Hi and welcome!
From his detailed tests pairing the ACA Mini with the Ciare CT440 bullet tweeter, Joseph Crow said, "I detected no hiss or buzz from the tweeter. This is rare since nearly all amplifiers I test require a fixed resistor L-pad to bring the amplifier out of the noise floor. This is not the case with the ACA Mini."
He concluded, "Considering the cost of only $135 USD for the kit, I would recommend the ACA Mini if you are looking for an amplifier solution to power very high sensitivity drivers in a bi-amp situation. It provides a smooth sound character and very low noise floor when operating in the sub-one-watt range." I concur. After all, for $135 and the fun of building it to find out, what do you have to lose?
IMHO, if you are looking for the ultimate "shimmer" listening to cymbals, you'll need to step up and find a First Watt SIT amp and use only the first watt that you need and not worry about the 24 watts not being used. ;-)
Nah, it sucks 
I have often thought that one attribute of true genius is to make complicated things relatively simple,Papa hit it out of the park! My friends call me "Professionally Unimpressed" color me duly impressed, and for what its worth I have been selling/playing with high end audio for decades.
I have often thought that one attribute of true genius is to make complicated things relatively simple,Papa hit it out of the park! My friends call me "Professionally Unimpressed" color me duly impressed, and for what its worth I have been selling/playing with high end audio for decades.
These test points are really great to use with those J-hooks. I found something similar on ebay and I am sure you can also find them on Amazon.
Those look great, thanks Chris! Listening to a little Grateful Dead Boston 6/12/76, Almost Heaven! I always considered this a birthday present as I was born 6/12, not quite '76 LOL!
Don't recall seeing any mention of how important it is to get the 2 channels bias matched? How close is close?
@Toys4Boys: If you haven't already, set the bias pretty high. I have VB at 370 mV, and it sounds really great. Nelson told me that the ACA Mini likes to be biased between 350 and 390 mV.
As for test points, you can just solder some cut off resistor leads into the test holes. I did this, and it made attaching probes with J hooks or even mini alligator plugs very easy. My "test points" are wires that stick straight up, so I can even attach a probe adaptor that has a push on termination...not sure what that kind is called.
I had enough connectors to attach them to both sides (L and R), so all I had to do is change which side was connected to the meters.
I also added female banana plug connectors. The wires on mine were really thick and looked like aluminum. I learned that they were tinned OFC copper. I had to trim off some of the wire to cram it into the speaker jacks, but it worked very well.
Enjoy!
As for test points, you can just solder some cut off resistor leads into the test holes. I did this, and it made attaching probes with J hooks or even mini alligator plugs very easy. My "test points" are wires that stick straight up, so I can even attach a probe adaptor that has a push on termination...not sure what that kind is called.
I had enough connectors to attach them to both sides (L and R), so all I had to do is change which side was connected to the meters.
I also added female banana plug connectors. The wires on mine were really thick and looked like aluminum. I learned that they were tinned OFC copper. I had to trim off some of the wire to cram it into the speaker jacks, but it worked very well.
Enjoy!
I get them as close as I can and then check the temp of each heatsink. When the temps are off/different, I know my ambient room temperature has changed and I touch up the bias. This is mainly going from winter-->summer-->winter in the middle of the US. I can get a bit more bias in the winter while maintaining temps below 60 deg C on the heatsinks.
Hi, @Chris Jones KS. If your heat sinks seem not to have the same temperature, it's possible that the cooler ones have the MOSFET bolt too loose. I found that, after tightening all bolts to a "just enough" point, they became a bit loose after the lock washers adjusted to the pressure and bent a bit more. One side was cooler than the other, even though both were biased the same. When I again tightened to the "just enough" point, both sides heated the same.
@petieboy: I suspect that the ACA Mini amp will be perfect for your tweeters, and probably also for your midrange. [Why not build two? I did.] The Mini can't drive the woofers of my sealed bookshelf speakers very well, but the treble is outstanding, even with those. With my more efficient and much larger floor standers, the ACA Mini is the best amp I've ever used. The treble detail is phenomenal.
Thanks, lastnamenelson. Everything is tight but the temps are my lazy way of knowing the bias has drifted with room temperature. It's quicker for me to test their temp than to pull out my multimeters. Confirming the temps are similar from front to back and side to side is oddly satisfying for me to do, too. Ha!
Both channels biasing nicely at 370mV. Those test clips are sweet, might have to order a bunch, fortunately one of the old meter probes I have are fine enuf to fit thru the test point.
Well, that is a reassuring recommendation, which makes me feel more confident in buying the mini for sure.
Thank you!
"and probably also for your midrange" For now i am very happy with the 2 amplifiers i have selected for midrange duties (original ACA & Crayon amplifiers) they both mesh very well with my Rogue amp running my woofers too. If i proceed purchasing the mini then yes i will also try the mini out on midrange as you suggest.
Can the ACA-mini also help produce a airy delicate treble as well as phenomenal detail ?
This is useful information thank you!
Yes for the price it would be silly not to try the mini eh. But you also suggest that a SIT would render the HF even more to my liking.
May i ask which SIT in particular? I am not too familiar with them. All i really know is they are quite a bit more expensive.
Or could the mini even be upgraded with better parts somewhere to help make him a better dedicated tweeter amp?
Such as better resistors or maybe something like 1uf Mundorf SGO at C1..... etc ? Or some kind of modification maybe ?
I am checking my parts count on the second ACAMini that I bought and am finding 1 discrepancy, R2 should be qty. 2 200K ohms, what I have are 20 ohm, red/blk/blk/org
@petieboy:
Re "Can the ACA-mini also help produce a airy delicate treble as well as phenomenal detail ?"
My speakers are inexpensive JBL Arena 170s, with soft dome tweeters. I think the treble with the ACA Mini is outstanding, better than I thought a cheap soft dome tweeter could do. But you have horn tweeters, so I can't venture a guess about how they'd do with the Mini. You'll have to build one and try it. But I expect that you'll like it.
Re "Can the ACA-mini also help produce a airy delicate treble as well as phenomenal detail ?"
My speakers are inexpensive JBL Arena 170s, with soft dome tweeters. I think the treble with the ACA Mini is outstanding, better than I thought a cheap soft dome tweeter could do. But you have horn tweeters, so I can't venture a guess about how they'd do with the Mini. You'll have to build one and try it. But I expect that you'll like it.
@Toys4Boys:
Are you measuring your resistors as you sort them? I found some of the color codes hard to figure out until I measured.
Are you measuring your resistors as you sort them? I found some of the color codes hard to figure out until I measured.
Okay, my bad! At least it has been a learning experience. While I did triple check the bands it was doomed to failure until I realized that there was a tab at the top of the Calculator to select 5 band, D'Oh or, as I too often find myself saying, Light Dawns On Marblehead, a small town on the coast of Mass. 😉
I should be receiving a Tubes4HiFi SP14 shortly, I'm anxious to see how the amp performs with my vinyl rig!