Tag Archives: vacuum tubes

MHDT Lab Pagoda

MHDT Laboratory Audio Devices has been producing their line of affordable NOS (non-oversampling) DACs since 2002. The Pagoda was introduced in 2014 and is a bit of a departure for MHDT Lab with its use of dual PCM1704 R-2R DAC chips. These chips are legendary (bordering on cult status) for their superb sound quality. It’s most unfortunate the PCM1704 family of chips are no longer being manufactured.

Some specs

  • 4 digital inputs (BNC, USB, RCA, Toslink)
  • 24/192 max on all inputs
  • no digital filter
  • no op-amps
  • no feedback
  • tube buffered output (GE5670 3 mica)
  • output level is 3.0v

With the current breakneck pace of DAC development the Pagoda might seem a bit long in the tooth for those who seek extremely high-res PCM and DSD rates. Obviously, this DAC is not for them. This DAC is for folks (like me) who find the NOS approach to sound more natural and engaging. Good design and implementation is key, of course, as it is with any audio component and my ears tell me the wizards at MHDT Lab know exactly what they’re doing.

With the vast majority of my music files being CD rips, getting 16/44.1 right is of utmost importance to me. Additionaly, I’ve explored the high resolution landscape in earnest over the course of several years and have acquired some nice downloads ranging from 24/44.1 to 24/384 and a smattering of DSD titles as well. I’ve found anything beyond 24/192 (or maybe even 24/96) is lost on me, as is oversampling to extremely high rates. I don’t care about DSD and care even less about MQA. Horses for courses.

While there’s been quite a bit written/shared regarding various DACs in the MHDT Lab line, the Pagoda has seen little online chatter. IMO it deserves better. The Pagoda paints a wonderfully analog sonic picture with gobs of detail, great dynamics, and no digital harshness. The sound isn’t mushy, soft, rolled-off, or “tubey” in any way. There is a certain rightness to the sound that is just remarkable regardless of bit depth/sample rate.

If you’re in the market for an affordable R-2R DAC you might want to give the Pagoda a listen.

MHDT Lab

Nice comprehensive reviews can be found at Head-Fi and TNT-Audio.

 

Vacuum tubes

While I’ve had some experience with vacuum tubes in the past, it’s been extremely limited to say the least. I have a tubed CD player (Ah! Njoe Tjoeb 4000) which utilizes two 6922 tubes in the output stage and a tube/solid state hybrid integrated amp (Response Audio RAM 301) which utilizes two 12AU7 tubes for the preamp stage. As for an all tubed design, I was a complete novice when I purchased the APPJ PA0901A  integrated SET amp a year ago. This minimalist integrated has only one pair of RCA inputs and a passive volume control to attenuate the output of its tube circuit (6N4/12AX7 feeding a single 6P14/EL84 per channel).

Rolling along

It wasn’t until recently I decided it was time to try some different tubes. Why now? First and foremost, I liked the sound with the stock Chinese tubes and wanted to be completely familiar with the sound quality before swapping them out. In fact, I liked the sound enough that I didn’t bother changing the tubes before the summer heat arrived .. I like to use a cooler running amp during summer.

Over the years I’ve read countless reports of huge changes rolling tubes and, while I know there must be some truth to it, I’ve often wondered if there isn’t just a bit of hyperbole involved. Audiophiles are often prone to such exaggeration when changing anything in their systems citing massive gains in sound quality, veils being lifted, larger goosebumps, etc., etc. Color me skeptical.

So, Christmas present to self:

  • Genalex Gold Lion 12AX7
  • Mullard EL84 (matched pair)

These 3 tubes cost me just under half of what the amp sold for a year ago and was about as much as I wanted to spend. The result .. massive gain in sound quality, 7 veils were lifted, 6mm goosebumps emerged, and ..

Seriously, the APPJ PA0901A sounds like a different amp. Tone, timber, clarity, extension, soundstage, vocals .. everything changed for the better. Of course I had hoped for a result such as this but honestly, I’m somewhat flabbergasted. This isn’t a subtle change, I actually uttered “wow” during my first listening with the new tubes. To say I’m pleased is an understatement.

