REVIEW / MEASUREMENTS: Drop + THX AAA 789 Linear Headphone Amplifier. And on Audioholics' THX Onyx DAC/amp "review" with a dash of MQA nonsense...

With much of my soundroom and other parts of the audio system sorted out to my satisfaction these days, I thought it would be time to start paying a little more attention to the headphone side of things. As you can see, in the last few weeks we've talked about the AKG K371 headphone, and prior to that some discussions on impedance and power.

Prior to about 2013, I was very much into headphone stuff when the kids were babies and louder music playback was simply not an option. Thankfully this all changed when the basement man-cave became available! ;-)

When writing about headphones and reviewing, it's important to have a good foundation set-up for "reference" listening. This means I would need a good headphone amplifier on my desktop Workstation computer; one that would support and optimize some of the more hard-to-drive headphones, especially those with challenging output impedances and lower sensitivities. In alignment with that goal, I have the Drop + THX AAA 789 Amplifier on my table these days as you can see above.

REVIEW / MEASUREMENTS: AKG K371 (closed-back, over-ear, dynamic driver) - An affordable, modern, standard studio headphone. (And on using the miniDSP [H]EARS rig.)

Hey guys and gals, the post here today will be on the longish side since this is the first time I'm writing a headphone review with some measurements. Best to take the opportunity to discuss the testing itself as well as product impressions.

As you can see above, today we'll be considering the AKG K371, an inexpensive (~US$120) "studio" 50mm dynamic headphone that's easy to drive, with a sound signature based on Harman research into headphone tonality - see this nice presentation from 2017 containing a review of the various research over the years.

I bought these headphones from the usual retail channels.

First let me show you some pictures of these particular headphones, and later, we'll get into measurements with the inexpensive miniDSP (H)EARS test fixture.

MEASUREMENTS: Melody Onix SP3 Mk. II (~2006) Class AB Tube Integrated Amplifier. (And it isn't "diminishing returns" on sound quality, often there are simply "no returns".)

Recently I was curious about trying a tube amp in my system and my dad who's into his vintage gear including some older tube devices offered me this amp to test out. It was time to take up the offer and have a listen plus put some tube gear on the test bench for a peek at the performance.

As you can see, for today's post, we have the Melody Onix SP3 Mark II which I believe was first released in 2004 for US$1000. This one I believe was bought in 2006. It's a relatively compact unit (12" x 8" x 13" or so), 56lb beast designed by Melody Australia, made in China. Over the years, there have been various reviews on this product from 6Moons (Best of 2005 list), Audioholics, Home Theater Review, High Fidelity Review among others. Here's the Melody company website. I think this model was discontinued by around 2010.

I've always liked the look of this box. There's a cage that normally protects fingers from the four large power tubes and individual smaller covers (you can see 3 on the right removed) that protects the 6 flanking tubes. Turn off the lights at night and it all looks very cool.

MEASUREMENTS / MUSINGS: Headphone impedance, sensitivity, efficiency, and amplifier output impedance. (And a quick thought on Darko's "All You Need Is...")

Some people have walls of headphones. Well the other day I thought I'd take out my little collection accumulated over the last few decades around the house, some of them used by the kids, and let's dump them on the sound room ottoman to have a look :-).

The majority are based on dynamic drivers with a couple of balanced armatures (Etymotic ER-4, 1MORE Quad Driver). I'm actually missing a few there that were in use that evening by others around the home - the Dekoni Blue (an officially sanctioned "modded" Fostex T50RP Mk 3) planar-magnetic, the AKG K371, and Apple AirPods Pro (wireless) which my wife had brought to work and "forgot" to bring home that evening.

I was curious about the impedances of these devices and thought it would be good to put together a summary article looking at this along with the power needed to drive headphones and correlating these characteristics with amplification.

Although I have spoken of the importance of mobile audio in the past, I really have been remiss in not putting enough emphasis on this trend or the importance of headphones in these blog pages over the years. Despite this, some of the most common E-mails I've received over the years have actually been about headphones. So let's make sure to incorporate some "head-fi" in the days ahead!

