A-6000 MKII - Integrated /Headphone Amplifier

UPDATE: tube rolling made a big improvement! I replaced the stock tubes with a pair of G.E. JAN 5670W from the bay (five bucks each). Bass is now much improved- sounds exactly right where it should be, nice and deep, kettle drums,kick bass, bass guitar , left hand of piano sound excellent now, no muddiness. The Qinpu now gives my QUAD 909 real competition and may even beat it driving the DeCapos (at 1/5th the price).My system's front end consists of:-musical fidelity v-link for digital music files from laptop (that thing is fabulous and is the only thing that made my computer music "listenable" after years of trying)-NAD S series CD player using SPDIF out w-Cambridge Audio DacMagic DAC-Transcendent Sound Grounded Grid tube preamp (best upgrade I ever made in 30 years of hi-fi experience).For power amps I use:-$2500 Transcendent Sound T8-LN 25 W tube OTL amplifier (sounds glorious, sweet and musical at _all_ times)-$1300 QUAD 909 130 W solid state amp (great midrange, not quite as musical as the T8 but very good)-$600 ClassDAudio 300w digital amp (sounds sweet and laid back, unlimited dynamics, dead quiet, doesn't sound harsh or digital, but a bit of overkill for my speakers)My speakers are relatively efficient (90DB) and very revealing Reference3A DeCapo I (no crossover).So, the reason I bought the Qinpu is that I was hoping to improve headphone listening with my Grados. The Grados are very unforgiving and I have suffered with excessive sibilance and harshness when listening to them through every headphone amp I have owned so far (especially with digital files), except the Bravo V2 (but two of those blew up within a couple months).Headphone amps:-$250 Creek OB-11-$50 CMOY mini altoids amp-$1300 Benchmark DAC1 Pre-$75 EBAY Bravo V2 tube headphone amp (blew two of them up driving the grados- they couldnt supply enough current)After about 6 hours of headphone listening with the Qinpu, I feel it is not as sweet sounding through the Grados as the Bravo was, but better than the solid state headphone amps, and it seems to have more power available so I am hoping it won't blow up due to the Grado's low impedance, high current demands. The bass seems a little thinner than I recall for the Bravo, and the mids are a little more "grainy" and digital sounding. But still less harsh than any of the solid state amps.Driving my Reference 3A speakers, I can definitely say that 16 watts is more than enough power. The bass is a little thinner than with either the T8 or the QUAD, and again the mids are not quite as sweet sounding as either of those amps-still a little grainy.But for $250 it is good value for the money. I hope the amp holds up.Also, the Qinpu does provide the opportunity for tube rolling, which I plan to do. All listening so far has been with the stock tubes.And one issue I found: With speaker cables connected, the headphone line-out is silenced. The supplied manual indicates the line-out could be used to drive a sub in tandem with the main speaker outs (low pass filter needed) but this does not work with my Qinpu.And I suspect (have not opened the unit to check for myself) that this is a "hybrid" unit. In other words, the preamp section uses tubes, but the power amp section probably is a simple solid state IC (this would explain the slight harshness compared to the Bravo V2).

