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Another Avondale Amp

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

  1. Chops54

    Chops54 pfm Member

    Have you considered fitting the LEDs and droppers to the CAP6s? With these fitted my CAP6s discharge in less than a minute once the juice is turned off. They're also a very useful indicator when the lid is off.
  2. bugbear

    bugbear pfm Member

    A pedant writes:

    Heat does not rise. Hot air rises, if it can (lower density than cold air). Heat can be readily directed via conduction (e.g. copper/aluminium)

  3. 337alant

    337alant Negatively Biased

    I set the trim pot to the mid position before fitting
    Check the fuse on the Meter's
    Check you have the meter red lead connected to the 10A socket not the standard socket for voltage etc.

  4. Mike Hanson

    Mike Hanson Really?

    That's an interesting idea. I do plan to feed my switch's LED from one CAP6, but I could install an internal LED into the other one. However, I notice that my CAP6 modules have an LED socket only on one side, so the other side would stay charged. :(
    Last edited: Oct 28, 2019
  5. Mike Hanson

    Mike Hanson Really?

    These came out of my Voyagers, so I'm assuming that the trim pots are already pretty close to where they need to be. I suppose a fresh set of boards could be more than "mA", so it might be smart to start on the 10A DMM socket.
  6. Chops54

    Chops54 pfm Member

    My CAP6 boards have a LED on both rails. Maybe later boards only have one? MiniCaps are like this and I modified mine to take a LED on the other rail. I have some later CAP6 boards stashed away and I'll dig one out later and take a look. Only one LED seems a bit daft tbh.
  7. Mike Hanson

    Mike Hanson Really?

    There are definitely ones out there with an LED on one side. I assumed that the LED connection was for an external LED, to show that the amp was on. You're additional idea of using them to monitor the CAP6 for a latent charge is probably beyond the initial intention.
  8. 337alant

    337alant Negatively Biased

    in the picture above it looks like you have both positives disconnected to each amp board but also at the Cap6 ? the +ve connectors should be connected at the Cap6 or you have no positive supply ?.

    With the Cap 6 fully discharged on both phases, disconnect the red +ve lead to one amp only, connect the red probe from your meter into the end of that lead and the black lead onto the +ve terminal on the amp board, I always fit a female spade connector onto the board +ve so my probe can be plugged in securely as you don't want to be connecting and disconnecting once the power is switched on.
    Now switch the power on and you should get a Ma reading, set it for 38ma stable over a period of 20mins
    When you switch the amp off drain both sides of the cap6 before connecting up the meter to the other board
    If you have 2 meters you can do them both at once and this saves time
  9. Mike Hanson

    Mike Hanson Really?

    Thanks, Alan, but the problem is definitely the missing resistors. I'm expecting delivery of those midweek, so I can proceed with the project.

    FYI, when I test the bias, I use alligator clips to ensure they remain attached.
  10. 337alant

    337alant Negatively Biased

    Each to their own I guess but it doesn't make any sense to me to buy a case with heat sink side panels and then bolt your power amps to the bottom plate via C channel ?

  11. Mike Hanson

    Mike Hanson Really?

    I'm not sure whether you're referring to BugBear or me. My case doesn't have heat-syncs on the side. It's a regular Pesante like this. Therefore, my only option is to add the extra aluminum sync. :)
  12. andrewsutton

    andrewsutton pfm Member

    You might find that the sides are better than the base for heat sinking as their vertical orientation improves heat transfer to air.
    Drill the sides. Mark, drill and tap the heat sink. I use 3x m3 screws as their heads fit between my fins. You could use something a bit bigger, I guess.
    Cheers Andy.
  13. 337alant

    337alant Negatively Biased

    Mike sorry I have never seen that Pesante before all previous models had had aluminium side panel heat sinks like the galaxy and it was good enough for the NCC 200 amps https://modushop.biz/site/index.php?route=product/category&path=67
    The case you have says steel case which isn't great as a heat sink, did you take the option for aluminium ?
    The Ncc200 amps are very stable but still need a bit of heat sinking besides the C Channel they are mounted on.
    As Andrew says the vertical heat sink veins is the best way to provide natural cooling
  14. 337alant

    337alant Negatively Biased

    Yes OK I see your missing 220 ohm resistors so you have no rail voltage to the FE

  15. Mike Hanson

    Mike Hanson Really?

