Valve Microphone Preamplifier

Published in SOS February 2012
Bookmark and Share

Reviews : Preamp


This two‑channel tube preamp offers a range of useful features, and all for a very modest asking price. Is it too good to be true?

Paul White

ART have a long‑standing reputation for delivering good, affordable audio processors, and their Pro MPA2 seems set to continue that tradition. Essentially, this device is a 2U-high, two‑channel mic preamp with switchable 48V phantom power and continuously variable input impedance. The latter is something that can have a significant effect on the sound of the connected microphone; in particular, many dynamic models, including passive ribbons, prefer to see a higher impedance.


The Pro MPA2 can be set up for dual‑mono, conventional stereo or M/S (Mid/Side) operation. In this last role, channel one is used for the 'Mid' mic and channel two for the 'Sides'. Further tonal variety is offered by the ability to run the 12AX7 valves at low or high anode voltages.

The Pro MPA2 certainly feels solid — it was rather heavier than I expected it to be when I lifted it — and the front panel looks stylish, with its detented, somewhat retro‑styled knobs and large, backlit, moving‑coil VU output meters that have adjustable calibration trims. Further LED bar-graph meters, labelled Tube Warmth and set between the VU meters, show the amount of tube drive being used. While the mic inputs and balanced XLR and TRS jack outputs are on the rear panel, a high‑impedance instrument input is conveniently positioned on the front panel, this taking precedence over the mic input when connected. A rear‑panel button allows the output level to be set to +4dBu or ‑10dBv, and the meter calibration automatically follows this setting.

The mic input is a solid-state design, with a rotary control to set the initial gain. This has only a 40dB range, but an extra 20dB of gain can be applied before the tube stage. Having an extra gain boost selectable in this way helps the preamp to run at lower gains while still maintaining a high signal‑to‑noise ratio, as many affordable mic preamps only deliver their quoted EIN figure when set close to maximum gain. A combination of the input gain and this 20dB 'boost' can be used to drive the tube stage as hard as you feel appropriate. A further 10dB is available via the output gain control, so there's an overall maximum gain of 70dB. (The manual claims 75dB with everything flat out, but I'm not sure where the extra 5dB comes from!)

Next to the input gain control is the one that governs input impedance, which ranges from 150Ω to 2.4kΩ. To keep the lows under control, there's a smooth, 6dB/octave low‑cut filter that can be swept from 10Hz to 200Hz. Four illuminated buttons beneath the VU meter are used to select 'normal' or +20dB of gain, phantom power, high or normal 'plate' voltage, and polarity inversion.

A further button mounted between the channels selects the M/S decoding matrix, so that an M/S mic pair fed through the unit will produce a standard stereo signal at the output. At the extreme right of the unit is a 'stereo' button that allows the rightmost output‑level control to function instead as a stereo balance, while the leftmost output‑level control operates as a master stereo level control.

The technical spec looks suitably impressive on paper, with a frequency response extending from 15Hz to 48kHz (+0, ‑1dB) when the valve anode‑voltage is set to normal. An equivalent input noise for the mic input is quoted as ‑129dBu A‑weighted, translating to a dynamic range of better than 110dB, again A‑weighted. Both mic inputs can accommodate signal levels of up to +10dBu before clipping, whereas the maximum instrument level is +17dBu (800kΩ impedance). The output stage can handle up to +27dB on the XLRs, and has a low 47Ω impedance, which is suitable for driving long cables.

ART Or Science?


So how does it sound? My first test was with a capacitor mic and, as expected, the input impedance made very little difference. (The active circuitry in the mic buffers the signal, making it less dependent on load impedance.) I set the input gain near maximum and used the output level control to achieve a decent recording level without switching in the 20dB boost. Only one or two of the tube drive LEDs came on, and this arrangement produced the most transparent, natural‑sounding result.

