Part II: 3e Audio - A5 Stereo and A7 Mono Class D + PFFB, TI TPA3251/3255 Amplifiers - power, distortion, and the subjective. (And a few photos for Swifties.)

Let's continue with Part II of the evaluation of 3e Audio's A5 and A7 Mono amplifiers. See Part I last time for the initial discussions, features, pictures and measurements around output impedance, frequency response and stereo crosstalk.

This time, we'll finish up with further measurements of output power, distortions, subjective discussions, and summary.

Unless a product can be purchased, there's probably no point publishing the results! So I timed this post to correlate with the opening of the 3e Audio AliExpress store for these products.

Part I: 3e Audio - A5 Stereo and A7 Mono Class D + PFFB, TI TPA3251/3255 Amplifiers - Features and initial measurements.

Every once awhile, a manufacturer will connect to see if I might be interested in testing out one of their upcoming products. Recently, 3e Audio (their mission being to Enhanced, Exceed, Enjoy) based in Shenzhen reached out for an honest, independent, evaluation of their new amplifiers. As usual, most of my hardware discussions are based on objective results which I believe significantly reduces personal subjective biases and advertising hype - no YouTube videos where reviewers make silly facial expressions to draw attention to the thumbnail image here folks. 🙄

You probably haven't heard of this brand, but the engineering-focused company has been around for a number of years selling boards to the DIY market with DSP, power supply, and Class D amplifiers. In August, they announced the release of their line of five fully-assembled "A5x A7x Series Next-Gen PFFB Amplifiers". In the picture above, we see the pre-release A7 Mono (260W into 4Ω 1% THD+N, single TPA3255, PBTL) and A5 (150W x 2 into 4Ω 1% THD+N, dual-TPA3251, PBTL) models sent here for evaluation.

As you might know, in this blog over the years I've been covering a number of these very reasonably priced TI TPA chip amps from the early generation TI TPA3116, to the early TPA3255 models (like the AOSHIDA A7), to the very high performance Topping PA5 MkII+ (TPA3251), to the recent inexpensive and higher powered Fosi Audio V3 Mono (TPA3255) with Post-Filter Feedback (PFFB). The inclusion of PFFB to 3e Audio's amplifiers is not new for this company as this feature has been available in their DIY boards since at least 2022. 3e Audio is aiming to exceed the performance of others that have come before; of course, we'll see about that on the testbench!

I'm not sure exactly what date 3e Audio will make these amps available or the prices. At the time of these tests, I was told that they will be taking orders on their AliExpress store in early December 2024. Final prices might change, but I was told that the amps will range from US$199 for the A5se (140W x 2 into 4Ω, 1% THD+N, single-TPA3251, BTL), to US$300 A7 models with power supply.

Part II: Fosi Audio V3 Mono Amp; Class D + PFFB, TI TPA3255 - Retail box with single 48V/10A power supply and filter. [Power, Distortion, and Subjective Impressions.] And on rejoicing over "Solved Problems" in audio.

Gotta love those Nordost-like flat speaker cables from AliExpress. The 90° locking banana connectors are a bit on the large side however. 😉

As we saw last week in Part I, I started reviewing the Fosi Audio V3 Mono amplifier, early August 2024 retail release, in the form of the stereo with 48V/10A power supply kit. We've already had an extensive look externally and inside the device, seen the benefit of PFFB for load invariance as well as discussed a couple of the issues I ran into (inverted polarity and the ground noise with 2 amps connected to one battery).

This time in Part II, let's proceed deeper into the measurements to explore the amount of power this little amplifier can provide, some details on distortion characteristics, and as usual, ending off with subjective impressions and summary of the product.

Part I: Fosi Audio V3 Mono Amp; Class D + PFFB, TI TPA3255 - Retail box with single 48V/10A power supply and filter. [With initial measurements.]

Over the last few months, I've been hearing a lot about this Fosi Audio Mono V3 (~US$140) amplifier which is typically sold as an individual unit with 48V/5A power supply, or as dual amps with 48V/10A supply, DC filter, and splitter cable (currently ~US$280).

