A look IN the Audio Precision APx555 B-Series. Thoughts on price and value in audio products.

From our "RETRO-MEASURE" of a 1980's cassette tape player a couple weeks back, let's make a 180° turn, look at some photos, and chat about "state of the art" performance gear this week!

A reader awhile back had the need to do some hardware work on the Audio Precision APx555 B-Series machine and in the process, was able to take a few photos of the innards, sharing it with me. The B-Series audio analyzer is the latest and greatest audio measurement device from AP. It was announced in December 2018 and here's a nice review from 2019 in audioXpress.

I thank my friend for sharing the images and helping me to understand some of what I'm looking at here. :-) There are no schematics publicly available of course so my comments will be in broad strokes and I'll leave it to the engineers reading this to examine deeper - click on the images for a higher resolution view.

I don't think I've ever seen pictures of the inside of these AP machines online but obviously the Internet is a big place so perhaps I have missed them. There is actually a good reason why you're not likely to see the insides of something like the APx555 - it's a calibrated device. It costs US$30,000+ to buy one of these. You'll be breaking 2 seals if you crack it open, that will also break calibration confirmation, and voids warranty the moment it's tampered with.

I have been told that the calibration is complex, resulting in a 4-page set of readings across all kinds of signals and analyses. It's an expensive and time-intensive process with custom software and precise external instruments to get the job done. Few companies are allowed to do this and typically the machine will need to be shipped back to AP.

At this price point and with the technical know-how that's needed to get the job done, I don't think it's a stretch to say that small boutique audiophile manufacturers likely do not have access to one of these to use in their research and development.

The picture above was taken with the cover off looking from the rear of the machine. At the top of that image is the front panel where all the input/output connectors are located and you will find different options installed. Here's a front panel image from the AP website:

As you can see, the machine is modular and arranged in 2 "compartments", a top portion and a bottom portion. The top part is where the analogue stuff plugs in, the bottom portion typically for various additional digital modules like the "Advanced Digital I/O", "PDM", "Digital Serial I/O" (eg. I2S) and Bluetooth (SBC, AAC, full aptX codecs supported). They also have a HDMI+ARC module.

For completeness, here's the back panel:

This device needs to be connected to a computer through the USB Type B 2.0/3.0 interface (ASIO driver supported) where tests are run using the AP software. This makes the system very flexible in that the software can be updated easily and likewise you can upgrade the computer, monitor, etc. over time. The APx555 also has firmware upgradability.

The XLR and BNC connectors (bottom right) are the Advanced Master Clock module. The RS-232 ports are for auxiliary in/out controls and one labelled "Software Options" for the AP KeyBox dongle to run certain software versions.

If you want to be impressed by a thorough user's manual, you can register and download the manual here. It's a 750+ page document with not only instructions on the myriad uses of this product (including speaker acoustic measurements) but contains interesting tidbits on measurement standards and the meaning of some of these tests (Chapter 80 p. 525 onward particularly relevant). Page 735 is a great description of units of measurement and we see from p. 741 on an excellent glossary of terms/acronyms with concise definitions. Excellent resource even for hobbyists like myself!

Let's have a closer look inside and behind that front panel:

We can see a nice separation of the analogue input and output sections. Each section separated to left and right channels with replication of the circuitry. The board looks very clean. "Everything in its place, a place for everything" as one would expect for a state-of-the-art device. As a reminder, we're looking at just the top compartment with its multiple circuit board layers here.

If we look at the portion on the right, here's a closer examination of the analogue output section. This section includes the Analog High Performance Sine Generator, capable of 5Hz to 204.457kHz output with superior signal purity than the digital generator. There's analogue square wave generation (<2μs rise time) and low-distortion sine burst as well supported:

The vertical boards appear to be power stages with transistors on them. Unbalanced output can go up to 13.3Vrms, double that to 26.7Vrms balanced.

The upper-level board to the right might be the signal generator portion itself with trim pots for calibration. There's a DAC function that allows the playback of arbitrary signals (0.001Hz-80.1kHz according to the literature). Interestingly, the device also allows simultaneous DAC and analogue generator to feed different signals to the analogue outputs (p. 43 manual).

And to the left of the signal generator / analogue output in the labelled image above, we see the analogue input portion which contains the ADC chips:

A close-up of the front portion of this board:

For each channel we have a pair of ADCs: AKM AK5394A, and Analog Devices AD7760. The AK5394A is a delta-sigma device that can operate up to 192kHz without a rising noise floor above 20kHz (great for measurements). Compared to others, this is a relatively expensive ADC and power-hungry (I've read that it may require up to 1W). The AK5394A has been discontinued for awhile now so presumably AP bought up a bunch of these for their devices.

