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Another Avondale Amp

Discussion in 'd.i.y.' started by Mike Hanson, Jul 10, 2019.

  1. Mike Hanson

    Mike Hanson Really?

    Now that I've finished replacing the NCC200 boards with NC220s in my Voyager mono amps, I'm using the NCC200s in a new amp. Here's the layout:

    [​IMG]

    • The case is a Modushop Pesante.
    • Power comes in the top right corner, with a fuse near the IEC socket. The raw power will run down the right side.
    • That's an Avondale SSM2 in the bottom right. The switch will be below it. (I believe I have to connect the sensor pins on the SSM.)
    • It's a single 500VA transformer, but one CAP6 per channel. Hence the terminal block.
    • The CAP6 modules will be rotated 180 degrees, so the AC input is on the outside, with DC up the center to the amp boards.
    • The NCC200s are positioned that way to enable short runs from the RCA inputs, without the need for shielded cable.
    • The gray rectangle represents a Velleman K4700 speaker protection kit
    • Both banana plugs and Neutrik Speakon connectors will be in that big space above the Velleman unit and transformer.
    Any serious issues?
     
  2. bugbear

    bugbear pfm Member

    Are you going to use a BIG piece of copper or Alu to shunt the heat out from the power trannies to the exterior?

    BugBear
     
  3. Mike Hanson

    Mike Hanson Really?

    That's a good point, and I was pondering whether that would be an issue. I've never noticed my NCC200s getting very warm in my Voyagers, but the prior case was made from 1/8" aluminium sheet. The Pesante case is quite thin in comparison.

    At the very least I was planning to sand the paint off, so it makes better contact with the case.

    I have some aluminum (both 1/8" and 3/8"), so I could insert a slab of that between the amp boards and the case. There's enough space for that to fit.

    Do you think it will be necessary?
     
  4. Mike Hanson

    Mike Hanson Really?

    Also note that there are vents in the bottom and top, so convection will allow cooler air into the bottom, with hot air escaping out the top.

    There's also enough space between the amp boards and CAP6 modules to strap in a couple of heat sinks, if that would help.

    Remember that these are NCC200s, not the newer QUDOS, and they seem to run cooler.
     
  5. andrewsutton

    andrewsutton pfm Member

    How are the 0v spade connectors joined to the reservoir caps?
    I have seen a few capacitor circuit boards where the 0v connectors are between the caps rather than on a short spur.
    A short spur reduces the ripple caused by the charging impulses.
    Cheers Andy.
     
  6. Mike Hanson

    Mike Hanson Really?

    I'm not sure if I understand the import of your question, but I'll explain my plan and hopefully we can come to understand each other.

    Each Avondale CAP6 has 0V input spades. I have a single transformer and two CAP6 modules, so I'm using a terminal block to star the transformer's centre tap to connect to the CAP6 modules. I'm not sure that that answers your question.

    Furthermore, that same 0V connection is recommended as the negative pole for each speaker output.
     
  7. andrewsutton

    andrewsutton pfm Member

    It is more about the other end, where the amps are connected.
    Connections to the amp earths should not join the connection between the final pair of reservoir caps but to a spur from that connection.
    Google that hifisonix document I suggested.
    Cheers Andy.
     
  8. Mike Hanson

    Mike Hanson Really?

    Yes, I've got that document printed, and I'm trying to make my way through it. I'm not to the wiring stage yet, so I have some time to mull it over.

    At this point, I'm following the lead of the docs provided by Avondale. FYI, the CAP6 has a ground plane that connects the input and output grounds. The CAP6 output ground goes to two separate ground points on the amp boards. The CAP6 input goes to the speaker negative. In a way this seems almost like a circle rather than a star, but "ground" is a mysterious thing.
     
  9. Mike Hanson

    Mike Hanson Really?

    This particular project is waiting in the wings while I build another amp for a friend who's visiting in a month. It's a bit different, as it has an Avondale SSM2, 330VA transformer, single CAP6, two NCC200s, and UPC1237 speaker protection module (with a separate transformer). For those who are interested, the layout is like this (front on the bottom):

    [​IMG]
    http://avzine.com/images/AvondaleAmpProblemA.png

    I started by hooking up the power input to the SSM2, then connected the switch and transformers to that. Finally, I connected the transformer to the CAP6. I confirmed that the voltage on the output of the CAP6 was ±50V. All good so far.

