The PMA-50 needed some break-in time to sound its best. Right out of the box, it was bright and brittle, but with 100 hours of use, it started to sound fuller and smoother, with substantially deeper bass. And it continued to improve with more break-in. It ran slightly warm to the touch.
To use headphones with the PMA-50, you just plug them into the jack on the front panel. If your headphones don’t have a ¼" plug, you’ll need an adapter (one may have come with your headphones). If you want to use speakers, you’ll need speaker cables with bare wire or banana-plug terminations. The speaker-cable binding posts won’t accept spade lugs. Speakers from 4 to 16 ohms will work with the PMA-50. When you plug in your headphones, it cuts off the speaker output.
Because they are easy to drive, I used some old Soliloquy SM-2A3 bookshelf speakers. Originally designed for compatibility with single-ended triode (SET) amplifiers, the SM-2A3s were rated at a highish 91dB sensitivity. A rear port loads the 5¼" mid/woofers. I used Kimber 4VS speaker cables to connect the PMA-50 to the speakers.
Departing from my usual reviewing routine, I started my PMA-50 listening sessions with headphones, since I expect that’s how many people will first use the amplifier. I tried the following ’phones: HiFiMAN HE-400, NAD Viso HP50, AKG K712, and Audeze LCD-X. The PMA-50 drove them all to satisfactory levels, though I’m no headbanger. The power-thirsty HiFiMAN HE-400 was the hardest to drive, but the PMA-50 handled it well when set to the mid- and high-gain positions, extracting a level of treble detail not always audible through those headphones. Most of my critical listening was done with the AKG K712 ’phones, since they were the type of medium-priced cans someone would likely use with the PMA-50. Though not unusually hard to drive, the K712s benefit from some amplifier power, so I set the PMA-50 to the medium-gain position.
It was easy to establish a Bluetooth link with my iPhone 6; I just pressed the Bluetooth button on the front panel and the PMA-50 started trying to pair. When it appeared in the iPhone settings under Bluetooth, I just pressed “PMA-50” on the menu and I was connected. You can play music from the smartphone, or stream music from on-line sites. When you want to switch back to the USB input to play music from the computer, press the input source selection button on the front panel.
The PMA-50 switched between PCM and DSD flawlessly, always displaying the correct format and sampling rate on the front panel. That should be no big deal, but it doesn’t always happen, even with very expensive gear.
Sound with Headphones
A novice hi-fi buyer who’s used to listening to a smartphone with earbuds or cans may find the PMA-50’s headphone amplifier its most immediately appealing feature, so that’s where I started. The PMA-50 sounded smooth and relaxed. There was no peakiness or etch present in the sound, although the high frequencies were extended. On Alex de Grassi’s Special Event 19 (DSD64/DSF, Blue Coast Music), the PMA-50 played the track “Shenandoah” with gobs of harmonic detail, and the drone effect of de Grassi’s unusual guitar came across clearly. Transients were accurately reproduced, but not overemphasized. I was reminded how excellent this recording is.
On Jordi Savall’s La Folia, 1490-1701 (ripped to AIF format from Alia Vox AFA 9805), the track “Folia: Rodrigo Martinez 1490” displayed exceptional transient response—the sharply struck castanets had an almost physical impact. However, the cascabels (sleigh bells) seemed a little recessed, indicating perhaps a bit of a treble suckout. The PMA-50 produced a lot of powerful bass from the headphones; however, it lacked the deep extension that I hear with the subwoofer I use with my speakers. Even with the bass-rich HiFiMAN headphones, I didn’t hear the subterranean frequencies on this track. The midrange seemed slightly elevated, making it easy to hear Savall’s viola da gamba playing the main theme. I could also distinguish between the harp and baroque guitar. (Since they play similar phrases, sometimes they tend to sound a bit alike.)