Plato's "Allegory of the Cave" is a point of reference in this review because, after experimenting with this Qinpu a-6000 MKIi amplifier, I have reluctantly realized that my sonic reality has been nothing but phantasmagoria.It should not have been difficult to accept. After all, I returned to the analog world after listening to a Tracy Chapman record on a system whose heart was a pair of vintage McIntosh 275 amplifiers driving a set of custom-made speakers. Although bewildered by the quality of the sound, it was easy for me to rationalize--due to my limited budget--that any Solid State system would be able to achieve an approximate result. And with such a delusional premise, during the last 2 years I have embarked on a quest to find a suitable match between vintage amplifiers and speakers. The journey has involved receivers such as a Pioneer SX-780, a Kenwood KR-9600, a Technics SA-400, a Yamaha CR-800, two Concepts 6.5, a Concept 11.0, a Marantz 2015 and an Onkyo TX-4500 MKII; along with several sets of speakers, such as Infinity Qe, Boston Acoustics CR6 and CR7, Infinity Sterling 2005, Technics SB-L200 or A/D/S L1290. After an impulse sale of my Concept 11.0 paired with the A/D/S speakers (the investment was triplicated), my favorite matches have been the Onkyo with the Technics speakers and the Marantz with the Infinity Qe. In fact, although the horn tweeter of the Technics is amazing, I just love the sound of those Emit tweeters.Well, as a result of the Qinpu, that is history.Putting that conception of reality in the past, however, has been a somewhat painful process, for it just seemed unacceptable that, as Plato suggests in his analysis, I had been perceiving the shadows for so long--including digital media. Indeed, for a few days I refused to accept that this hybrid amplifier would be capable to ameliorate the sound of this format to the point that I kept A/B-ing a vinyl and a CD recording of Coltrane's Blue Train until I walked to the turntable to flip the record, but the music continued playing from the CD player.If fidelity entails the reproduction of a recorded live performance as faithfully as possible and high relates to the excitement of listening to it through an affordable piece of equipment, then this amplifier is definitely Hi-Fi.As suggested by the aforementioned equipment, I am far from an audiophile. So much so that I engage in the blasphemous practice of utilizing average speaker wires and interconnects. Moreover, although I have auditioned several tube amplifiers, this is the first time I have owned one to test with leisure. This review, therefore, elucidates my limited experience, filtered by my ignorance about superior equipment such as the one described in other reviews--some of which, incidentally, has been displaced by their owners after experimenting with the Qinpu. (I am rather grateful to all reviewers for allowing me to delve into the world of tube amplification with their sincere observations).IMPRESSIONSHaving read and seen so many images of this amplifier before its purchase, weight, dimensions and looks seemed like an after-thought upon unboxing. I was very pleased with all of them, but the principle of instant gratification drove me to install it immediately, relying on the phono stage included in the Onkyo TX-4500 mkII, which was paired with the Technics SB-L200. My uneducated ears noticed a difference in soundstage and instrument separation immediately, but the midrange seemed distorted. The set up was shifted to the Marantz 2015 and there was a considerable improvement. I then switched the connections to rely solely on the Marantz and, initially, it sounded so much better than the Quinpu that I almost decided to return it. Taming the remnants of my impulsivity, I retrieved a TCC TC-450 phono preamp from a closet, connected it directly to the Qinpu and my jaw almost dropped. Coltrane's "Resolution" had never sounded so real, so alive. I continued to A/B between the two amplifiers until I was convinced that the Marantz indeed sounds tubey, but that I liked the Qinpu better. As so many reviewers have explained, soundstage, coloration, instrument separation, warmth, liquidity, vocals, etc., seem incomparable to that of a solid state unit. The sound, rather than being pushed from the speakers, flows out with cadence. In terms of power, going above 10:00 seemed beyond the point. I did it anyway for testing purposes, and it more than filled the room without noticeable distortion.Yet, I still continued to refuse the acceptance of this new sonic reality. So, I ordered some tubes in order to roll accordingly: GE 5670 five stars, Raytheon JAN 5670, and Bendix 2C51.While the valves arrived, I tested the Qinpu's capabilities with all types of digital media, even more vinyl, and several tuners. I became increasingly dissatisfied with the sound as the stock Chinese tubes burned in. As clarity, soundstage and instrument separation increased, the bass continued to fade away. I loved the three-dimensional aspect of the sound, as others have described. Yet, even the Technics SB-L200, with their 10-inch diameter woofer and 90db efficiency, did not seem to provide a pleasant bass experience, even though I am not a bass fan. I have to admit