]Ac by rock solid, on Flickr

    Now please don't take the piss out of my ancient 'scope or my complete lack of knowledge in these matters....but is that bad? (or is it just 50Hz noise creeping through)
    scope set to 10mv/cm time 2ms/cm (+ signal at top - at bottom)

    Also
    I have a couple of the old 2014 VBE group buy boards...is it worth trying to cram them into my case layout (for the front end of the NCC300 mono voyager builds?)

    Thanks again for your thoughts and suggestions
     
    torstoi likes this.
  6. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Ah a proper scope! Nice:)

    As I believe I said up thread the amount of ripple is directly proportional to the load current. Measuring it with nothing connected tells you very little! 50mV to 1V ISH would be more normal, depending on amount of smoothing capacitance and the load current. If going CRC it can be much lower and the wave shape will be much more "rounded". FWIW if the amp was playing music into a load then the ripple would go up and down in level with the music and there would be half wave rectified distortion from the output stage on top of that to some degree (don't worry about it!).

    Have you got the timebase variable control set to "Cal"? The waveform is 100Hz and that is not what is showing on your scope. Other than that all looks as expected.
     
    torstoi likes this.
  7. MJS

    MJS Technical Tinkerer

    That scope doesn't have the horizontal sweep in the calibrated position. You also appear to have half-wave rectification - the caps are only getting charged on alternate cycles rather than every one. Compare it to this full-wave rectified linear bench supply I have.
    [​IMG]
    The positive rail is drawing more current than the negative in my case.
     
    Arkless Electronics likes this.
  8. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    No ...not set to cal? If you look closely you can JUST make out the dot is next to the R of variable..

    Glad that looks normal!
    I'm waiting for some 2R2 resistors to put on the boards ...(didn't want to go to 4R7)
    Also have some hand made 10uh inductors fo go on as well

    You might remember we talked about half wave rectified boards earlier in the post

    Ps
    Glad you like the scope.. though it does take 10 minutes to warm up and working properly these days
     
  9. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If it is half wave rectification then 50Hz but it's very unusual to find half wave being used as full wave needs only a few more parts and is so much better. Obviously you need the timebase in "Cal" position to show frequency correctly.... assuming the scope is in calibration itself!

    I've been assuming the board is for use with a power amp? If so then 2R2 or 4R7 are way too high in value. If for a pre amp then fine and the high values will give excellent rejection of ripple. If for a power amp use just the inductors.
     
    Mike Hanson and MJS like this.
  10. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner


    Did not know that :oops:
    It is for a power amp (back end of NCC 300 board)
    Ok...will scrap the resistors and just put in another set of inductors...so two per side of each board ... sound better?
     
  11. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If it was to drive just the input stages then the larger value resistors would have been fine but to drive the output stages... nope. Assume you want to drive 4R speakers for a moment... what do you think will happen if it has to go via 2R2 or 4R7 resistors?;)
     
  12. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    That makes a lot of sense!

    Thank you for taking the time to explain ...I know my build will sound all the better for your good advice at this stage
     
    Arkless Electronics likes this.
  13. Mike Hanson

    Mike Hanson Lovely!

    The NCC300 board has regulators built into the input stage. Does that impact your advice?
     
  14. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    If you are talking of a separate supply for the input stages then no. Regulators should negate any advantage of a separate supply though.
     
  15. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Mike I think Jez's reply relates to using the boards in a voyager configuration...as I intend to use
    If your using the jumpers...then don't use the resistors?

    Edit
    Forget that...I was too slow to reply!!
     
  16. Mike Hanson

    Mike Hanson Lovely!

    I suspected that the regulators would negate the impact of those resistors.

    As you probably know, Les builds (at least) two configurations of the NCC300 amps: One with a single supply shared by both front and back end, and the other with a separate supply for each. I started this thread with a build having separate supplies, but I'm also building another set with a single supply. I'll be able to compare them to see if I can hear any difference. ;)
     
  17. Mike Hanson

    Mike Hanson Lovely!

    The Voyager moniker is a bit ambiguous. I've always construed it to mean having a separate, regulated supply for the input stage (e.g. transformer, CAP6, VBE/HRC200). With the NCC200 and NCC220, that's clear cut, so "Voyager" is a binary distinction.

    The NCC300, in contrast, has that regulated supply built onto the board. Your only option is whether to provide a separate unregulated supply for the input regulators (with jumpers removed), or run them off the same supply (with jumpers in place).

    If you use that separate supply on the input stage of the NCC300, then it's most like a Voyager build involving the NCC2x0. If the entire NCC300 is driven by one supply, does that built-in regulation on the input side still make it a Voyager config?

    If you have a regulated supply (like the input stage of the NCC300), then Jez is stating that the unrelated supply that feeds that isn't so impactful. Therefore, it probably wouldn't matter if it's resisters or inductors between the banks/pairs of capacitors.

    FYI, on Les' NCM1 boards, the input supply is smoothed by a single bank/pair of capacitors, so the resistor vs. inductor battle isn't resolved there. ;)
     
    Mynamemynaim likes this.
  18. jpk

    jpk pfm Member

    When fed from one PSU you could try if there is a difference between having the front end and power stage wired separately to the PSU or having them hooked together with the jumpers onboard...
     
    Mynamemynaim likes this.
  19. Mike Hanson

    Mike Hanson Lovely!

    Given I've never seen Les publish any pictures in that configuration, I assume it's not a worthwhile alternative.
     
  20. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    I think we have both been on each others threads so much (which is great to share information)
    that we don't know who's is whos anymore:rolleyes:
     

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