I have been playing with a Qinpu A-3 tube amp for over four weeks now, and have been very happy with it. So, I want to take this opportunity to report on my findings. I am always looking for the next "best bang for the buck" and this sweet little amp seems to fit that bill perfectly for my needs. This is a small compact $299 amp based on the 6N3/5670/2C51 tube. It is a tube hybrid that is primarily a speaker amp with 8.5 watts/channel output, via a pair of nice speaker terminals which accept normal banana plug cables or bare wire cables. It's features also include RCA stereo input and 1/8" mini input with a front mounted input selector, as well as a 1/8" mini-out on the rear for headphones or amplifiers. The 1/8" output was originally intended to be used to drive an amplified subwoofer or another amp as pre-amp, but it is capable of driving headphones as well. Both outputs (pre-amp out and speaker) are active at the same time.
Qinpu provided the following data/specs, which I think may be overly conservative:
cherry wood decorating panel
Output Power: 2 x 8.5 W ( 8Ω RMS）
Frequency Response: 20Hz-40kHz
S/N Ratio: ≥71dB(A Weighted）
Crosstalk Attenuation: ≥45dB
Input Sensitivity: ≤420mV
Overloading Level: ≥10V
Input Impedance: 15kΩ
Dimension: L 260mm × W 140mm × H 110mm
Power output claimed via the 1/8" jack @ 600 ohm is 15mw; 300 ohm = 11mw; 150 ohm = 7mw; 32 ohm = 2mw. Qinpu does not recommend to use the amp on less than 100 ohm headphones. However, my observations make me feel that it has higher output power than claimed, at least for headphones with 45 ohm (ESW10) or higher impedance (HD600). I would have guessed closer to 3-4x the claimed output, which still puts the 1/8" jack's power levels nearer to those of many portable amps. Again, this is primarily a speaker amp with subwoofer/preamp out that happens to have enough power to drive headphones, and does it without the usual bass roll-off you would expect with low impedance loads. The Apogee mini-DAC also has a 1/8" line out that can drive some headphones. Qinpu also does not recommand customers change the 6n3 tubes, but we all know Skylab and I had no problem ignoring that. We both tried some NOS tubes with it, but with different results.
So, my main interest in the amp was it's 8 watt/channel speaker outputs which I needed to drive a Stax SRD-7 Pro transformer for listening to several high-end headphones like Stax O2 Mk1 and Mk2, Sennheiser HE60, and HE Audio Jade. Around the time I acquired the A-3 I picked up a pair of AKG K1000 which seem to thrive on being driven by low power speaker amps, adding one more thing that I could test with the amp. Skylab did a a very nice review of it as a headphone amp here: REVIEW: Qinpu Q-2 and A-3 Amplifiers and V-5 Speakers - Head-Fi: Covering Headphones, Earphones and Portable Audio
He made some tube recommendations as follows, and I acquired a matched set of almost all of those - including JAN GE 5670, JAN Sylvania 5670 and JAN Sylvania 2C51, but passing on the Western Electric 396A:
Originally Posted by Skylab
The 5670/2C51 that the A-3 uses offer a lot of options. The JAN-GE 5670 can be had for $5 per tube or less, NOS, and sound good in the A-3 and far better than the stock tubes. The Sylvania 2C51 is better, but a little more expensive and a little harder to get. Still, we're not talking about much money - normally less than $10 per tube. Some people rave about the Western Electric 396A, but these are $50 each usually, and do not make sense in the context of the A-3. Further, I was not very impressed with the 396A.
