Transformer pre-amps are nothing new. The breed first took off in the UK with the arrival of the Music First Passive Magnetic Pre amplifier in 2003, and similar models from other brands have appeared in the succeeding years. No active electronics are involved, they are neither solid-state or thermionic, and nor do they need any external power source. And yet despite this – indeed, perhaps because of it – they have arguably proved themselves more transparent to the music than any other pre-amplifier, free also of any audible hiss or grain. A good example truly opens rather than constricts the sound, in no small part because they provide just about textbook impedance matching between components.
The Townshend Audio Allegri passive pre-amp is not new either, first appearing around four or five years ago. But after spending some time away from full-time reviewing of audio equipment it’s only in recent months that I’ve managed to catch up with this intriguing example of the passive transformer control unit, one that is somewhat different in look and performance to most others on the market.
Nowhere have I yet found any review that compares the Townshend Audio Allegri with that original Music First transformer pre-amp, so I’m hoping to join some dots with this overview of these closely priced examples of the transformer volume control (TVC).
In June 2016, prices are £1950 for the Allegri, and £2040 for the original MFA Passive Magnetic, now renamed the Classic. The latter has effectively been superseded with improved versions anyway, first by the Classic V2, which will be covered in detail in a separate review; and by the Baby Reference V2, the current flagship of the Music First range, available at three times the price of the original.
Out of isolation
All the TVC units I’ve heard to date have been based on the isolating line transformer, with multiple taps on the secondary windings to set desired attenuation level via rotary switches. The transformers inside these TVCs are normally quite large, several centimetres tall in screening cans, demanding chunky boxes to house them. The Allegri though takes two little unscreened autotransformers, one for each stereo channel, allowing it to fit into a slim metal case just 45 mm high (minus rubber feet), and only 127 mm wide. However it does stretch back a full 304 mm – about the same depth as classic hi-fi separates like a CD player.
Autotransformers have long had a useful place in audio electronics, even if like other examples of transformer technology they’ve fallen out of popular use today. Constant-voltage loudspeaker setups is one application, such as basic PA systems used for public announcements at large sporting events. Here autotransformers are used in the speaker column to step down the 100 V sent over long, long cabling. And fans of the BBC LS3/5A monitor speaker will remember that early 15 ohm models used an autotransformer to match tweeter output within the little speaker’s complex crossover.
The autotransformer relies on a similar principal of magnetic induction as a regular line transformer, but has only one coil winding over its core, where a normal transformer has independent primary and secondary windings, electrically isolated from each other. My understanding is that there may be some advantages in going the autotransformer route, starting with a smaller and lighter transformer since the core can be made smaller, and less copper wire is required. That makes them cheaper to manufacture, which should benefit the buyer.
There may be some electrical advantages too, such as lower parasitic capacitance and leakage reactance; the former can roll off response like an intrinsic low-pass filter. The latter can give rise to resonance at ultrasonic frequencies, leading to raised HF output, although any well-designed isolating transformer will only exhibit mild resonance, and that far above the intended passband.
By adopting autotransformers, it does mean that the Allegri is denied one of the major advantages of the TVC pre-amp, namely the total separation of source and load, since the two sides maintain a common electrical ground. That may not be such an issue in a purely analogue system using record player or reel tape player; but when connecting linear amplifiers to digital sources – and in particular, computers – it can be a definite boon to sever all electrical connection between those RF noisy sources and the sensitive analogue electronics.
As I discovered when using the Allegri in a stereo system that serves double-duty as a multi-channel surround system, audible mains buzz would make this TVC solution untenable here. The setup will be familiar to anyone who’s integrated a two-channel music system with a multi-channel rig – when surround sound is required, the front LR outputs of the AV processor pass through a spare pair of inputs on the music pre-amp, which has been set to unity gain, leaving the AV pre-amp in overall control of volume to speakers front and rear. In my case, a small potential difference between ground lines of AV processor and power amp was a probable cause of this low-level buzz through the front speakers. It’s here that an isolation transformer can prove a godsend by isolating different grounds.
Build and Construction
Gently radiused corners on the 5.9 mm-thick fascia also extend along the full length of the casework, lending the Allegri an overall softer, friendlier look than a simple sharp-edged box. And as a fully passive box of electronics that doesn’t feature any power source, there’s no need for any power LED to indicate operation. It’s always on.
The front panel has two milled-alloy control knobs finished in the lighter silver colour of the case, with a subtle three-face bevel on their fronts that, and a scored line along their shaft also helps to indicate at which position the knob is currently pointing.
