January 2006


Singlepower Audio MPX-3 Headphone Amplifier
Review By Rick Jensen
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  I had never reviewed a headphone amp before having the opportunity to spend time with the Singlepower MPX-3.  And in some ways it is much easier to audition this type of amplifier for reasons that should seem obvious:

However, it isn't all peaches and cream (although we should admit, in all transparency, that this is not a tough row to hoe).  The very elements that make the environment a positive and pleasurable one, as noted above, are precisely those that confer a certain uniqueness on the listening experience.  I recognize that this has been said before, but it is a first time for me:  the personal and "pure", i. e. undiluted, nature of listening through headphones, imperfect thought it may be, makes it somewhat more difficult to find reference points that are usable and useful.

One more preliminary observation:  as a result of listening to the MPX-3, I discovered that there is an entire subculture of headphone crazies out there.  I had seen some vague references to them in the past but had paid little attention.  Let me state, though, that your average reviewer cannot match either the headphone experience or the intense passion of these fanatics – and I mean "fanatics" in a good way.  On forums such as Head-Fi one will find a not insubstantial group of people who know their headphones and related equipment intimately and are pretty articulate about it, who experiment with every possible tweak (almost as much as do ardent vinylphiles or compulsive tube rollers – come to think of it, many of them are vinylphiles and tube rollers) and who know their stuff.  One such review of this same unit made use of several amps, a couple of ‘phones, many power cords, and multiple cables and went into great detail about the characteristics of the MPX-3.

That is enough for the modesty that underlies this auditioning:  this was a challenging and most pleasant experience.  I volunteered to Steve Rochlin for this duty because I wanted to hear a fine headphone amplifier over a period of time.  I had had the pleasure of sampling some very good amplifiers at CES and Home Entertainment shows over the past few years and it was enough to make me want to try some more.  So when Mikhail Rotenberg of Single Power offered one of his well-regarded units for review, it was a no-brainer and I spoke up very quickly.

Overview
The amplifier that was sent to me was the MPX-3, which is in the middle of the Singlepower line.  The middle of the line is no embarrassment:  at a suggested price of $949, and with a long list of possible and very popular options, this is not a frivolous purchase for the iPod crowd.  Singlepower also make four of five other principal models, with many variations on each one, that go from base prices of $649 to around $9,000 or more.  While each of the models above the MPX-3 will build on the parts and the design of those below it in the line, the most important enhancements at every step are in the power supply.  Singlepower are among those manufacturers of high-end equipment for whom the power supply is the sine qua non of good reproduction:  they go so far as to say that "an audio amplifier is essentially a modulated power supply."

My version of the MPX-3 was the 6sn7, if one can call it that.  It has the 6sn7 tubes; hence the name.  The amplifier is an elegant albeit simple industrial design:  it reeks of being a serious piece of equipment and is very nicely finished at the same time.  The tubes are laid out diagonally across half of the top surface, with the transformer and capacitors taking up the remainder of the surface.  There is no "crowding", however – this is an uncluttered design that honors its dedication to a single purpose.

Similarly, the front panel is the picture of neatness and elegance.  There is an on-off switch that is fairly robust, dials for gain and balance (the latter being very welcome, given the sensitivity that one may have to small differences in amplitude and the very real possibility of differences in sensitivity between the ears), and a 0.25-inch jack for the headphones.

The rear panel has gold RCA input jacks for three separate sources and the standard plug for the power cord.  The entire surface is a glossy piano black that is most attractive.  And while neither tiny nor lightweight, the MPX-3 does not weigh down a sturdy shelf or take up too much room. The parts used in the MPX-3 are of high quality:  Noble volume control, silver for the (silver-ceramic) sockets, the (silver-Teflon) wiring, and the solder, OFC wire for the signal path, and a heavily filtered power supply.

The unit I auditioned had, as additional options, a power supply capacitor upgrade and an output capacitor upgrade.  The former is, per Rotenberg, the most popular option with the goal of smoothing the sound via smoothing the power supply.  The latter option upgrades the output capacitors to very low ESR, with correspondingly low resistance and with "almost zero memory effect" in the interest of greater transparency.  The cost with these two options is $1,170.

Just to highlight some of the other possible upgrades, they include at least four additional capacitor upgrades, with each supposedly having a slightly different improvement (speed, neutrality, transparency), Goldpoint stepped attenuators, Cardas or Neutrik jacks, an option allowing the MPX-3 to be used as a preamp, and probably more.  One can certainly add to the stock MPX-3, at a modest increase in cost.  However, I will focus on the "midrange" version noted above, which is very fine indeed.