I find that I am in agreement with him about how nice this little amps sounds, and I might even like the stock tubes a little more than Skylab did. It is indeed very nice sounding for the price. The stock chinese tubes on the A-3 aren't as bad as I think Skylab made them out to be, or my stock tubes are different, because a $25 matched pair of JAN Sylvania 2C51 are only a little better, not a lot better. I have used the A-3 with several sources, including iMod with DLO Homedock HD optical out into PS Audio Digital Link III DAC, and the DLO dock's RCA out into Portable Vcap Dock and then into the A-3, as well as Samsung DVD and Macbook pro via optical into PS Audio DAC and then into the A-3. I finished up with using my Apogee mini-DAC as the source, which didn't have as good of synergy with the A-3 as the PS Audio or iMod/Vcaps. I listened to a variety of headphones out of the 1/8" jack in the rear, and I used the speaker output to feed a Stax SRD-7 Pro transformer, as well as using the speaker output to drive my AKG K1000. I have spent less time with the headphone out than speaker out, but I have listened enough to get a good feel for the sound.
The A-3 sounds very good with my HD600, surprisingly so. I like the sound of the A-3 with HD600 better than I recall did with my old DV336i or my current Head-Direct EF1, while the Maxed Woo WA6 does surpass the A-3 fairly easily with HD600. With the HD600 and APS V3 cable the A-3 is fairly transparent, crisp and detailed without being overly bassy, too warm or cold sounding. There is a good sense of space and air as well. The amp does a good job of getting out of the way and letting the music flow, and I never felt a lack of power with the HD600 although it doesn't reach the ear-splitting volume of the EF1. It does feel effortless in reproducing the music, until you hit the limit at about 2 o'clock on the volume knob.
With low impedance headphones like ATH-A900 and Denon D2000 the A-3 offers a little bit of a bass boost compared to high impedance phones - with powerful but controlled bass, and blends a sense of richness with air and detail. Even then, with low impedance phones it almost reaches the level of the EF-1 in sound quality (but not volume), while with high impedance phones I would guess it is probably closer to the DV336i in sound quality as well (sold so can't compare now). It also does a nice job of filling in the mids of the ATH-A900 and AH-D2000, without overly boosting the mids on the Edition 9. I like the EF1 a bit more with Grado RS-1, but the A-3 doesn't suffer at all with them while not being my first choice. Clipping does occur earlier with low impedance phones than other desktop amps, but there is no noticeable bass roll-off as impedance drops. The main downfall with RS-1 and D2000 is that the max volume attainable is lower than with the EF-1 which has noticeably more power and warmth with them. The ATH-ESW10 and Edition 9 are much more efficient with the A-3 than the D2000, and will play quite a bit louder with the A-3 than the RS-1/D2000. So, the HD600 will play fairly loud with the A-3, while the low impedance phones sound good with the A-3 but they will not play nearly as loud before clipping. You don't get earth shattering levels with any full size headphone, but what you do get out of it is nice sound.
The surprise came with listening to my IEM. Typically, I have not enjoyed IEM on any previous tube amp except for my maxed WA6. With my EF1 and Millett Starving Student and TTVJ Millett I cannot use IEM without a Shure in-line volume attenuator because the EF1 leaks sound at zero volume, and with both there is channel imbalance at very low volumes with sensitive headphones and IEM. With the A-3 I can use very sensitive IEM at very low volumes with no channel imbalance at the lower end of the knob. And with the Phonak Audeo and IE8 there is almost no hiss at zero volume, although with the W3 the hiss is a little greater, and even more with the ES3X - still it is a very mild background hiss to deal with that is well below the level of the music playing with any of them (falling between the hiss level of Apogee Duet and ALO Amphora with high sensitivity IEM). The A-3 sounds very good with my Westone 3 and Sennheiser IE8, like they were made for each other. With my Westone ES3X customs and Phonak Audeo IEM (grey filters) I felt the A-3 could stand to be a little warmer sounding, but detail was nice and the sound was not harsh. I would not hesitate to use the amp with W3 and IE8, but with the others I would pick something else if rolling tubes didn't warm them up a bit. I had to install the black filters in my Phonak to enjoy them more.
