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I have a standard - non dx - version here. It's a great amplifier, you can't buy a better one for the money. Highly recommended.

Easiest by far, needs bare minimum adjustments, very very quiet. I remember a very old tube radio from my Grandpa's time, it does sound much like it. Vocals are simply amazing and puts up a great soundstage. Listening for 6 months now, coupled with BA-3 frontend pre, trying various types of music, it keeps getting better and better. I was thinking of making Aleph J during Christmas, but going to postpone it for some more time...for a year atleast :)

Kit shipped earlier than expected following my pre-order (thanks!) and was in smaller boxes than I expected (cool!). I spent time studying the forum and videos on YouTube. Also took most of the advice I read including getting the proper tools for the job based on the list in the build guide, which is very good. I took my time on the build having never done one before. Spent a lot of time laying out the parts at each step, and was definitely patient with my novice soldering skills. End of build story - amp powered up perfectly first try, and I've been watching the bias adjustment as it stabilizes at normal class A operating temps. It sounds wonderful on my simple shop speakers. The sound reminds me very much of when I first heard a Soundstream Class A 40 in 1987 (my introduction to Nelson Pass design and class A amplification). The real test will come later when I hook it in to a tri-amp setup, where it will handle 450Hz and up, alongside a First Watt M2.

The kit with associated documentation and support was terrific overall. I feel like I have a chance of undertaking a more complicated build in the future. Thanks to NP and the crew at diyaudio. Time lapse vids of this build are posted, also the first power-up minutes, search "4thgc racer amp camp amp 1.6" on the goog machine. Total build time ~8 hours not including study time, majority of that was fiddling with chassis dry fit and order of operations for the wiring and final assembly. I added eight small washers to make things align comfortably - four at the nuts holding the rear panel on, and four between the mounting rails and the face plate as I was having trouble getting the heat sinks square to the faceplate without forcing it.

Soldering the 4 boards (2×stereo setup) was about 2 hours. Building the chassis was a couple of evenings. I built them with a twist, i used linear powersupplies. 1 transformer for each board, and a dual CRC board. And they have plenty of power for my Lowther 8" in a FLH JMLC 200 horn (about 106 dB or so efficency). Do i like the sound (?) - I just ordered the Aleph J boards...

The assembly was easy due to the good instructions.
The PCB assembly is simple,
the assembly in the small case is a bit fiddly.

I have built 2 monoblocks, the connection panel
I reduced accordingly.
The switch on the rear panel switches between RCA- and XLR-inputs.

I increased the series resistor (R13) for the LED from 10KOhm to 1MOhm,
the LED was way too bright for me.

I have a timer-relais built in,
because the amplifier made noises when switching on and off (output capacitor charge).
When powering up, the amplifier will now initially run on a 10 ohm load resistor,
after approx. 30 seconds, the speakers switch over.
The noises when switching on / off are thereby minimized.

Sonically, I was very positively surprised, I did not expect much.
All the more I am pleased about the very good sound result.

Greetings from good old Germany

Firstly, the build and the instructions for the ACA 1.6 were a joy. It's a great first-timer project.

I have a Musical Paradise MP301 MK3 that I A/B with and I can now honestly say that the MP301 is one of the best values in HiFi, especially at the entry level. The ACA, in comparison, bests the MP301 in a couple of regards, especially range and clarity, both of which are already great with the MP301. The ACA, as mentioned by other reviewers, provides a wonderful bass presentation, which can be missing in a tube-based SET. What the ACA lacks is oomph. It drives my 96 db Zu Omen Dirty Weekends very well, up to normal listening levels. But for party levels, I'll need to let the MP301 handle the job. I am feeding both amps with a Cambridge Audio CXN DAC/Network player.

I suspect I would have better success if I had two ACA's, one for each channel. But like others have said, I find it amazing that a solid state amp can sound so lovely. 90% of the time, I'll be listening to the ACA. Now, I am very curious to hear other project amps.

The kit was easy to build and sounds fantastic. I have it in my main system right now driving B&W 803s (90 db sensitivity). The bass is incredible especially for only 8 or so watts. No problem with volume - it goes plenty loud. My preamp is an Aikido design (TubeCad.com) with 4 5687 tubes and regulated supply for both high and low voltages.

A Class A amp that exceeds the sum of its parts.