With the MPX-3 I used two different headphones, the first the Sennheiser HD-600s with Cardas cable and the second stock Shure E4c's.  I will say up front that both sounded terrific, the best I have heard either, and both sounded very different as one might expect. Signal sources were my Proceed CD player, a Linn LP-12, and a Sony CD Walkman (for fun), and I tried all but the Walkman both direct (or for the Linn, with my conrad-johnson Premier 15) and through the conrad-johnson Premier 17LS.

Listening Impressions
My first impressions of the sound of the MPX-3 were disarming.  I cannot say that it was love at first sound – my immediate reaction was that the presentation was too lush and too "deep."  I do not think that this has anything to do with break-in (although I should admit that I have never obsessed about break-in).  Rather, I had not had the experience of hearing the 600s through a really good amplifier.

With no headphone amp in my system, my previous listening had been either via my home theater setup (which allows for headphones through a mid-priced receiver) or via my old Stax Gammas. The latter, which I still have and which still work quite well, use an adaptor that runs off the speaker taps of the power amplifier.  I had not used the Stax ‘phones that often because of the necessity to connect and disconnect the adaptor from the amplifier:  you could leave them in the line, but that would mean that your speaker connections run through the unimpressive adaptor unit, a price I did not wish to pay.  In any event, the Stax had always had tremendous detail, but strike me still as tilted up in the treble much more than their finest electrostatic units – the sound was a bit "hollowed-out."  And the HD-600s through the HT receiver; well, it's not really worth discussing.

So the MPX-3 startled and displaced me and caused me to wonder if what I was hearing was correct.  Alternating between analog and digital helped to give some signposts.  Listening to the Mozart Clarinet Concerto [Solistes Europeens de Luxembourg, private label SEL 1991/10, a CD recording that I have had for years and know well, I did not find it to be overly lush; indeed, the general tone was light, which is characteristic of the performance.  I thought I perceived a slight constriction in the space between instruments, as though it was a bit congested, and a recessed feel in the lower midrange.  But – as well as I know this recording – this was the first time really hearing it on a high-resolution, high-isolation system.

A current CD that I have been listening to a great deal is Flowers of Avalon from Tracy Grammer, which features Grammer singing songs of her late partner, Dave Carter. Over my speakers, this recording has very full bass, a snappy, slightly prominent midrange, and a pinch of echo.  Pitch accuracy is very good; you can really appreciate Grammer's lovely, natural, folksy voice.  Via the MPX-3, that voice is spot on.  The bass was very full and round, almost sounding enhanced.  While you don't get the visceral impact through the headphones that comes from large speakers, the bass response is deep and prominent, with real nuance and timbral definition. Dobro and banjo were less brittle than before.  I had seen Grammer perform live about three weeks prior from about eight feet away, and the MPX-3 definitely delivers a "you are there" experience; it sounded very close to the live performance.  On "Laughlin Boy", a fast-paced song, I noticed a minor narrowing of the voice, almost a honkiness, like a cupped-mouth sound that is not the case via the speakers.  I could not really determine if that was due to the headphones, the amplifier, or the recording.  In any case, it was not a serious flaw.  In general, this recording, full of mandolin, guitar, dobro, violin and other strings, comes through with great definition and an utter lack of any syrupy texture that I might have expected from first hearing.

Switching to LP was nonetheless a relief and a pleasure.  Eva Cassidy's Songbird [S&P 501] was first up and the entire sonic picture was better by far.  Delicacy with lots of body, I noted.  "Fields of Gold" had the quality of not shouting and yet playing loud enough, just like live music.  Perhaps that is due to the relative isolation afforded by the headphones, but it speaks to the accuracy of the amplifier.  Again, we are fortunate in my area to hear quite a bit of folk music in small venues, and the MPX-3 does an admirable job of recreating that space and that sound.

Some others among my usual recordings that sang nicely through the MPX-3 were Dire Straits "Communiqué", where the near-infallible pitch accuracy of Mark Knopfler's guitar was a treat, and Art Pepper Meets the Rhythm Section [Analogue Productions ART 010] where the sax was as good as I have heard, again, perhaps due to the total absence of any ambient noise.  The noise floor of the MPX-3 seems to be very low – even late at night, it's darn quiet.  Finally, the title track of "Come to Find" by Doug MacLeod on the Audioquest LP [AQ-1027] provoked a wow! – I could swear I felt the percussion of bass drum and guitar right in the gut, even if that is highly unlikely.