The left knob is the source selector with six numbered (rather than named) positions, from 1 to 6. The right-hand knob controls volume from a 24-pole two-wafer switch, again numbered with white silk-screen printing, this time from 1 (minimum volume) up to 24 (maximum). (Earlier versions of Allegri had attenuation level spelled out in ‘–dB’ steps around the volume knob.)
These switches are reasonably positive in use although they lack the reassuring precision of the best high-end switchgear. Both knobs, for example, have a little ‘play’ that lets the knob wobble fractionally between selections, caused by the use of long extension rods that connect to rotary switches – set far back in the example of the source selector. And with knobs only 30 mm diameter and sticky switches resisting movement, some focused twisting is required to quickly change volume, for instance. This is not being petty – these are the only human interface element on a pre-amp such as this, and they need to be comfortable, positive and precise between finger and thumb.
It’s worth noting the spread of volume settings available from the Allegri. On any stepped attenuator-based volume control, the spacing of discrete gain settings will to some degree be a matter of taste, and one greatly affected by choice of partnering source and amplifiers, not to mention speaker sensitivity.
The chosen volume steps have changed since an early review (PDF) of the Townshend Allegri was published in Hi-Fi Critic magazine, where Martin Colloms criticised the spacing through the middle of the range as being too wide. And where the original ranged from +4 dB (at position 24) down to –63 dB (position 1), the newer sample that I tested still runs from about +4 dB, now down to about –50 dB. Additionally there’s a full mute position available from a simple toggle switch sited between the two knobs.
In trials in different systems, the minimum setting of –50 dB was found to be much too loud for late-night listening. Meanwhile, the availability of positive gain at the top of the scale is a moot point given the high output of any modern source component, making the two topmost volume settings all but redundant.
Max Townshend explained that he is still able to build a unit to order with any custom attenuation points along the 24-position range, which would remedy my complaint about misspaced volume steps.
Packing in six ins and two outs means the rear panel is a mass of sockets. Looking from the back, six numbered pairs range from the right for the six inputs; another two pairs on the far left provide the pre-amp outputs. Those two pairs of outputs make bi-amping a doddle, and there should still be no problem with impedance matching at any volume setting with most systems.
With an RCA socket centre-to-centre spacing of just 14 mm, it’s a tight space to squeeze in phono plugs, especially those of the more generous ‘audiophile’ persuasion. Eichmann Bullet Plugs fit easily enough, as do the WBT-0110 locking plugs favoured by Nordost; but Neutrik Profi plugs (ground before signal), as found on Townshend Audio’s own Fractal F1 interconnects won’t insert without splaying outward slightly.
There are no XLR balanced connectors here, nor even available to order, as a circuit topology based around autotransformers simply does not allow balanced operation. It might be feasible to build a balanced version by doubling up the number of autotransformers to accomodate a three-rail signal path, but that would demand a wholly new design of pre-amp.
Inside the Allegri, manufacture is more modern-looking than other TVC pre-amp I’ve seen. Where many such units are built around meticulous point-to-point wiring between transformers, socketry and switchgear, the Allegri is based on two printed circuit board to mount the little autotransformers, plus PCB-mounted input/output sockets. The two rotary switches are also soldered to PCBs, as is the Mute switch, with all wiring between boards being ribbon type that plug into the respective boards. While this approach may be frowned upon by audio purists, it’s one way to speed up and lower cost of production.
The autotransformers in the Allegri each comprise about 100 m of polyester-enamelled copper wire, 0.8 mm in diameter.
The magnetic core of any transformer plays a key role in its electro-magnetic performance; not to mention its harder-to-measure subjective sonic signature. Ultra-thin metal laminations are used in the Allegri’s autotransformer, originally 80 % nickel mu-metal, but with the current model now at 49 %, all without any audible differences I’m told.
The spec states the unit is DC coupled with no capacitor in the signal path, which is standard for a passive pre-amp anyway. It is worth remembering that the presence of continuous DC running through a transformer’s windings can degrade performance.
Ideally there should be no stray DC from the source anyway, although some D-A convertors, for instance, may omit blocking capacitors for the perfectly valid reason that any capacitor in the signal path is likely to mess up the sound somehow.
But unlike a normal isolation transformer which will block DC by design – since transformers only operate with changing, AC signals – an autotransformer meanwhile has a path to ground and will transmit DC, albeit proportional to volume setting. Thus at full volume (unity gain), nearly all residual DC will flow, tapering off at minimum volume settings.
The Townshend Audio Allegri has one advertised trick up its sleeve not found on any other pre-amp, with or without transformers – Fractal-Wire™.
Fractal-Wire was first developed for the Townshend F1 interconnect. Like the deep cryogenic treatment Townshend Audio uses in its DCT cables, the copper conductor is subject to an industrial process to enhance its conductivity. Technical details are scant though.