If you only get 1 amp kit, GET THIS ONE. It is a well thought out kit of premium parts & a beautiful chassis to put them in. The build Instructions are A+++ Easy to follow & the end result is simply amazing. Listening on my Zu DWII's, this amp sounds very clear & detailed, with a Wide Soundstage. The Bass is tight and powerful. I have also listened to it on my AR3a and was surprised at the volume this amp could drive those inefficient speakers to. NOTHING to Dislike about this amp.
Thank you to the DIY Crew for making this possible & to Nelson Pass for giving it to the World.

This has to be one of the best amplifier kits around. The quality, fit, finish, and most importantly, the sound, is fantastic. With the clear assembly instructions that are available online this kit goes together so easy. It's a great kit for novices learning soldering skills as well. Can't thank everyone enough for making ACA available to everyone!

I've been searching for a good amp for years. I even tried the Benchmark AHB-2 (which retails for $3,000 and is a Stereophile Class A component) for a month but wasn't satisfied with it.

It took me a few evenings to get everything soldered together, but the diyaudio kit made it a breeze. The diyaudio chassis is also beautiful and has a very high WAF.

Now I have two of these magical little amps powering KEF LS50s in a balanced monoblock configuration, and it's heaven. The bang for the buck is unbelievable. Nelson Pass is truly the zen master of amplifier design, and diyaudio has also done a superb job putting this kit together. Kudos all around!

I couldn't be happier with the result. A pair of these in "bridged mode" are replacing my 15 year old, high end amplifier. I'm not sure quiet yet, but I think I prefer the non-bridged sound while using a single amp in my system. Has anyone else compared the sound of a bridged pair with using a single ACA in their system? The construction process was a breeze, and what a great way to, basically, receive lectures on amplifier building from a master builder, Mr. Pass. It was a huge shock to me how great this amp sounded once it was broken in and up to temp. A huge improvement over my previous amp. A big thank you to Mr. Pass and his team for sharing so much beautiful sound/music for such a reasonable cost.

Very fun DIY project.
The Amp sounds awsome.

Perfect kit and an sounds amazing. Great value for the money. Have two and run them balanced wirh my PAP OB’s.

Piece of mind - high quality, easy to buy, trusted.

Firstly, thanks a lot to the diyaudio store for the new international shipping option witch proved itself extremely efficient (one week from order to delivery here in France with customs pre-paid), this is a really good move overall.
Now for the kit itself, I cannot say anything else than it's perfect. The board is beautifully made, with plated through holes everywhere, the parts are neatly spread on plastic bags and are top notch (non magnetic resistors, wima and elna capacitors, bourns trimmers and a little paper witch lists the resistors values for the matched fets).
As for the result, to my ears (witch are far from perfect I must admit) the curves are just identical as what you get with the miniDSP but with added clarity (at least that's what I feel) and the noise floor is deeep under ground level ;) Also, the pots give a n easy way to balance gain between different amps.
I'm thrilled :)

Very good and very easy built project .
Excellent performance.

The board quality is beautiful and easy to build. Sounds absolutely fantastic, it's my everyday headphone amp, super happy with it. I chose to use a Burr-Brown OPA2134PA Op-Amp and Fairchild finals.

This 24v power supply made an amp that I already loved sound even better and gave it even more power. It now plays as loud as I could want from an amp especially when paired with my subwoofer through the speaker level inputs. I have totally fallen in love with this amp and can say it is the best listening experience I have ever had. And this is just after I paid well over $1000 for a REGA Elex-R amplifier. This amp kit outperforms my Rega amp with clarity very noticeably. I wish I could return the Rega honestly. I biased the DC output to 11.9 volts on both channels after trying it at ~ 12.2 volts. I found it sounded better with the lower number and I am loving this thing now.

Great boards, better quality than Ebay boards by a bunch! Well laid out and easy to read, gathering up my parts to start stuffing, will be ordering chassis soon, thanks a bunch!

Only a few components for a fantastic project. Easy to build following building guide . With my MOFO provides a very great stage.
Very great pleasure to listen. Yhank you!

Have bought 2 of this boards. Threw one together with parts from my parts bin, an old metal case I had almost discarded, and an LT regulator, +/- 24 VDC. I cannot believe how good it sounds. My ARC LS25 has not been used since. I am now ordering "boutique" parts and am building a better looking unit in a nice new diy audio rack case. I doubt if the new parts could make it sound even better than the first one., but I will feel better knowing I used top quality parts. Honestly though, its all in the circuit. Nelson Pass is a kind, generous, genius, designer.

