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!

Power

So, how many volts / watts can this little amp put out?

Using my usual 0.1% THD+N threshold, this amp is capable of 102W into a 4Ω load with both channels driven. If we put the threshold at 1% THD+N, yes it's capable of >120W both channels driven (Topping puts the spec at 125W).

Here's a look using TRS balanced input:

The only difference is that the THD+N is a little lower. Otherwise as expected, there's no significant change in output power limit.

Let's use an 8Ω load (TRS input):

Using the 0.1% THD+N threshold, we get 56W output into 8Ω which increases to about 65W at 1% THD+N (consistent with Topping's spec).

Output level linearity is excellent with only +/-0.03dB deviation from expected through the 120dB range! We can see the clipping into 0dBFS.

Single-Tone Distortion

Already from the power graphs above, we have a sense that this amp is capable of better than -100dB THD+N results depending on the output level. Let's have a look at some 1kHz FFTs; we'll examine both left and right channels, RCA and TRS inputs starting at 2V into 4Ω (1W):

At this 1W output level, while the THD+N isn't that different between single-ended and balanced input, we can see that with a balanced signal, we've cleaned up the 60Hz mains hum nicely. The amp is approaching -100dB on the THD+N at this 2V output level for both RCA and TRS/balanced, excellent for any amplifier at basically any price.

I'm a "first watt is the most important" guy which is why I've focused mostly on 2V into 4Ω as the core of my resolution testing with amps. IMO it's those little low-voltage "microdynamic" nuances that I find most interesting about hi-fi and typically when listening to music, amps are asked to perform at <1W most of the time. Transients are short-lived and unless egregious, distortions at these higher power levels are typically not audible (Benchmark discusses this as well). If an amp like this is able to convey better-than-CD resolution (at best 16-bit audio has 6.02*16 bits + 1.76 dB = 98dB dynamic range) all within 1W into a low 4Ω load, I'm certainly impressed!

Audio Science Review standardizes their THD+N/SINAD at 5W (4.47V into 4Ω) which is fine as well, this puts a little more demand on the amp and voltage-wise would be a 7dB gain. This will push the SINAD higher (lower THD+N). Let's see what I get at 5W for comparison:

As expected, a nice jump in SINAD to 103dB with single-ended RCA, and 104dB balanced. (This correlates well to ASR's results of the P5AII with 102dB RCA, 105dB TRS). Again, I would say the main difference is the resistance to mains noise with balanced input. Overall noise level doesn't change too much hence the THD+N doesn't drop much between RCA and TRS. It's this noise level component that drops more when testing DACs between balanced and RCA out.

Beyond 1kHz, let's do a sweep across the audible spectrum to make sure there are no untoward anomalies. Here's the graph at 5W using the balanced input:

Nothing scary. Above 2kHz, the harmonic distortions rise but THD+N doesn't get any worse than -97dB. For the most part, the 3rd harmonic predominates with some variability between 2-6kHz.

For fun, let's have a look at 5W into 8Ω with balanced input:

About -105dB THD+N. All else being equal, we typically see slightly better distortion figures into the higher impedance load.

Before leaving this section, let's have a look at the FFT with even higher power - let's try 10Vrms into 4Ω or 25W continuous, both channels driven of course using RCA and TRS inputs:

As expected, still nice and clean since the clipping point is further up at 100W (~20Vrms).

Multi-Tone Distortion

Let's get into some multi-tone testing which feeds more complex test signals for the amplifier to negotiate. Here's a panel of standard dual-tone intermodulation signals at 2V (1W) and 10V (25W) into 4Ω:

This intermodulation panel of results is what I also did with the Hypex nCore NC252MP back in 2020 so we can compare. On the whole it's a toss-up between the two. The Hypex does a better job on the SMPTE signal and at higher power 10V CCIF/ITU-R presumably in part because it is a more powerful amplifier capable of 200+W into 4Ω. The Topping has better 2V CCIF/ITU-R with much lower "d2L" 1kHz intermodulation tone (more audibly significant than the high-frequency sidebands) and performed really well on the Linkwitz signal, based on a test that the late Siegfried Linkwitz discussed for his amp testing for IM and zero-crossing anomalies, that spreads the intermodulation tones across the audible spectrum.

Next, we can look at the TIM ("Transient InterModulation") test signal. Again, let's stick with just the TRS input and at 2V and 10V:

24/192 signal, 96kHz bandwidth.