In general, the MPX-3 seemed to spread the soundstage out as well as I might expect from headphone listening (without any processing) even if it is most likely illusory.  I find it hard to characterize the lateral width, although there didn't seem to be too much congestion in the virtual space that was created.  Never did the sound seem too concentrated in the center of my head, either. The Franck Sonata in A from Johanna Martzy [Coup d'Archet 001], in glorious mono, offered a distant perspective as it does via the speaker system (and I am not sure how).  The sound is centered, of course, but it seems to breathe, with the piano set just behind the violin, which seems to attest to some timing accuracy both in the beautiful recording and in the reproduction thereof.

While most of the listening was done with the HD-600s, I went back and listened to many of the same recordings with the Shure in-ear ‘phones.  I normally use these for travel along with my iPod but thought that they were of sufficiently good quality that they would shine through the MPX-3.  And shine they did – little could one have been prepared for just how sweet those little babies could be; after lots of iPod listening (to both compressed and lossless recordings), the great source material brought the Shures to a whole new level in my eyes.  Gone were the thinness and a moderate stridency that seemed to be part of having tiny little ‘phones; if anything, the Shures sounded at least as neutral and musical as did the HD-600s, albeit with slightly less bass impact.  With this distinguished company, they were allowed to sing.  And while the subjective impression of the two different ‘phones was different, the contribution of the amplifier appeared to be consistent across the various recordings sampled.

Conclusions
It is rather difficult to imagine how headphone listening can get much better than it is through the Singlepower MPX-3.  That is not to say that I have not heard, for very brief moments, some outstanding headphone-amp combinations.  But I have not previously had the opportunity, or the inclination, to get intimate with this most intimate of listening modes.  As has been said many times before, if you really want to hear what is on a recording, listen to it through some good headphones and a good system.  However, I suspect that often those who have said as much are referring to all the extra detail that one picks up.  What the MPX-3 does is to convey the emotional content of the music as well and as much as the detail, which tells me that it is doing a thorough job of both capturing all the bits of music as well as avoiding the pitfall of screwing them up, which would of course be much more noticeable through high-quality headphones.

Overall, I can say that this amplifier has been close to a revelation in allowing one to hear deep down inside the music, as one might hope with headphones, without having one's ears assaulted or experiencing even mild fatigue.

Note that Singlepower sells direct and via a very few Internet dealers.  Mikhail Rotenberg says that the customer is involved in the configuration of his unit, and there is necessarily a consultation between each customer and the company.  He believes that he can deliver greater value for money; certainly, the fine reputation that the products enjoy among the headphone cognoscenti seems to support his confidence.  Hence, in order to hear the amplifier, short of having a friend with one at home, one would have to order from Singlepower.  In view of the outstanding quality of the MPX-3, I would counsel anyone so interested to read through the comments on some of the sites like Head-Fi as noted earlier and then to give a call to Singlepower.  While their return policy is a good one, a necessity for a direct seller, Rotenberg says that it has hardly ever been used.  No one seems to want to send the units back, except for upgrades.  That is testament to a very fine set of products from a company that seems to know the market that it wants to serve.  So while I cannot say that I have joined the headphones-only crowd – after all, I do like to listen to music through fine loudspeakers – I can say that the Singlepower MPX-3 has given me a glimpse into their passion.  The amplifier reproduces music extraordinarily well at a bargain price, if you are inclined to some privacy in your listening.  Being alone isn't quite so bad if you have the MPX-3 with you.

Specifications
Type: stereo headphone amplifier

Input Impedance: 100K ohm

Output Impedance: < 20 Ohms

Power Supply Capacitance: 1340 uF

Rectification: silicon

Power Output < 0.5 watts

Usable Headphone Range: 16 to 2000 Ohms

Total Distortion < 0.1%

Volume Control: Noble

Input RCA: Gold Plated Teflon insert

Output Headphone Jack: Neutrik Standard Chrome Nose

Other: Milled aluminum volume knob, 1/8-inch thick aluminum chassis piano black powder coated

Base price: $949, as tested: $1,170

Company Information
Singlepower Audio
Voice: (303)-523-0581
E-mail: Info@SinglePower.com
Website: www.singlepoweraudio.com