    No, I'm pretty sure it's the steel panel.
    I've got that big slab of aluminum (3/8" thick), which should help.

    For comparison, my Voyagers have QUDOS boards, and the case sleds for those are 1/8" aluminum, with the C channel bolted straight on. The heat doesn't seem to be an issue, so I'm hoping that the NCC200s in my stereo amps are fine with the mass of aluminum.
  16. laverda

    laverda pfm Member

    I have a used a Pensate case previously and found it a bit flimsy to be honest...the steel chassis did need further support. I used a slab of 3mm ali (as that was what I had) and the addition of two extra feet to hold it up.

  17. Mike Hanson

    Mike Hanson Really?

    Yeah, it's not the sturdiest of cases, but it seems to be "good enough". If I eventually build an NCC300 amp, I'll probably go for the Dissipante instead.

    FYI, I received delivery of the 220 ohm resistors today, and attempted to solder them in. Unfortunately, I discovered that the solder pads were missing on one of the boards. (I'm not sure where that pair came from. At one point I thought they may have been chiily's, but we've ruled that out.) I may be able to work around it, but I don't want to send those potentially flaky boards to my friend. Instead, I swapped over the ones that I was planning to put into my own amp.

    Next I adjusted the bias to a steady 36mA on each board. Looking good!

    Finally, I hooked up an input and a single speaker on one channel. Frustratingly, there was no sound. I tried the other channel, and still nothing.

    Then I had a hunch. I'm using a UPC1237 speaker protection module from ebay. If I jumper over it, I hear music!!!! I'm not sure whether I've hooked up that unit incorrectly, or whether it's defective.
    • I'm feeding it with a 16VAC transformer (apparently it can take 12-18VAC).
    • I've got positive input and output for both channels.
    • I have a single negative input on one channel, just to connect to the unit's ground plane. Recall that Avondale recommends that the speaker negatives be connected to the transformer CT, and my Voyagers do that with a separate feed for the ground of the speaker protection. I've used the same approach with this.
    Here's a picture of it in situ:


    Here's the spec sheet for the 1237 chip: http://pdf.datasheetcatalog.com/datasheet/nec/UPC1237.pdf

    Perhaps I need to attach all of those ground wires, and feed it only through the speaker protection module.

    Does anyone have any experience with these things?
    Last edited: Oct 30, 2019
  18. Pete MB&D

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

    When you power it up does the relay operate after 3 seconds you should see the contacts move, power it up independantly from the amp.
    Do you have seprate fuses for each transformer?

  19. S-Man

    S-Man Kinkless Tetrode Admirer

    The UPC1237 is an excellent chip and works very well for DC protection. How it is implemented on that particular board, I have no idea.

    Have you checked the DC offset of the amp? Maybe the board is actually doing its job?

    With regard to heatsinking you need to have a good think about conduction and convection. Adding the alu slab as you mention, will improve the heatspreading (conduction) for the output devices. Then it's down to "do you have enough surface area?" for convection cooling to be effective; I would suggest that you do unless your supply rails are high and you want to drive difficult loads at high levels. Steel is 3X less thermally conductive than aluminium, and steel cases are generally thinner.
    By the way, the worst possible case is for the output devices to get hot and the Vbe mutlitpier transistor to be effectively cooled (which could happen if the airflow through the vents is good and you don't add any alu heatspreading). This could result in thermal runaway.
  20. Mike Hanson

    Mike Hanson Really?

    There's a single fuse for the whole amp. Power is fed into an Avondale SSM2, which feeds the two transformers (a toroid for the audio and another for the speaker protection module). I definitely the SSM2 relays click as expected, but there nary a sound from the UPC1237 module.

    I actually purchased two of these, one for each amp that I'm currently building. I just tested the other one, and it doesn't click at all either. I suppose it's possible that they're both defective. :(

    I've tested the voltage coming into the board, and it's just north of 17VAC, within the range of 12-18VAC specified.

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