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Neumann V402

Dual-channel Mic Preamp By Hugh Robjohns
Published October 2020

Neumann V402

Does Neumann's first standalone mic preamp live up to their enviable reputation?

Though best known for their microphones, and more recently loudspeakers and headphones, between the 1960s and the 1990s Neumann also manufactured bespoke mixing consoles, which included very high-quality microphone preamps. And while Neumann have never before offered a standalone mic preamp, they've just launched a new one called the V402. The model's V prefix continues the house identifier long used by Neumann for their console preamp modules. As might be expected from a company of Neumann's standing, the V402 is intended to be as "transparent and pure as modern state-of-the-art electronics allow — neither adding nor subtracting anything produced by the microphone", and is proudly proclaimed as being "handmade in Germany".

Form & Function

From a user's point of view, the V402 is a straightforward dual-channel microphone preamplifier. It's a transformerless design that includes an unbalanced instrument input for each channel and, more surprisingly, a built-in 'studio-grade' headphone amplifier. The unit is presented as a 2U rackmount chassis with an attractive 'champagne' anodised front panel, with matching knobs, silver ring-illuminated buttons, and a black-painted case. This chunky metalwork means it weighs a hefty 6.2kg, and it extends 242mm behind the rack ears.

Unusually for a mic preamp, theV402 is equipped with a ground-lift facility.Unusually for a mic preamp, theV402 is equipped with a ground-lift facility.The rear panel is equipped with a quartet of XLRs for the electronically balanced (mic) inputs and line outputs, along with an IEC mains power inlet. One uncommon feature here is a recessed slide switch amidst the XLR connectors, which disconnects the chassis ground from pin one on all four of them (the inputs as well as the outputs) to break any ground loops, if necessary. The internal linear power supply accepts either 100-120 or 220-240 V AC mains supplies, and the IEC socket has an integral mains switch (there's no mains power switch on the front panel, though, which would have been nice).

On the front panel, Neumann's classic red diamond badge sits proudly at the top left, with the two channels' controls arranged above one another. Each channel starts with a standard quarter-inch unbalanced instrument input socket, followed by a large rotary gain knob operating an ALPS 'Blue Beauty' conductive-plastic potentiometer, which has a 41-detent action and provides +20 to +60 dB of gain in approximately 1dB steps. Five illuminated buttons select the high-impedance instrument input in place of the rear-panel mic input, apply 48V phantom power and introduce a -20dB pad, polarity inversion and a second-order (12dB/oct) 60Hz high-pass filter.

Output level monitoring is provided on a slightly old-fashioned-looking horizontal bar-graph meter, which comprises 10 LEDs per channel that illuminate at 6dB intervals. The lowest green LED corresponds to an output level of -24dBu and the fifth (of six) green LEDs lights at 0dBu, which is the only other calibration mark. Above the greens are two yellow and two red LEDs, with the penultimate red LED equating to +24dBu. The top red LED illuminates with its neighbour but remains on for much longer to serve as a 'peak' indicator. Functionally, this metering delivers everything you need, though some might feel it looks a little crude for what's clearly intended as a high-end product.

Three more (non-detented) rotary knobs to the right of the meters form the headphone amplifier section, with separate channel contribution mix-level controls and a master volume. Another illuminated button toggles between a mono or stereo output, presented on a single quarter-inch TRS headphone socket on the front panel. A few companies now build headphone amplifiers into standalone microphone preamps, and the facility is potentially valuable for two reasons. First, it's undoubtedly useful for the recording engineer when setting up, for example when searching for the optimum mic placement around an instrument, or for judging perspective and imaging from a stereo array. Second, if an aux input is provided, it can also be used by an artist for latency-free headphone monitoring (the aux catering for the backing track).

While Neumann's promotional materials suggest that the V402's headphone facility can be used for both those applications, I think it's only really going to be useful for the engineer, since there's no aux input. While you can, of course, route a backing track through one channel, this is only an option when recording a source in mono on the other channel. I consider this a missed opportunity. This facility could have been so much more useful had Neumann provided a separate external stereo aux input to accept a backing track from a DAW. There's plenty of space on the rear for a couple of extra input sockets, and the existing headphone controls could have been configured, for example, as an external input level, a balance control between the two mic channel feeds, and a master volume.

Technical Performance

Surprisingly, the V402's published technical specifications are not as comprehensive as I was expecting. Having said that, there aren't many equipment specs that list a 'Maximum Working Altitude'! (2000 metres, if you're planning any Alpine recording sessions).