I have already seen a number of reviews and YouTube videos typically with the pre-release product supplied by the company; honestly guys, many of the reviews seem superficial with essentially "Trust me, bro!" opinions rather than presentation of facts. For this review, let me grab the 2 amps + single 48V/10A kit from the Amazon retail pipeline to have a look at the final product. This review is not sponsored by Fosi Audio. With measurements, I believe this would be as bias-free as a review can be.

As you might already be aware, this inexpensive amplifier represents an evolution of their TI TPA3255 Class D "chip amp" product line. The company incorporated community feedback and developed this as a monoblock design (through Kickstarter funding, as usual due diligence needed when participating in crowd-funding) with no volume control so as to optimize resolution, accepts true balanced (XLR/TRS) input, and also incorporates Post-Filter Feedback (PFFB) to lower output impedance (increase damping factor) for load independence.

The company publishes a power rating of 240W into 4Ω, 1% THD; 120W into 8Ω. That should be more than enough for most reasonably efficient speakers of normal load, in normal smallish listening rooms.

Let's take a good look...

Part II: Topping PA5 Mk II Plus (PA5II+) Class D amplifier review. Power, Distortion, the Subjective and on Hi-Res amplification.

I mentioned previously that this is a very unobtrusive amp. With the shipped plastic protector off, notice the low contrast of the lettering with the black front makes it even less obtrusive! This was why I left the plastic protector on to take the photos last time to better show the labels for the switches.

I introduced the Topping PA5 Mk II Plus last time in Part I with some initial measurements. This time let's keep going as we explore the power capabilities of this little audio amplifier, examine playback fidelity, and discuss a bit of the subjective performance.

Unless otherwise specified, these measurements were done with the amplifier connected to standard 4Ω and 8Ω power resistors as load, both channels driven, 20Hz-20kHz bandwidth for distortion measurements, unweighted. The Linear Audio AutoRanger allowed automatic gain/attenuation to keep the signal from getting too "hot". Signal from the AutoRanger is fed to the prototype Cosmos Scaler as a preamp for the E1DA Cosmos ADC operating in mono mode. High resolution signal generator DAC is the SMSL DO100 connected to Intona USB isolator. No special cabling, the 3' female XLR-to-TRS balanced cable was just something decent and generic like this, likewise generic RCA was totally fine. Seriously audiophiles, that's all we need for hi-fi sound quality.

Let's get to it!

Part I: Topping PA5 Mk II Plus (PA5II+) Class D amplifier review. (And RME ADI-2 Remote, "cultural pressure" for subjectivist audiophile reviews to include measurements?)

Over the last few months, I've been exploring the performance of the TI TPA3255 Class D chip amps including the AIYIMA A08 Pro, Fosi Audio TB10D, and AOSHIDA A7. Overall, we've seen very good results from these little amplifiers and I think they represent a level of low-distortion performance at a price point that is very attractive to many hi-fi hobbyists.

Depending on the power supply mated to the amplifier, measurements have been showing low output impedance up to 10kHz typically (<0.2Ω up to 10kHz), something like 80+W into 4Ω with less than 0.1% THD+N, and a -80dB Triple-Tone TD+N result at 1W into 4Ω which is excellent considering the prices of these little amps typically at less than US$150 depending on the features you want like Bluetooth input, VU meter, etc.!

Given the track record of these TI devices so far, this time, let's look at another chip amp which is based on an undisclosed part, not the TPA3255, although I can confirm it is a TI TPA chip. In my discussions with John Yang at Topping, the intent is to allow audiophiles to judge the product based on sound quality merits rather than focus too much on exactly which Class D part was used since the design around the chip is very important. Fair enough, and that's exactly what we aim to do here anyways since even with the previous TPA3255 amps reviewed, there were objective differences to find even if subjectively, differences might not be as noticeable.

I bought this Topping PA5 Mk II Plus (which I'll abbreviate as PA5II+ for simplicity) myself from Amazon, currently around US$325 with the intent to use in my own system. Since I'm interested in "high-fidelity" (not merely "euphonia"), I was interested to see how well this would compete with the DIY Hypex nCore NC252MP we measured a few years back. I like the feature set that it offers. On paper, it should provide the power I need and if the hi-fidelity performance is excellent, it could certainly be a listening "reference" here even though to be honest, I still love the Hypex's capabilities and would have no issue with enjoying the music from the inexpensive TPA3255 devices either.