    Then I did the rest of the wiring, and prepared the check the bias. That's where I've hit a wall. I have two DMMs, so I hooked up one to each of the NCC200s. I turned on the amp, and both meters are reading 0ma. Nothing! Nada!

    I've confirmed that all of my connections between the CAP6 and NCC200s are good. I've double checked that I had the meters properly connected between the CAP6 (+) and amp (+). Everything looks good, but no current flows. Here's another shot with the wiring between the CAP6 and NCC200s, with the (+) connectors disconnected for my bias test:

    [​IMG]
    http://avzine.com/images/AvondaleAmpProblemB.png

    The one thing I didn't try was twisting on the trimmer pots, as I figured there must be at least a little current flowing, even at the lowest setting. Perhaps that's my next step.

    BTW, between each test I connect a 240R (5W) to drain both sides of the CAP6, so that I don't zap anything inadvertently.

    Before I blow something up, are there are words of wisdom for how I should proceed?
     
  10. Mark65

    Mark65 pfm Member

    You are 4 X 220R resistors missing, suggesting the boards were previously used with separate front end power supply
     
  11. Mike Hanson

    Mike Hanson Really?

    Thanks for spotting that! Yes these were used boards, but I had thought they were stock configuration. I'll check the schematic, and compare them to others that I have here.
     
  12. andrewsutton

    andrewsutton pfm Member

    Check your multimeters.
    I have tried to set the bias on a few occasions with a faulty meter. Meter fuses may well be the problem.
    Cheers Andy.
     
  13. James Evans

    James Evans Bedroom Bodger

    Those 220R resistors will be it. Put those back in, but test one board at a time so you don't risk both potentially going up in smoke.
     
  14. Mike Hanson

    Mike Hanson Really?

    Thanks for the suggestion, James. I'll be careful. :)
     
  15. 337alant

    337alant Negatively Biased

    Below was/is my preferred layout in one of my first on my NCC200's
    Even with the Pesanti I would bolt the power amp boards to the case side heatsinks not just the base plate, remember heat rises

    [​IMG]NCC 200 in 3U MODU case by Alan Towell, on Flickr

    Alan
     
  16. Mike Hanson

    Mike Hanson Really?

    I've got a big slab of aluminum (8x4x⅜") between the NCC200 heat syncs and the base of the case, and the Pesanti has vents to let the heat escape. Hopefully that's sufficient.

    BTW, my Voyagers have NCC220 boards, with comparable cooling ability, and they don't seem to get very hot. The transistors are just warm to the touch.
     
  17. chiily

    chiily PFM Special Builder

    Hey Mike, those look like my old NCC200 boards. And yes, they did used to have their front ends powered by a VBE board.
     
  18. Mike Hanson

    Mike Hanson Really?

    Yes, I think you're right. I had a transformer with output voltage too high, and one of my own boards fried.

    [​IMG]

    That's when I got yours as a replacement. Later I swapped them for NCC220s, freeing them up to go into my friend's amp. I had forgotten that they came out of my Voyagers (because they had the diodes, but not their series resistors).

    I still have the original NCC200 that was the companion to the fried board. Les recently sourced me a compatible unit, and they're destined for the amp that started this thread. :)

    And I still have the two transformers with the wrong voltage. I'm not sure if I'll ever find a project for them. They're 40VAC, rather than 35VAC, which was just enough to burn out the board (after playing for an hour).
     
    Last edited: Oct 27, 2019
  19. laverda

    laverda pfm Member

    :)
    NCC300s would be a nice project for 40v transformers....:)
     
  20. Mike Hanson

    Mike Hanson Really?

    Hmmm. That's an interesting idea. The issue is whether I need to keep building amps. :D

    • I've currently got a set of mono Voyagers in my office (500VA transformer, VBE, and QUDOS)
    • I'm almost finished the stereo amp for my friend (330VA transformer, single CAP6, and NCC200s).
    • I'm building the NCC200 stereo amp for my family room (500VA transformer, 2xCAP6, and NCC200s)
    • My friend is returning the NAP110 that I loaned him (upgraded with the Avondale CAP module and NCC200s). I was planning to hook it up to my computer speakers, which is overkill.
    If I built one of the NCC300 amps (just for the sake of using the transformers), then that would only compound my situation. We'll see. ;)
     

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