Reviews of Attainable Hi-Fi & Home-Theater Equipment

Reviews of Attainable Hi-Fi & Home-Theater Equipment

Trends Audio PA-10.1DTrends Audio established its brand by producing low-powered digital amplifiers. These were based on the Tripath chips (very popular among DIYers), implemented with quality parts, given adequate power supplies, put in nice-looking boxes, and shipped out the door at reasonable prices. These little amps include a volume knob that can be switched in or out of circuit via a jumper, making them a simple way to connect a line-level source to your speakers. Building on that success, Trends has expanded its product range to include sources, preamplifiers, speakers, even cables -- everything you need for a small hi-fi system.

The PA-10.1D is a headphone amplifier and preamplifier ($299 USD) that uses a dual-triode tube for voltage gain and MOSFETs for a high-current output stage, and is claimed to deliver up to 3W into a 33-ohm load. That’s standard enough fare, but the PA-10.1D puts a few twists on the typical design. Having a single, easily accessible tube encourages tube rolling anyway, but the PA-10.1D lets you choose between 6DJ8/6922 or 12AU7 types by moving a few jumpers. One of its inputs is switchable between CD/DAC and PC/iPod. When the latter is selected, the gain is doubled to make up for the typically lower outputs of these devices -- a handy aid in system matching.

The D in the model name refers to the device’s dual sets of preamplifier outputs. This permits biamping -- using two power amplifier channels for each speaker -- or driving your speaker amplifiers and an external subwoofer or two. Of course, there is also that front-mounted headphone jack, which is the focus of this review. I was a little disappointed that it was only a 1/8" minijack rather than the full-sized 1/4," but there are two good reasons for that. These days, only full-sized professional headphones -- and not even all of those -- come terminated with 1/4" plugs. Also, having looked inside the cramped interior of the PA-10.1D, there could’ve been a problem squeezing in the longer 1/4" jack.

Trends Audio PA10.1D rearThe PA-10.1D is built to match other Trends Audio components. It’s a high-quality aluminum box measuring 3"W x 1.8"H x 4.5"D, with the tube poking up a little above the center of the top plate. The overall feel -- particularly of the RCA inputs and outputs on the rear panel -- is reassuringly robust for the modest price. The PA-10.1D gets its power from an external supply that Trends says provides very low-ripple 24V DC, but they also note that it would be easy to change to a different type of power supply. In a number of places, Trends suggests a lead-acid battery.

The PA-10.1D arrives with its tube separately boxed. The SE version ships with a Russian-made 6H23n, a well-respected 6922 variant, while the GE version includes a US-made 5814A, which is equivalent to a 12AU7. The jumpers will be configured for the tube shipped with the amplifier; all you have to do is plug in the tube, the power supply, and your other gear. Trends recommends 22 hours of burn-in, after which you may want to check the bias voltage. Both amplifiers shipped to me remained very close to their 16.5mV targets. (I received two units because the first one displayed a severe and intermittent channel imbalance. The second sample functioned properly with both tube types.)

Two aspects of the PA-10.1D’s design affect its use as a headphone amplifier. The first is that its relatively high output impedance -- I measured about 80 ohms -- means that the PA-10.1D will alter the frequency response of headphones that have wide impedance swings. For example, I noticed an increase in the midbass when driving the Beyerdynamic T70s with the Trends compared with the way they sounded with two other amplifiers. The high output impedance also means that the PA-10.1D may have trouble controlling the bass of headphones that are not well damped. It’s fair to note that the headphone outputs on many components -- even some expensive headphone amplifiers -- also have relatively high impedances, but an output impedance of only a few ohms is generally preferred.

Typical portable players and computer soundcards can manage a maximum output of only about 250mV. On its high gain setting of 6x, the PA-10.1D will bring these up to a suitable level to drive most power amplifiers and the vast majority of headphones. The standard output level for CD players and DACs is 2V. Even at the PA-10.1D’s low gain setting of 3x, the amplified output will be pretty hot. On the positive side, that means that it should have no trouble driving ’phones such as the notoriously inefficient HiFiMAN HE-6s. I didn’t have a pair of those to test, but the PA-10.1D was able to produce ear-shattering volumes with the HE-500 (89dB at 1mW) and Audeze LCD-2 (91dB). When I used efficient headphones, on the other hand, the usable range of the PA-10.1D’s volume knob was substantially reduced. I rarely found myself turning it past the 8 o’clock position, and very fine adjustments were difficult.