While APPJ has since discontinued the PA0901A in favor of it’s newer 1501A model, Tube Depot sells it’s own (re-branded?) version found here: TubeCube | 7 Stereo Vacuum Tube Amplifier. Highly recommended. And roll some tubes!

mullard el84

The gear

After more than 2 years using a Bluesound Node 2 I decided it was time to revisit my favorite macOS music players. So, I brought my old Mac mini out of storage, did a bit of housekeeping, and downloaded the latest offerings from Sonic Studio, Damien Plisson, and Jussi Laako. I’m glad I did. Amarra, Audirvana Plus, and HQPlayer have all seen quite a bit of development since I last used them. I’ve also acquired a new DAC and USB/SPDIF converter. So much for being off the merry-go-round.

The basics

  • Mac mini
  • Schiit Audio Eitr
  • MHDT Lab Pagoda
  • Decware SE84UFO
  • Omega Super 3i

Software

  • macOS High Sierra
  • Amarra Luxe and sQ+
  • Audirvana Plus
  • HQPlayer

Cables

  • AudioQuest Carbon USB
  • Black Cat Cable SilverStar! 75
  • Better Cables Silver Serpent RCA
  • DIY solid silver loudspeaker cables

Miscellaneous

  • Bluesound Node 2
  • Chromecast Audio
  • Brick Wall PW8R15AUD
  • Salamander Synergy
  • IsoAcoustics Aperta
  • Sanus Steel Series

Music library and services

  • flac on an Oyen Digital MiniPro via FireWire
  • Tidal
  • Pandora

A new direction

After many years pairing high-powered amps with low-efficiency loudspeakers I decided to go in the opposite direction. Why? Mainly curiosity. I’ve never had the opportunity to hear high-efficiency single-driver loudspeakers in my system and thought it was time. And tubes. I find tubes fascinating, single-ended triode in particular. Cost of these amps was always somewhat prohibitive for me and is why, for the most part, I shied away. Enter Chi-Fi. Initially I think many of us audiophiles balked at the spate of cheap (and cheaply made) electronics coming out of China. After all, how could anything so inexpensive be remotely “hifi”?

APPJ PA0901A integrated amp

For me, it was the oddly named PA0901A that caught my eye. This minuscule “integrated” from APPJ is a single-ended triode design rated at 3.5 wpc with an SMPS (yes, you read that right) and uses one 12AX7 and two EL84s. The use of an SMPS in the design allows for it’s small form factor (approx. 5” x 5” x 5”). The sound quality is simply astonishing at this price-point ($189).

Omega Super 3i loudspeakers

Omega Speaker Systems has been on my radar for as long as I’ve been reading about high-efficiency loudspeakers. Louis Chochos has been building his single-driver designs for 14 of his 34 years in the speaker industry. I purchased the Super 3i’s in the beautifully finished EKO Ash Tweed for $695. These speakers have an efficiency rating of 94.5 dB at 8 ohms and are a perfect match for the little Chi-Fi wonder amp. Coherent. Fast. Addicting.

Fleawatt Audio TPA3116D2 integrated amp

I also purchased a low-powered solid state integrated amp from Fleawatt Audio recently. This class d integrated amp (25 wpc) is built around the TPA3116D2 chip which was the darling of the DIY community at one time. Derek Sanderson builds these creations as a hobby and sells to members of the audiophile community at such a low cost it’s almost ridiculous*. Mine, which has significant upgrades, cost me $250. While not actually Chi-Fi, much of the parts were sourced from China but nicely built right here in the USA.

From a conversation with Derek: “The somewhat lower dampening factor, 3D imaging and smooth highs are very much like a single ended triode amplifier, but with more power.” He wasn’t kidding. Incredible sound for so little cash. I’ll be using this nice cool-running amp in the summer months when I’ll want a break from those lovely little glass heaters.

It’s a great time to be an audiophile.

*Derek is now on hiatus.