Engaging the boost and adjusting the input gain to push the tube-drive LED meter around halfway introduced a subtle warmth that I found quite usable, but as I pushed things harder to get the meter bouncing around close to the top, the sound became noticeably overdriven. This degree of drive would probably only be used on certain instruments, or maybe as an obvious effect on some pop and urban vocal styles.

Bringing the drive down to a low level and switching on the high tube-voltage brought about a subtle thickening of the sound, which, again, I found musically useful. In combination with a higher drive level, the sound again became progressively warm, then thick, then quite distorted as the pre‑tube gain was increased. At modest drive levels, this can be useful in bolstering a weak vocal, but I'm not a fan of vocals driven to the point where the distortion is obvious, so probably wouldn't venture much more than halfway up the drive LED meter.

Using a passive ribbon mic, the output level got significantly louder at the higher end of the impedance dial, along with a subtle brightening of tonality. The variable input impedance will be of particular benefit for anyone working with such microphones.

Lasting Impressions

The rear panel of the MPA Pro2 sports balanced analogue inputs and outputs, and  4dBU/-10dBV switching.The rear panel of the MPA Pro2 sports balanced analogue inputs and outputs, and 4dBU/-10dBV switching.

Despite its relatively low cost, the ART Pro MPA2 delivers on both sound quality and versatility. It doesn't match the transparency of some of the more costly high‑end preamps, but it gets close enough for most home studio applications — and out-performs many audio interface on‑board preamps — while also having the ability to produce very controllable tube character. The two tube‑voltage options provide another subtle but useful variation in tonality, and the variable input impedance is invaluable for use with passive ribbon mics or other insensitive dynamic models.

I was also pleased to see the M/S facility built‑in, as M/S recording is a very useful technique that's often neglected in the smaller studio; having on‑board decoding means that anyone with a suitable figure‑of‑eight mic plus one other mic can have a go and hear the benefits of this approach for themselves.

You may not feel you need an additional mic preamp if you have some built into your audio interface already, but I find that many of the mic amps built into audio interfaces, especially at the more affordable end of the market, are susceptible to picking up digital interference from the Firewire or USB circuitry when run at high gain settings — and this, again, is a particular problem when using passive ribbon mics. The MPA Pro 2 would be an ideal remedy for that particular disease.


In a nutshell, the Pro MPA2 is great value for money. Not only does it sound pretty good, but it's one of the few budget tube preamps to run the tubes at a suitable voltage, and it's extremely versatile, with several useful tricks tucked up its sleeve that many of its competitors lack.


The SPL Gold Mike costs only slightly more than the Pro MPA2 and is still top of my favourites list for affordable tube preamps, though it doesn't have as many features as the Pro MPA2. Specifically, there's no variable impedance and no M/S decoding. TL Audio's mic preamps also perform consistently well, but they tend to be more expensive.

ART Pro MPA 2 £316$269
Keenly priced.
Good basic sound quality.
Useful extra features, such as variable input impedance and M/S decoding.
Switchable valve voltage and variable drive provide a range of useful 'warmth' options.
No obvious cons at this price.
The Pro MPA2 is a strong performer, offering better sound quality than most built‑in 'interface' mic preamps, but it is the extra features that may swing the sale for some users, especially those wanting to use passive ribbon mics or undertake M/S recording.
Standard version £316; Limited Edition (upgraded tubes and blue LEDs) £349; with digital output £448. Prices include VAT.
Sonic 8 +44 (0)330 2020 160.

SOS Readers Ads


of Second-User Gear for sale now — don't miss out!

Neve 1073LB & 1073LB EQ

500-series Microphone Preamplifier & Equaliser

Thumbnail for article: Neve 1073LB & 1073LB EQ

Neve’s venerable 1073 preamp and equaliser are both now available in API’s popular ‘Lunchbox’ format. Were they worth waiting for?

