Lots of features and perfect linearity - a perfect first amplifier

Class D amplifiers have seen significant advancements over the past few years. Initially, they were often dismissed as low-quality ’toys’ due to various sonic issues, but step by step companies like Aiyima have progressively improved their designs, and we are now at a watershed moment when one of the final ‘complaints’ about class D amplfiier from the ’naysayers’ has been addressed. So both Aiyima and Fosi Audio have recently implemented Amplifiers that should have perfect linearity independent of the load impedance of the speakers they are driving.

A70.jpg

I have had a long history with different amplifiers from Aiyima over the past few years, so having finally gotten my hands on the A70, I thought I would put together both an initial review but also add describe my own journey with different Class D amplifiers. I think the A70 is a significant amplifier that might be the best amplifier for beginners in this hobby.

So, lets get into the details and why I think it would be a great first amplifier.

Introduction

The Aiyima A70 is the latest iteration in Aiyima’s line of Class D amplifiers, building on the foundation laid by previous generations of Aiyima amplifiers including the highly acclaimed A07. Over the past few years, Aiyima has progressively enhanced their amplifiers, adding new features, even sometimes removing features but always refining their designs to address what they feel is the most competitive amplifier they can provide at the time.

Some background on Aiyima Amplifiers

Before I get into the details of the A70, I thought I might set some context as I have had a lot of Aiyima (and Fosi Audio) amplifiers over the past few years ( and yes my wife thinks I am a bit crazy - “What another little box?” ) so I thought I would a bit indulgent and look back over some of my previous Class D amplifiers.

So, Feel free to skip this next section if you are only interested in the A70 itself.

A04: My First Aiyima Product

The AIYIMA A04 was my first introduction to Aiyima’s product line and was a vast improvement over my earlier class D “experiments” that I had bought on aliexpress. Using the TPA3251 chip, the A04 delivered a theoretical power output of 175W*2, which was impressive for its size and price point. At the time it worked wonderful well for me in a small “working from home” setup and I also believe it was very popular on Amazon and AliExpress, as well as in various audio forums as that is where I learned about it.

However, its main limitation was its power output (which is why I highlighted theoretical above), which was fine for a small rooms but distortion especially in the bass region would take over if you pushed the power too much. But this was a great start.

A07: A Significant Step Forward

The A07 marked a pivotal moment in Aiyima’s development. From everything I had read from both objective reviewers like Amir over on AudioScienceReview, to subjective reviewers like the “The CheapAudio Man” on Youtube, this was a groundbreaking amplifier, in what could be achieved with a small box Class D amplifier at less than $100. For this design Aiyima adopted the TPA3255 chip, which provided higher power, lowered distortion, and had a better signal-to-noise ratio than the TPA3251.

This model addressed the power demands of more robust speaker systems, and so I immediately upgraded from both the A04 but also my speaker setup, and its upgraded power supply (over 36V with the A04) ensured better performance and reliability. I ultimately ended up with two A07’s as during Covid, I expanded the rooms within my house where I would work remotely from. I believe the A07 quickly became a favorite among audiophiles and topped Amazon sales charts in Europe and America.

It also almost singled handedly spawned an Audio “tweakers dream” by supporting interchangeable op-amp chips also enhanced its flexibility and upgradability, making it a standout product. But what happended next was interesting, in that we started to see some great competition both with different chipsets but also with Amplifiers using the TPA3255 chipset.

A05, A08, A08 Pro

While I recognized the specific targeted features of next few Aiyima Amplifiers, the A08 with an embedded power supply and the A08 Pro (retro styling with a UV meter), I chose to skip these models in my journey. They offered some innovations but didn’t align with my immediate needs until later models. They were probably a clever move testing the market with different features, but they weren’t really for me. But I did at this time buy a cheaper Aiyima A05 for my second WFH setup, though ultimately I replaced it with a second A07, the A05 was a fine amplifier though not in the same class as the TPA3255 chipset amplifiers as it used a TPA3221 chipset which was less powerful.

