Hugh Robjohns tests this fully‑featured, dual path channel strip, with circuitry designed by the legendary Mr Rupert Neve.
Amek's Pure Path series is the latest result of their collaboration with legendary audio circuitry designer Mr Rupert Neve. The 'Channel In A Box' provides a complete dual‑path channel strip with mic and line inputs, comprehensive EQ, compressor/limiter and output faders in an elegant 1U rackmount box with cleverly illuminated Amek and Pure Path logos on the rack ears! That this is a quality product is self‑evident, but it also has the pedigree of Neve's lifetime of experience designing some of the best audio consoles in the world.
The surface‑mount circuitry employs both discrete transistors and high‑spec op amps biased towards Class‑A operation to minimise crossover distortion. An internal switched‑mode power unit accommodates mains supplies between 100 and 240V, drawing around 15W. This doesn't seem like a huge amount of power, so the fan incorporated within the PSU comes as something of a surprise! Inevitably, some audible noise results and I would recommend that potential users audition the unit (in the literal sense) before parting with their money in order to confirm that its acoustical output will not prove distracting.
The rear panel provides a pair of XLRs for the mic section I/O, plus a third XLR for connecting an external fader. The same provisions are repeated for the line I/O and remote fader. A quarter‑inch TRS jack socket enables stereo linking of the compressor with that of a second unit, and the obligatory IEC mains inlet and fuse holder complete the facilities.
There are two independent signal paths for the mic input and line input, equating to the channel and mix paths in a console, each with completely separate outputs. The various signal processing stages can be split flexibly between the two paths and the only thing you can't do — and this seems a bit of a shame — is mix the two signal paths at the output. All the buttons are internally illuminated and the control knobs are well laid out, with clear pointers.
The unit is built to exemplary standards and boasts excellent technical specifications. The microphone input stage features a switched gain control spanning 0 to +72dB in 6dB steps alongside a separate ±6dB trim control. The circuitry employs the familiar TLA (transformer‑like amplifier) design, claimed to behave much like a classic transformer‑input circuit but with sonic and technical advantages. Frequency response extends from below 10Hz to over 60kHz within 1dB and distortion is below 0.002 percent.
The relatively high 5kΩ input impedance is optimised for use with 150Ω microphone sources and ensures very little signal or capacitive loss, even with long cable runs. The state‑of‑the‑art noise figures actually improve steadily with increasing gain and the lower the source impedance the better the figures become! At unity gain, signals up to +20dBu can be accommodated, allowing the stage to accept line inputs, albeit with a lower than usual impedance (this is unlikely to cause any problems with modern solid‑state output stages). The usual phantom power and polarity reversal switches are provided.
The transformer‑coupled line input features a ‑6 to +12dB gain trim and its own polarity reversal switch. Despite the transformer, the frequency response remains perfectly flat to below 10Hz and is only 1dB down at 60kHz. Internal jumpers allow the input to be reconfigured as a 'virtual earth' mix‑buss amplifier, permitting the outputs from multiple units to be combined, creating a high‑quality, small‑scale mixing console in a rack.
The three‑pole XLR for feeding an external fader appears to be high‑level unbalanced audio and can be controlled through linear‑law controls of between 5 and 10kΩ. The associated button switches output gain control between the front‑panel rotary fader and the external fader. The passive output stages are transformer coupled and capable of +22dBu. Rotary faders on the front panel offer +10dB of gain with a centre detent at the unity position.
Arranged above the mic and line input section is an LED bar‑graph meter scaled between ‑30 and +10dB (green below and red above the zero mark). An associated button selects whether this meter is fed from the mic or line signal path and another button at the opposite end of the unit (adjacent to the output faders) determines whether the metered signal is derived from the input stages (default) or post‑fader output. A pair of internal jumpers permit pre‑fader metering, if required.
The equaliser, which may be allocated to either the mic or line signal paths, or placed in the side‑chain of the compressor, is divided into three sections, each of which can be bypassed or activated independently. High‑ and low‑pass filters comprise the first section, each with fixed 18dB/octave slopes and sweepable turnover frequencies. The high‑pass section spans 22 to 300Hz and the low‑pass from 2.5 to 25kHz.
The low‑ and high‑frequency EQ bands each provide a generous ±18dB of cut or boost, sweep frequency control and a button for switching to Peak mode — the default shelving mode provides a 12dB/octave slope from the selected frequency whilst the peak mode retains the 12dB/octave slope but changes the response shape to a symmetrical bell centred on the selected frequency. The Glow and Sheen buttons make the slope considerably more gentle and provide a much more subtle tonal shaping characteristic which is quite aptly described in the control labels. The Q factor is around 0.7 allowing reasonably precise tonal correction.
The low and high mid‑frequency bands form the third equaliser section, each having classic parametric controls. Cut and boost spans ±18dB and the Q controls allow continuously adjustable settings between a broad 0.2 and a more precise 0.7. The LMF band can be tuned across a frequency range from 20200Hz, with a x5 button shifting this to 100Hz1kHz. The HMF band is identically equipped but spans the range between 500Hz and 5kHz, or 2.5 and 25kHz with the x5 button depressed.
The compressor is an all‑analogue design which draws on the most successful of Mr Rupert Neve's previous dynamics stages. The compressor can be allocated to either the mic or line signal path, and simplicity with flexibility are the key words here. The Threshold can be set between ‑40 and +20dBu with the Ratio variable from 1:1 up to 40:1 for hard limiting — the law allows fine control around the critical 1:1 to 3:1 area. Both Attack and Release times are manually set (no automatic or programme dependent settings offered) and range from 0.3300mS and 0.110 seconds respectively. A make‑up Gain control ranges from ‑10 to +20dB. By default, the transfer characteristic has a fairly hard knee, but a button labelled '&MM' ('& Much More') bestows a much more gentle transition which worked well where creative compression effects were required as opposed to accurate dynamic control.
A button links the compressor side‑chain signal with that of another unit, via a rear‑panel socket (all compressor controls must be mirrored on both units). A Key button allows the input channel not passing through the compressor to be used as a key signal, providing a voice‑over ('ducker') mode. The gain‑reduction bar‑graph meter tracks a 40dB range.
The mic stage of the Channel in a Box would almost justify its price alone. Even though over 70dB of gain is available, the noise and distortion performance are amongst the best available. What's more, I couldn't tell the difference between a condenser mic through a five foot cable or through 50 metres of multicore — it is that capable and that tolerant — yet every nuance of a harmonically complex 12‑string guitar was conveyed with precision and clarity.
The Pure Path Channel in a Box is an impressive piece of equipment with a sublime sound to justify its high price. If you are looking for a top‑notch recording channel which is simple to operate, provides enormous flexibility and has a subtle character but with lots of panache, then this must be on your shortlist.
- Quality sound, circuits and build.
- The flexibility of an in‑line channel strip.
- Mr Rupert Neve was here!
- Another fan in the studio...
A pedigree mic preamp design from the pen of Mr Rupert Neve, complete with all the flexibility associated with an in‑line console channel strip including filters, 4‑band EQ and a nice compressor.