One concern for the potential buyer of the PA-10.1D, particularly someone new to vacuum tubes, is that it might be noisy. With moderately sensitive headphones, the PA-10.1D was commendably quiet. To hear any hiss, I had to turn the volume up to a level that would have been deafening had I begun playing music. With high-sensitivity designs -- greater than 100dB (at 1mW) -- I did notice a low-level hum. This hum was thoroughly masked by most music, but I heard it between tracks and in very soft orchestral passages. That it was there at all was a little baffling, since the PA-10.1D is DC powered, but it persisted no matter where I plugged it in or what equipment was connected to it. For that reason, and the relatively high gain, the PA-10.1D is best suited for use with less efficient ’phones -- which are, after all, the ones that are most in need of a headphone amp.


I began my listening to the PA-10.1D with the 6H23n tube, which had some stereotypical tube characteristics. A very forgiving top end made all recordings easy on the ears, reducing the brightness of commercial rock and smoothing the edges of early CDs. A prominent midbass and saturated midrange gave voices and instruments extra body. Pairing the Trends with my fifth-generation iPod helped to flesh out the Apple’s sound, which is usually rather thin. My Ayre Acoustics C-5xeMP universal disc player, on the other hand, already has a well-developed bass and lower midrange. Using it with the 6H23n resulted in a sound that was a bit on the thick side. That created a powerful wall of sound with the title track of Derek and the Dominos’ Layla and Other Assorted Love Songs (SACD/CD, Polydor B0003640-36). With other music, this thickness was a mixed bag. Orchestras sounded full, but it was sometimes difficult to pick out individual instrumental lines.

The 5814A tube offered a different perspective. What I heard was still unmistakably tubey, but the overall effect was lighter and more open. The midbass was softer than with the 6H23n, while the high frequencies were slightly more extended. The midrange was warm and present, but less dense than with the 6H23n. This worked very well with sparse recordings, such as Eva Cassidy’s Simply Eva (CD, Blix Street G2-10099), where it added a little glow to her voice while keeping her acoustic guitar light and natural. Large-scale orchestral music lacked a little grandeur, but its constituent parts were easier to discriminate than with the Russian tube. The soundstage was also moderately wider with the 5814A, but I hadn’t found it especially constricted with the 6H23n.

Trends Audio PS10.D

Of the two tubes, the 6H23n had the greater bass weight and extension. In the San Francisco Symphony’s performance of Mahler’s Symphony No.6 under the direction of Michael Tilson Thomas (SACD/CD, SFS 821936-0001-2), the "hammer blows" in the fourth movement are represented by a very large bass drum. Through the HiFiMAN HE-500s, the PA-10.1D made that bass drum sound appropriately big. The Trends made the ’phones move enough air that I felt as well as heard the drum, but the pressure wave was more a puff than a stroke. Put another way, the intensity ramped up quickly rather than having a definite leading edge. Similarly, the bass lines in Bill Frisell’s All We Are Saying . . . (CD, Savoy Jazz SVY17836) dug deep, but their punchy quality in some of the upbeat numbers -- as in "Revolution" and "Come Together," where bass notes are often augmented with kick drum -- turned a little soft and rounded. Again, this warm and somewhat woolly quality was in keeping with the stereotypical -- some would say classic -- tube sound.

I didn’t have any 12AU7 tubes lying about, but I did have two 6922s to compare with the supplied 6H23n. Switching to an Electro Harmonix tube significantly extended the frequency response in both directions, giving sparkling highs and deeper, better-defined lows. Transients -- the leading edges of notes -- were quicker and more precise with the EH than with the stock tube, and the soundstage was wider, though slightly less deep. A Sovtek tube delivered smooth and delicate highs with, probably, a little less extension. The Sovtek tube’s bass and transient response were somewhere in between those of the stock 6H23n and the EH, but this tube gave the most three-dimensional soundstage, with well-defined spatial relationships among performers, though the stage was somewhat narrower than with either of the other 6DJ8 types.