Max Townshend was the first to commercially provide cryogenically treated audio cables, following experiments made by Keith Howard for alma mater Hi-Fi News (‘The Freezing Issue’, July 2001, p70-73). With several other companies quickly following and offering similar freezing services for audio kit, Max started to explore other treatments to improve conductor performance.
From the Townshend Audio literature, ‘This is as big a breakthrough as was achieved and much imitated when we discovered the benefits of Enhanced Deep Cryogenic Treatment (also applied to Fractal-Wire™). But this time we’re keeping the details to ourselves!’
The contribution to the final sound of the Allegri pre-amp that’s made by the Fractal-Wire process remains unknown, although reference with an identical Allegri unit using untreated wire could prove illuminating.
Responding to my request for any more information about this new technique, Max only revealed that ‘the secret process involves radiation, amongst other things. This reduces the resistance of the copper by 12 % and makes it electronically transparent.’
That’s not giving much away, especially since ‘radiation’ in the usual sense could refer to anything from ultraviolet up to X-ray or gamma. I did learn though that the ‘fractal’ name is an allusion to the manner in which a treated conductor may help regressively reproduce musical details within the details of the details of the details… And Max did reveal that the raw copper wire undergoes its secret radiation treatment in the US. But that was it.
Like the finest imaginable ductile copper, he simply could not be drawn any further.
A stepped volume control of any description has the advantage of offering precise volume settings that can be restored at will; but this quickly becomes a disadvantage when you’re trying to calibrate two setups, and the required gain setting falls between the clicks of the volume knob.
Before some earnest listening against known references, I needed to carefully match volume levels between the Allegri and other pre-amps: a difference of much more than one decibel can result in the louder setup being judged as having better sound quality.
A glance at the attenuation specification of the current Allegri showed that there were several usable volume settings which would correspond exactly with preset positions on the Music First. However my listening suggested either wildly different sound signatures between units; or the volume playing field was not as level as expected.
As discussed, the available volume steps of the Allegri have been adjusted since it first launched, so I set out to confirm the current settings to ensure it could be matched to other control units like the Music First Passive Magnetic Preamplifier.
Measuring actual gain of the Allegri proved useful as it became apparent that the unit I was reviewing corresponded to neither the earlier edition, nor to the scheme prescribed by Martin Colloms. Minor channel imbalances were revealed at some volume settings that an engineer might find noteworthy, including one setting which repeats the attenuation of a neighbouring position on one channel.
The table shows that the attenuation settings of the current Allegri resemble the original at the top (loudest) end of the scale, then roughly 1 dB steps through the middle of the range, falling to larger 3-5 dB steps toward the bottom.
Initial measurement of position ‘1’ saw the biggest left/right channel imbalance of 2.5 dB, although perhaps at the least important position if positive gain is not required. After re-checking this result, it became apparent that it might be a switch issue, as gain would flicker between two steady states. The table shows the better result, after some wiggling of the switch.
At other positions the channel matching was usually within around 0.5 dB; but moving from position ‘7’ to ‘8’ saw right channel rise by 2 dB (–22 to -20 dB) while left channel remained fixed at –21.8 dB.
For reference, the Music First fitted unit with Stevens & Billington TX102 transformers was found to be within 0.1 dB of indicated specification at most settings; and L/R channels were typically matched to within an impressive 0.01 dB.
The Allegri’s minimum volume setting of circa –50 dB may not allow sufficiently quiet playback for some tastes, even less satisfactory than the advertised –52 dB. A gain setting of –56 dB or lower here would be of benefit to late-night listeners.
Under measurement, the Allegri proved to have an effectively flat response to 50 kHz, then gently falling (around –6 dB at 70 kHz), which is a reasonable and sensible bandwidth. The MFA meanwhile was essentially flat to beyond 100 kHz. Distortion was incredibly low across the spectrum, rising slightly at very low frequencies (sub-30 Hz) and higher amplitude (2 V rms), which may be the result of mild core saturation.
As one would hope for a good transformer volume control, the Allegri is supremely quiet when wired in circuit. While it does add some noise to the signal – almost-inevitable thermal noise from its inherent DC resistance – it is so vanishingly low that it will be inaudible, below the contribution of even the quietest of partnering line sources and power amplifiers. For the uninitiated to the capabilities of the TVC, just removing the barely-there hiss and hum of an active pre-amp can be a revelation in itself.
Crucially, there was no LF hum intrusion whatsoever when used in a stereo system. Music appeared to rise from a silent black backdrop.
