Balancing ACT
By Andrew Harrison, Hi-Fi News & Record Review, November 1999
Chord in the ACT! A fine balance between pro-inspired phono stage, Wilson-Benesch arm and Michell turntable could lead to vinyl nirvana.
Chord Electronics' Phono Stage was the starting-point for assembling this record playing system. Any MC cartridge-equipped turntable could have been used to try the phono pre-amp in its standard configuration - but that would have been only half the story. Less than half in fact, because the specialty, the unquestionable forte of this head amp, is its balanced circuitry.
To use the Chord unit as its designers really intended requires a tonearm specifically wired in balanced mode, that is, plumbed internally with four discrete shielded wires running through armtube and pillar, terminated with four RCA plugs. For this review, Wilson-Benesch supplied just such a tonearm, a balanced-wired ACT Two. Since I was personally unfamiliar with the character of this arm and the effect this would have on the overall sound, a standard-wired ACT Two was also supplied for comparison.
Pick-up cartridges are traditionally connected to the amplifier by two phono plugs, for left and right channels, where the 'cold' connection at the cartridge (L-/blue and R-/green) is wired as the coaxial's outer screen in the arm leadout cable. This has been the way of doing the job almost exclusively from the early days of high-fidelity record playing.
Where this application of a balanced mode differs is in the routing of the signal source, + and - for each channel, from headshell to first amplification stage. Each channel takes two separate and dedicated connections, with a braid shield over the conductor, running back from RCA plug shroud to the headshell, where it is left free-floating.
Inside the Chord Phono Stage, a dual-differential circuit keeps the signal in balanced common-mode form, providing an output at a pair of Neutrik XLR connectors. Circuit board jumpers allow a choice of five input sensitivities to match differing cartridge requirements. Two more jumpers will also allow the Phono Stage to be configured for standard single-ended use. All the electronics for this self-contained unit are mounted on a dual-mono circuit board, with power supply sited at the opposite end in the very substantial milled-from-solid alloy chassis. There is no power switch to spoil the functional lines: on the rear side four solid RCA phono input sockets, an earthing post, and two XLR output sockets.
An arm and phono amp alone do not a vinyl system make. The Wilson-Benesch tonearm was used on a Michell Orbe, whose more humble relation - the Gyro SE - had impressed me some months ago [May'99]. The particular need here was for a 'transparent' turntable which would allow easy arm switching; this would facilitate making comparisons between the system in balanced and single-ended mode, using the two ACT Two tonearms ready set-up on their own base platforms. Michell turntables are the first type I've used that have a pre-balanced sub-chassis ideal for changing arms, even allowing vastly different arm weights and designs, without having to re-balance the whole sub-system.
Compared to the Gyro SE, an Orbe has a larger and massier platter - made from the same acrylic/carbon compound but extended fully down to where the gold-plated weights would hang - plus a record clamp and electronic QC power supply as standard. The sub-chassis casting is filled witn an effective damping compound, a black putty-like substance, and the motor unit's on/off switch features a green light embedded within to show its powered-up state. There is now an SE version of the Orbe, which lacks the full version's acrylic bases and dust cover, available for UKP****, against the originals UKP****. This can still be upgraded by buying the perspex boxwork later.
Applying trusted electrical engineering principles to a largely unchallenged connection standard is not a guarantee in itself of success. Balanced mode connection is used routinely in professional audio, in studios, theatres and stage concerts, where its relative immunity to the problems of hum and interference have made it a universal standard method for analogue (and digital) audio routing, especially microphone leads where the very low signal output of a dynamic microphone is instrinsically susceptible to RF and mains interference. And it is precisely for this reason that a balanced connection makes very good sense for a pick-up cartridge. Here the signal levels are even smaller than than these of most microphones, and considering the unrelenting scrutiny available to the pernicious audiophile with his or her clinically-revealing amplification and loudspeakers, it is worth ensuring that that nothing is left to chance in the delicate span between cartridge and amplification.
How does theory relate to practice? In order to get a feel for the combined synergy of the cartridge and tonearm, in regular single-ended mode, I first set up the standard ACT Two, with the phonostage configured by internal jumpers accordingly.
Incredibly transparent and insightful, the combination worked well, very well considering the diversity of manufacturers. There is Wilson Benesch, from the home of British Steel, using its special advanced composites and CAD-inspired craftmanship; Michell Engineering, a long-standing champion of quality metal and plastics engineering in North London; Chord Electronics of Kent, pioneer of high-frequency PSUs and aerospace-quality engineering, applied to performance amplification at high and low signal levels; and Ortofon in Denmark, long-time specialists in the fine art of moving-coil pick-up design and manufacture.