Cloud Microphones Cloudlifters

In-line Microphone Preamplifiers

Thumbnail for article: Cloud Microphones Cloudlifters

Do these in-line mic preamplifiers mean you can use a passive ribbon mic with any preamp?

Slate Pro Audio Fox | Media

Dual-channel Microphone Preamplifier

Thumbnail for article: Slate Pro Audio Fox | Media

Test plots to accompany the article.

Cloud Microphones Cloudlifter

Audio Examples

Audio files to accompany the article.

Slate Pro Audio Fox

Dual-channel Microphone Preamplifier

Thumbnail for article: Slate Pro Audio Fox

With two channels and four ‘flavours’ on offer, Slate’s mic preamp promises plenty of flexibility. Does it also deliver on quality?

Neve 4081

Four-channel Microphone Preamplifier

Thumbnail for article: Neve 4081

Neve believe that there’s scope to bring classic designs up to date — and that’s exactly what they’ve done here, taking their revered 1081 mic preamplifier as the starting point.

Radial Tonebone PZ Pre

Acoustic Instrument Preamp

Thumbnail for article: Radial Tonebone PZ Pre

James Dunkley is on the case of the Radial Tonebone PZ Preamp.

Drawmer HQ

Preamplifier & D‑A Converter

Thumbnail for article: Drawmer HQ

Can a preamp and D‑A converter successfully straddle the pro-audio and hi‑fi markets? Drawmer believe it can...

Studio Projects VTB1

Microphone Preamplifier

Thumbnail for article: Studio Projects VTB1

This hybrid mic preamp can go from solid‑state clean to valve warmth — and for a surprisingly low price, too. Is there a catch?

Dave Hill Designs Europa 1

Microphone Preamp

Thumbnail for article: Dave Hill Designs Europa 1

This novel preamp design features a variable impedance and slew rate — which opens up a whole new world of possibilities from your mic locker...

MC AudioLab TP1tp

Valve Microphone Preamp

Thumbnail for article: MC AudioLab TP1tp

Can Sicilian manufacturers MC AudioLab bring a touch of Mediterranean magic to your recordings with their new boutique preamp?

Manley MicMAID

Mic & Preamp Switcher

Thumbnail for article: Manley MicMAID

The patchbay remains the cornerstone of most commercial studios, but using one to patch mics into different preamps can be risky — which is where the MicMAID comes in...

T-Rex SpinDoctor

Valve Preamplifier

Thumbnail for article: T-Rex SpinDoctor

Is a high-quality valve preamp in a programmable pedal just what the SpinDoctor ordered?

BAE 1073 MPF

Dual Solid-state Preamp

Thumbnail for article: BAE 1073 MPF

There are now several Neve 1073-inspired preamps available — but theyre not always 100 percent faithful to the original design. How close does this new contender from BAE come?

Focusrite Octopre MkII & MkII Dynamic

Eight-channel Microphone Preamps

Thumbnail for article: Focusrite Octopre MkII &  MkII  Dynamic

With upgraded mic amps and A-D conversion in their MkII versions, do Focusrites latest eight-channel preamps still lead the way at this price point?

Empirical Labs EL9 Mike-E

Microphone Preamplifier & Compressor

Thumbnail for article: Empirical Labs EL9 Mike-E

Empirical Labs, purveyors of some of the most versatile compressors around, apply their dynamics expertise to a mic preamp.

Benchmark MPA1

Dual-channel Microphone Preamplifier

Thumbnail for article: Benchmark MPA1

Benchmark strive to make their products exactly that: something against which the competition should be judged. So how does their new preamp measure up?


Dual-channel Microphone Preamplifier

Thumbnail for article: AEA RPQ

AEA have tweaked the design of their TRP ribbon-mic preamp, already something of a favourite, to create a device thats much more versatile — and without compromising on quality.

A-Designs Pacifica

Two-channel Microphone Preamplifier

Thumbnail for article: A-Designs Pacifica

Striking a useful balance between the transparent and the characterful, this high-quality, US-made preamp design brings versatility to the studio and some colour to the rack...

