Gonna 24vdc my ACAs

Discussion in 'Solid State Gear' started by Thermionics, Sep 1, 2018.

  1. Thermionics

    Thermionics Post Whore In Training

    With the 2.2k mod already in place and with the bias set at 12.5vdc, this should (hopefully) get my ACAs up to approximately 8W output. Not earth-shattering, but an improvement over the 5.5W or so that they're currently pushing - especially given that they're driving vintage bubba'd Vandersteen Model IIs.

    I'll let you know how it goes - they'll probably need a bit more breathing space than they've currently got. Just need the dang Mouser shipment to arrive! :)

    [EDIT - turns out this will bump them to 8 watts!]

    Last edited: Sep 12, 2018
  2. StevenZ

    StevenZ Active Member

    Is this a common mod people do to these?
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  3. Thermionics

    Thermionics Post Whore In Training

    Yes. The reason that the original ACA 1.0 / 1.1 monoblocks were default 19.5v was that there was a significant price difference between the ubiquitous 19.5v power brick (laptop / thin-mini-ITX standard) and a 24v power brick with the requisite 5-6A of current. With the new ACA 1.6 (bridgeable stereo amps), they are 24v by default, so Papa Pass made the details of the 24v mod to the legacy ACA available and lots of folks have been converting. The Meanwell PSU is about $45 (as opposed to less than half that for a used laptop power supply), but it should be worth it.

    In hindsight, I think this will put me at closer to 8W. I'm becoming mad with power!
  4. MikeyFresh

    MikeyFresh Moderator Staff Member

    When this shipment arrives, please do a continuity check with the Meanwell's IEC ground prong and it's umbilical DC plug's outer (-) barrel ring (everything unpowered of course).

    Chances are the ground prong is not connected in any way to the output side of the supply. If it isn't, that allows substantial AC leakage current to sail right through, but a simple ground shunt eliminates it.

    I don't have an ACA, but I do have more than one Meanwell SMPS and the AC leakage current shunt to ground trick makes an enormous difference in my opinion, looks something like this:



    I'd bet your amps are resolving enough to be poster child material for this mod, as recent evidence suggests the AC leakage current from most SMPS units is at least as bad as the actual switching noise itself, and probably worse in terms of doing harm to the sound quality.

    Or, perhaps these amps have a circuit that fully rejects AC leakage on the DC input already?
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  5. Thermionics

    Thermionics Post Whore In Training

    Apparently, Meanwell has learned its lesson. There is continuity between the ground lug on the IEC connector and the barrel of the DC connector. One less thing to worry about!

    I'll be swapping over the amps tonight or tomorrow night (need to replace a resistor and re-bias to 12.5V). I'll provide an update after I've let 'em play for a while.

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  6. Thermionics

    Thermionics Post Whore In Training

    I realized I never followed up on this thread. Mostly because I've simply been listening to music. The amps are running hotter (Class A, natch), and have a little more 'oomph' for when you need that push over the cliff (to quote Nigel Tufnel). They have not lost any of their inherent sweetness / authority and are an even better match for my redneck Vandersteen II basement speakers.

    No additional noise (in fact, the background may be a bit quieter).
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  7. These really are nifty sounding little amps.
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  8. Thermionics

    Thermionics Post Whore In Training

  9. I got in on the latest ACA buy, and ordered 3 parts kits for building 3 mono blocks for my K402 horns with EV DH1A drivers. I have zero experience in building or soldering (although I did take some welding classes in college), and I am looking forward to the is build. Did you buy the whole kit or did you start with a parts kit too? Any tips or info would be greatly appreciated.

  10. Thermionics

    Thermionics Post Whore In Training

    I bought the chassis and boards (old version) and sourced the other components myself.
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  11. mhardy6647

    mhardy6647 SeƱor Member

    power, schmower.

  12. Where did you get the chassis?
  13. Thermionics

    Thermionics Post Whore In Training

    It was the old style (single heat-sink) Pass ACA 1.1 chassis. Unfortunately, it was discontinued when they introduced the bridgeable ACA.
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  14. Before I started to build mine this past summer I first spent some time practicing my soldering on a couple of inexpensive kits from Parts Express. This definitely lowered my anxiety level when it came time to start slapping together the thing I really didn't want to screw up.

    Ultimately, the actual assembly of the ACA went surprisingly well. (It should be even more straightforward now that there is a finished V1.6 build guide to follow and extra wire included in the kit.) In short, if this putz can put together one of these things any putz can.

    The one thing I would strongly suggest is using a multi-meter with alligator clips on the leads when you set the bias because trying to maintain two separate slippy points of contact by yourself whilst also fiddling with a tiny and very touchy pot screw is no fun, not even a little. (I ended up dragging my wife into it, which made things easier, but not by as much as you might imagine.) Also, there is a significant lag time between each adjustment you make and the reading you eventually get on your meter. In other words, you'll need to wait between adjustments-- and there will lots of them, trust me.

    The good news is the rest of the assembly is actually pretty fun-- and, as a bonus, these amps also sound pretty darn swell.
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  15. Thermionics

    Thermionics Post Whore In Training

    I can vouch for the 'pretty darn swell' aspect. Up to building these amps, I was strictly a tube-amp builder. I liked the results so much that now I'm building one of Pete Millett's Korg NuTube triode / Class D hybrid amps!

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  16. I need to get some alligator clips for my multimeter then.
  17. opa1

    opa1 Moderator Staff Member

    I looked up the PM amp. Now that's different!
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  18. Thermionics

    Thermionics Post Whore In Training

    This will be the 7th or 8th (I've lost count) PM project I've built. The guy is (or should be) legendary in the audio DIY community.
    Last edited: Dec 5, 2018 at 10:27 AM
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