June 2009

World Premiere!
Trend Audio PA-10 Hybrid Preamplifier And Headphone Amplifier
With the Benchmark DAC1 USB and ASL HB1 thrown into the mix.
Review By A. Colin Flood

  I waxed enthusiastically over Trend's $119 chip amplifier almost two years ago. I said their palm-size amplifier was "an excellent value in the right situations." So this year, Trend sent me their new PA-10 pre-amplifier. Ever since I got my winged Audio-Technica ATH-A700 cans, I pondered using a digital-to-analog converter (DAC) and/or headphone amplifier at work. So I reviewed the PA-10 as a headphone amplifier using my ATH-A700 and superb Sennheiser HD 650 cans, supplied by HeadRoom. This is my fifth article in a series of headphone reviews.

The new Trend Audio PA-10 hybrid amplifier functions as a headphone amplifier and pre-amplifier. It is a hybrid design, with one tube for voltage amplification and two MOSFETs as output drivers. MOSFETs are metal–oxide–semiconductor field-effect transistors used to amplify or switch electronic signals. Trend's Marketing Director David Ho says this tube and transistor combination provides "the warm, comfortable tube sound and in addition, guarantee the high fidelity and sufficient driving power to the next power amplifier stage."

The PA-10 comes in two flavors. Each version has a single driver tube, the size of a thumb, sticking out of the top like a groundhog checking to see if it is springtime. There is the Standard Edition, with a Chinese Beijing 6N11, and there is the Special Edition, with a Russian 6H23n tube. The 6H23n is a double-triode tube. It is equivalent to the European ECC88/E88CC tubes and can be used in any 6922, 6DJ8 or ECC88 circuit. The PA-10 can also use classic 12AU7 tubes. There are no bias meters, though adjustment screws are inside. Tube changes are set with internal jumpers.

"Comparing the two types of provided tubes," Ho said, " Beijing 6N11 is providing the balance sound in full range and good fidelity and Russian 6H23n is providing a relative thicker and warmer mid-range and heavier bass." Before shipping, Trend presets the jumpers and sets the DC bias voltage for the packaged vacuum tube. The review unit came with both, but since it came biased for the Russian tube, I reviewed it that way. The standard Chinese edition is $225, while the special Russian edition is $265. The tubes come wrapped in plastic and a cardboard box.

The PA-10 circuitry is Class A, using 100 percent of the input signal. Class A amplifiers are typically more linear and less complex than other types, leading to cleaner, more effortless sound, but the amplifiers are very inefficient. Therefore, this circuit topology is most commonly used in small-signal stages or low-power applications, including tube amplifiers. A monster amplifier, like the incredible Pass X250, is Class A in the initial, low watt stages.

Except for the groundhog tube sticking out of the top, the PA-10 looks like its brother, the  charming TA-10 power amplifier. On the aluminum face plate, there is a silver knob, the size of a bottle screw top, and four black screws. The only headphone output is a mini-headphone jack. On the back is a set of two audio inputs. Besides the normal RCA inputs for CD (with 3X high gain), inputs labeled Phono provide higher gain for PC sound cards. The PA-10 can not function as a turntable pre-amplifier as it does not support RIAA equalization. A tiny switch slides between the inputs. There is one set of RCA plugs on the back for normal audio output, and a slim "Good n' Plenty" stick to toggle power. The power supply is a small wall wart, like those of a calculator. The case is aluminum.

Unlike the last headphone amplifier I reviewed, the full size ASL HB1 headphone amplifier, I am back in the land of Gulliver ; everything is small again. The PA-10 snuggles in nicely beside my monitor. The PA-10 does not have a protective tube cage. Otherwise, its small size invites portable use. Think zippy Mazda Miata.

No wires are included. HeadRoom sent a passel of connections for their Micro DAC and amplifier combo review. I plugged the PA-10 into the USB ports on my Dell PC at work and my clone at home. Music was 1.4 Mbps wav files with Windows Media Player. I also used it on a $40 Magnavox DVD player (Walmart).

Warming Up And Technicals
The tube takes a few minutes to warm up to its best sound, making the amplifier slow for Windows use. The PA-10 has no auto-stand by feature, so it is easy to leave it on all day. Once on, a LED on the circuit board fills the tube and the socket with a charming blue glow. After a movie or a few discs, the unit is toasty to the touch. The PA-10 did not come with a manual. No bother though. Except for making a mistake with the wrong tube and the input switch on the back, there was no need to consult one. Technical notes for tube rolling are online at the Trends Audio website. Since the preamplifier tubes drive the MOSFETs, not the output stage, the life of tubes should be generally quite long compared to output tubes in power amplifiers.

In addition to tube rolling, tweaking audiophiles "can also try to upgrade the coupling caps of audio output (C3, C6 - block 10uF caps)," Ho emailed, "and headphone output (C4, C7 - tank 1000uF caps). The power filtering caps C2, C5 can also be upgraded."  

The volume knob has a slim indent, like it was scratched with a thumbnail, to indicate position. About 10:00 on the dial, the PA-10 sound opens up. Beyond that point however, the PA-10 runs out of steam. By 3:00 on the dial, it begins to sound harsh on the ATH-A700s, without ever getting as loud as the three previously reviewed amplifiers. On the DVD/CD player, the sweet spot was closer to 9:00; quickly sounding harsh above that. With the HD 650 cans, the PA-10 doesn't sound harsh, but it does not get too loud and still lacks push. In fact, everything sounded much better with the HD 650s. Although not as comfortable at the ATH-A700 wings, they are clearly better headphones and the PA-10 sounded best with them (review forthcoming).

