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.

Notes on DAC DSD (1-bit PDM) measurements going forward...

In the early 2000's, we witnessed the battle over hi-res audio in the form of SACD vs. DVD-A. SACD, the brainchild of Sony, utilized a 1-bit Pulse Density Modulation (PDM) method they called DSD (an advertising term) whereas DVD-A had the ability to store up to 24-bit, 192kHz Pulse Code Modulated (PCM) digital audio data (multichannel up to 24/96).

From the beginning, there were concerns about this push towards 1-bit systems into the consumer space along with claims that 1-bit PDM should form some kind of archival foundation for music. There were critics include Lipshitz and Vanderkooy - see their paper "Why Professional 1-Bit Sigma-Delta Conversion is a Bad Idea" from the September 2000 AES. And the next year in May 2001, they followed up with "Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality Applications". Even Bob Stuart chimed in on the unsuitability of DSD for "high-resolution audio" back in 2004. This is no surprise since Meridian was firmly with DVD-A including developing the MLP compression system which subsequently has been licensed by Dolby and renamed TrueHD; it looks like Dolby and Meridian had an arrangement dating back even to 1998.

These concerns around fidelity and the unsuitability of 1-bit PDM as an editable format in audio production are why in the professional world, we see audio recorded and edited in 24/352.8 "DXD" and Sony's own "DSD-Wide" (8-bit/2.8MHz) instead of DSD64/1-bit "DSD-Narrow".

While this was playing out in the academic/professional arena, the advertising industry including the "mainstream audiophile media" championed DSD and published all kinds of flowery words suggesting how it sounded "more natural", or "analogue-like" compared to PCM. While I don't think we can put an exact date on when DVD-Audio officially died as a viable commercial product, I think by 2005 it was quite clear that hi-res physical formats were not going to be mainstream and DVD-A did not have the number of titles available compared to SACD. My sense is that the hybrid-SACD feature with both DSD and CD-compatible layers was a major differentiating factor that has resulted in still a trickle of SACDs released these days.

I'm bring this stuff up now as an extension to the discussions around SoX-DSD and the Philips Test SACD articles last year during my series on the Topping D90SE review because I've been thinking about how best to standardize the DSD test signals I use when testing. Different DACs tend to handle DSD playback differently and I wanted to make sure that my test signal parameters are at least somewhat in line with the music encoded on an SACD or maybe DSD128 download these days.

MUSINGS: The hunt for -150dB THD with the Victor's 1kHz Oscillator; A look at Paul K.'s Multitone Loopback Analyzer; And the pinnacle of audio streamer pricing? The Wadax Atlantis Reference Server. (And REW IMD vs. Level Step!)

I like a good challenge ;-). A few weeks ago, in my post on the E1DA Cosmos APU, in the comments, MG discussed achieving THD -155dB on the Victor's Oscillator! In my original post, I showed a picture of -141dB. Subsequently, I then fiddled around with the set-up and achieved around -148dB.

Well, on one of my lazy afternoons, I thought I might as well give this another try. The aim - at least THD of -150dB. So I packed up some parts I needed and moved it into the quietest room (electrically and acoustically) in my house. Bits and pieces laid out on my ottoman where I place drinks on late night listening sessions. ;-)

Clearly this would have to be run off battery power to remove any mains hum. I went with my trusty RME ADI-2 Pro FS ADC, powered by a 12V/8300mAh TalentCell lithium battery pack for convenience in case I needed to fool around with input voltage settings. The E1DA Cosmos APU was powered with a 5V battery pack.

A Look at ADC Noise Limits and Distortion - Or "How much difference does the Cosmos APU make?" And a look at 2-channel Room EQ Wizard measurements!

I received a few questions as a follow-up to last week's post about the E1DA Cosmos APU basically around the question: "When do I need a pre-amp/notch filter like that if I have a high resolution ADC?"

That's a great question! Let's spend some time looking into this...

Now, the first thing to be mindful of is that our DACs and ADCs are not perfectly linear devices, nor have limitless low-noise performance of course. This is why we measure the limits of DACs to gauge the extent of "accuracy". And ADCs likewise have limits as well to their intrinsic noise level and potential for distortion. As we approach the limit of the ADC's performance, it will start introducing its own characteristics into the captured signal which could look like noise anomalies as well as harmonics - like DACs, there is an ADC THD+N.

In this post, let's run some practical "experiments" of sorts using the Cosmos ADC and RME ADI-2 Pro FS to examine these ADC limits when measuring DAC dynamic range and THD+N/SINAD with and without the aid of the Cosmos APU.

MEASUREMENTS: DSD Testing with SoX-DSD Signals Part II (RME ADI-2 Pro FS R Black Edition, DSD Direct, Filter @ 50/150kHz) [Updated with 44.1kHz PCM --> DSD.]