The important point is not how the PA-10.1D sounded with these other tubes, but that I heard substantial changes when I made the substitutions. That means that the rest of the circuitry was sufficiently transparent to deliver a wide variety of sonic flavors. The tubes that Trends has chosen to include with the two different models are about color rather than linearity. That makes them a good complement to the company’s Tripath-based amps, which some find a bit sterile, and to many headphones as well.


Because the sound of the PA-10.1D is so easily altered by changing its tube, detailed comparisons with other headphone amplifiers made little sense. Still, some context is needed. The PA-10.1D could deliver voltage swings -- and the current to support them -- far in excess of what you get directly from the headphone outputs of portable devices, or from full-sized components for which headphone listening wasn’t a design priority. That translates to better drive -- especially for large, inefficient headphones. When such ’phones are inadequately driven, the music becomes squashed and uninvolving. Those built-in headphone sockets also tend to have a significant amount of noise. At worst, that noise is sufficient to distract you from the music. At best, it puts a veil between you and the performance. In almost all cases, running the output through the PA-10.1D will be an improvement.

Last year, I spent some time with an early version of the Apex Audio Peak headphone amplifier/preamplifier. This device is similar to the PA-10.1D in marrying a single tube for voltage gain to a MOSFET output stage for delivering the current. The Peak costs $1400 -- nearly five times as much as the PA-10.1D. What, if anything, do you get for all that extra money?

One distinct advantage of the Peak over the PA-10.1D is a much lower output impedance -- 2 ohms -- which allows the Peak to take firm control of a wider variety of headphones. Although the PA-10.1D did much better at driving insensitive headphones than the average headphone jack or portable device, the Peak had a greater sense of effortlessness. Soundstages were both wider and deeper. And the Peak offered up a greater amount of detail. Those qualities may well justify the Peak’s higher price for dedicated headphone listeners who have top-notch ’phones and sources. For those looking to have some fun tube rolling without breaking the bank, the PA-10.1D provides a great platform on which to experiment. And you’ll have plenty of money left over to buy more tubes.


When I first heard about the PA-10.1D, I thought its single input with dual outputs was an odd combination that would greatly limit its appeal. I no longer think that. While the PA-10.1D doesn’t fit the typical hi-fi mold, this configuration -- with the headphone output -- is very well suited to desktop systems in which a computer is the sole source. The low power and low price of Trends Audio’s amplifiers make them ideal for a biamped setup. Many desktop systems rely on subwoofers, and the dual outputs could be handy there as well, though Trends doesn’t mention this application. I didn’t test the PA-10.1D as a preamplifier, but my findings about its performance as a headphone amp should largely carry over.

The PA-10.1D performed at its best when used with moderately sensitive to insensitive headphones that present a relatively flat impedance. In that context, it impressed me with its low noise and ample power. Most of all, I appreciated the ability of the PA-10.1D to change its character so completely when I changed tubes. Given the huge variety of compatible tubes available at reasonable prices, the buyer of the PA-10.1D will enjoy great latitude in tailoring the sound to his or her preference, or in changing it as the mood strikes. Such flexibility, combined with well-executed circuitry and very respectable build quality, make the Trends Audio PA-10.1D a good value.

. . . S. Andrea Sundaram

Associated Equipment

  • Headphones -- Ultrasone Pro 2900, HiFiMAN HE-500, Beyerdynamic T70, Etymotic Research ER-4PT, PSB M4U 2
  • Headphone amplifiers -- Grace Design m902, Apex Audio Peak
  • Digital sources -- Ayre Acoustics C-5xeMP universal disc player, Apple iPod (fifth generation)
  • Interconnects -- QED Silver Spiral
  • Power conditioner -- Equi=Tech Son of Q

Trends Audio PA-10.1D Headphone Amplifier/Preamplifier
Price: $299 USD.
Warranty: Two years parts and labor; one year, tube.

Trends Audio
ITOK Media Limited
Unit E, 13/F, World Tech Centre
95 How Ming Street
Kwun Tong, Hong Kong
Phone: +852 2304-0730
Fax: +852 2566-5740