A07 Pro: Was it an Enhancement to the Classic A07 ?

My next Aiyima purchase was the A07 Pro which in theory built on the success of the A07, but the A07 Pro was introduced to cater to a broader range of consumers with features like Bluetooth and tone controls (which were not “defeatable” so hard to know what ’neutral’ was). So, in my opinion, it probably didn’t deserve the “Pro” and probably the only purchase that I regret.

It was marginally better than the A07, but it also might have indirectly led to Fosi Audio developing the V3, which entered the market soon afterward, but that Amplifier focused on just being a better A07 without the features of the A07 Pro, so rather than adding features like bluetooth the V3 focused on providing better cooling and some higher quality internal components to get higher output levels and potentially a “clearer” sound.

A07 Max: Addressing Market Demands

But I do think competition is great and while I imagine Aiyima would not admit it, the A07 Max was developed to win back the crown from the V3 and meet the increasing demands for high-performance audio solutions.

This time the key feature was a bridgeable mono function, allowing for single and dual-channel switching. So I got the ability to run 2 A07 Max’s as Monoblocks. And Aiyima also matched the Fosi Audio V3 by optimizing the heat dissipation design to manage the heat generated when using dual channels with 48V power, significantly improving power output and reliability, all this at a lower price than the V3. The A07 MAX is still a stunning bargain Amplifier, even as I write this while listening to the A70.

The Load Dependency issue, PFFB and road to the A70

With the A07 Max, Aiyima are getting into the area of challenging some of the more traditional power-amp mono-block amplifiers companies, but those Mono-block amplifiers are many times more expensive than Aiyima’s offerings but they did have the advange of not being load-dependent as they were typically class A or class A/B designs. So to reach this “next” level Aiyima would have to solve load dependency within their amplifiers.

I remember after reviews for the A07 Max (and the V3) appeared, thinking that the stakes were changing and these\ little amplifiers were being used in much more series ‘audiophile setups’ (even being reviewed by higher profile ‘subjective’ reviewers on Youtube who would normally only review ’expensive’ amplifiers) but in those setups and reviews there was one common complaint being voiced
about ‘mismatches’ between these class D amplifiers and the high-end speakers they were being paired with.

This might be where a class D amplifier could sound extra ‘sharp’ or ‘dull’ in the higher end regions beyond 10K depending on the speaker it was paired with. This was because some speakers ( more high-end speakers ) will have dramatic ‘swings’ in impedance around their tweeters (especially when the tweeters use more exotic materials).

So, this problem had been solved many years before within much more expensive class D amplifiers who had implemented Post Filter Feedback(PFFB) within their amplifiers and in turned out that that same TPA3255 amplifier chipset that Aiyima had been using since the A07 days had the ability to be adapted to support PFFB, so the stage was set for this last bit of puzzle.

A70: The Logical Next Step

The A70 represents the logical next step in Aiyima’s evolution. By incorporating PFFB it solves this load dependency issue but then from their experience and possible due to some competition from Fosi Audio’s ZA3, the A70 also includes some great features like XLR balanced input (as well as the more typical RCA) and a 12V trigger function.

So, this is where I am now, with my new A70 to play with so, lets get stuck into the details of what you get with the A70.

Unboxing experience

The Aiyima A70 arrives in a well-packaged box, ensuring the amplifier and accessories are secure during transit. box.jpeg

So inside the box, we get: • Aiyima A70 Amplifier • Power Adapter 48V 5amp • User Manual contents.jpeg

Taking out the amplifier and power supply: contents with power in box.jpeg

I bought my A70 from Amazon.de - here is a non affliated link but that version comes with 48V with a 5A power supply, since the A70 can be powered with even more impressive power supply I also decided to buy the 10A x 48V GaN power supply also from Amazon.de - also non affliated link

Comparing power supplies

The difference in size between the 10A and the 5A is pretty dramatic:

power supplies compared.jpeg power supplies cimpared.jpeg

Build Quality and Design

When unboxed I think the A70 looks pretty nice: ontable.jpeg

Obviously Aiyima have gone for a more ‘boxy’ style that they had with the A07 Max or that Fosi Audio have with their recent amplifiers. But I think it looks well.

