Product: Phono 2 Ci
Manufacturer: AQVOX - Germany
Price: 700 €
Reviewer: Werner Ogiers - TNT Belgium
Reviewed: April, 2006
Phonostages are my pet audio components. The design of a really good MC preamplifier is an extremely challenging job: the tiny input signals are in the range of tens of nanovolts (60-80dB below the nominal output level of a moving coil): this is not about counting beans, it is about counting individual electrons. Small wonder then that often original and wonderful circuits are employed to extract the best from the vinyl record. Hence my fascination.
One or two voices in the industry pointed my attention to the unassuming box that is the subject of this article. This AQVOX Phono 2 Ci is, allegedly, 'a good one'. AQVOX is a young German manufacturer operating on the divide between serious consumer audio and professional studio gear, surely a position with an interesting perspective. The present portfolio includes this phonostage, a USB-enabled stereo DAC, and a stereo microphone preamp plus 24 bit / 192kHz recording ADC.
The main designer for AQVOX is Carlos Candeias, who gathered some fame for his work on the upper-end CEC products. Most of Candeias' designs, AQVOX and CEC alike, prominently feature a transistor-based amplifier circuit dubbed 'LEF', or 'Load-Effect Free', something that is touted on the companies' websites with a curious mix of in-depth explanation and mystique. More on LEF in a later installment of this review.
The AQVOX Phono 2 Ci scores exceedingly high on my interest-o-meter, going off the beaten path whenever and wherever possible. Count this: 1) switching power supply, 2) no loop feedback, 3) current or voltage input, 4) RCA and balanced in, 5) RCA and balanced out, 6) no IC opamps, 7) attractive pricing .. this is most definitely not a run of the mill RIAA preamp. In fact, the 2 Ci allows so many different configurations that it is more of a collection of phonostages housed in one box. The prospect of reviewing all of these thoroughly is positively daunting! That's why we split the work: in this first part you'll get an overview of the product and my listening impressions. In the second part of this review Mark Wheeler will put down his verdict, and I'll go into the technical details of this fascinating phono preamplifier.
Ignoring the balanced XLR inputs for a while the Phono 2 Ci is almost like a normal well-endowed phono preamplifier. DIP switches on the back are used to set gain, with choices between nominal (suitable for MMs), '+6dB' and '+20dB' (for MCs). In addition to this, per-channel rotary controls on the front panel give another stepless +0 to +10dB. Other banks of backside DIPs serve for cartridge load, with 100, 1000, and 47000 Ohms present, alongside capacitances of 47pF, 100pF, 220pF, or 470pF on top of a default 47pF.
The output is simultaneously present at unbalanced RCA connectors as well as truly-balanced XLRs. The unit is capacitatively coupled and thus the output is always free of DC and subsonic rumble. An additional, and quite steep, subsonic filter can be switched in and out of circuit at the front. Other things of interest, at the back, are a ground terminal that accepts bare wire, spades, and even banana plugs (but not the crocodiles used on e.g. Incognito-wired Regas or the Michell TecnoArm) and a button that lifts the internal ground connection of the amplifier, handy in case of hum problems.
And then there is of course that press button labelled 'RCA/XLR Input'...
...which allows one to connect a cartridge to the balanced XLR inputs, turning the AQVOX into a totally different animal. While the RCA inputs operate in standard voltage mode, compatible with any cartridge, the XLRs are current inputs, and should be used with moving coil cartridges only: a current-mode input presents a near-short to the cartridge, and works only properly when the cartridge impedance is low and resistive. Now this is not the only current-mode phonostage on the market (other examples are 47Labs, the various Dynavectors, the ESE Nibiru, Jean Hiraga's DIY design from the seventies, ...), but the AQVOX is to my knowledge the only one combining this principle of operation with a balanced input. Using the XLR inputs comes with the requirements of a tonearm with suitable cabling and some care on behalf of the user: this is definitely a case where reading the manual pays off!
The front panel gain controllers are particularly welcome, for a multitude of reasons. For starters, many phono cartridges, and not just affordable ones, suffer audible channel imbalances. It is very nice being able to compensate for this close to the source. Then there is the confusing fact that a current-mode amplifier's effective gain depends not just on its circuit, but also on the cartridge's generator particulars. In other words, gain is more or less a surprise (see below for my experiences). Again, it is extremely nice to be able to trim gain closer to the desired value. And lastly, variable gain comes in as a necessity when directly connecting an ADC (analogue-to-digital convertor) to the phonostage. These days this is not so far-fetched as it seams: this may happen during LP-to-CD transfers (both my recording ADCs lack input level controls), when connecting to a serious AV-receiver (they often digitise the analogue input), or indeed to the Lyngdorf TDA2200 digital integrated amplifier.