I listened to the same tracks on all the amplifiers, including my usual test CDs, and a lot of movies. In each review, I compare two particular rock and jazz discs:

Jimmie One
"Whole Lotta Love" on the classic Led Zeppelin II did not grab me immediately. Even with a little more twist on the dial, the PA-10 doesn't get up and dance. I cranked the dial halfway to get the textures of the music to stand out. While the guitars have some rasp to them, and the treble does not have that hard, solid-state edge, the PA-10 does not have the startling capabilities of the HeadRoom Micro combo or the expensive Benchmark DAC1 USB.

Like most tube amplifiers, the PA-10 is more like a smooth Omega single driver speaker. There is a warmth and lushness to the mid-range, especially noticeable in the critical vocals. This charming Lilliputian amplifier never sounded flat or dull. It is easy to listen to it. It does not however, have the power to provide an emotional ride. I could say the same thing about boom boxes. With detachable speakers set-up properly, even boom boxes can sound good (see Stereos, As They Relate to Indoor Sport), but they don't have the sonic qualities that audiophiles cherish.

Jimmie Two
On Diana Krall's incomparable Stepping Out, the first impression of the PA-10 confirms a smooth mid-range and weak bass. The all important mid-range vocals have the "naturalness" of tubes. Voices are convincing, detailed, coherent and physically present. They have textural reality. As wonderful as the mid-range was, the bass simply did not have the energy and punch to make the deepest notes come alive. The slow, growling draw of the bow across the cello strings on "Jimmie" was neither sensuous nor enticing. It was neither warm nor bloomy. Even at full power, the PA-10 could not buzz the bass like bees. It does not have the awesome depth of the solid-state HeadRoom Micros and Benchmark DAC1 USB. For example, left-hand work on pianos missed the gravity and decay that adds real weight to the performance. Castanets lacked impressive attack and ambience.

With the ATH-A700 cans, the soundstage is big and wide, with everything sounding more dynamic. The bass has more impact, mid-range more presence and treble is crisp and clean. Almost too crisp and clean. In fact, crank the PA-10 up past midnight and the high-end sharpens as harsh as a grouchy old lady. While drums have more realistic body and impact than the Sennheiser 650s, the more comfortable ATH-A700 quickly wore out the ears at higher volumes.

With both cans, nowhere was the bass more disappointing than with action movies. Gunshots, and other special movie effects, that should rattle the walls, barely shook them. Not that the sound was awful. It wasn't. Had I not heard the more expensive amplifiers, I never would have noticed the PA-10 weaknesses.

Similar Scores
I am a notorious low grader for Enjoy the Music.com categories, awarding four Blue Notes only where the component shines with above average performance. I save five Blue Notes for excellence that is the best it could possibly be. Enjoyment is my own category. None of the headphone amplifiers reviewed so far however are clearly standout, best bets, regardless of money, in my own humble opinion. Choosing a headphone amplifier is a matter of difficult choices. Money, size and sound all play equal parts. Even the Benchmark DAC1 USB did not get everything right; it did not have that smooth, warm mid-range of the hybrid amplifiers.

The two types of headphone amplifiers in this series sound awfully close to each other. The sound of the solid-state units resembles each other, while the two hybrids sound more like each other than the solid-state ones. Chips sound like chips and tubes sound like tubes. The HeadRoom Micro combo and the DAC1 USB sound solid and clear, while the hybrid amplifiers sound warm and friendly. This resemblance however, does not bode well for the PA-10...

Both the ASL and Trend hybrids are half the price of the HeadRoom Micro combo, but only a quarter of the DAC1 USB's cost. Compared to the price of my headphones, the price of the either hybrid is quite reasonable. The Special Edition of the PA-10 costs $265. Unfortunately, this price puts it within shooting range of the $300 ASL HB1.

Like the ASL HB1, the PA-10 is not highly accurate, but has a charming coloration that sounds like music and grabs your attention. Like the HB1, there are more things right with this unit than wrong. I gave the HB1 four Blue Notes for Tonality, Midrange, Enjoyment and Value. The PA-10 has the same weaknesses and strengths in the same categories, except the HB1 has the edge in all of them.

Both hybrid amplifiers are weaker in Sub-bass and High-frequency, stronger in Tonality, Mid-range and Enjoyment, than the two solid-state headphone amplifiers. Yet, where the PA-10 is weak in the Sub-bass, for example, the HB1 is a little less weak. Where both hybrids fared poorly, the HB1 semi truck pulled more weight than the zippy PA-10 Miata. Where both hybrids have the mid-range warmth that tube lovers expect, the HB1 edges the PA-10 out with a slightly richer, fuller sound.

The HB1 advantage is not "a 1/100s of a second, Michael Phelps grab for the gold" lead either. The HB1 clearly sounds stronger in the categories where the PA-10 is weak. Sub-bass is a more solid. High-frequency is a tad sweeter. The HB1 tops the PA-10 in Tonality too, with three of a kind beating two pair. These capabilities give the ASL HB1 the edge for Enjoyment, and therefore, Value for the Money.

Specifications
Type: Vacuum tube headphone amplifier
Signal-to-Noise Ratio: 92dB 
Power Output: 3.0 Watts per channel on 33 Ohm Headphone 
Frequency Response: 15 Hz to 100 kHz @ 1dB 
Input Impedance: 100k Ohms 
THD+Noise: 0.05% @ 10k ohm, 0.15% @ 33 ohm 
Power Supply: DC 24V-26.5V (max.) 
Dimensions: 76 x 46 x 114 (WxHxD in mm) 
Weight: 1.1 lbs
Price: Standard Chinese edition $225
         Special Russian edition $265

Company Information
ITOK Media Ltd
Room 1011-12, 10/F Tower1
Millennium City 1
388 Kwun Tong Rd
Kwun Tong
Hong Kong

E-mail: sales@trendsaudio.com
Website: www.TrendsAudio.com