I finally finished building an ACA mini. I say finally as I had previously built one that failed to work and the problem solving would have led to far more trouble than a rebuild. Not a difficult build - a lot simpler than a Whammy for instance, but part selection is fairly important - especially for the trimmer resistors. Additionally there are two BOMs and one is slightly buried in the build guide thread over on diyAudio.
Long story short I elected to start over and got a new board. I got the essentials kit with pcb, mosfets and jfets and sourced the other parts myself. This saved money (being in the EU) which I then immediately spent on more expensive components than I would have gotten.
Nichicon capacitors and vishay resistors stuff the board, I got a Leicke power transformer as a like for like alternative to a Mean Well.
The build was super simple and complete in a little over ninety minutes including part sorting. Biasing the circuit took longer and I found this excellent video guide.
Essentially each channel needs two trimmer resistors that effect one another tuned to get as close as possible to target voltages. You then wait for the circuit to stabilise and tune again, repeat until there is no more drift. This was precision work and I took an evening over it.
This done I mounted the amp in a small acrylic and metal stand thing (made by Topping) I had lying around and set it up.
So this is a very low power amp at only 5W into 8 ohms and 8W into 4 ohms so I was unsure and curious as to what I would get out of my Dali Spektor 1 desktops rated at 40-100W into 6 ohm. The answer was a really, really nice sound. Louder than the BasX A-100 - I had to turn things down- and while there is minimal difference I feel like things are a little more sparkly in the treble and sub bass is a a little more textured. All in all everything sounds like the nicest, cleanest vinyl with a little digital precision sprinkled over it. Stereo imaging is really good. Like, really.
In short, I love the sound it makes.
Next up will be a permanent chassis with an internal power transformer, input selection and passive attenuator prior to the amp.
[Edit] Just wanted to add it is very responds very well to dacs. Different dacs bring out a different aspect of the same sound. At the moment I am mainly using the Audio-gd R2R11 because it gives the ACA mini lovely bass presence on acoustic music.
Plug your headphones in (no resistor networks - straight to the speaker jacks). And use a 25K pot, nothing higher. Well, of course you can go higher but you’ll kill the killer slam it has.
Some further listening and the following observations:
The thing that sets this apart from what I had previously heard is placement and imaging. It’s much, much more detailed. Sounds travel around the music space instead of jumping. There is depth as well as width. The kind of difference I head going from mid range to the bottom end of high end headphones. A step in quality rather than quantity.
I am aware I probably have a lot of subconscious bias about this amp so I am trying not to over sell it. I think it is partly a result of me not having heard better than a sub $200 speaker amp in the last thirty years. At the same time I am really surprised at the sound coming out of the speakers I already know really well.
Anyone who has a low end two channel speaker amp and a soldering iron, I really, really recommend this project build. It costs between $200 and what you want to spend on it. I think my parts list upped the price to about $300 plus whatever you want to spend on housing it. I feel like this is a bargain.
From my experience really doesn’t seem like you’re overselling it to me lol, while I’ve not heard the mini (don’t know how different that is) I have heard a regular aca (and 2 in mono), and it’s really shocking how good they are assuming you have nice speakers that are sensitive enough to pair with it. Imo there’s really not many cheaper solid state options that will get you this level of quality for the price, imo this has some of the characteristics and value proposition you get with some flea watt tube amps
A bit ago I made a post talking about how I felt the best speakers I had ever heard were mainly high efficiency, but really at this point I think it’s just down to the fact you can use these lower quantity but very high quality amps for best value which you can’t do with the less sensitive stuff lol
Placed in an enclosure with an internal Mean Well SMPS. According to the designer the ACA Mini is designed to run on a switching power supply. Locking lever power toggle cost nearly as much as the chassis but it is soooo pretty.
seriously nice job, if you case and dress that up too…oh my 