The AQVOX balanced current-mode input is about as odd a moving coil interface as it gets, and thus compatibility issues are to be expected with some cartridges. Luckily I had four entirely different types available, and luckily there still was the Technics SL-1200 review sample with its detachable headshells, duly pressed into service alongside the regular GyroDec with SME IV. Denon DL-103
The first trial was with the trusty DL-103. This has a regular low-output generator, 0.35mV, married to a coil impedance of 40 Ohms. Intuitively the latter seems to be on the high side for use with the nearly short-circuited current input. In practice all went well, electrically that is, the Denon/AQVOX combination sounding optimal with the gain controls in the +6/9dB region.
The sound, however, was something of a mixed bag. Treble was very pure, silky, and natural, much in line with what I expect from a competent feedback-less design. Deep down bass definition and tunefulness was truly wonderful. But alas, the DL-103 exhibits a slight leanness in the SL-1200's arm, and the Phono 2 Ci tended to exaggerate this. The resulting sound had a see-through clarity that would be beguiling if not for a certain distant character and a lack of body. I can perfectly imagine that some people would like this type of sound, but a universal combination this was not.
Grado Statement Platinum
Next one was the Grado Statement Platinum, the low-output moving-iron cartridge that gave such a disappointing account of itself during the SL-1200 review. Grado specifies it as 0.5mV output from 2 Ohms resistance combined with 2 millihenries inductance (see Grado website as well as the product manual). The very low coil resistance suggests a high effective gain when combined with the current input. On the other hand, that enormous inductance surely will attenuate all treble when combined with the low 20 Ohms input impedance of the Phono 2 Ci, something like -21dB at 20kHz! No-one in his right mind would attempt to drive a current-mode phono stage with such a generator. So that's what I did. And it worked! In fact, the Grado now outpaced the DL-103, adding plenty of bass warmth and emotion to the mix, with almost none of the uncontrolled sibilance I had experienced in the past from this cartridge.
So what happened? Had Ohm's Law suddenly be suspended? Of course not. Using the handy Peak Atlas LCR40 gizmo I went and measured the Platinum's true impedance: 2 Ohms in series with .. a mere 60 microhenries. The published Grado specs are plain wrong, shame on them. With this sort of impedance the expected drop at 20kHz is a fairly insignificant 0.6dB, just enough to act as a sweetener, just enough to make me hate this reviewing business even more .. Benz Micro MC Scheu
Over then to the Benz Micro MC Scheu. Being a high-output MC this is, again, not something one would use with a current input. This cartridge's figures are 2mV at 5cm/s and 50 Ohms. Once more the combination worked well, although even with the gain controls set to 0 there was a slight excess of gain. Not that this harmed the sound, which was pure, liquid, warm, dynamic, and rhythmic, with filigrane treble, and above all, elegant. I'm speaking of serious quality levels now, but keep in mind that the success experienced in this particular case is not a license to freely mix high-output MCs with current-input phonostages.
The Scheu's generator impedance of 50 Ohms is remarkably low for its 2mV output, and this probably helps in interfacing. Something like a Denon DL-110 delivers a near-identical 1.6mV, but needs 160 Ohms coil resistance for that. Such a cartridge probably won't work here! Not that it matters: the Phono 2 Ci clearly deserves a better cartridge, and anyway, there are always the voltage-mode inputs as a back-up.)
Jan Allaerts MC1b
Even more serious levels of quality were attained with the Jan Allaerts MC1b (0.5mV, 20 Ohms). Interfacing was wholly unproblematic, although the preferred gain settings were once more +6/9dB, just as with the weaker-output DL-103.
With this GyroDec/SME/Allaerts combo I indulged in the archetypical record-after-record sessions as, indeed, the AQVOX proved to be totally addictive in this setup. It consistently carries a purity of sound all over the tonal spectrum, where other phonostages tend to be a little dirty and/or uneven. This purity and lack of 'mud' gives rise to a see-through stereo picture, a fine transparency, and natural, convincing dynamics. The sound is analytical in the sense that it allows you to easily focus on any instrument line in the mix, but it is not in the least clinical and always remains sweet and pure. Even when there seems to be a lack of overt lushness and drama, I always found this phonostage totally inviting so it must be doing something very very good indeed.