PreSonus DigiMax D8

Eight-channel Mic Pre & A-D Converter

Thumbnail for article: PreSonus DigiMax D8

Presonus combine their respected analogue and digital technology in this affordable ADAT-equipped preamp.

SPL Rackpack

Modular Preamp & Processor System

Thumbnail for article: SPL Rackpack

Sound Performance Lab have developed an enviable reputation for their hardware products, and now you can buy more for less with their modular rack system.

Audient Mico

Dual Microphone Preamplifier

Thumbnail for article: Audient Mico

With two channels of mic preamp, a phase-alignment control, digital outputs and clean signal path, the Mico offers you an awful lot of Audient for the money.

Universal Audio Twin-finity 710

Hybrid Microphone Preamplifier

Thumbnail for article: Universal Audio Twin-finity 710

Which is best, tube or solid state? When it comes to investing in a preamp, thats a question you may no longer need to ask...

Golden Age Project Pre 73

Microphone Preamplifier

Thumbnail for article: Golden Age Project Pre 73

This highly affordable device is based on the circuitry used in Neves legendary 1073. So can you really get a classic vintage preamp sound on a budget?

Arsenal Audio R20 & R24

Microphone Preamplifier & EQ

Thumbnail for article: Arsenal Audio R20 & R24

This new brand by revered high-end equipment manufacturers API is much more affordable than their established lines. So there must be a catch, right?

Grace Design M201

Microphone Preamplifier

Thumbnail for article: Grace Design M201

Regular readers will know that our Technical Editor isn't prone to excessive use of hyperbole — so when he calls a product "awesome", "stunning" and "sublime", it's probably time to sit up and take notice...

Thermionic Culture Rooster

Valve Microphone Preamp & EQ

Thumbnail for article: Thermionic Culture Rooster

Is this latest addition to the Thermionic Culture flock something for the company to crow about?

Focusrite ISA One

Mic Preamp

Thumbnail for article: Focusrite ISA One

The ISA preamp range has graced professional recording facilities the world over — but this classy single-channel model is within reach of the home and project studio.

Synchronia Sound Skulptor

DIY Mic Preamp System

Thumbnail for article: Synchronia Sound Skulptor

The DIY approach to audio equipment needn't mean bargain basement, and if you apply this principle to high-end vintage gear it might just save you a small fortune — without compromising on quality.

Sebatron VMP 2000eVU

Valve Mic Preamp

Thumbnail for article: Sebatron VMP 2000eVU

Australian company Sebatron aim to start building their brand in the UK with this 'character' preamp.

WIN Great Prizes in SOS Competitions!


Home | Search | News | Current Issue | Tablet Mag | Articles | Forum | Blog | Subscribe | Shop | Readers Ads

Advertise | Information | Privacy Policy | Support | Login Help


Email: Contact SOS

Telephone: +44 (0)1954 789888

Fax: +44 (0)1954 789895

Registered Office: Media House, Trafalgar Way, Bar Hill, Cambridge, CB23 8SQ, United Kingdom.

Sound On Sound Ltd is registered in England and Wales.

Company number: 3015516 VAT number: GB 638 5307 26


We accept the following payment methods in our web Shop:

Pay by PayPal - fast and secure  VISA  MasterCard  Solo  Electron  Maestro (used to be Switch)  

All contents copyright © SOS Publications Group and/or its licensors, 1985-2016. All rights reserved.
The contents of this article are subject to worldwide copyright protection and reproduction in whole or part, whether mechanical or electronic, is expressly forbidden without the prior written consent of the Publishers. Great care has been taken to ensure accuracy in the preparation of this article but neither Sound On Sound Limited nor the publishers can be held responsible for its contents.
The views expressed are those of the contributors and not necessarily those of the publishers.

Web site designed & maintained by PB Associates | SOS | Relative Media