The AD7760 is a higher speed part that can perform conversion up to the 1MHz that the AP supports. Note that there is a resolution difference between the two chips so precision is highest up to 96kHz bandwidth (192kHz) and drops beyond that which is fine since we're talking about ultra-ultrasonic frequencies!

We can see a few relays probably for changing the impedance and the input board also has an "autoranging" feature for various input levels. Maximum voltage input of 160Vrms unbalanced, and 300Vrms balanced split across 11 ranges!

The APx555 incorporates a precise analogue notch filter for each input. This >100dB (!) filter removes the fundamental ("1st harmonic") leaving the residual signal to analyze with a specification of -120dB THD+N "typically". Presumably the large Xilinx and Cyclone FPGAs are part of the magic performing the analogue/digital signal integration and bandpass filtering. As per AP block diagram in Technical Note 124:

To the rear of the machine, we see what looks like a "computer" portion.

There's a SODIMM DDR3-1866 RAM stick (probably 4GB if it's a dual-sided board). There's a low-power CPU under the heatsink. Some FPGAs seen. Presumably all of this is to handle communications primarily through the USB-B port (the rectangular connector in middle-top of the picture). The machine runs its own OS, one could guess it's some type of Linux variant and likely explains the size of the firmware updates. A fan to keep the section cool.

A reader sent me a picture of the chip under that heatsink:

Looks like we have a Teledyne / QorIQ T1022 (PDF here) dual-core 1.4GHz processor, ~7-8W max, based on the e5500 RISC PowerPC architecture.

Just beside that computer/USB communications portion is where the power supply sits. The power supply is a custom unit, but looks similar to what one might find in a computer. Note there's another fan behind the power supply (removed in image):

Since moderate noise isn't a problem in a lab environment, these machines can be unpleasant if one is working from a quiet home environment I am told. I guess best to not have them running in your soundroom. :-) 

Here's the front section of the analogue signal generator section where we see relays galore! A number of them would be used to change output impedance for the generator for balanced and unbalanced output (40-600Ω range, mute, feature to run balanced XLR with only +/- connected and so on). We see some transistors on the vertical boards to drive the analogue outs.

My friend took a picture just underneath the signal generator board also:

Another Altera/Intel Cyclone V FPGA. Not sure what this is for. The use of all these FPGAs means a significant level of programmability and upgradability.

Looking at the lower compartment, here's the "Advanced Digital I/O" module that comes standard. You can see the circuitry for S/PDIF/AES. Trimmer pots for precise calibration of parameters like AES level, rise time and even optical TX jitter:

There's a metal plate that shields this underlayer from the top analogue in/out compartment. Optional boards are installed in the space over to the left of this image.

Looking at these pictures, this is obviously a "high tech" product filled with plenty of advanced know-how. Just look at the sheer number of parts needed to put this thing together and what would have clearly amounted to years of team efforts in research and development! Although we're just looking at the hardware here, let's not forget the years of software/firmware/FPGA development as well. The quality is described as top notch with really no professional competition in sight. ~US$30,000 is certainly not an astronomical price for a state-of-the-art machine like this. In fact, my friend tells me it's "worth every penny" for precise audio design work. He has in fact found that AP's published specs for this machine are at times conservative for the performance it's actually capable of.

Perhaps like me, while reading and looking at these innards, you might also be thinking about the high-priced audiophile products in magazines or see at the local dealers. These days, asking price for many audiophile products easily compete with the AP's "mere" $30,000. If we look inside audiophile "high end" electronics that cost $30,000, would we see similar levels of technology and would we admire the sheer amount of work needed to produce such a machine?

Looking around audiophile sites, we have source electronics like the Lampizator Pacific DAC "demanding" this kind of price - have a look at the circuit board here. Old-skool products like the Audio Note UK Jinro integrated amp for example also "demands" this kind of cash, check out the picture of the innards in Stereophile; is there enough in there to be worth $30G even with a very healthy markup?

Without even discussing the most expensive products in their lineup, how about these Nordost Odin Supreme Reference Power Cords for a mere US$16,800/2.5m. An absolute steal at half the price of one of these APx555B machines! (Maybe AP should consider these cables for even better performance? ;-)

HiFi Inside (ex-HiFi Shock) has a large collection of naked audio hardware pictures as well if you're into these kinds of photos BTW.