Usually viewed as a ‘passive’ device, even a transformer pre-amp can potentially impart conspicuous changes upon the sound. But after an extended period of listening and cross-reference with other pre-amp units, I found the Allegri to be agreeable self-effacing – and far more aptly named than perhaps was initially intended.
As background, the name is a nod to the Allegri String Quartet, as led by second violinist Rafael Todes, himself a keen audiophile and writer on all matters hi-fi. Max Townshend recognised Rafael’s sharp-eared input while the new pre-amp was still in development, and subsequently named the finished product in the quartet’s honour.
Where that name became eerily pertinent was in the sheer speed with which music can trip from the speakers when the Allegri is on gain duty. It preserves the immediacy of recorded sound in way that challenged my Music First reference point, even while it was not a clear winner overall.
Let’s focus on where and just how well the Allegri gets it right.
The Allegri excelled in dynamic description. Tinkly piano and breathless panting combine in a frenetic syncopation to set the pace of ‘These Precious Things’ [Tori Amos, Little Earthquakes], and through the Allegri the combination was able to startle this listener with in-room dynamic presence, as piano-and-pants sprung from nowhere over the Eno-like reversed ambient wash.
A sonorous Bösendorfer low B is struck, left to a long sustain, until tight tom-toms and a reverberant snare punch through from a more distant mono perspective. It’s a very ‘real’ sound, and not one that can be enjoyed when lesser pre-amps are throttling the transients.
The reference MFA was a trace less ‘startling’ in its presentation, drawing attention instead to a slightly wider stereo picture and a kinder, more rounded lead vocal. Bass was stronger overall through the Music First, showing a firmer low-end foundation. More than just more weight to bass drum and floor toms, it revealed the explosive microphone pop from Tori’s vocals that are scattered throughout the song.
So tonally the Allegri was found to have a slightly lighter voicing. And while there’s no denying it could carry subterranean LF information, it tended to draw attention to its expressive midrange character and lighter, airy treble.
Given the right – perhaps that should be wrong – provocation, the Allegri could start to sound a trace tonally hard in that upper mid and treble. An example would be how it handled the Garbage classic ‘Stupid Girl’: at once as fleet and well-paced in the rhythm section as the partnering system has ever allowed. This includes accurately conveying the pitch of the simple repeated bass riff notes, centred on a low F#, where a less accomplished chain of hi-fi components can render it more like a repetitive and unpitched thud-thud-thudthud-thud, blurred beneath the kick drum.
Yet while the pace couldn’t be faulted, the wash of fuzz guitars was promoted to the point of ’11’ in rock’n’roll terms, sometimes sounding grungier than deemed accurate. It was a trace of glare that could appear in denser mixes, where the Music First refused to harden up quite the same way.
‘Crisp’ and ‘tight’ recur as descriptive one-worders for the Allegri, and this includes the Allegri’s way with orchestral pieces. This was heard as a tauter tuning of timpani, such as within Mravinsky’s UK premiére of Shostakovich 8th Symphony. The kettle drums can be heard at various times on any playback system of course, but the Allegri was the pre-amp that could preserve their place and tune in the tumultuous build up at the end of the – rather apt again – allegro third movement.
In stereo soundstaging, the Music First just edged out the Allegri in side-to-side width, where the former excelled at melting speaker boundaries away; but the latter could show a fractionally deeper, if more mono-focused, soundstage.
In 200 words or less
The Allegri pre-amp is a smart fully-manual passive pre-amp with very little colour of its own – an incredible feat for any audio component. Build quality is satisfactory although at nearly £2000 I would want better feeling (and performing) rotary switches behind the control knobs. As a reviewer and inveterate tweaker, I found the lack of balanced connections more than a mild inconvenience, doubly so as I recall how well an isolation transformer-based volume control can freely convert between balanced and unbalanced sources and amplifiers – systems built only from unbalanced components won’t miss this drawback of course. Whether the pre-amp’s lack of galvanic isolation was affecting the sound is hard to say. The Allegri tone could hint at an upper-mid sheen which might have roots in RF- or ground noise passing through. Or perhaps it’s just a vaunted result of the secret treatment made unto the inductor windings which tilts the balance somehow. Make no mistake though, the Townshend Allegri has transformative powers when replacing an active pre-amp in a two-box amp system, restoring dynamics and speed, unleashing an open and accessible sound that keeps the music in crisp focus.
Apple Mac mini (Late 2012), Audirvana Plus 2.5.3
Music First Passive Magnetic Pre amplifier
Mytek Stereo192-DSD & Brooklyn DACs
Bowers & Wilkins 802D
Cables from Nordost, Atlas Cable and Computer Audio Design
Isotek Titan mains conditioner