Used with Chord CPA3200/SPM1200C amplification into Harbeth LS3/5As, the sound was very precise, and able to allow unhindered analysis into the nature of the recording. Comparison with another phono preamp, the Kinshaw Perception Phono Centre, showed the Chord unit to have greater clarity and transparency, but with equally deep bass extension, leaving drum strikes from Gene Krupa [Krupa Rocks, Columbia 33CX10133] with better incision. Piano and bass within the same piece were better separated, in spite of the recording's monophonic provenance. The Linn Linto is a closer companion to the Chord phono stage sonically, as they both share an open clarity with cool precision, suggestion that any coloration or opacity heard at the speakers didn't originate in the phono amp. The combination sounded fast and clean, with little trace of smear or cloudiness to provide an impure 'analogue sound' that is oft mistaken for natural warmth. Top end harmonics were beautifully clean and unsullied, with the Ortofon MC Jubilee seemingly never more at home than in the stiff embrace of the carbon-fibre arm. The unhindered treble extension, combined with fast well-timed rhythms and bass-lines, bracketed the wide-open midband, thw whole dredging out unheard detail from records. All this detail, it must be added, presented in a wholly musical and believable soundstage.
Having familiarised myself with the turntable system with standard unbalanced wiring, I exchanged tonearms and reset the Chord phono stage input. As you may have gathered, I was highly impressed by the performance of the regular turntable. The cleanliness of sound, denying sub-chassised turntables' supposed bloom and euphonic warmth, was itself cause for excitement. But it didn't really prepare me for what was to come.
It was the nearest thing to real performed music - or, a step removed, the mastertape - I have heard in a long while. All the more surprising when it is issued from thirty or 40-year old recordings from a 'dead' format.
The difference between balanced and unbalanced tonearm/phono stage is not one of 'better bass' or 'better clarity', for example. It is one of grand scale and lifelike dynamics. And stereo image tangibility. When a chord is struck in an operatic piece, it appears with the full force of a mass of instruments playing in concert. Voices are larger and more substantial, with their position within the stage held pinsharp.
Soprano voices, potentially enthralling heard live but somehow often grainy and impure on digital and analogue hi-fi replay, became entrancing, as heard from Victoria de los Angeles and Elizabeth Schwarzkopf in Offenbach's The Tales Of Hoffman [Conservatoire Orch/Cluytens, Angel 36413]. I especially enjoyed the unforced flow available across all styles of music, like an old pressing of Pink Floyd's More [1969, Columbia SCX 6346] which showed me the songcrafting talents of Waters in 'Green is the Colour' and 'Cymbaline', the bassist never more at home than when stringing out a tune with a handful of minor chords. And that 'old' pressing, occasional surface clicks notwithstanding, sounded fresher today than I had believed possible.
Every aspect of sound improved going balanced: dynamics were enhanced, for example the impact and 'weight' of jazz beats on the Krupa album, where the recording became even less small-and-mono sounding. Stereo recordings sounded wider and even taller; that is instruments seemed better differentiated on the vertical axis - not a phenomenon I am used to experiencing.
In two words, the balanced combination proved truly stunning. It provided the kind of step forward that left me wondering why, increased cost and complexity aside for a moment, more high-end vinyl replay systems are not wired this way.
It provided the kind of tight, deep bass from a single pair of '3/5As that was thought out of reach to a Grade 2 monitor. It showed a perceived dynamic mastery that held my interest in previously ignored music. It also showed me faults and flaws in some pressings that I'd rather ignore, but it was a pittance to pay against the greater reward of unhindered musical enjoyment.
It is not a cheap combination: the Orbe will cost UKP****, or UKP**** in pared-down SE form. Add to this a balanced ACT Two at UKP****, Chord phono stage at UKP**** and an Ortofon MC Jubilee cartridge at UKP****, and you have a total outlay of (gulp!) UKP****.
It would be irresponsible to get too excited, when this amount of money ought anyway to bring absolute excellence. Often, though, lavishing large quantities of cash on a high-end system carries no instant guarantee of musical satisfaction. This one, I believe, does, and sounds better than any CD-playing front-end I have heard at twice the price. if records are your medium, and especially if you have fully-balanced amplification to exploit, you'll be daft not to hear what is possible.