I don't see many testers running this kind of measurement these days. The test is interesting I think because it can show anomalies in reproducing transients. The PA5II+ performed well. Have a look at the Hypex NC252MP which is almost perfect into 10V. However a -113dB 10V result with the PA5II+ is absolutely nothing to worry about.

Next, the Decade Multitone 32 at 2V average into 4Ω:

Beautiful. Notice that I have the peak values in red. It takes about 2 minutes to grab the 32 average result which means that in all that time with continuous output, there was no spurious noise captured beyond that red zone. To make this more challenging, there's a fridge nearby that turned on while testing and since I was doing this in my basement, the clothes washer and dryer were also running in the laundry room just around the corner. I know some audiophiles freak out about "bad power" causing problems. Unless really bad, this amp at least seems to be able to handle it. :-)

Again, we see the 60Hz hum with some harmonics using unbalanced RCA input. Otherwise we're seeing at least 100dB range between the signal peak and distortion/noise floor across audible spectrum with balanced input.

Okay, now time for the Triple-Tone TD+N (48/960/5472Hz) test which is what I've been using over the years as a single number for resolution comparison among amplifiers:

Beautiful. This is the kind of FFT one might expect from a DAC rather than amplifier pushing current into 4Ω. Notice the difference between this amplifier as compared to a typical inexpensive TI TPA3255 device like say the AIYIMA A08 PRO which is already not bad at all:

Subjective Evaluation

So with all these graphs, numbers, and technical discussions, you must be wondering - "How does this thing sound?"

Over a few evenings, I listened to the Sabaj A20d 2022 DAC (XLR to TRS) using its volume control connected to the Topping PA5II+ then to my Paradigm Reference Signature S8 as the most direct playback from this amp. Raspberry Pi streamer used to supply music to the Sabaj DAC. The first thing I noticed was that without sound playing, this amp is dead silent. No hiss, hum, noise, interference, nothing; "black background" as some might be apt to describe this. Once I play music, within the power envelope of this amplifier, it simply delivers what I would consider as transparent sound.

Yes, we can listen to individual albums and opine on this or that characteristic about the sound quality, as is typical of most subjective-only reviews:

The Rolling Stones' new Hackney Diamonds (2023, DR6) is delivered with the classic rock and blues style of Mick, Keith, and Ronnie we're familiar with for decades now which I think will make many rock fans happy. To me this is certainly a very fine latter-day Stones album.

The tracks "Angry", "Driving Me Too Hard" and "Whole Wide World" are my favorites on this album thus far. I might pick up a couple others with repeated listening. With Jagger at 80 now, Richards 79, and Wood at 76, not sure how many more new tunes will be coming from these guys so make sure to enjoy the creative output from these boys; this could be the "bookend". Good stuff overall!

Oh yeah, the bluesy track "Sweet Sounds of Heaven" with Lady Gaga mainly as backing vocals is pretty good as well with a nice building up of intensity as it ends. Listen for all kinds of guests in these songs like Elton John, Stevie Wonder, and Paul McCartney. The late Charlie Watts played on "Mess It Up" and "Live By The Sword".

The PA5II+ had no issues playing these kinds of recordings. Nothing here particularly "high fidelity" (DR6 folks!) that would challenge anything a decent amplifier can negotiate.

Roger Waters - Dark Side Of The Moon Redux (2023, DR9). Staying with some "classic" artists, Roger Waters is now 80 years old as well. And 50 years since the release of the first Dark Side, we have a new reimagined rework of those 10 original songs by Waters. Slower. More introspective. In many ways more organic. More emotional. Less technically flashy. An old dog looking back at his old tricks. It sets the scene with Waters the narrator in his first sentence: "The memories of a man in his old age, are the deeds of a man in his prime..." (from "Free Fall").

I actually quite like this album as a companion piece to the original. Tracks like "Time" take on a new foreboding loneliness as the aged protagonist contemplates the passing of the years, and the end - leading to "The Great Gig In The Sky".

There's more in this album for an audiophile amplifier to show off. Incidental birdsongs feature throughout the album as well as some interestingly placed effects like that plane flying overhead on "The Great Gig" which the PA5II+ played with a nice dimensionality - just close your eyes and imagine. Also portions of "Any Colour You Like" have nice spatial effects which sounded great through the amp and speakers.

By the way, I love the remake of "Money" here. Sung in deep raspy growling devilish vocals, this is devious stuff. "How much ya givin' away? Ahhhh... None."