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.

HOW-TO: Partial Frequency Correction with Acourate. Spotify HiFi coming and a look at the evolution of music sales/formats from 1980-2020.

Over the years, I've discussed the use of DSP room correction in these pages (here and here for the more recent articles). In Acourate, there's no single-step macro to tell the software to limit the correction to certain frequencies as far as I can tell. Instead, I saw this comment by Dr. Uli Brueggemann in one of Mitch Barnett's early articles (2013) hinting at a way to modify the inversion step of the filter to accomplish that task. This post is a step-by-step procedure for those interested in doing just such a thing with the software.

Note that even though I'm showing the process here, I'm certainly not suggesting that it's necessary whatsoever. In my listening, a full-spectrum room correction sounds great with the frequency-dependent-windowing (FDW) algorithm Acourate uses. Over the years with friends and family who have had the time to sit and listen, I have never had anyone complain that my usual full-spectrum filter did not sound better than the uncorrected sound in my room (and on occasion, I have measured and applied DSP to my friends'/family's sound systems as well to similar effect).

It's always great to have options though!

RETRO-MEASURE: Pioneer CT-S605 Cassette Recorder/Player (1989). On cassette quality / fidelity. Cassettes are "coming back"? And sentimental associations...

After the usual recent posts on DACs, DSP, speaker measurements, let's discuss something very different this week!

The other month, I was cleaning out some stuff from my basement and came across an old cache of "compact cassette tapes" which I had recorded back in my high school and early university years. I also still have a handful of old pre-recorded tapes that provided the soundtrack of those times in life.

Within this collection were some made in the mid-'80s until about the mid-'90s when affordable CD burners (~$500 I think around 1996) came on the market and I quickly shifted to making "mix-CDs" rather than mix tapes. In fact, I found some almost brand new tapes that I forgot I still had:

Left: Fuji DR-I standard Type I Fe2O3 "Normal Bias". Right: Maxell XL II Type II CrO2 "High Bias". Center: Sony Metal-SR basic level Type IV "Metal Bias" for "Digital Excellence" - back in the day :-).

MEASUREMENTS: Emotiva Airmotiv B1+ bookshelf speakers. A comment about Andrew Robinson's Fluance Reference XL8S video review and "Do measurements ultimately matter?".

Emotiva Airmotiv B1+: Comes with small manual, and some stick-on rubber footers in the plastic bag. Fabric covers in background.

Since mid-2020, I've been on a quest to find some replacement speakers for my computer desktop. Along the path, I've listened to and measured speakers like my old AudioEngine A2, the active Edifier S2000 MkIII, borrowed the Tannoy REVEAL 501a, the passive Fluance Reference XL8S, and of course tried the KEF LS50.

For this post, let's look at the Emotiva Airmotiv B1+ 2-way bookshelf speakers (US$229/pair), released in early 2020. Externally, these look like their predecessor, the Airmotiv B1 that first came out in 2016. I bought this pair direct from Emotiva in late 2020, arriving a little before Christmas.

REVIEW / MEASUREMENTS: HiFiBerry DSP Add-On with the DAC2 HD. A quick Roon 1.8 network/endpoint issue and remote access request.

This post is in many ways a continuation of the HiFiBerry DAC2 HD measurements presented last time with the devices sent to me by Doug Gardner for testing. For some background, this DSP Add-on is related to the BeoCreate project which was documented in this 2018 thesis in collaboration with Bang & Olufsen. The idea was to create an open-source system to allow consumers to build or update their own loudspeakers to be active devices. It looks like this DSP Add-On board leverages that software to do its magic.

As you can see in the thesis, the final BeoCreate product was a board which included 4-channel amplified outputs, digital S/PDIF input and output, DAC, and of course the programmable DSP subsystem. A Raspberry Pi could be added to provide network streaming capabilities.

For completeness, I want to mention that this DSP Add-On is also compatible with HiFiBerry's DAC2 Pro (~US$50-60) board. Notice that the DAC2 Pro is a less expensive DAC than the DAC2 HD and sports headphone out. The converter chip seems to be the TI PCM5122 (same as previous gen DAC+ Pro) based on what's listed in the specs sheet but I have not seen confirmation that is indeed the case.