The maximum microphone input level is a reasonable +8dBu, and engaging the pad option raises that to a whopping +28dBu, so capacitor mics in front of kick drums and line-level sources can both be accommodated without problems. The mic input impedance is around 3kΩ, which is slightly higher than many, and adequate for most modern line output sources too. (I say 'most' because some line sources may struggle to drive this relatively low-impedance load — line inputs are usually above 10kΩ).

The instrument input is substantially flat from 10Hz to 10kHz, with a very mild roll-off above that.The instrument input is substantially flat from 10Hz to 10kHz, with a very mild roll-off above that.For instruments, the DI input presents an impedance of 3.3MΩ, and the maximum instrument signal level is a substantial +21dBu, so there's no problem there with hot guitar pickups or wayward resonant synths. Usefully, selecting the DI input also alters the preamp's gain range to span 0 to +40 dB. This is a sensible feature, though the change isn't immediately obvious (the markings still read 0 to +60 dB).

Phantom power is the standard +48V supply capable of delivering the full 10mA IEC requirement, and the headphone amplifier is rated at +20dBu into a 150Ω load, which works out to around 0.4W into each earpiece. It is certainly more than loud enough for all the headphones I tried it with (ranging from 32 to 250 Ω).

Another unusual specification that caught my eye is the -3dB bandwidth, which is given as 10Hz to 100kHz at 40dB of gain. The mention of gain implies that the V402's frequency response is affected by the gain setting. In the world of electronics, all amplifier circuits have a specified 'gain-bandwidth product', meaning the higher the gain, the narrower the bandwidth. In the case of the V402, the upshot of this is that the -3dB point comes down to around 40kHz when the gain is increased to 60dB and, in turn, that means that the frequency response at 20kHz falls by about -0.5dB compared to the level with 40dB (or less) of gain. The HF phase shift increases, too.

This isn't a huge roll-off, obviously, and anyone beyond their teenage years probably wouldn't even notice. But given Neumann's claim that this preamp "adds nothing and takes nothing away" it was a surprise, as it's clearly doing the latter when at maximum gain. For comparison, a dual-channel mic preamp that I measured prior to this Neumann one costs half as much, yet provides 10dB more maximum gain while remaining completely flat to at least 80kHz at all gain settings. And a good eight-channel preamp costing under £100just a shade over $100 per channel also performs perfectly in this respect. So the V402 can't really be regarded as state-of-the-art in comparison. But this isn't the only spec that matters, of course, and when I put my findings to Neumann they said that they'd prioritised other factors in the design, such as resistance to external interference, which they consider to be a bigger problem in practice.

The internal layout is roomy, but extremely well engineered with a linear power supply (top right), headphone amplifier (bottom right), the two preamp channels mounted one above the other (centre) and the I/O board with extensive EMC filtering (top left).The internal layout is roomy, but extremely well engineered with a linear power supply (top right), headphone amplifier (bottom right), the two preamp channels mounted one above the other (centre) and the I/O board with extensive EMC filtering (top left).

Whipping the lid off the V402 revealed a well-engineered arrangement of separate boards linked with ribbon cables for the linear power supply, the headphone amp, the meters, the XLR connectors and two individual preamp channels mounted one above the other, all using SMD components. The various input signal-conditioning options appear to be controlled through sealed relays and, as far as I can see, the front-end preamp circuitry is built around a couple of OPA1611s together with some OPA1678s (all very high-performance bipolar op-amps) with one of the 1678s probably handling the instrument input too. OPA1679s (the quad version of the same op-amp) are used to drive the balanced line outputs and (separately) the headphones. The circuit board carrying the XLR connectors is adorned with some sophisticated common-mode filtering circuitry to keep RF nasties out of the preamps, which is good to see.

An FFT plot from an Audio Precision analyser showing the spectrum at maximum gain. The spikes to the left of the 1kHz test tone mostly relate to the pickup of external mains interference in the connecting cables, while those to the right are harmonic distortions generated in the preamp itself. Nevertheless, all of these artefacts are well below -85dBu even at full gain, and 110dB below the preamp's maximum signal output level, which is a good result.An FFT plot from an Audio Precision analyser showing the spectrum at maximum gain. The spikes to the left of the 1kHz test tone mostly relate to the pickup of external mains interference in the connecting cables, while those to the right are harmonic distortions generated in the preamp itself. Nevertheless, all of these artefacts are well below -85dBu even at full gain, and 110dB below the preamp's maximum signal output level, which is a good result.