REVIEW / MEASUREMENTS: AIYIMA A08 PRO - TI TPA3255 Class D amp with AAC/LDAC/AptX Bluetooth input. On "giant killers" and "CHEAP" amps. Goodbye TIDAL MQA.

Over the last while it has been interesting checking out some TI TPA3255 "PurePath" chip Class D audio amplifiers such as the Fosi Audio TB10D [Upgraded] and AOSHIDA A7.

As you can see in the image above, I've got another one to put on the test bench for a look and listen - the AIYIMA A08 PRO (currently <US$130). Depending who you read/listen/watch, you'll see supporters who like the amp, sometimes calling it a "giant killer" of sorts, such as this blog post, or there are detractors like Andrew Robinson who seem to think these kinds of amps are only good in the nearfield and below 60dB SPL (see from 10:30). We'll talk about this below. :-)

As usual, let's start with a peek at what you get for a low price...

MEASUREMENTS: Fosi Audio TB10D [Upgraded Version] stereo amplifier (TI TPA3255 Class D). Ethernet is inherently "isolated".

 

Not much time this week to play with the toys as I'll be heading off on vacation for a few weeks. However, I did receive the Fosi Audio TB10D [Updated Version] (<US$80) above recently that I wanted to use as an inexpensive "utility" amplifier for various measurements and experiments. It's also based on the TI TPA3255 Class D chip amplifier; same as the AOSHIDA A7 recently reviewed.

As you can see in the unboxed picture above, there are no frills, just the amplifier and a 32V/5A power supply (same specs as AOSHIDA).

This is the "Updated Version" with improvements as discussed by the Cheap Audio Man back in late 2022. Presumably this update was released around September or October 2022. I see ASR measured this amplifier in September 2022 - not sure which version that was. I purchased this amp from the usual retail channels.

Due to the time constraints, I'll focus more on "core" measurements and compare especially to the AOSHIDA.

REVIEW/MEASUREMENTS: AOSHIDA A7 Class D TI TPA3255 amplifier. Good sound. Good power. Economical.

Above, you see the small AOSHIDA A7 Class D amplifier which we'll go in depth with in this post. It's inexpensive and can be purchased for less than US$150 these days. This design is also sold as the Douk Audio H7 with a different color scheme, presumably the innards must be very similar if not identical. I preferred the look of the black AOSHIDA version with orange-ringed VU meter. I purchased this amplifier through the usual retail channels.

Over the years, it has been good to see the evolution of Class D designs and the inexpensive "chip" amplifiers. Internally, this is based on the TI TPA3255 "PurePath" chip (released in 2016) rated to provide up to 315Wpc into 4Ω stereo but at 10% THD when provided with adequate power (data sheet max is 53.5V). Notice the italics to emphasize that these numbers must be put into context. For audiophiles who want lower distortion in their amps (like <1% THD), we would be looking at much more conservative power figures than that 300+W being promoted for these amps.

(The chip also has a mono configuration that's spec'ed at up to 600W into 2Ω which would not apply for this review.)

MEASUREMENTS: S.M.S.L. A6 as amplifier [ICEpower 50ASX2(SE) Class D module]. (And DAC output - AKM AK4452 AMPT.)

Over the years, there have been devices I've been meaning to measure but one thing or another got in the way. This SMSL A6 amplifier was something I discussed here on the blog back in 2017 (a subjective review and measurements of DAC output). Over the years, this device has been happily amplifying signals for my dad's Klipsch Forté which is quite a sensitive speaker of 96dB SPL/m/2.83V; certainly by now it is very much "burned in". ;-)

I wanted to measure this device as an amplifier out of interest, knowing that inside this is the Bang & Olufsen ICEpower 50ASX2(SE) Class D module. While the datasheet for this amplifier module is already very detailed, there's nothing like measuring oneself!