REVIEW / MEASUREMENTS: HiFiBerry DAC2 HD HAT for Raspberry Pi

It has been awhile since I've measured any of the Raspberry Pi DAC HAT boards. In fact, it was back in 2016 that I got the HiFiBerry DAC+ Pro which I still use for basic streaming in the living room these days. Thanks to blog reader Doug Gardner, he sent me both his HiFiBerry DAC2 HD (~US$100) and DSP add-on (~US$60) boards you see above for testing. Doug was also very helpful in providing some background information and discussions on subjective impressions.

The DAC2 HD was released last year (around June 2020) and is based on the TI/Burr-Brown PCM1796 "Advanced Segment" DAC chip, an upgrade from the TI/BB PCM5122 found in the DAC+ Pro board. With the majority of my DAC measurements recently being ESS and AKM products, it's good to have a listen and look again at a TI/Burr-Brown-based product. Note that the PCM1796 is not a new component by a long shot! It has been available since 2004 I think (earliest specs sheet Dec 2003). My TEAC UD-501 and ASUS Xonar Essence One from 2013 were both based on dual PCM1795, a close sibling.

While I will be looking at the DSP add-on daughterboard (version 1.1, dated April 2020) more next time, for now, suffice it to say that this is based on the Analog Devices ADAU1452 chip, a 32-bit, 295MHz DSP.

RETRO-MEASURE: Spendor SA1 (1976) monitor bookshelf speakers (The foam tweeter ring tweak!? And on "Listen For Yourself!".)

 

For this week's blog post, let's have a look at another "retro-measure"! This time, I had the opportunity to listen and test out the early-version Spendor SA1 speaker which hails from 1976. Remember that over the years, Spendor has released newer versions of this "classic"; most recently around 2009 as reviewed here in Stereophile.

This is another speaker I borrowed from my friend linnrd and I spoke about it back in late 2019 when I visited his place. This time, let's have a proper listen with measurements and compare the performance objectively and subjectively!

The "Spendor Mini Monitor Type SA1" came out just before the classic BBC LS3/5A design around 1975. Like the LS3/5A, these monitors were designed to be used in mobile recording vehicles.

REVIEW/MEASUREMENTS: SMSL (S.M.S.L.) M100 Mk II Hi-Res DAC (USB, S/PDIF Toslink and Coaxial In, ESS Sabre 9018Q2C, below US$100)

 

[Disclosure: Over the years, I have measured and reviewed products I have either bought or borrowed from friends. The product discussed in this post was sent to me by Aoshida Audio for an honest review and impressions which I can keep to use. It would only be fair that I provide the free shipping and "lowest price guarantee" links to Aoshida if readers want to purchase this DAC or others discussed. Considering that a major part of my review process is objective in nature and standardized over many years, I trust that much of what I present will remain free of bias. Note that I will be selective of what I agree to measure/review of this nature - accessible and high fidelity products that might be of interest to readers, or more innovative devices will obviously be most appropriate for what I do.]

As you can see in the image above, today let's have a look at another very inexpensive DAC product from S.M.S.L. with high-resolution ability. Over the years, I have reviewed/measured other devices from this company including the SMSL A6 integrated amp, the SMSL iDEA DAC, and more recently I've been enjoying the SMSL SA300 Class-D desktop amplifier. These are examples of "accessible" audio products, well within the price range of basically any music lover, "audiophile" or not.

So it is with this DAC. The S.M.S.L. M100 Mk II currently costs less than US$95, needs little power, and accepts USB/TosLink/Coax S/PDIF inputs. As you can see, it's shaped as a rectangular prism. The size is smaller than the photo might suggest measuring at about 2 1/8" x 2 1/4" x 3 5/8" long, weighing around 0.5lb (250gm). The enclosure is aluminum with shiny plexiglass front panel; the package feel solid. Inside the box is an assortment of printed manuals in English, Chinese and Japanese along with a basic white USB-A to micro-USB cable.