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microphone amplifier

ma-2.2 true class a mic preamp

product review

Sound on Sound magazine by Hugh Robjohns

Making its way quietly north from New Zealand, Buzz Audio's MA-2.2 brings New World purity to the microphone amplifier market. Dave Foister says, 'g'day, blue'.

The Buzz Audio SOC1.1 stereo optical compressor was reviewed in SOS May 2002, and I recall being impressed with its performance. The latest offering is a dual-channel microphone preamp using fully differential, discrete solid-state Class-A circuitry — the stuff of sonic legends.

The MA 2.2 is a fairly conventional 1U rackmounting box, although it extends over 300mm deep and weighs enough to warrant rear support in a rack. The rear panel carries an XLR mic input and two outputs for each channel. One output is on a TRS quarter-inch socket, and the other on an XLR, but both are unbalanced as standard. The designer argues that this arrangement avoids an extra amplifier stage and maintains the shortest possible signal path. In most situations this works perfectly well — indeed my reference GML mic preamps have unbalanced outputs for the same reasons, and I've never had a problem, even when driving long output cables. Nevertheless, should a balanced output be required, it is possible to install line output transformers to balance the XLR output — the Lundahl 1517 transformer is specified and can be retrofitted by the user (if able to solder).

Under normal conditions, signal and chassis grounds are linked, but an earth-lift switch on the rear panel can be used to separate them with a 10 ohm resistor to prevent ground loops. The mains inlet is the ubiquitous IEC with an integral fuse, and there is a voltage selector for 110V and 220V working.

In Control

The front panel is simplicity itself, with a classic look and feel. The controls are recessed, and comprise one red LED, five toggle switches, and a large rotary gain control, the whole set being repeated for the second channel. The first pair of switches activate a polarity reversal and a 20dB pad, and both introduce alarming splats on the output when operated. An overload LED is set to illuminate at +18dBu (6dB below the unit's maximum output level), but can be realigned to other thresholds if required. The large Gain control spans a range of 16-64dB and, although continuously variable, is detented to feel a like a rotary switch. On the opposite side of the gain control are three more toggle switches: Mute, Phantom, and an input impedance selector. The first two are self explanatory, and the last offers a choice of either a relatively high 3k ohm impedance, or a more conventional 1.2k ohm. The unit can also be specified with a 600 ohm (or virtually any other) input impedance option, more suited to vintage ribbon microphones, if required. At the extreme right-hand side of the unit is another toggle switch, this time to power the unit on and off, complete with blue LED. In addition to the output transformer and very low-impedance input impedance options, the unit can also be specified to have a higher maximum gain, or an electronically balanced output stage as an alternative to the transformer option.

Internally, the unit is built to the best professional standards, using very high-grade components mounted on three PCBs, one for each channel and a third for the PSU. Daughter cards on the two audio boards carry discrete amplifier stages (two for the input side and one to drive the output) and local power regulation circuitry. The power transformer is mounted at the rear of the chassis behind the PSU circuit board, and steel dividers run the depth of the case between the boards. This not only increases the mechanical strength of the unit, but also minimises stray magnetic and electrical interference — internally, between the cards, and externally.

The specifications quote impressive levels of distortion (better than 0.005 percent at 1kHz), common mode rejection (70dB), and bandwidth (20Hz-250kHz at 64dB gain). However, the noise performance seems poor at -74dB (no reference level, but A-weighted and with a shorted input), and the EIN figure is unusually high at -133.5dB (again, no reference and A-weighted, but with a 150(omega) source).

Using the MA-2.2

So much for the figures, the important question is: what does the MA 2.2 sound like? Fast is the word that first springs to mind — this is a very dynamic, detailed preamp, with a clean, neutral, and open character. It compared very well against my reference GML8304, especially at the bottom end, which is where most budget mic preamps fall down. The upper end seemed slightly smoother and a tad more extended on the GML (but there was very little in it), and the Buzz seemed to sound a little 'bigger' overall. The MA 2.2 is very quiet (despite the disconcerting specs) and seemed to cope with everything I threw at it very well. Close-miked vocals, acoustic guitar (including the challenging twelve-string test), and percussion were all captured very cleanly, with superb precision and detail, and the preamp gave them all a very slightly 'larger than life' quality.

Using it to handle a simple stereo pair of Sennheiser MKH40 cardioids covering a chamber orchestra and small choir, I found it was capable of processing very complex signals accurately without adding any unwanted character of its own. The gain matching between channels also seemed exact. The gain range is more than adequate for any musical application, and the fine resolution between the detents allows precise stereo matching. It is wise to select the mute option before changing the polarity, pad or phantom switches, but the rest of the facilities are pretty much standard fare. However, the switchable input impedance offers the ability to change the character of some microphones in a subtle and often interesting way. I wouldn't like to say which setting is right for any particular mic, and not all seem to show a character change anyway, but it is a fun feature which adds the possibility of a little extra creativity and individuality.

As it employs Class-A circuitry, the MA 2.2 tends to run fairly warm, so it would be a sensible precaution to ensure a good flow of air through the unit. Overall, this is a well-thought-out, high-performance product, which provides a very attractive alternative to the almost identically priced Focusrite Red 8 in the UK. It could also be short-listed with a number of other high-end units, including the more expensive GML8302, and the cheaper DACS Micamp and Amek DMA. If 'clean and detailed' is your thing, as opposed to 'thermionic warmth', check out this Buzz unit at your earliest opportunity.
[December 2002]

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