Music First Audio Classic Headphone Preamplifier

Hardware Review

Music First Audio Classic Headphone Preamplifier
Tuesday, December 20, 2016
Passive preamplifer/headphone amplifier
Richard Barclay

With 40 years of transformer design experience, Jonathan Billington has been manufacturing bespoke and award-winning transformer-based passive preamps under the Music First Audio brand since 2003. Hand-built in his Hastings workshop in East Sussex, his latest creation, the Classic Headphone Preamplifier, expands the functionality of the globally-revered Classic with the inclusion of an active headphone section. Having never before heard a Music First passive pre, and as The Ear’s resident headphone expert, I was especially thrilled to be among the first to review this new model.

Passive purity
Proponents cite the elimination of noisy electronics as a clear advantage of passive preamps over their active counterparts. With no power supply, transistor or valve components present to modulate, distort and effectively ‘grunge-up’ the signal, listeners are free to listen to the source rather than the ‘sound’ of their preamp. As great as this is in theory, it was not easy to achieve in practice due to other compromises inherent in traditional passive preamp design. Unavoidable mismatches between input and output impedances and non-linear relationships between frequency response, dynamics and attenuation level in resistor-based designs, for example, made passive preamps very much a hit-and-miss endeavour.

That was of course until the introduction of transformer-based volume controls (TVCs). Unlike their resistive counterparts, TVCs attenuate the signal by lowering the voltage and exchanging it for current. This means that - as long as the signal is being attenuated - the impedance match between source and power amp will actually improve instead of worsen, overcoming arguably the biggest downside previously associated with passive attenuation.

 

 

 

A new Classic
Music First Audio’s new Classic Headphone Preamplifier is a single-ended two-channel passive preamp with the addition an active headphone output. Priced at £2,400 and costing £360 more than the existing Classic Preamplifier, the stock model uses the same TX102 tapped attenuation transformers and is equipped with a total of six pairs of stereo inputs and two pairs of stereo outputs for bi-amping, meeting the analogue connectivity requirements of most audiophiles. A 1/4-inch headphone output is located near the bottom left corner of the faceplate and is well and truly dwarfed by the two, gratifyingly oversized and tactile input and volume knobs that bring symmetry to the unit’s clean and simplistic design. The 24-position volume controller provides 52dB of attenuation, in 2dB steps for the most part (the intervals widen as you approach maximum signal attenuation/lowest volume). 

Discretely located on the rear of the unit is a toggle switch to easily alternate between driving the main system via the pre-outs and listening privately via the built-in headphone amp, muting whichever output is not selected. The transformer-based volume control enables the input and output grounds to be isolated from each other - a useful tool for ground loop elimination - and the switch for this can be found on the underside of the unit. The preamp ships with a standard 12V supply to power the headphone amp, with the option to upgrade this to a regulated linear design. Many other aspects of the design can also be customised on request, indeed Music First goes to great lengths to fulfil customers’ individual needs.

Headphone capability
The preamp’s active headphone section uses the AD8397 chip, a very linear, low-noise, high-output current op-amp from Analog Devices. Billington explains, “The AD8397 has two voltage feedback operational amplifiers capable of driving heavy loads with excellent linearity. The common-emitter, rail-to-rail output stage surpasses the output voltage capability of typical emitter-follower output stages and can swing to within 0.5V of either rail while driving a 25Ω load. The low-distortion, high-output current, and wide-output dynamic range make the AD8397 ideal for applications that require a large signal swing into a heavy load.”  Power output figures of 120mW RMS into 33Ω and 30mW RMS into 330Ω therefore seem rather anticlimactic. It certainly won’t win any wattage wars but, as we all know, specifications aren’t everything. It’s the quality, not the quantity, that matters and without giving too much away at this point I was pleasantly surprised by the performance of this modestly specced headphone circuit.

 

 

The Classic Headphone Preamplifier should not be mistaken for a specialist headphone amp - it is still first and foremost a high-end passive pre - and unlike some dedicated headphone amps I have reviewed, it does not provide switchable gain. The gain has instead been fixed at 6X to try to facilitate a range of headphone designs. On material with decent headroom, owners of traditional over-ear style cans à la open-back Sennheisers will in practice be able to enjoy most of the turning range of the 24-position volume control. Users of sensitive in-ear monitors (IEMs) may however, struggle with being restricted to the first quarter and the consequent lack of fine-adjustment on the stepped attenuator, especially when listening to music that has been mastered loudly.

In situ
My main reference systems are a somewhat unconventional mix of vintage and modern. At its core is a Yamaha A-S3000 integrated that drives vintage Tannoy Monitor Gold 15 loudspeakers and modern Tannoy Prestige Autograph Mini monitors. I also use the A-S3000 as an active pre to service a Quad 909 power amp into Quad ESL 63 loudspeakers. These three pairings prioritise scale, speed or cohesion, respectively, so I have all bases covered, you could say!  Equipped with two pairs of pre-outs, the Classic Headphone Preamplifier conveniently slotted in and replaced my Yamaha A-S3000’s preamp in both systems.