And "I'm in the high-fidelity first-class traveling section / And I think I need a Learjet" should be the motto for some of the "High-End", high-priced, poor value audio salesmen like Synergistic Research's Ted Denney (if unfamiliar, have a look at this stuff). 🤪

This album might split Pink Floyd fans. I suspect it will also depend on how you feel about the numerous spoken vocals.

Alright, let's get back to the "sunnier side of life" with a flair of yesteryear. Laufey is an artist from Iceland and above we see the covers for her two studio albums - Everything I Know About Love (2022, DR8), and Bewitched (2023, DR8). On both albums, there's quite a bit of retro anachronistic romantic pop that probably could have populated the airwaves in the 1950s (although there's the occasional use of mild expletives like "damn"). The recording and production value is clearly from the 21st Century. [These albums are very "child friendly" compared to the coarsening and sexualization of language and imagery in pop music over the decades.]

Simply sweet tunes with a fair bit of sentimentality and melancholy around lost love at times. On Everything, check out "Valentine" for some really seriously old-skool nostalgia. On Bewitched, check out "Dreamer", "California and Me" with its Philharmonia Orchestra backing, the higher tempo "From The Start". 

Clean sounding, well produced female vocals which should sound very nice on an audiophile system; another option to Diana Krall or Norah Jones. :-) 

Ferry Corsten - Blueprint (2017, DR7). An interesting "progressive trance" album from this Dutch artist; electronica crossed with a voiceover stage-play reminiscent of Jeff Wayne's The War Of The Worlds. Sci-fi-inspired background story with elements of aliens, cybernetics, the misunderstood outcast geek, spiritual themes such as reincarnation, and even romance (a bit cheesy, but hey, it's fictional, fantasy, fun). There are bits here that also remind me of the movie Contact.

Like with the Rolling Stones release above, there's a limited edition audio BluRay with a 5.1 mix and Auro-3D version if you have a decoder. As expected, lots of interesting synthetic sounds, deep 20Hz bass on this one right from the start on "Reception" with lush synth strings, multi-layered vocals, dramatic choruses. The up-tempo synthpop "Your Face" and "Here We Are" are enjoyable, as is the upbeat instrumental "Venera (Vee's Theme)". The distant sirens in "Piece of You" sound great using ambiophonics and in multichannel. Like with Dark Side Redux, there's a fair amount of narration here.

[On a side note, Auro-3D encoding is a bit like HDCD or MQA in that it embeds metadata and content down in the lowest 6-8 bits of a 24-bit lossless stream such as a 5.1 24/96 DTS-HD Master Audio track on BluRay. Their position is that 18-bit audio is all we need - not unreasonable. With decoding, the base layer content is used to reconstruct the height layers towards something like 9.1 (which is 5.1 + 4 height channels).]

This album will provide a nice workout for your DAC, amp, and speakers. If you have it, do not skip out on using the subwoofer ("Something to Believe In", "Edge of the Sky"). Needless to say, the PA5II+ did a great job with this recording. Absolutely no complaints for bass reproduction, clean-sounding treble ("A World Beyond"), and tight transients.

Notice the JAS Hi-Res Audio logo on the box for this amp. Interesting to have a look at the definition of what constitutes "hi-res" in that link. Doesn't seem like that many hoops to jump through based on the summary. For example, is there anything about mandatory minimum dynamic range for the JAS?

Summary & Conclusions

So audiophile friends, are you looking for a high-fidelity, lower priced amplifier that's capable of a clean 100W into 4Ω and around 60W into 8Ω? Something that's capable of resolving better-than-16-bit resolution at 1W, and truly "hi-res", not just "hi-fi"? Well, you've got it here in the Topping PA5 Mk II Plus, currently priced around US$330.

Here's my AMOAR scoresheet with some "vital stats":

The score sheet above is with the TRS balanced input which would be the optimal way to use this amplifier. The only difference with RCA input would be a lesser Triple-Tone Distortion Factor which would still be excellent at almost -100dB.

Nice to have high Damping Factor in a Class D amp with an average >200x making this amp highly load-invariant. Not surprisingly, the -105dB TD+N score at 1W, 4Ω is the best that I have recorded over the years. For reference, in comparison, the Hypex nCore NC252MP with XLR input scored -91dB on this Triple-Tone Distortion test.