 

Okay guys and gals, a rare "mid-week" update on DSD testing, a "Part II" follow-up to the previous article.

As I mentioned as an update in that article, I have a suspicion that the Topping DX3 Pro might not be using "DSD Direct" in its playback. However, I do have the RME ADI-2 Pro FS R Black Edition here as well. As you might know, I've been using the RME line of ADC/DACs for awhile now. These are certainly some very well thought out and high performance units with a ton of customization options.

Two of these options are shown in the screen in the picture above - "DSD Direct" and "DSD Filter". The "DSD Direct" is either OFF/ON, and "DSD Filter" either 50kHz/150kHz and is only activated when "DSD Direct" is ON, in recognition of course that DSD noise shaping does create significant ultrasonic content that in general probably should be filtered out; how much filtering is up to you.

MEASUREMENTS: RME ADI-2 Pro FS R Black Edition as DAC.

 

Well friends, it's time to publish some measurements of my new RME ADI-2 Pro FS R Black Edition ("FS R BE") unit as DAC. For background, refer to the Preview from August and a couple weeks back, I had published results discussing the ADC function.

As you might be aware, since 2018, I've been using the older RME ADI-2 Pro FS ("Pro FS") for ADC and DAC duties in my measurements. It has performed like a champ and in fact, given that the ADC function is almost identical between the two units, there's certainly no reason to retire the "Pro FS" from measurement duties.

What we know is that as a DAC, the "FS R BE" should perform better than the "Pro FS" due to the fact that the internal AKM chip has been upgraded to the AK4493 from the previous AK4490. On paper, this represents a +5dB improvement in SNR and +1dB improvement in THD+N so we're not looking at Earth-shattering differences in specs numbers. Let's see if we're able to measure these differences on the test bench and identify any other changes to the DAC's performance along the way...

MEASUREMENTS: RME ADI-2 Pro FS R Black Edition as ADC.

About a month ago, I posted this preview of the RME ADI-2 Pro FS R Black Edition AD/DA converter. It has been a wonderful month of simply listening to this device without a care around performing measurements. For listening, I have it set up as per the image in my sound room with the Raspberry Pi "Touch" running RoPieee previously discussed.

So far, from a subjective perspective, it has been a joy to listen to music with this machine.

Alas, as a "more objective" audiophile, it came time to have a look at the performance for this device to check if I'm missing any significant limitations. Over the years, I've discussed limitations to human hearing as well as the idea that many of our audio electronics these days have surpassed human auditory perception such that while measurements of DACs or amplifiers can show limitations, often these are beyond the resolution thresholds of human hearing/perception. Remember that while not all measurable anomalies need to be chased after when the goal is simply to be able to enjoy music, technical "ideals" are useful for devices one may want to use as a "reference".

So to start, today let's just focus on the ADC side of this RME device. Remember that the RME ADI-2 Pro FS R Black Edition (again, let me just call it the "FS R BE" for short) is an evolutionary step from the ADI-2 Pro FS ("Pro FS") that I started using 2 years ago. Consider this article as building on some of what we already know about the Pro FS as an ADC from 2018 with requisite repeated tests comparing the two machines and using today's software.

PREVIEW: RME ADI-2 Pro FS R Black Edition AD/DA Converter

Look what showed up at my door (finally!) the other day. This is the latest hardware update to the RME ADI-2 Pro line of converters, the RME ADI-2 Pro FS R "Black Edition" - quite the mouthful! Let's just use "FS R BE" for the rest of this article for short in reference to the name.

Currently, the street price is around US$2,000.

Back in mid January, RME debuted this latest iteration of the ADI-2 Pro at NAMM 2020. Since 2018, I have been in contact with Matthias Carstens (co-founder of RME) off and on about the ADI-2 Pro FS that I have been using for measurements on this blog. Shortly after NAMM, I contacted Matthias about getting an upgrade as I could use two of these ADI-2 Pro devices - one for the soundroom and another for my test bench - when the company starts shipping these.

MEASUREMENTS: "Noisy" Switching Power Supplies vs. Lithium Battery Packs (12V battery with RME ADI-2 Pro FS & Topping D10 DAC results)

Perhaps we don't think about it much or give it enough credit. I believe one of the advances in the last few decades that has provided the foundation for technological progress we enjoy today is the lithium ion battery. Li batteries were commercially released in 1991 and since then, thanks to the energy density available, combined with increasingly efficient electronics, all kinds of things these days can run off battery power - cars being the poster-child of this advancement...

A few weeks ago, I showed the little Class-D amplifier system running off a battery. How about we try out my RME ADI-2 Pro FS on batteries:

What you see here is the device connected to the Talentcell 6000mAh 12V Li-Ion battery pack. Since the RME ADC has become my standard for measurements in the last year, I have wanted to make it "portable". Talentcell makes an even smaller 3000mAh 12V battery which would work fine. While a little larger in size and weight, the 6000mAh unit is still lightweight and will be able to power the ADC/DAC for >5 hours - enough for any recording and measurement I would want to do in a single sitting.