I know, tube DACs, amps, cables, AP audio analyzers serve different purposes so it's comparing "apples and oranges". Nonetheless, like many "high end" devices, the AP is a rather niche product as well and I'm sure they don't make too many every year such that you can say the company is able to lower the price per unit due to economy of scale. As tech products developed through engineering, I think there's something to be said about the intellectual ability and creativity required when we consider the intrinsic value of the electronics.

I hope this has been fun "audiophile geek porn" for the more-objective "hard core"!

--------------------

To end, I think this post gives us an opportunity to consider the idea of value in the technological products we buy.

As in all financial transactions, whether it's paying the guy mowing your lawn or buying investments, we are inevitably faced with finding the balance between "price" and "value". As Warren Buffett said: "Price is what you pay, value is what you get". Both will vary over time, although price tends to be the one that fluctuates more. Sentiment and demand are the foundations for supporting an actual transaction price; just because something is advertised at an MSRP means little unless a transaction has actually happened and settled at that number.

I think for most of us here, thinking about price isn't as interesting as considering the value of something. While there are different ways to think about this, it's probably useful to break the concept up into subtypes: absolute value, relative value, and perceived value.

Absolute value refers to the intrinsic abilities, unique features, workmanship/labour costs, and material costs of the product.

Relative value is determined by looking around at competitors and trying to uncover relative abilities/characteristics of a product within the arena of others. 

Perceived value is determined by the buyer him/herself and "Gotta have it!" emotional sentiments. The need for gratification of that desire drives demand.

For an expensive purchase, decision-making is typically complex, and we integrate all 3 definitions of "value". As a "more objective" audiophile, I typically tend to lean towards examining the "absolute value" of a device first. Product specifications, features, objective measurements and tests give me an idea about the intrinsic abilities of the product which I can then judge using the concept of high fidelity as the goal because sound quality is the "prime objective" in audiophilia, right? However, as human, I certainly will not deny myself the pleasures of owning something "cool" if that's what I desire (high perceived value) and of course I still would like to get a good deal in the process (good relative value compared to other similar devices by other companies).

Notice that the priorities I list above are somewhat different to the goals in advertising or if I may be blunt, much of the subjective reviews I read/watch online or in print media surrounding new products. Typically, the advertiser's goal is to increase if not blatantly hype up the perceived value primarily. Techniques like celebrity endorsements can be a very powerful tool to enhance the perception. I suppose in a way "big name" senior reviewers and prominent audio magazines have a psychological effect like those celebrity endorsements as well. As sophisticated consumers, I trust we're all well aware of this dynamic.

Inevitably, I believe the more dubious a product - like expensive cables, unorthodox room tweaks, bit-perfect luxury computer streamers - the more the company must bolster perceived value since there are no actual gains to be had by spending more money.

I see that these days, many subjective reviewers have become a bit more cautious about their claims (good that they're recognizing the limitations of their own hearing/memory/abilities). At times we see attempts to compare products, but usually this is in the domain of "look and feel", material workmanship (which of course will affect price) or other subjective characteristics rather than through claimed reliable comments about sonic quality. Frequently we end up with summary statements like this about sound quality:

"For absolute hi-fi sounding resolution, I would go with SuperDuper's Amp One. However, if I wanted a luscious soundstage and great spatial depth, I preferred UltraPrime Amp A!"

Such a statement would provide quotable endorsements for both manufacturers and neither SuperDuper nor UltraPrime should be offended. The Golden Ear reviewer retains his air of connoisseurship, and everybody's happy right? But has the consumer truly learned anything?

Since I have no interest in purchasing an APx555B as a hobbyist, personally the "demand" is low. However, I can still appreciate the absolute value of what has been accomplished and the results this machine produces. The years of R&D invested by the company has yielded a product that is able to perform in unique ways. If I were an audio engineer aiming to make a high performance product, there is no question that a $30,000 investment would likely bring me great rewards. As long as there is a need to design these high performance audio products, there will be a demand for the AP box.

On the other extreme are those expensive audiophile products I listed above. For some, an Audio Note tube amp, Lampizator tube DAC, and the Nordost Odin power cable are presumably of high perceived value such that they are worth the asking price. However, I think many of us would question the absolute value of these products or their relative value compared to competitors. In fact, one might even argue with good confidence that much less expensive products could perform just as well if not better for high fidelity audio reproduction. The uniqueness of these products is not necessarily with what they can do (certainly not with that power cable IMO!), but what emotions some attach to them. The moment emotional sentiment is undermined, so too demand and whatever perceived value.

--------------------

Well friends, it's Spring Break time! I hope you're all enjoying some good weather... Even though I'm not going anywhere special this year, it's still good to catch some R&R.

Hope you're all enjoying the music!