The 20V Power Factor implies 100W into 4Ω at <0.1% THD+N and a measured 56W into 8Ω shown in the data above, continuous, both channels driven. Of course the amp can supply a bit more power into 1% and 10% THD but distortion rises very quickly. I suspect for the vast majority of home users with reasonable "average" speaker sensitivities in smallish to medium rooms, this will not be a problem.

As an example, for myself, when I estimated how much power I need, I came up with about 70W into an 8Ω load but that's with extra headroom, going beyond my typical listening reference volume, and of course using highly uncompressed music, sitting at my sweet spot. So, the PA5II+ can supply 56W with <0.1% THD. How many dB difference is there between 70W and 56W? For an 8Ω load, the difference is 23.7Vrms for 70W vs. 21.2Vrms at 56W - that's only -0.97dB difference (use the online calculator). So, within the limits of the extra headroom I've applied to my estimate, I can be quite secure that I won't be missing that extra 1dB from my Paradigm Reference Signature S8 speakers (89dB/2.8V/m anechoic, typically +3dB to 92dB estimated in room) in my sound room which is approximately 14'x18'x8'.

I think as audiophiles, it's important that we keep the variables and understanding of these interactions in mind so that we can apply the knowledge to our hobby as wise and experienced practitioners of "high fidelity" audio. Knowledge can also help us be resilient from snake-oilish hype based on "bigger numbers" especially when we're dealing with logarithmic properties like the "dB" or wattage which is calculated by the square of voltage.

Energy efficiency is good for this Topping amp, to be expected as a Class D device. Typically when I'm listening to music at normal levels averaging 70-80dB SPL, the amplifier hangs out at around 9-10W.

Going forward, what else can we ask for in hi-fi amps quality-wise? Obviously there's nothing wrong with asking for more power. Maybe an amp with excellent resolution like the PA5II+ with better than -100dB THD+N by 1W into 4Ω, capable of clean 30Vrms <0.1% THD, with say +6dB higher gain. This would give us 112.5W into 8Ω and 225W into 4Ω, somewhere between the Benchmark AHB-2 and Hypex nCore NC252MP in stereo mode. I suppose the higher frequency distortion amount can be reduced such that the CCIF/ITU-R intermodulation test result looks better especially at the higher output levels. I suppose we could also ask for the frequency response to be "ruler flat" from 20Hz - 20kHz with smooth -0.5dB into 40kHz would be awesome. Keep damping factor >200x (4Ω) across the audible frequencies for "load invariance". Of course, still make sure to offer good reliability and price, say <US$500 for basic 2-channel amplification, since value is always important and access to quality for the masses is something I'd like to see. There's no place for pretentious elitism in hi-fi IMO, regardless of one's wealth, I think it's simply good to be wise with money when there are all kinds of other things we can spend it on! 😉

[The more powerful Topping PA7+ would be a candidate with many of the characteristics above.]

While certain audiophiles might find the idea ridiculous, or even repulsive, I think just like with DACs, there comes a time when devices at very reasonable prices simply become "perceptibly perfect" as defined by the limits of human hearing with the intent of "high-fidelity" transparency. With modern Class D amplifiers like the Topping PA5 Mk II Plus, I'm pretty sure we're darn close, if not already beyond for most use cases at home already. With the electronics becoming more and more "hi-res" capable, we are reminded that the most important hardware components are still the speakers/transducers and room.

Well done Topping for bringing the performance of Class D chip amp designs to the next level. To me, the ability to achieve dynamic range and frequency response beyond 16-bit CD resolution at 1W into 4Ω is a landmark of "Hi-Res" amplification. Whether we absolutely need this is similar to discussions we've had about the audibility of 24-bit audio (see here, here). Furthermore, I appreciate the unassuming appearance, 12V trigger, and both RCA and balanced inputs. A controlled blind listening test at typical listening levels (~75dB SPL average for pop/rock) with average sensitivity speakers (90+dB/2.8V/m in room) in a small/medium-sized room using this amp compared to other very-high-fidelity designs by Benchmark, Hypex, Purifi I think would be educational if anyone wanted to seriously compare! (Needless to say, we're not likely to see serious listening tests done by typical audiophile "slick" magazines these days.)

Hope you're enjoying the hi-fi music, dear audiophiles.

Time to check out the much anticipated "Taylor's Version" of 1989 (2014) this weekend in multichannel/Atmos! This album remains Taylor Swift's best selling album to date. BTW, the song "This Love" has excellent 3D envelopment when listened in ambiophonics with crosstalk cancellation.