MEASUREMENTS: RME ADI-2 Pro FS as DAC (Part II - frequency response, noise, distortion and jitter)

As we saw previously, the RME ADI-2 Pro FS is based on the AKM AK4490 DAC chip and provides a good assortment of features like filter settings. We've seen that the headphone output amplifier provides plenty of power and the beginnings of what looks like a highly accurate DAC; consistent with my subjective opinion.

Time for part 2 of the objective evaluation today as we continue to explore the DAC output quality.

MEASUREMENTS: RME ADI-2 Pro FS as DAC (Part I - output levels & digital filter settings)

After having explored a couple weeks back the ADC capabilities of the RME ADI-2 Pro FS, for this installment, let's start with evaluating the DAC output quality of the device and in the process examine the objective fidelity with audio playback.

Remember, with that previous article, I had already discussed my subjective opinions based on listening sessions. My opinion has not changed in the last number of weeks as I'm still very much enjoying the sound I hear hooked up to my main system. Subjectively, the output sounds very clean, has a neutral tonality and low noise level very much like the Oppo UDP-205 and other high quality DACs. As usual, it will be interesting to compare measured results among the different devices I put through the test bench.

But before we do that... Let's start with the basics and some of the "microscopic" measurements I usually begin with - things like output levels, filter settings, etc...

MEASUREMENTS: RME ADI-2 Pro FS ADC performance and as measurement hardware.

I discussed the features and some listening impressions of the RME ADI-2 Pro FS ADC/DAC a couple weeks ago. As I noted at that time, my main aim in owning this device is for the purpose of using it as an ADC for measurements here on the blog going forward.

For the purpose of measurements, we want a tool that can allow us to obtain reproducible results and good accuracy. Over the years, I've achieved reproducible results with consistently minimal inter-test variation by standardizing the way I run most measurements with the digital sources, cables, standard procedures, and types of tests I run. What I want is better accuracy - an ADC that has lower noise floor for improved resolution, doesn't add as much of its own distortions, have higher timing accuracy (eg. for jitter tests), and perhaps more features to expand the measurement quality (eg. higher sample rate to capture impulse responses more accurately, and can handle wider input levels for the range of devices tested).

Given that this is the priority, instead of measurements of DAC performance first, let's get straight to describing the characteristics of and using the ADI-2 Pro as a measurement tool which means we'll need to get a taste of how well the analogue-to-digital capability performs. Let's compare the results I'm getting from the RME to my previous measurement ADC device over the last couple years, the Focusrite Forte for a sense of the changes in resolution I can expect from the new upgrade.

PREVIEW: RME ADI-2 Pro FS AD/DA Converter

I. Prologue

For those who have followed along on the blog, you may recall that this blog started with some arguments I had with folks on an audiophile forum around the audibility of high bitrate MP3. Back in those days (err... late 2012), there were all kinds of claims made by quite a few hobbyists that they could "easily" differentiate lossless FLAC from 320kbps MP3. I'm sure there are still many in the audiophile forums who hold this view although I think things have softened about the magnitude of differentiability (I think this shift has changed with high-res audio as well).

That disagreement was enough to push me to put out a blind test, to start looking into what I could do to help further my own understanding and awareness around audio hardware. The articles on this blog basically have been the culmination of that pursuit in hopes that the ideas and tests have been useful for others also on this journey looking for some clarity, typically found with more objective analysis.

Objective testing requires disciplined procedures and tools. Methods to reduce variables so that we can have reasonable "apples-to-apples" comparisons and reduce or eliminate psychological biases when we make decisions and search out facts beyond opinions colored by idiosyncratic preferences. Whether it's using an ABX tool, asking a partner/spouse/family/friend/neighbor to change something without our knowledge when listening, or measurement devices - letting the tool demonstrate changes - I believe we can find answers to uncertainties or prove claims. I personally believe objective testing is not only something "nice to have" with reviews, but an essential part of developing insight into the devices being tested and our own perceptual and cognitive limitations.

That's a long intro which brings us to today's preview of a new tool. :-)

When it comes to using an ADC for measurements, over the years, I've gradually upgraded starting with my old Creative E-MU 0404USB from 2012, to the Focusrite Forte in 2016, and now, let's start with a look and listen to the RME ADI-2 Pro FS ADC/DAC. The aim has been that each step brings with it more accuracy for the measurements and this third iteration of the measurement hardware should bring with it opportunities to explore further and continue the process of finding clarity in a hobby that for too long IMO has been filled just with mere opinions - or even worse perpetuation of myths. (Remember, nothing wrong with opinions... But let's make sure it's grounded in objectivity!)