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Avondale NCC300 Monos Underway

Discussion in 'd.i.y.' started by Mike Hanson, Jul 5, 2021.

  1. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Right... The Avondale amps are not particularly reliable and have issues with SOAR and a complete lack of protection circuitry. I know of several cases of them self immolating in exactly this way and without my phono stages, which are without fault in this, being involved. In this instance it has been a combination of the user leaving the volume up very high whilst changing records and the excessive rail voltages of the power amp. There was a good reason why Quad used current limiting when employing a single pair of OPT's from + & - 50V rails in the 405.... in many cases people are using 55 - 60V rails with the Avondale amps and this sort of thing is not unexpected. Some are even using 60V rails and 4R speakers!
    S-Man likes this.
  2. On the subject of the 300 boards. Have you seen the new SE400’s? And the SE230’s?
  3. S-Man

    S-Man Kinkless Tetrode Admirer

    I've had my disagreements with Jez, but he is absolutely correct on this one.

    40V rails for the single output boards and 50V rails for the NCC300 front end are my recommendations.
    (My Leach amp has run the same o/p devices as the 300 on 59V rails for many years. But it has >200V VAS Trs, SOA protection and fuses (and sounds fabulous)).

    The 50V limit is set by the ZTXs. I discussed this with Les and he said he has never seen a ZTX fail due to going above 50V.
    So you can listen to the man with the experience or you can stick to the datasheet - your choice ;)
  4. Chops54

    Chops54 pfm Member

    Thank you S-man for the explanation. I was never aware of such issues with Avondale amplifiers. FWIW I run the output of my NCC200s at 48 volts and my NCC300s at 54 volts. They both have LS protection. I have been thinking about changing the transformers in my 300 so that would give me the opportunity to reduce the output voltage. Maybe I also need to consider some other means of protection. You mention fuses in the power supply rails. What would happen if only one fuse blew?
  5. OldSkool

    OldSkool pfm Member

    Yes I have and they look very interesting!
    4 pairs of o/p trannies on the SE400's in a NCC300 sized board and 2 pairs on the SE230 in a NCC200/220 sized board. Sounds like Les has a different configuration for the front end differential amp and VAS stages too, so the last part of the Naim DNA has gone :)
    I'm nearing completion of a Qudos amp build with dual output trannies, but I may well be tempted to try the SE230's when they become available. Sounds like the 400's will only be available in Avondale built mono amps.
  6. OldSkool

    OldSkool pfm Member

    I agree Jez, I had a Qudos board self destruct in exactly the same manner - lifting the stylus at the end of a record without the volume muted. The volume wasn't actually set that high but I was running a Schiit Loki equaliser with the bass boosted somewhat, I think the bass transient took out one of the output devices. I'm on 50V rails and although my speakers are nominally 6R they measure just under 4R at DC!
    Les was very good and replaced my boards free of charge and I've not had a problem since in over a year, but I've always been careful to mute now when playing vinyl. This is partly why I'm currently building a pair with dual output devices as the current sharing should put the devices well into their SOA.
    Arkless Electronics likes this.
  7. gavreid

    gavreid pfm Member

    These 130s were built by Les and sold as complete units (you can just about see from the tested sticker) so I don't know how they were set in terms of rail voltage. I suspect that most, if not all, M130s in the wild are the same - I'm just glad that my kids were off in Wales for a few days otherwise they would have been terrified. As I said previously, I don't blame Jez.
    Arkless Electronics likes this.
  8. Yes I think I’ll get the SE230 boards to replace the Qudos. He’s also working on regulator boards to match them!
  9. ramona

    ramona Music lover

    The probs are placed to the wrong resistors, should go to the resistors connecting to the base of the driver transistors, there is an upper track of the pcb for this, so it's the end of the resistors next to the missing resistors named RC1 and RC2.