that some acapella versions that I played sounded extremely impressive, especially Lara Fabian's "Je suis malade."The tubes arrived and, as I had gathered from reviews, their respective qualities revealed significant improvements. Undoubtedly, the Bendix are superior, bringing the bass back to the point of sounding almost SS, but their superior definition of vocals and soundstage makes the experience of listening to anything, including Metallica or Peter Brötzmann, feel very real and satisfying (I happen to like both). I seem to enjoy the Raytheon set more, but believe that the GE five stars are a great value, especially for those who like their music loud, as their gain seems to be higher. The Raytheons provide all the advantage of tubes, but with a neutrality that fails to fatigue the ears. Or is that what the tube reality is all about?In my experience with any tube combination, the Qinpu works better with digital media, especially CDs, than with vinyl--although instrument separation is enhanced in the latter format. I listen mostly to Jazz in vinyl and it is rather satisfying to discover musical details that had been overshadowed before. Older records, such as pre-Liberty Blue Note, Prestige yellow "fireworks," Six-Eye Columbia, or early Impulse!, reveal nuances that I had simply not noticed before. Also, they sound fuller than DMMs or recent releases. Even with an Ortofon 30 stylus, I could not understand the superiority ascribed to a Six-Eye Columbia pressing of Miles Davis' "Kind of Blue." Now I do, for the tubes definitely bring it out.I will explore the Qinpu with a better phono pre-amp, as this may be causing the limitations I am perceiving with vinyl. Although I was also very pleased by pairing it with the Infinity Qes, I will try more efficient speakers in the future. I used a four channel speaker selector (with impedance matching) in order to connect 2 sets of speakers simultaneously. This quadraphonic or surround-sound set-up seems to have enhanced the 3-dimensional aspect inherent in the tube experience and I rather like it.Given the price and performance of this unit, I am not surprised that so many reviewers have been pleased with it, to the point of finding it superior than some of their high-end equipment. In my case, I simply like its sound reproduction better than any other equipment I have and find it very difficult to readjust to solid state reproduction while driving or in my office.It is important to note that the headphone problem reported by others was replicated in my unit: no stereo sound unless plugging the headphones a quarter of the way into the input. This problem should be resolved in further upgrades.The operating temperature seems about the same as the one from other receivers I own. On the fifth day, however, I placed a small computer fan under the toroidal transformer as a probably unnecessary safety procedure to prolong its life. Sound quality does not seem to be affected.As a minimalist, I love the design of the unit, especially the brushed aluminum finish (if it had been black, in spite of the positive reviews, I would not have ordered it). The wood accent provides a touch that balances the modernist design with contemporary aesthetics. I am not fond of blue LED illumination, but that will not be a problem because, as with all of my equipment--except the speakers, of course--the Quinpu sits behind closed doors in a specially designed audio-closet (the set-up is still aesthetically pleasing and the only black items in that place are cables or vinyl).I like the sound and looks of the Qinpu so much, however, that I may simply bring it out. Looking at it may reinforce the acceptance that there is a more satisfying sonic reality beyond solid state.

Am using this to power a pair of Cambridge S30 bookshelf's (90dB sensitivity), Musical fidelity V-DAC-II, Toslink from a 2008 iMac and playing Apple Losless music (ripped from CDs. The Speakers are spectacular and create a live presence. This amp is able to comfortably drive them and produce a good quality sound. I replaced the stock tubes with the GE JAN 5670 tubes, but they sound worse than stock to my ears - the lively quality of presence is gone. So the stock tubes are back on.However, I am not sensing a "tubey" sound (something my nORH ACA2b pre-amp was able to produce). Still debating whether to keep or try additional tubes.Update Sep 12 2013: I ordered a Musical Paradise MP-301 Mk3 for quite a bit more money (about $400 shipped). Build quality is superb, only time will tell if it stays reliable. I was quite afraid that it may have a lot of hum issues (there were folks having these on the Mk2 model). Fortunately for my application (driving speakers), I see no issues with hum and its dead quiet. I initially had issues with one of the preamp pentode tubes being busted (so one channel would cut off), but on reporting, new preamp tubes have been sent by the company. It does not have the extension I used to experience with the NorH preamp, but its not bad. It allows me to experiment with more tubes (both the preamp and the power amp tubes). I cannot say one is better than the other but I find the MP more interesting. Of course, as with everything else, YMMV.I am returning the Qinpu.