An expanded frequency response plot comparing the signal amplitude between 10 and 30 kHz at 40dB gain (red) and 60dB gain (blue). The response at 20kHz is virtually a flat line with 40dB gain, but is clearly falling at 60dB.An expanded frequency response plot comparing the signal amplitude between 10 and 30 kHz at 40dB gain (red) and 60dB gain (blue). The response at 20kHz is virtually a flat line with 40dB gain, but is clearly falling at 60dB.The overall response at maximum gain with and without the high-pass filter engaged.The overall response at maximum gain with and without the high-pass filter engaged.Responses at 5-click intervals  This Audio Precision plot shows the level and frequency responses in 5-detent increments of the gain control. It reveals very little gain bunching as the control is turned towards the maximum gain setting, which is a very good result.Responses at 5-click intervals This Audio Precision plot shows the level and frequency responses in 5-detent increments of the gain control. It reveals very little gain bunching as the control is turned towards the maximum gain setting, which is a very good result.The maximum output level before clipping is a very healthy +28dBu, and the THD performance ranged from an extremely impressive 0.0005 percent at 20dB gain to a still very good 0.04 percent at 60dB gain. With detented potentiometers the gain-matching accuracy between channels is inherently a little variable, but the V402's channels were within 0.5dB at most settings, and there's pleasantly little gain-bunching towards the loud end of the control.

Checking the residual noise floor, it measured -107dBu at 20dB gain, rising to -66dBu when flat out at a measured 61dB of gain, which gives an EIN figure of -127dBu (unweighted, 20Hz-20kHz, 150Ω source). While this can't be described as state-of-the-art either (the best would typically be 2-3 dB quieter), it's similar to other professional preamps and perfectly decent for most situations. Crosstalk between channels was very impressive indeed, measuring -85dB at 10kHz.

Verdict

Neumann's first ever standalone mic preamp is elegant, attractive and substantial. It's constructed to very high electrical and mechanical standards and is equipped with all the usual facilities and features expected of a good-quality microphone preamp, plus a good built-in headphone amplifier.

That said, some aspects of its design prevent it from living up to the bold marketing claims being made for it. The lack of an external stereo input to the headphone amplifier makes what is technically a high-quality facility of use only to engineers when setting up mics; it's unworkable as a practical latency-free artist monitoring system. And while the high-frequency roll-off at maximum gain is largely insignificant in practice, there really is no excuse for it in a product as expensive as this and which doesn't offer unusually high gains or other novel and exotic features. In short, it's a standard preamp with standard facilities and it sounds subjectively good, but it doesn't quite shine as you'd expect of something with this badge and price tag.

Distortion Product Ratio 20dB / 60dB. Two overlaid plots showing the levels and very neutral balance of harmonic distortion products at minimum gain (blue) compared with the same at maximum gain (red).Distortion Product Ratio 20dB / 60dB. Two overlaid plots showing the levels and very neutral balance of harmonic distortion products at minimum gain (blue) compared with the same at maximum gain (red).

Thankfully though, the V402 does meet the claims of delivering a clean and transparent sound, it has commendably low levels of harmonic distortion and crosstalk, even at high gains, and it is more than quiet enough for most applications. Moreover, the controls all feel solid and reliable and there's no doubt that the V402 can get the job done perfectly well.

Alternatives

If the built-in headphone amp isn't important, check out the AEA RPQ2, Millennia HV37, DACS Micamp II, the Rupert Neve Designs Portico 5012 or the Grace Design M201 MkII, some of which offer other useful facilities. The Neve 1073DPX does include a headphone amp, as well as EQ. But the price/performance/facilities benchmark for this type of product has undoubtedly been established by Cranborne Audio's exceptional EC2.

Pros

  • Clean and transparent sound.
  • All the standard preamp facilities are included.
  • Headphone amp allows easy auditioning when setting up mics.
  • Extremely well built.

Cons

  • Headphone amplifier is not useful for artist monitoring.
  • Average technical performance.

Summary

Neumann's first ever standalone microphone preamp is a substantial bit of kit, but at this price it doesn't really live up to the hype in a very competitive marketplace.

information

£2420 including VAT.

Sennheiser UK Ltd +44 (0) 1628 402 200.

www.sennheiser.co.uk

www.neumann.com

$2900.

Neumann USA +1 860 434 9190.

www.neumann.com

Published October 2020