As someone who grew up with ‘step-free’ volume potentiometers, the 3dB ascents across the first quarter-turn of the Classic’s TVC took some getting used to, though it was perhaps ill-advised to begin the audition with 15-inch Tannoys that boast 95dB/1w power sensitivity!  Finer steps would be preferable, even the 2dB intervals across the attenuator’s remaining three quarter-turns seem unwieldy. There is however a significant cost implication to increasing the number of transformer taps, so a compromise must be reached (bespoke taps are however available on request).

Putting music first
The lack of fine control over volume levels was soon eclipsed by the serene flow of lifelike acoustics that began pouring effortlessly into my listening space. Track after track, the Classic Headphone Preamplifier displayed improved articulation and separation across the board, with the spatial relationships and tonal distinctions between different instruments being more faithfully preserved. Transients were crisper and more vibrantly detailed, but not to the extent of sounding artificially etched. Rather, the edges of notes displayed clearer start and end points and were no longer ‘fuzzed’ by the subtle but nonetheless masking presence of electrical hash. Reverb tails exhibited less grain and shimmered in the air for longer before fading more seamlessly to black. Mids were projected with a heightened palpability and transcending realism, and bass became more organic in texture but retained enough grip to avoid unwanted overhang and bleed into the rest of the spectrum. The A-S3000 is Yamaha’s flagship integrated and is no slouch by any means, however the Music First’s absence of active preamp circuitry allowed it to retrieve even more natural detail from the source, it quite simply put the music first (pun intended!). The relative absence of grunge led to a lower perceived noise floor and improved the expression of micro-dynamics, increasing intelligibility at quieter listening levels. At higher volumes, the Classic showcased its innate clarity and dynamism whilst remaining utterly composed, never revealing signs of strain, and holding the listener captive to every note played.

 

 

The trusted Sennheiser HD600 and recently reviewed new flagship HD800S were my weapons of choice upon turning my attention to the Classic’s active headphone section. Despite their high nominal impedances, I find neither headphone to be especially fussy over partnering amplification. Both scale very well however, and the HD800S in particular is superb at revealing strengths and weaknesses in connected ancillaries. Though both models are tuned to provide a neutral listening experience and to my ears strike an outstanding balance between detail and musicality, the 600 prioritises upper-mid frequencies to proffer greater intimacy, whilst the 800S renders a more expansive and layered soundscape with improved frequency extension at both ends of the spectrum. The respective tonal and spatial characteristics of each open-back headphone were faithfully upheld by the Classic. Despite the seemingly humble op-amp specs detailed earlier, no objectionable power compression or ‘hardening’ of the presentation occurred at louder levels (for my typical listening habits at least) and the clarity, control, separation and textures on display made for a suitably resolving and musical listening experience. Its built-in headphone section of course does not match the performance or functionality of a dedicated headphone amplifier with discrete components, and owners of particularly demanding earspeakers, or those for whom headphone listening is an especially important priority, should not view the Classic Headphone Preamplifier as a replacement for one. However, for those eager to reap the benefits of a TVC preamp in their main loudspeaker system and seek a convenient way to periodically enjoy headphones on the same system, the Music First is undoubtedly a great solution.

Verdict
The Music First Audio Classic Headphone Preamplifier provides as clear a window into recorded music as I have thus far experienced from my system. The ease with which it is able to fluidly express clarity, openness, separation and dynamics without favour or compromise is simply stunning. As special a passive preamp as it is, the Classic won’t be ideal for everyone (in its stock configuration at least). Preferred listening levels, together with the gain-staging of the power amp/s it will drive, may necessitate enlisting Music First’s bespoke service to optimise the preamp’s suitability in its destined environment. A gain switch on the active headphone output to facilitate a broader range of transducers would certainly increase its appeal to earspeaker enthusiasts. And while the headphone stage may not match the performance one that uses discrete components, it holds up well against comparable built-in stages and is a welcome addition to what is a truly superb passive preamp.

Specifications: 

Type: Passive transformer preamplifier with headphone output and TX102 Mk3.4 transformers
24-position volume control from -52dB to 0dB providing 52dB of attenuation/gain
Inputs: 6 pairs stereo RCA unbalanced
Outputs: 2 pairs stereo RCA unbalanced
Ground-lift switch
Headphone amp / preamp toggle
Headphone section:
Analog Devices AD8397 headphone op-amp
Linear Technology LT3080 Regulator
Input impedance: 47kΩ
Output impedance: < 0.5Ω
Voltage gain: 6X
Power output: 120mW RMS into 33Ω, 30mW into 330Ω
Dimensions (H x W x D): 90mm X 290mm X 180mm

Price: 
£2,400
Manufacturer Details: 

Music First Audio
T +44 (0) 1424 858260
www.mfaudio.co.uk