This ICEpower module is rated at 2x47W into 4Ω, both channels driven to 1% THD+N. The power rating halves to 25W/channel into 8Ω. Within the ICEpower ASX series, there is also the 250ASX2 that will supply up to 250W/channel into 4Ω, and 125W/channel to 8Ω if you need more power.

The nice thing about this Class D module is that it's inexpensive and easily available for hobbyists such as through PartsExpress (current price US$118), sometimes through Amazon as well. You could buy one of these and get a simple case such as this Ghent Audio one and assemble it for yourself quickly.

MEASUREMENTS: S.M.S.L. SA300 - Infineon MERUS-based Class D desktop amplifier. (Screwed up New York Times - Wirecutter/Butterworth measurements/review?! And Klipsch on TIM.)

"BAS" on screen indicates I'm using the bass-boost EQ here.

Today, let's have a look at the little SMSL SA300 desktop amplifier I'm showing above sitting beside the Topping DX3 Pro V2 DAC (previously measured and reviewed here).

As mentioned previously, I found myself in the position of needing to update my computer workstation desktop speaker system. I figured, instead of staying with powered/active speakers, since I do have a few bookshelf speakers around the home, why not try some passives on the desktop as well?

While active speakers are great in that the built-in amplifiers and transducers can be well-matched and optimized, the ability to "mix-n-match" passive speakers while opening up the potential to upgrade amplifiers I think is fun for the hobbyist. As such, I found myself drawn to getting a small low-power Class D amplifier like this.

Since the amplifier will likely be left on 24/7, I wanted something that's highly efficient but provides adequate power. This SMSL device internally is powered by the Infineon Technologies MERUS MA12070 Class D amplifier which uses their "multi-level" modulation such that the switching output can have half-voltage levels which adds an extra level of control and power savings. The device is rated to provide up to 2x30W continuous into 8Ω or 2x80W into 4Ω but realize this is with 10% THD+N. What will be more interesting to me is how much power is available into something like 4Ω with ≤0.1% THD+N, and the noise this switching device produces. Let's see if this amp lives up to hopes of "high-fidelity" playback...

MEASUREMENTS: Hypex nCore NC252MP Amplifier (+ Subjective opinions around objective testing, and CES2020)

Alright, you knew this was coming from the post last week with assembly details for this amp.

As discussed, this is an easily assembled single-board OEM Class D stereo amplifier rated at 150Wrms into 8Ω, 250W into 4Ω, and 180W into 2Ω. The enclosure comes from Ghent Audio. The amplifier is based on the Hypex nCore "phase shift controlled self-oscillating loop" design.

Let's run this box through my usual MOAR testbench as previously described and see what kind of data we get. In general for these tests, the signal path for measurements looks like this:

RME ADI-2 Pro FS AKM DAC (signal generator) --> XLR --> Douk/Nobsound NS-05P passive attenuator --> XLR --> Hypex NC252MP amplifier --> Test leads --> BNC unbalanced input of Linear Audio Autoranger MK II --> Balanced TRS/XLR --> RME ADI-2 Pro ADC --> USB --> Surface Pro 3 laptop

I'll also have some oscilloscope measurements where the test leads will be directed towards the oscilloscope instead of Autoranger and RME ADI-2 Pro.

MEASUREMENTS: Yeeco TI TPA3116 Class D Amplifier (aka Nobsound NS-01G, Douk Audio F900S, Mogu F900S)

As I posted back in June of this year, we can get inexpensive little amplifiers these days based on Class D chips such as the TI TPA3116D2 (first released in 2012) which is what is inside the device here:

Yeeco TPA3116 amp being probed... Notice that input is through the AUX phono jack in front from the RME DAC.

As you can see, I have a "Yeeco" branded device but these are produced in China and will come in a number of brands like the Nobsound NS-01G from Douk Audio, and other names like Fac"Mogu" discussed in this review and here's Z Review with an older version.

I mentioned in the previous post that once I have the amplifier measurement rig going I was going to have a look at the output from this little amplifier. I figure this would be a good device to start with using the MOAR amplifier procedure described last time.

So what does US$30 buy us in terms of sound quality in 2019?!