Here is what it looks like compared to 2 V3 Monos: a70_with_v3.jpeg

Overall I do like the look of the A70 here is a photo of my garage setup with the A70 with my Polk ES20: A70 with Piolk.jpeg

I do like how the front panel is exceptional minimal on the A70 with basically a volume knob that toggles between the RCA, XLR inputs and powering up the A70: A70 with SU1.jpeg

With the A70 design there is less concern about changing the volume accidentally when switching it on, since this is not a mono-block, but I can imagine some people might prefer a separate power switch.

Also, there is no audible ‘click’ when you switch on or off the A70 so no nasty surprises.

Connections on the Back

The back panel is equipped with various inputs and outputs, including RCA, XLR, and a subwoofer output. back_no_connections.jpeg

I like how recent Aiyima Amplifiers like the A07 Max have much better binding posts and has staggered them and the A70 follows this trend making it much easier to connect your speakers.

As someone who ended up replacing their A07’s due to a lack of XLR inputs, I think its great that we get the choice with the A70.

As a quick test, I decided to ‘fully load’ the connections with both XLR inputs from an SMSL D6s DAC and RCA inputs from an WiiM Pro plus: connections from sise.jpeg

I also like that Aiyima have added a +3dB boost switch with the RCA input - this allows much better level matching.

connections on back 2.jpeg

Trigger

Having a Trigger input is a nice extra feature and matches that feature on the Fosi Audio ZA3. I have an WiiM Pro with trigger output, so it’s a good combination with the A70. Once I start streaming some music the WiiM Pro wakes up the A70 to start streaming doing a significant saving on your electricity bill the power which with the 48V x 10A power supply can be significant.

Subwoofer

This is one of the reasons I think this is a great starter Amplifier, you don’t need a subwoofer but the A70 allows you to slowly grow your system over a number of years.

In my garage setup I have paired the A70 with a simple Yamaha Subwoofer and I used an Umik-1 measurement microphone to blend the Subwoofer output with my main Polk Speakers.

The LPF configuration ‘dial’ is on the left just above the trigger input where you can set the LPF from 150Hz up to 600Hz. Your subwoofer will probably have a similar configuration so my advice is to pick one device as the master and set the other one to the maximum value and just change this on the master.

While it is nice that Aiyima have included an LPF configuration, I do think it is a missed opportunity because if this was instead a High Pass Filter configuration, on the speaker output rather than just apply to the subwoofer output, it would have made more sense, removing the need for speakers to attempt to reproduce low frequencies when you have a subwoofer means much less distortion and therefore being able to drive the speakers even louder but it is a minor quibble.

Here is a full view of the setup: A70 full setup.jpeg

Sound Quality

Given the purpose of this Amplifier and especially with the internal PFFB circuitry is to accurately reproduce the sound of the source material coming in via XLR or RCA, you should no expect the A70 to ‘colour’ the sound. But if previously had a class D amplifier like the Aiyima A07 or the Fosi Audio V3 and had some speakers with high impedance ‘swings’ you should now find the A70 much more linear and ’true to the source’ and therefore it may sound different depending on your setup.

Bass

The Aiyima A70 delivers powerful and well-controlled bass, thanks to the implementation of the TPA3255 chipset with PFFB there should be less distortion. The bass response is tight and punchy, making it suitable for genres that demand a strong low-end presence. Thanks to the subwoofer output you can (and should) use a subwoofer to tune the bass response your preference.

Midrange

The midrange is clear and exceptionally detailed, if you are coming from an older amplifier you might be astonished how clean the A70 will appear. It will be providing a natural and balanced representation of vocals and instruments. Both male and female vocals are rendered with excellent transparency.

