There is way too many conflicting information about the amplifier.
One thing is this amplifier does originate from the era of T-Amplifiers. The patent for the technology expired and is now available for other companies to use.
A class D amplifier that operates and has an internal fan that kicks on at 65℃ is not efficient by any standards. Even the SNR doesn't lie.
AX5689 is an 8-channel digital Class-D amplifier controller with digital inputs, not a Class D amplifier.
https://www.axign.nl/wp-content/uploads/AX5689_ProductBrief_v1.0.pdf
Reading words like low-latency in a controller worries me because that means there is latency. They also have contradictory statements in section 3 of the first page about SNR vs the SNR as quoted by SMSL for the SA400.
The actual amplifier portion is
https://www.st.com/resource/en/datasheet/sta516be.pdf
The original date of the first release of the STA516 1st February, 2007!
This is one amplifier I would stay well clear of. The origins of the design are ancient in today's audio world. The published specs don't add up when you compare the two main parts of the amplifier design.
There is no doubt that SMSL is cranking out new amplifiers at a huge speed. They are building as many variants as possible in the hopes that one or two will hit the market. Considering the packaging that SMSL uses for their amplifier chassis's are largely the same, 2 main depth differences only and some with spikes to raise the amplifier for cooling, they are obviously going for a broad attack with the hopes that one or two of the new amplifiers will hit the market and sell well.
I'm a huge fan of the DA-9, and have contributed a great deal on the DA-9 thread. Yes, my unit had QC problems which were easily cured by myself and the amplifier is dead quiet, has an expansive soundstage compared to it's predecessor which had XLR inputs but they dodged the words balanced inputs all together because the DA-8s did NOT have balanced inputs, just XLR inputs. Even the DA-9 is playing a little bit of a trick by saying that it's a true balanced input when it is in fact using an op-amp which is not how a true balanced input works. I don't have any complaints with how the XLR input works however as it does sound better than the RCA level inputs and not because of increased gain. I think the op-amp is playing some very effective trickery to how we hear sound. I wish SMSL would publish the schematic in full, but they would never do that.
I am very comfortable saying buyer beware of this amplifier. The amount of information that I've read from the chip manufacturers themselves, and the examples for circuitry design lead me to this statement. There are too many unknowns with this amplifier. And who ever heard of an Class D amplifier from 2021 that requires forced cooling that was designed and sold as new even in the past few years. There is the Mytek Digital 2 channel that uses a heavily modified PASCAL amplifier that does run a little bit on the warm side that does have a fan, but that is an amplifier that has much more credibility and controllability of the gain settings and is a proven performer.
With a lot of the inexpensive stereo equipment on the market it's very easy to be tricked into believing something is better because it's newly announced. We have to do our own research and understand how these devices are built before we start to say things like "This amplifier produced no "hiss-noise", so it must be a good amplifier". That is a totally amateur statement. Saying that playing at 100-110db volume, well what weighting did you use? How far away was the microphone placed? What is your room like? These are all variables that must be taken into account.
It's fantastic that many companies are offering an over abundance of choice today and that the prices have come down significantly as a result. It's also very important for the buyer to be educated and to understand how to read schematics, testing procedures when the specs are published. Without some technical knowledge, it's very easy to be fooled and sold with clever marketing and pretty pictures.
I am not trashing the amplifier in any way. I do want to make that clear. I think it probably has a place in the market. Would I buy one? No. Does that mean you shouldn't buy one? No again. Read everything you can and gain an understanding of the technology behind the design, the implementation before you make a purchase. Unfortunately most of us can't hear these amplifiers for ourselves before we make a purchase, so we have to make an almost impulse purchase based on the information that is provided to us from the manufacturers. And they've proven themselves to be unreliable sources of information on not only specifications, but on simple things like quality control.
Just my more than 2 cents. The important thing that we all must do is to research, read all the documented information of chipsets, and what we can learn of the possible implementation methods of certain chips. We have to be smart. We have to learn about what the schematics of a chip tell us.
I'm a huge SMSL fan, and will continue to buy SMSL product as long as the quality control doesn't go way-way down. It is also my greatest concern as they will be announcing yet another "new headphone" amplifier in the coming days. Making this many new models with an existing workforce will cause strain on quality control, even if they employ many new employees. You have to train them. You have to oversee the work.
Please bare in mind that "hiss-noise" is something that shouldn't exist in even tube amplifier if designed correctly. It shouldn't be audible, unless your tweeters are 105+db/watt efficient. You really shouldn't have any issues with "hiss-noise" if all of your components are set-up correctly, and gain matched properly. Gain is not a volume control. It is to match one devices output with another's input. These youtube experts are not all created equal. Not all of them have the technical knowledge to properly test equipment.