  10. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Thanks for that Romona:)

    That might explain why the reading for the equivalent volts was a bit awry
  11. ramona

    ramona Music lover

    Thanks for the info. Since you don't recall the previous Avondale sound (only that it was uninteresting to you) could you describe the changes in sound (always to your opinion/taste) these modifications made to the original NCC300 ?
    It could be interesting to see what aspects of the sound could be changed. Even if someone actually likes Avondale sound it could be that there are some minor things that are not to his taste.

    Although there are numerous threads (here and in other forums) discussing this circuit and parts selection, I believe that NCC300 / Qudos and late modifications of HackeNAP (paralleling output transistors) are pushing the envelope further and we could actually come up with new findings.
    Mynamemynaim likes this.
  12. Chops54

    Chops54 pfm Member

    I wasn't overly impressed with my ncc300s when I first put them in my system. Over the last few weeks though they really seem to have come on song. They were just a bit ordinary sounding at first but now they seem to have real authority. A friend came over this week to see me and after listening to some music remarked that they had some serious grip. Bass is excellent but not overpowering whilst the midrange is just so easy on the ear. My 211s haven't had a look in for weeks :(
    Mynamemynaim likes this.
  13. 337alant

    337alant Negatively Biased

    IMHO -- I have been using Avondale amps over the last 10 years with 53V rails and they are excellent and very reliable amps, and I have thrashed the living day lights out of mine, trust me but I have always had proper heat sinking on my cases, there is nothing wrong with any of the design's its poor implementation that can lead to failure.
    If you buy modules of Les with a pre set Bias you still must put the effort into checking that is perfectly stable in the enclosure you chose before using it.
    The Quasi complimentary NCC-200 was rock solid IMO (34 - 38ma bias)
    The fully complimentary NCC-220 sounds better but has quadruple bias (100 - 120ma) so it has much greater potential for thermal run away
    I see many people with totally inadequate heat sinking on the output transistors, quite frankly I think the NAIM sled approach is inadequate with no ventilation and an inadequate heat sinking just bolted to a base plate ?.
    The NCC 300 steps up the sound quality again IMO, but Bias is high 120ma so make sure the output transistors and bias transistor are properly heat sinked together and you should have no problem.

    Also when setting BIAS on the NCC-220 and NCC-300 this should be done over a couple of hours with the "lid on", I have noted that a little tweak can take 15mins to settle then tweak again and again until it is fully stable.
    If you substitute the NCC-200 for NCC-220 should not use more than 100ma Bias IMHO and even then if the enclose is not suitable then just don't do it.

  14. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Totally agree with the above!

    My last two amps (ncc200 based in 2u case then ncc220 based in 3u case) have been used hard and left on 24/7 (in the Naim tradition)
    I've now completed one ncc300 (in 2u case) and on the way to building it's twin....
    Tests on the first show little heat generated when keeping to Les's 120mA recommended bias
    I'm hopeful that these can be left on permanently as the boards seem to take 20mins at least to "settle down" after switching on

    [​IMG][/url]2021-08-01_10-08-27 by rock solid, on Flickr

    [​IMG][/url]2021-08-01_10-07-55 by rock solid, on Flickr

    [​IMG][/url]2021-08-01_10-07-20 by rock solid, on Flickr
    337alant and Mike Hanson like this.
  15. laverda

    laverda pfm Member

  16. Chops54

    Chops54 pfm Member

    Do yourself and the planet a favour and turn your kit off when not in use. My 300s only take ten minutes to warm up so it’s no big deal.
    Arkless Electronics likes this.
  17. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Hard to break the habit of a lifetime ..:(
    Mike Hanson likes this.
  18. gavreid

    gavreid pfm Member

    I'm going to sell the M130s, the good one and the other to be rebuilt - it possibly only needs a good cleanup and a new 220 board. Any interest here drop me a pm
  19. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    It's nothing to do with bias or heatsinking! It's due to lack of SOAR for the output devices as explained above and ANY AND ALL amplifiers using a single pair of bipolar output devices on rails of 50V plus and no current limiting/protection will be equally prone to such blow ups.

    Stick to a max of 40V rails and all should be well.
  20. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    So ncc300 with two pairs should be ok up to Les's stated maximum of 60v ? (IYO) please

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