When properly used these are astonishingly low noise. Very pleased.

Excellent service and fast shipping as usual. Awesome to be able to buy these in this quantity thanks to the store!

I've wanted to build an amp for a very long time but have never had the courage. I finally got the courage and ordered the ACA amp kit. I'm so glad I did! The build was very enjoyable and not as difficult as I thought. The documentation was superb. The sound and build quality are excellent. It mildly reminds me of a mini version of the First Watt J2 that I own. Paired with Zu Omen IIs it really is a joy to listen to. Highly recommended build.

I put it together in a few hours time and had no difficulty. I followed the online guide and it worked the first time I fired it up. It sounds great too. Now I need a preamp kit in the same form factor (hint).

I think there are several reasons to build this. You get a design that you know is rock solid and guaranteed to sound good, you get high quality parts, you get an excellent idiot-proof build guide and you get excellent support if necessary. I built this over the course of two evenings and I cannot recommend it enough. The feeling of pride of having built an amplifier that sounds good and looks good is worth every penny. I know it's assembly rather than true DIY, but it inspires confidence, and that is the aim.

I have this hooked up to a pair of Monitor Audio BX5 speakers and use an O2 Objective amp as a pre-amp with my phone as a source. The room is small and the 5W per channel fill it more than adequately and the sound is fantastic. Thank you to all involved in bringing this to the community, I have definitely started on a building journey!

A very enjoyable build. The video build tutorial provided excellent instruction and tips. Built the unit in one session.
Hooked up ipod through Cambridge Audio id 100 digital dock. Clear, clean and well defined music reproduction. Hard to believe that 5 watts can resolve highs, mids and bass with this much definition. Pure class A operation. Pure listening Bliss. Next move will be to hook up to an external DAC. Thank you Nelson Pass and DIYaudio.

These work very well and look great. Could not be more pleased with the project. Modifications I made were to eliminate the dc connector and switch as I control all things audio with a power strip anyway. There is nothing wrong with them, just chose not to use them. As well opted to use 1/4 inch copper strap for the "ground" connection as it made for easier connections. Likely there is no measurable sonic difference. But seemed like a better choice considering the work that connection across the positive speaker terminals and DC ground is performing. Since this review is about the chassis only. Will leave out the part about the amazing amount of audio that this thing delivers.. : ) No regrets buying these kits.

Be warned. This is a gateway amp. Once you get this built you are going to want to build another. Seriously, I've already ordered boards for an Aleph J. I expect I'll shortly start giving blood to pay for the costs of the DIY electronics I'm going to build.

On a serious note. The folks on the forum (especially 6L6) were incredibly helpful. I do not have a ton of experience building electronics. Prior to this amp I put together a pair of Bagby Continuums based on the Meniscusaudio kit.

If you can get ahold of one do so right away. You will not be sad. The continuums are not the most efficient of speakers, but coupled with the Amp (and my Jotunheim DAC) for use near field at my computer.... Sonic Bliss!

Thanks to 6L6's great build guide on DIYaudio. The sound is superb too, clearly better than the Class D amps and NAD D3020 I had been using. With the 19V power supply heat sinks do not get beyond pleasantly warm.

Quick delivery even overseas! PCBs are premium quality, really well made! Happy to start my F5 project with such a smooth transaction. Still some way to go till completed amp but it started well.
Greetings from Latvia

Coupled to speakers with with 98db sensitivity, a watt from this amplifier is simply put: astonishing! The first night we found ourselves identifying and padding vibrating pictures because of the incredibly deep bass. It is crystal clear across the audio range. It sounds great!

Well, you'd be surprised how much you might do with this no gain amplifier. You should read up on it and if it seems you'd like to give it a try you will be rewarded with a new and lovely perspective.

It will show you what you need to know about your preamp. It will show you how a speaker can be really controlled. I use mine to drive a pair of high efficiency sub woofers because of the control afforded. It is a great tool in making music and taking a full assessment of where your stereo is at. I have built the F4, F5t, F6 and the Aleph J, all very good experiences and all still in service but the one that taught me the most about stereos is the F4.

All of the kits here are a great bargain and very well made. The gift from Nelson Pass and his supporters is not to be passed up. Build this amp! You'll be educated and it'll be fun!