My regular phono preamp is a modified MkI Trichord Dino+. I don't know how it compares to the present-day MkII Dino (which gets good reviews, even in Germany), but mine sounds a bit sweeter than a regular MkI, thanks to a slightly re-engineered RIAA-curve and Epcos MKV polypropylene-in-oil capacitors. In fact, I also have a Delphini MkII (just a board, sitting in my DIY line preamp's housing), and I deem the Dino more musical, if less precise. Anyway, next to the AQVOX the Dino sounds a bit rounder and meatier at the bottom, is superficially as sweet, and images a bit more convincingly in dimensionality as well as levels of focus. However, closer listening reveals that the Trichord carries less information in the bass and is overall slightly thicker and dirtier. Good as the Dino is, the AQVOX is comprehensively cleaner, preciser, still more musical, and thus overall better.
By now you'd have gathered that I was very happy indeed with the sounds emanating from the AQVOX in current mode. The only complaint would be that overall its inherent gain in this mode is at the low side: I would have preferred to run cartridges like the Allaerts at 3-6dB on the gain controls, thus leaving some room for cartridges with a lower output. This complaint, however, should be balanced by three things. First, gain does not come for free in a two-stage open-loop design like this, and making the circuit louder would probably harm its sonics. Second, I did all of my serious listening with a unity-gain line stage. Most other users' preamps will have some gain that redresses my complaint. Third, the balanced outputs, which I did not use, have an additional 6dB when used with a true balanced input on the line stage, so there you go ..
As the current mode of operation is one of the 2 Ci's unique selling points I devoted only a short time to the 'normal' voltage mode, using the MC1b.
My feelings then were of a somewhat less confident presentation, with less stable imaging. Luckily the fine tonality experienced with current mode remained, including the wonderful bass definition and treble purity. I'd gather that voltage mode gives you 80% of what the Phono 2 Ci is capable of (maybe more with a high-output MM), and that still brings it to a very high level. Although ultimately every owner should strive to use the current input, one should not feel cheated if resorting, temporarily or even long-term, to voltage mode.
AQVOX also compete in the arena of pro sound. The closest I can get to that is in my home office, where a system is dedicated for transferring LPs to CDs courtesy of a Rotel RX-970 phonostage (non-stock with 0.1% RIAA components and a completely variable frequency curve above 2120HZ) piped into an M-Audio Firewire Audiophile (again, with modified input stage prior to the ADC chip). In current mode the MC Scheu got too much gain, driving the ADC slightly into clipping, so I had to revert to voltage mode. The Phono 2 Ci's volume controls proved of great use matching the level of any LP to the ADC's input range and also redressing slight channel imbalances. Overall the AQVOX led to superior transfers, and the hacked Rotel's unique variable RIAA was more than offset by the Phono 2 Ci's much greater dynamism, transparency, and general lack of crud and distortions.
The AQVOX proved a fine component to live with. Fit and finish are good and the looks are, to my eyes, nicely understated and elegant. The gain control knobs have a solid feel to them and, more importantly, tweaking them during replay induces no crackle or other untoward sounds. Knowing where exactly these gain potentiometers are in the LEF circuit I can assure you that this is an indicator of AQVOX's circuit design and engineering qualities. Likewise the optional subsonic filter seems to do its job in a most unobtrusive way. Whether in or out I could not detect its influence, although this was admittedly done on the ESL-63s which are not truly full-range. (Incidentally, I had the impression that the Phono 2 Ci's removal of subsonic junk allowed me to push the Quads to higher levels than I'm used to.) While not the most quiet phonostage around noise levels were very low in current mode, and just-noticeable in voltage mode.
The switching power supply did its work admirably, without the mechanical rattle and hums I am used to from almost every linear supply (our house has a pretty bad mains). On the other hand, the Phono 2 Ci was prone to some electrical humming and buzzing in the main system as well as in the PC recording system, and this regardless the state of its Ground Lift switch. This unit is extremely sensitive to ground loops and I could only silence it by replacing its standard 3-wire mains cable with an ungrounded 2-wire type.
Throughout the review period the AQVOX Phono 2 Ci entertained me with its natural dynamics, beguiling clarity, unforced precision, and astonishing consistency. While its tonal balance is a shade lighter than the norm, with somewhat less saturated colours, I must say this matched very well with my ESL-63s and with all of the cartridges tried bar the DL-103.
Offering innovative circuitry, fine build quality and aesthetics, and a pragmatic choice of functionality, and of course the attractive pricing, this truly is a phonostage for the twentyfirst century. Highly desirable!!!
[Go on to Part 2]
© Copyright 2006 Werner Ogiers - www.tnt-audio.com