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, "
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 ; 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
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:
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.
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 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.
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.