Next up is the A-3 speaker out and Stax transformer, with my K1000 plugged into the tranformer's speaker out. I could rotate the knob on the Stax SRD-7 Pro to switch between full size electrostatics and my K1000 which seem to thrive on speaker power over headphone outs. I liked the speaker output even more than the headphone output. The sound was very good when driving a Stax O2 Mk1 and it delivered better dynamics and impact than my maxed Woo GES, at the expense of some refinement and micro-detail offered by the Woo. Blutarsky agreed with me that while the Woo GES drives the O2 Mk2 better than the A-3/SRD-7 pro, the A-3 sounds a little tighter and punchier and more dynamic with the O2 Mk1. There were a few times when I fooled him into thinking he was listening to the O2 Mk1 on the GES when it was actually the A-3 with transformer. I think the Mk1 seem to be harder to drive than the Mk2, which is why they are not quite as good on the GES as they are with a speaker amp and transformer. Again, the GES still wins at micro-detail and refinement, but there is no way a $300 amp and $400 transformer should get to within even 80-90% of a maxed GES in terms of enjoyment of the music with Stax O2, yet the A-3/SRD-7 Pro does just that. With the Koss ESP950 and HE Audio Jade I still preferred the Woo GES, but the A-3 with transformer acquitted itself well with them.
Vs other amps driving the SRD-7 Pro, I moved the A-3 to my bedroom rig and used the Apogee mini-DAC as my source. I prefer the A-3 over the Nuforce Icon driving the Stax O2 due to the forward mids of the Nuforce not having good synergy with the forward mids of the O2 Mk2. However, with the Sennheiser HE60 the extra bass of the Nuforce Icon was more appreciated over that of the A-3. The Travagans Red with AD743 is closer to the performance of the A-3 with the Stax O2, but slightly less rich sounding and slightly brighter. It's all a matter of synergy and which headphones I am using - only with the K1000 do I sometimes like the Travagans Red's 5 watt speaker output more (adds a little more sparkle and detail or crispness to the K1000 treble).
Since the speaker outputs were really enjoyable with driving electrostatic transformers, I then moved on to listening with the K1000 hooked up to the transformer's speaker pass-through. With the K1000 the A-3 speaker outputs threw a slightly more airy image than my Single Power Square Wave XL via headphone out, which throws a slightly darker image while driving the K1000. Channel separation of the Square Wave XL however was greater, and the bass with the Square Wave XL was more powerful as well. The K1000 sound via A-3 wasn't quite as crisp and detailed as the speaker output of my Travagans Red with AD743 opamps, and not quite as bassy as the speaker out of my Nuforce Icon, but the lack of coloration and natural tone was appreciated. To try to improve the sound I tried plugging the K1000 directly into the A-3 (instead of into the rear of the Stax transformer), and this improved the detail with the K1000 a bit, so some of this is a fault of the SRD-7 pro, not the A-3.
In comparing the dynamic headphone amps above, they all have good detail but with a slightly smaller soundstage than my high-end amps like Woo WA6, GES and Single Power. However, I think the A-3 does offer a little bigger or more spacious soundstage than the EF1 or Millett SSH do. The imaging of the A-3 is good, and instruments do not mush together or splay out too far and wide. The soundstage is still not as big as the WA6 or Single Power, but they cost 4x more money too.
In summary, I think the A-3 offers a great value for a headphone/speaker amp with selectable inputs. I expect that one would have to spend a lot more money to clearly pull away from the A-3's sonic performance, although if you are into very high volume levels you may want to look elsewhere or use the speaker output for your inefficient headphones. I would pick this amp over over the Nuforce Icon and Travagans Red for speaker output to drive a Stax transformer. With the K1000 the A-3 is respectable and very close behind the Square Wave and Travagans Red - but sounds better if I switch the Apogee mini-DAC to the PS Audio Digital Link III DAC and I don't put the stax transformer in the loop. For driving most of my full size headphones it's sound quality competes very well with similarly priced amps like the EF1, Travagans or Millett Starving Student that I compared it to, but it works best with HD600 due to it's power levels declining with impedance. With any IEM it beats the EF1, Travagans Red and Millett Starving Student hands down, due to the low noise and more precise volume control at low volumes.
A tube glow shot - everyone loves those: