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Avondale NCC300 Monos Underway

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

  1. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Sorry...meant SSM2

    About £60
  2. Mike Hanson

    Mike Hanson Lovely!

    Well I wired up the power and switch to the SSM in one unit, and unfortunately don't hear any relay clicking, and no power is getting to the output of the SSM. I tried the other, with the same result. I've checked all the connections for continuity where expected, and all seems fine. Fuses seem fine. I even hooked up the transformer and NPM1 in one unit, in case it wanted a load to "wake up", but all to no avail. I'll give Les a call in the morning, to see what he suggests.

    In the meantime, I've started to plan the layout for my next NCC300 build, as I have all the parts for it: a full dual mono in a big 4U Dissipante case.
  3. Mike Hanson

    Mike Hanson Lovely!

    I knew it had to be missing something stupid, and after a quick chat with Avondale, I realized I had forgot to short the thermal sensor connections. (I'm not using sensors in these.) I'm glad that's sorted.

    Perhaps I'll get a bit more time later today to test these further.
    Mynamemynaim likes this.
  4. Mike Hanson

    Mike Hanson Lovely!

    I've finished hooking up the transformer to the NCM1 and SPM. All voltages look fine, and the various relays click as expected.

    Next step is wiring up the NCM1 to the NCC300!
  5. say it as it is

    say it as it is pfm Member

    yes I remember Les saying about the link wire
  6. Mike Hanson

    Mike Hanson Lovely!

    I've decided to switch gears onto the NCC300 dual-mono build in the 4U Dissipante case. A friend is coming to visit from far away, and I hope to get it done in time for him to take the amp back home with him. I'll start another thread for that.
  7. gavreid

    gavreid pfm Member

    Re my little 'mishap' reported up thread, Les and his team have now rebuilt the amp - not just offered a new board as requested - and entirely FoC. It is felt that the heat sink on the Qudos board may not have been tight enough for whetever reason. They have also turned it around in record time now that they are installed at the new premises. I can't speak highly enough of what they have done for me. All's well that ends well as they say :)
  8. Mike Hanson

    Mike Hanson Lovely!

    Now that I finished my friend's NCC300 Dual-Mono in a big Case, I've resumed work on my own mono pair.

    I've hooked up the outputs (both Neutrik speakON and Keystone binding posts). The wire is 12AWG silver-coated multi-strand, with PTFE. I know it's overkill, but I had it kicking around. :)


    After looking at this picture, I realized I should move the one spade on the positive post to be sandwiched with the other. You'll notice I'm running a separate ground wire for each output type. I would have preferred to fork the positive from the SPM1, but I didn't have a spade connector that would house two chunky wires.

    I've also added a thermal shutoff, which I've connected to the SSM. I used double-sided thermal tape to attach it to the NCC300's heat spreader.

    Next up I have to measure the +/- voltages from the input supply on the NCM1, then tweak the voltages on the NCC300's input regulators to be 5V below those. I'm using 18AWG silver-coated PTFE to power the input stage.

    Following that I have is wire up the output stage's supply, and adjust the bias to 120mA. I'm using 14AWG silver-coated PTFE to power the output stage.

    I could likely just use 18AWG throughout, as the runs are so short, but the difference in cost is fairly insignificant, and who knows... perhaps the audiophile fairies will appreciate the larger runways. :D

    BTW, you may recall that my mains sometimes rise to the point where the supply for the output stage approaches 64VDC, beyond the recommended 60V max. I chatted with Avondale, and they indicated the output stage would handle it if I removed the pair of 2.2µF 63V tantalums. Alternatively, I could retain that extra bit of ripple rejection by replacing them with higher rated caps, so I used 100V Vishay electrolytics instead. (Apparently the type of cap isn't critical here.) You can see one of those caps near the B- terminal.
    Last edited: Dec 17, 2021
    AlanL, Mynamemynaim and Gervais Cote like this.
  9. Mike Hanson

    Mike Hanson Lovely!

    They're making music, although I haven't got the power switch LEDs wired in yet (later today). Here are some pics of the wiring:




    One thing I noticed when setting the bias: it took LONG time for the amp to warm up and the bias to stabilize. I did the one amp last night, and the other this morning. I checked the one I did last night again, and it took over 30 minutes for it to rise up to 115mA (just a touch less than the 120mA that Les recommends, in case case it decides to inch up a bit). It was an exponential curve, so it quickly rose to 80mA after about 5 minutes, and took the next half hour to hit 115mA.

    If you prefer to turn your gear on only when you're listening, then most of the first album is going to sound substandard. I guess that's why I leave mine on all the time. ;)
    337alant, iant, S-Man and 3 others like this.
  10. Marra

    Marra pfm Member

    Nice work there Mike. Sounding good I bet.
    Mike Hanson likes this.
  11. Gervais Cote

    Gervais Cote Predator

    My Treshold FET TWO preamp takes at least 1/2 hour to warm up and stop sounding harsh when using it after plugging it. That’s probably why the designer Mr. Neilson Pass decided not to put any on/off switch on it.
    And my old Naim NAP 110 needs 5 rock songs in a row at medium volume to start singing when turned on.
    Classe Audio had many preamps in the 80’s without any real power switch as well so there must be a reason why......
  12. geoturbo

    geoturbo pfm Member

    Well done, Mike.

