Tube-Tech MP2A

Its price tag might give you the blues, but if you can afford it, the Tube-Tech MP2A could make all your preamp dreams come true.

in today's audio industry, there aren't too many companies left who refuse to build their products down to a price simply to sell more units. One such company is Denmark's Lydkraft, founded in 1977, whose valve-based Tube-Tech line of preamps, EQs and compressors has held the high ground in build quality, sonic performance and price since 1985. Initially they based their products on classic existing designs, but their current range comprises some 16 hardware devices and four software plug-ins. The Tube-Tech MP2A stereo microphone preamplifier is the latest addition, superseding the venerable MP1A, which was first introduced in 1987.

Outside In

Liveried in Tube-Tech's signature blue metal casing and white lettering, the MP2A could be thought of as an upgrade of the MP1A, which incorporates the updated specification and feature set of the RM-series PM1A, introduced in 2008. The MP2A's twin-channel control complement comprises detented coarse and fine gain controls and five switches. Metering is minimalist, with just an overload LED to indicate the onset of clipping. The final front-panel features are the quarter-inch-jack DI inputs for each channel, plus a rotary mains switch and its red jewel light. Round the back you'll find balanced XLR inputs and outputs, an externally mounted mains transformer and the power inlet, fuse and voltage selector.

Being a valve-based design with a push-pull output section, the MP2A features both input and output transformers on each channel. The input transformers are the highly regarded Swedish-made Lundahl 1571s, and the output transformers appear to be of custom design. Each channel has two ECC83/12AX7 tubes as the preamp section with a single ECC82/12AU7 for the push-pull output stage.

The input transformer has 10dB of gain built in. The coarse control adds from +20 to +60 dB of gain to this in 10dB increments. The fine knob modifies this further, over -10 to +10 dB in 2dB steps. When combined with the -20dB pad, this gives the MP2A a total gain range of -10 to +70 dB in 2dB steps on its microphone inputs. The 1MΩ DI input bypasses both transformer and pad, and thus has a gain range of 0 to +60 dB, again in 2dB steps.

The central positions in each channel's five-switch bank are filled by the -20dB pad, phase and 48V phantom-power in/out switches. The three-position switch on the right brings in a high-pass filter at your choice of 20 or 40 Hz, and its opposite number allows you to vary the input impedance of the microphone input between 600Ω, 1.2kΩ and 2.4kΩ. The general rule of thumb for low-impedance dynamic and condenser microphones is that the preamplifier input impedance should be approximately 10 times the output impedance of the microphone, so the MPX2A will accommodate microphones with output impedances in the approximate 60Ω to 240Ω range. However, life isn't always that simple since dynamic microphones, in particular, do not always seem to follow that rule of thumb as slavishly as you might think. For example, AKG's D112 has an output impedance of 200Ω and follows the approximation in being designed for a 2kΩ input impedance, whereas their D5 has a 600Ω output impedance but, perversely, is also designed for a 2kΩ input. A Sennheiser MD441 U has a 200Ω output impedance, but is rated for a minimum input impedance of 1kΩ, whereas their MD 421 II, with the same output impedance, is said to be happy at 200Ω. So the moral of the story is that you should check your microphones' specification sheets and, if you wish, experiment from there.

In the MP2A, whilst the input transformers will add their normal warmth and richness to the sound passing through them, the valves are going to do the heavy lifting when it comes to gain. If you haven't worked with high-quality valve equipment before, the performance that the MP2A is capable of might come as a bit of a surprise. Although valves lost out to transistors and ICs as the price of mainstream hi-fi and pro-audio equipment plummeted, they have retained a following at the more esoteric extremes of both markets for both their intrinsic sound and performance capabilities. Valve amplifiers are capable of very wide bandwidths with low distortion (even including the effects of transformers) and the MP2A is no exception — its -3dB points are at 5Hz and 60kHz and THD is less than 0.1 percent.

Feeling The Glow

Although in absolute terms valves may be noisier than transistors, careful design, high-quality components, transformers and DC heater voltages have kept the MP2A's noise floor down to better than -82dBU with +20dB of gain and better than -60dBU at +60dB of gain. With the MP2A I found that I could always get more than enough level from close-miked sources without the noise floor ever becoming intrusive. Perhaps because of the high headroom that came with the new, upgraded circuit design — and its wide frequency response — the MP2A sounded extremely open and detailed with every microphone and source that I tried through it. It was also capable of producing a beautifully weighty and extended bottom end. With that bass capability available, the high-pass filters came in very useful for cutting down handling and stand-related thumps. The DI input worked well with both electric guitar and bass, and I've never heard my K&K piezo acoustic pickups sound quite as good as they did through the MP2A.

The three switchable input impedances didn't do all that much for me with my studio microphones. My own high-end, solid-state, transformer-balanced stereo mic preamp has a fixed input impedance of 1.2kΩ and I'm well-used to the sound that I get from that with my microphones. At that impedance setting, the MP2A was in the same general ballpark, sound-wise, across my microphone assortment, all of which have between 150Ω and 200Ω output impedances. Increasing the input impedance on the MP2A from 1.2kΩ to 2.4kΩ produced a slight and sometimes very subtle increase in brightness with 150Ω dynamic microphones. I found it difficult to convince myself that I could hear any differences at the higher impedance with my various capacitor mics, all of which have an output impedance of 150Ω.

True blue! Tube-Tech's blue-and-white livery extends all the way round.Dropping the impedance from 1.2kΩ to 600Ω gave the same order of result, with my dynamic mics sounding perhaps a little quieter and darker, although this was as slight and as subtle as before. Again, I couldn't hear anything of any consequence happening with my condenser microphones. My 150Ω stereo ribbon mic responded much like the condensers. The bass produced by that mic sounded wonderful at all impedance settings, although I did manage to persuade myself that it sounded slightly better balanced across its frequency spectrum at the 1.2kΩ setting.

However, a distinct difference appeared with an elderly Shure SM57 (another dynamic mic with a 150Ω output impedance) that I tried as an afterthought. I've always thought of the SM57 as a 'shouty' live vocal mic, as its in-built broad high-mid-range hump helps it to cut through a mix. Dropping the MP2A's input impedance down to 600Ω squashed that high-mid hump and made the SM57 sound much better balanced, more detailed and slightly quieter than at the higher impedances.

Apart from the very evident effect of dropping the impedance to 600Ω on the old SM57, I'm not personally convinced that any of the subtle differences that I heard from increasing or decreasing the impedance with my studio microphones would actually carry over into a full mix. I certainly don't recall ever feeling in the past that there was any inadequacy in my own mic pre that would have been cured by the availability of higher or lower input impedance settings.

Conclusion

To my ears, there's a musicality in the sound of high-end valve equipment that just doesn't seem to exist in more mundane gear. There's a warmth, a richness and an effortless sense of space in good valve units that I don't find elsewhere, and the MP2A is no exception to that rule. If you want to experience valve performance at the highest level in a microphone preamplifier, then the Tube-Tech MP2A is one of the best ways that I can think of to do that.

Unfortunately, even with the advent of relatively low-cost Far Eastern manufacturing, valve equipment that's capable of this level of performance remains expensive. As I said at the outset, companies like Lydkraft, who are committed to quality and not focused on price, are few and far between these days. We should be forever grateful that they, and a few companies like them, continue to pursue that particular strategy. Being able to justify the expenditure required to put a Tube-Tech MP2A dual microphone preamplifier into your studio is not going to be the easiest of tasks for the majority of us — but if you can, you really should!