REVIEW / MEASUREMENTS: Pass Labs / First Watt SIT-2 stereo Class A amplifier. [And Stereophile steps in with MQA yet again...]

 

Greetings all. For this post, as you can see above, I've got something exotic to review / measure here at chez Archimago. It's a Pass Labs / First Watt SIT-2 stereo amplifier which was made in limited quantities back around 2011-2013.

This amplifier comes with a nice backstory; that of the silicon carbide (SiC) "Static Induction Transistor" which you can read about here (aka V-FET). The thought is that these transistors behave in a "triode-like" manner, hence perhaps they will be able to convey a "tube-like" sound. Furthermore, this device follows the general audiophile philosophy of "simplicity and minimalism" (quoted from the manual) as principles that would result in a device sounding "good". As such, this amplifier has only a single SIT gain stage, operates in Class A, built with minimal components, employs no feedback, and as expected, accepts single-ended input only.

Online I found this user manual and Japanese product flier for those wanting a bit more information from the company. The cost of this amplifier when it first came out was around US$5000.

REVIEW / MEASUREMENTS: (Mass)Drop + HiFiMan HE-4XX Planar Magnetic Headphones (with Brainwavz XL Round Hybrid earpads). Maintenance if the earcup detaches.

Well, as I've mentioned previously, I don't really need more headphones. ;-) Alas, I could not resist picking up these minty Drop + HIFIMAN HE-4XX Planar Magnetics locally used at a price I could not refuse! I also love how they look with the classic headband. The matte "midnight blue" color looks like a dark charcoal with a subtle powder bluish tinge.

I know there have been different opinions on the build quality of these headphones. Some of the early units had issues with right-left imbalance, driver failures, and broken hinges. According to this post, it looks like replacements with serial number 5XXX have many issues fixed. My unit here has serial number 57XX.

The hinge where it interfaces with the headband feels robust on this unit and I think the build quality is very good. The steel gimbal and metal sliders seem like they will be able to hold up to daily use. No complaints there. I did have an issue with the part interfacing the ear cup which I'll discuss below.

The stock cable is a little short for my taste at around 5'/1.5m (6' would be better for my desktop use). Notice that the cable is angled 90°, terminated with a 3.5mm connector which is fine for mobile use. I think a straight cable would have been preferred since most buyers would likely be using these open headphones at home almost exclusively. I like the soft, pliable nature of the cable although I have read some complaints that it can kink and fail. I don't think there's an issue, replacements are not expensive anyway.

REVIEW / MEASUREMENTS: (Anthony) Gallo Acoustics A'Diva Ti (~2005) & Nucleus Micro Speakers (~2000).

Hey ladies and gents, let's switch from discussing headphones this week and have a look and listen at some speakers.

You've probably seen speakers like the ones above over the years. These are the "iconic" Gallo Acoustics A'Diva Ti speakers from the UK. These specific ones are probably something like 16 years old and the 5" diameter A'Diva orb (with 3" driver) is in fact the larger of the 2 speakers from Gallo we'll be talking about today.

Here's the smaller 4" diameter (also 3" driver) little brother - the Nucleus Micro. Note that this is the "non-Ti" version which is from the previous generation, made around year 2000 with presumably a different driver. Unlike the stainless steel protective grille of the A'Diva, the fabric grille is easily removed for photography:

Modding the Dekoni Blue ("Arch-Mod5"). Streaming audio: Apple Music to be "true hi-res lossless" stereo with multichannel (Atmos) in June.

A couple weeks back, I measured the Dekoni Blue headphone which as I noted, is itself a "modded" Fostex T50RP Mk 3 planar-magnetic (aka "Regular Phase", aka "isodynamic") headphone. It would be completely remiss of me if in a review/discussion of the Dekoni/Fostex I were not to spend some time talking about modding!

Modding has an very long tradition in the 'head-fi' world and I think it's been generally recognized that the Fostex headphones are the classic headphones to perform surgeries on. Much of what I'll be talking about here will be nothing new to those deep into this stuff already. For more on modding, check out this Headphonesty article for a background.

To start, as always, we need a plan and a "vision". As I mentioned in the last article, the Dekoni Blue sounds pretty good for the most part, so my job isn't to change the performance completely, but to rather refine what is there. If a headphone sound highly objectionable, one should really just move on and buy something else! Let's review the measurements I published last time for the Dekoni Blue with the supplied earpads and see what we can try...

MEASUREMENTS: AKG Q701 "Quincy Jones Signature" (2012) & AKG K260 (vintage 1987-1988). And recent interviews with audiophile cable/power people [Shunyata / AudioQuest].