Treble

The treble is smooth and extended and as I mentioned previously there should be no mixmatch with your speakers, this class D amplifier is designed to be linear no matter the speakers it is connected too without becoming harsh or fatiguing. The A70 strikes a fine balance, delivering crisp highs that enhance the overall listening experience.

Overall Sound

The Aiyima A70 excels in delivering a clean and powerful sound. The amplifier’s performance is consistent across different speakers, thanks to the PFFB technology that improves linearity and reduces distortion.

Specifications and Measurements

Here are the published specifications from Aiyima :

•	Amplifier Type: Class D
•	Chipset: TPA3255 with PFFB
•	Max Power Output: 300W but realistically 185W into 4Ohms with 48W 10A 
•	THD+N: < 0.0015% at 1W, 1kHz
•	Signal-to-Noise Ratio: > 116dB with 48V 
•	Frequency Response: 20Hz - 20kHz ± 1dB
•	Inputs: RCA, XLR
•	Outputs: Speaker terminals, Subwoofer output
•	Dimensions: 146 x 79 x 90mm(5.74 x 3.11 x 3.54inch)
•	Weight: 903g

But I do believe you should always get independently verified measurements, so we are lucky that Amir over at ASR was given an pre-release model of the A70, see below for some details.

Measurements

I would encourage anyone reading this review to check out Amir’s full technical review over on AudioScienceReview

but I thought I show a few of the key parts of his report below and I will update this review with further measurements as they appear.

Frequency Response

Amir measured the frequency response to verify the PFFB implementation, and it is mostly flat across the entire auditory range: AIYIMA A70 Class D Stereo Amplifier with PFFB balanced Frequency Response Measurement.png

So there was roughly 0.3dB difference between a 4 Ohm or 8 Ohm as the frequency approached 20Khz.

SINAD / THD+N

Distortion measurements show that the amplifier maintains low THD+N across the entire frequency spectrum.

Note: Amir tested a pre-release model, Aiyima have suggested that they have further reduced the distortion and increase the SINAD values that the A70 achieves but for now here are the Audio Precision values:

From the RCA: AIYIMA A70 Class D Stereo Amplifier with PFFB RCA Measurement.png

From the XLR which is very similar to Aiyima rated THD+N values of 0.0015%: AIYIMA A70 Class D Stereo Amplifier with PFFB balanced Measurement.png

Power Measurements

AIYIMA A70 Class D Stereo Amplifier with PFFB balanced Power into 4 ohm Measurement.png

With Amir power measurements you can see it can deliver up to 139W of power which is excellent but it should be noted that this is somewhat less than the 300W (which is really a theoretical max at 10% THD ) or the more practical value of 185W at 1% THD, so either those final production refinements that Aiyima state that they have made to the production units have helped (as Amir tested a pre-release model) or Aiyima are stretching the truth a little.

But even 139W of power per channel is more than adequate for any normal medium-sized listening space.

Rating

Given its impressive build quality, excellent sound performance, and practical features, I have given the Aiyima A70 a top pragmatic rating of 5 out of 5.

It is almost a perfect amplifier, it has the sound quality and the features you might want, except maybe the lack of a low pass filter on the subwoofer output holds it back from absolute perfection at this price point, but this is a minor issue compared to the overall capabilities of this amplifier.

Conclusion

The Aiyima A70 is a near-endgame Class D amplifier, showcasing how far Aiyima has come since the early days of A04 and A07. With its powerful and clean linear sound, robust build quality, and practical features, it is an excellent choice for anyone with a small to medium-sized listening space.

Since, you should have no concern about matching speaker impedance, I do think this can be a great first amplifier, you can start with simple RCA inputs and your current speakers but then upgrade to XLR and more demanding speakers over time, even adding a subwoofer on your journey when you feel like a bass upgrade.
The A70 has both the power and the capabilities to support anyone starting off in this hobby.