    Could it be the heatsinks are kind of generous and the NCC300s could get along well also with smaller heatsinks?
    (I.e. reading between the lines, what would be the best way to dimension their heatsinks?)
  13. Mike Hanson

    Mike Hanson Lovely!

    My buddy (the recipient of my earlier NCC300 build) keeps his gear off except when listening, and confirmed the timing from his own observations. He intends to continue his off/on shenanigans, while I'll leave my stuff turned on.
  14. Mike Hanson

    Mike Hanson Lovely!

    I've only played it through the Minimus 7, but very good so far.
  15. laverda

    laverda pfm Member

    My 300s have been powered on 24/7 for 'years now', as is all my other kit in this system.
    337alant and Mike Hanson like this.
  16. S-Man

    S-Man Kinkless Tetrode Admirer

    It's quite a complex subject and depends on speaker efficiency, impedance and how loud you want to play. It is also dependent on rail voltages.
    In general, yes, you could use smaller heatsinks. Ideally the output devices + the drivers + the bias tr should all be thermally coupled together... the bias tr should be adjusting for 4 Vbe drops.
    The NCC board has the drivers on their own heatsinks - with a much shorter thermal time constant - so these are mostly not included in the thermal feedback loop, although the 0.22R emitter resistors do help to reduce the changes in quiescent current over temperature.

    I ran my NCC with much smaller heatsinks (forced air heatsink with no airflow!) and it did have a tendency to thermal runaway especially when I increased the rail voltage from 40V to 48 V. This is an extreme example though, but was instructive to see what would happen. It now runs with a fan at very low airflow and runs very cool. The fan has its own thermal feedback loop so it speeds up if the output stage gets hot.

    So, in summary, you can use smaller heatsinks but the overall positive temp coefficient of the amp means that you have to know what you are doing and/or fit a thermal trip. Probably best to just stick with generous heatsinks and enjoy peace of mind and the butch aesthetics ;).
    337alant and Mike Hanson like this.
  17. Mike Hanson

    Mike Hanson Lovely!

    The NCC300 monos have had a few days to settle in, and settle in they have! I'm astonished at how much life the NCC300 injects into the music, compared to the very capable Voyager QUDOS before them. The sense of notes "hovering in the air" is quite intriguing, and it boogies like there's no tomorrow. This is my office system, where I spend much of my time, and I constantly find myself pausing work to listen for a while (much more than I did before).

    Recall that I built a dual-mono NCC300 prior to this, which I sent to a friend. The difference between the two builds was that my friend's had a pair of big Kemets per channel, powering the entire NCC300. Mine are using the NCM1 modules, which have a separate supply for input and output stages. With my friend's amp, I wasn't entirely happy with the sound of my Ergo IX. It just seemed a bit rough and overwhelming. In comparison, my amps sound much more refined through the Ergo IX.

    Overall, I'm really pleased.

    The Voyagers QUDOS will go to the family room, where I'm running the SMPS NCC200 stereo amp ATM. Before I do, I've replaced the two pairs of inductors in the output stage's CAP6 with wire links (from CLCLC to CCC), which should increase body and slam, especially in the bass department. I'll compare it to the amp that hasn't had that change, to see how much one can discern the difference.
    retseldrib and mega lord like this.
  18. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Please do of interest to me!!
    Mike Hanson likes this.
  19. Mike Hanson

    Mike Hanson Lovely!

    I just did a quick comparison, and so far there's no clear winner. I initially playing music normally, but realized the stereo mix would invalidate the test. Then I told the Squeezebox to play the left channel out of both output channels, which gave me a better source for comparison.

    With my stunt speakers (the little Realistic Minimus 7), I couldn't discern any special difference.

    Then I hooked up the Royd RR3, but again it was inclusive.

    I'm going to sleep on it, then try it again tomorrow. I may swap speakers to see if the room is impacting the results. If it's a wash, then I'll just remove the inductors from the second amp, and call it done. If it turns out that the one with the inductors is better, then I have enough 12uH units to put them back into both amps.
  20. Chops54

    Chops54 pfm Member

    Some interesting ideas there Mike. I’ve been thinking about C R and L in the power supplies for as long as I’ve been building NCCs. I’m not a tech, just a keen diyer and my knowledge is limited so I often just have to go with the flow. My conclusion is that inductors are not required for low current draw like the front end when a resistor will do the job just fine so CRCRC fits the bill. Where large current draw is required CLCRC can work well so I’ve gone with that. I’m also led to believe that two inductors one after the other is not a good idea hence the CLCRC. It’s important that the inductor goes in line first. I’ve been using 12uH inductors and 4.7R resistors but I’m going to dump the 4.7R in favour of 1R or less. Caps are 6800 x 6 in the output supply and 5600 x 6 in the front end supply. I’m tempted to up the last pair of caps in each supply to 10000uf and 6800uf after I’ve done a few listening sessions with the smaller resistors.
    337alant likes this.

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