For today's post, let's have a listen and look at the two AKG headphone models above separated by about 25 years in age. On the left we have the AKG Q701 "Quincy Jones" Signature Reference-Class Premium Headphone which was released in 2011. I bought this one (I preferred the black rather than some of the funky colors like neon green) in late 2012.

On the right, we have a rather uncommon AKG K260 - first edition released in 1987-1988, borrowed from my friend linnrd locally. A later versions of this headphone was relabeled with the "Professional" name attached. There's also a Philips version from back in the day using AKG as OEM. This particular one here is used but still in good condition which I cleaned up a bit before more critical listening and measurements.

Notice the "AKG look" with the leather or faux-leather headbands and the thin plastic/metal semicircular arches up top.

REVIEW / MEASUREMENTS: Dekoni Blue ("Approved" Fostex T50RP Mk 3 mod). And the importance of the room for hi-fi reviews (Wilson Chronosonic XVX speakers in Stereophile).

As you can see in the image above and might know already, these are essentially Fostex T50RP Mk 3 headphones which have been out since 2015. In 2018, the Dekoni company (which makes aftermarket headphone pads and accessories mainly) decided to make a licensed version of the Fostex with their own earpads and blue esthetics - hence the Dekoni Blue (~US$250). If you want a little more background, here's Dekoni's "Short Essay..." on the product.

If you've used Fostex headphones before, I think you'll appreciate that the stock ear pads are thin and rather uncomfortable so upgraded earpads are mandatory for long-term use. When I got these, it was less expensive that a new Fostex + upgraded earpads.

MEASUREMENTS: Sennheiser HD650 (~2010-2012) and HD800 (~2010). A comparison of two "Reference Class" headphones, and a look/listen to the "Sennheiser veil / darkness". [Inexpensive 2TB SSD and inflation in consumer electronics...]

As you can see in the picture above, this is a bit of what the "box opening" looks like when you buy either one of these "Reference Class" Sennheiser headphones.

Much has already been said about the headphones being measured today. The Sennheiser HD650 was originally released back in 2003. Of interest historically, there was a fire in the Ireland factory back in 2004 so there probably are not many older pre-fire HD650's floating out there. Tyll Hertsens' article about the Sennheiser HD580/600/650 is a great summary and SolderDude has a ton of stuff on the HD650 on DIY-Audio-Heaven. SBAF has this "compendium" on the HD650 which I think covers everything... and more! Oh yeah, even NwAvGuy got one of these back in 2011.

These days, there's the Massdrop x Sennheiser HD6XX which would be the latest version of the HD650 discussed here, while the Sennheiser HD660S looks similar but has redesigned drivers.

Likewise, you already no doubt would have read about the Sennheiser HD800 over the years. These came out in 2009, sporting the large 56mm "ring radiator" driver (vs. 42mm transducer of the HD650). The HD800 has since been revised with the HD800S in 2016 (here's Tyll's take with mods discussions). Multiple reviews on Head-Fi. The HD800S sounds very similar to the HD800 to me.

For this post, let's look at measurements comparing the two and I'll put in my 2¢ on the sonic differences as I hear them.

Home Network: The ASUS ROG Rapture GT-AX11000 WiFi-6 Router & QNAP QSW-M2108-2C mixed 2.5GbE + 10GbE switch. (Internet jitter and "one number" audio objectivism.)

QNAP multi-gigabit switch being installed behind the basement home electrical panel.

Well guys & gals, it seems like every year, I'll post at least an article on computer networking.

I know, this isn't specifically audiophile-related but for us computer/streaming digital audiophiles, that computer network infrastructure we run at home is important and certainly being home-bound in the midst of the COVID-19 pandemic, a smoothly running network has become even more important for work, education, socialization and play these days.

So with both my kids now teenagers in high school, myself and the wife having to do more work from home, and the ongoing (exhausting) use of video conferencing, I figure I might as well optimize the system and hopefully forego thinking about this for a few years. ;-)

So today, let's talk about wireless, router features, and multi-gig wired home ethernet.

The top image is my new WiFi router. The 4lb, 802.11ax "Wi-Fi 6" capable, tri-band (2.4 + dual-5GHz), up to 160MHz bandwidth in 5GHz, DFS, 12-stream, 8-antennae, 1.8GHz quad ARMv8 64-bit cores, 1GB RAM, 256MB firmware, 2.5GbE-port, ASUS ROG Rapture GT-AX11000; from now on I'll just call it the "GT-AX11000".

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 playback of some of the more hard-to-drive headphones - 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.

[See Addendum update as of Acourate 2.0.]

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 :-).