Moon Professional: 3500MP mic preamp

Many of you may be wondering who Moon Professional is and why you should pay any attention to another company making mic preamps. These too were my first questions when their first product was introduced to me, so I'll save you the research and give you the short story. Moon Professional developed out of the Moon audiophile line from Simaudio, a well-respected A/V component manufacturer who has been winning awards and building high-end equipment since the 1980s. Moon Professional will be releasing products geared for the pro audio market, employing the R&D fundamentals gathered over many years of designing audiophile amplifiers, preamplifiers, and DACs.

The Moon 3500MP is a two-channel microphone preamp in the pedigree of true audiophile equipment. The form factor is a typical 2RU-height unit, and its cosmetics belie its audiophile roots. The black, satin finished, 14 gauge steel and aluminum chassis looks and feels like high-end stereo equipment, with chrome toggle switches, subtle LEDs, and matching black gain and trim knobs. The sparse rear panel sports one XLR input and output for each channel, as well as an IEC power socket and a recessed rocker switch for mains power. The front panel's large rotary gain knob, ranging from 8 dB to 66 dB in 3.5 dB steps, is paired with a small attenuator with 3.5 dB of continuously-variable trim. Three toggle switches per channel select phantom power, polarity reverse, and mute, with each switch paired to an LED indicator. The only other switch on the front panel is the power switch, which Moon recommends leaving on at all times. I left the unit on for weeks, and the chassis never became warm, so its idle power consumption is minimal. The unit weighs in at a hefty 18 lb, owing much of that to its heat dissipating metal chassis and internal power supply.

The circuit design and layout maximizes the audio and noise specs, which truly match or exceed any mic preamp you can find. Moon chose to use a shielded internal power supply, and to minimize AC noise and power-related issues, two toroidal transformers separately power the preamp circuit and the phantom and control circuits. It turns out that two smaller toroidal transformers out-perform one larger transformer with regards to magnetic field generation and AC noise radiation. Each preamp channel uses its own gold-plated copper circuit board with metal film resistors and polypropylene capacitors. The gain controls use Swiss-made rotary switches and 0.1% metal- film resistors which allow very precise gain matching between channels. The circuits themselves are fully- balanced differential amplifiers, which maintain a balanced audio signal throughout the AC-coupled, transformerless signal path. There are no electrolytic caps in the signal path, except for the phantom power circuit. The input impedance is a healthy 3400 ohms (6800 ohms with phantom power switched on), while the high-current output stage can easily drive 600 ohm inputs up to +32 dBu levels, even with long cable runs. This purist approach to circuit design creates an amplifier with stellar specifications, boasting 250 kHz bandwidth and impressively-low noise and distortion measurements.

For the past several years, audio processors have glorified colored transformers, transistors, and adjustable feedback and loading, but let me be the first to say that neutral (and natural) is the new color. If you haven't had a chance to use a truly natural sounding preamp, you may be surprised how powerful they can be. I had the good fortune to host the Moon preamp in my studio for almost two months, during which time I recorded many different sources with many different mics. Overall, the preamp provides a wide-open soundstage - in frequency response, dynamic range, and depth of field. In the case of the Moon, by wide frequency response, I don't simply mean open and airy, I mean transparent like it's not there - like your ears are the mics. The experience of hearing the 3500MP goes along with only two other "wow" moments I have had with other mic preamps, whose names start with GML and Manley. To my ears, the area where a great mic preamp really shines is its ability to pass the low-frequency and midrange content without coloring the dynamics or altering the harmonic structure. There are many preamps that boast incredibly wide frequency responses, but the impact and clarity of most musical sounds lie in the 40 Hz-2 kHz range, not the ultra high frequencies. While transformers and certain amplifier topologies "warm up" or otherwise color the audio signal in pleasing ways, the 3500MP's transformerless, fully-balanced signal path provides transparent gain to the microphone, which really shows in the midrange detail and space around the instruments. Don't get me wrong, I produce commercial music, and I love the extreme tonal control of preamps like the Chandler Germanium [Tape Op #89, #51], but the Moon made me smile the first time I heard it. Below are some of the highlights of its use in the studio.

On solo cello in a relatively small room, I auditioned three different ribbon mics, two from AEA and one from Cathedral Pipes, and the Moon clearly revealed the tonal differences between the mics as well as reproduced a resonant frequency in the room that I had never before noticed. This was a mono recording that was doubled, and the cello's presence and realism came through even without a stereo pair of microphones. The low frequencies were naturally and musically represented, and the low-mids never became too built-up or smeary. The Moon also shone on vocal sessions. I usually go between three LDC tube mics for vocals, depending on how forward or natural I want the sound to be, but with the Moon as the preamp, I found that the warmer microphones could be gently EQ'ed brighter and vice-versa without imparting much of a processed timbre to the vocals. One noticeable side-effect of the clarity of this preamp was the pronounced impact that plosives and glottal sounds made. P-pops could sometimes peak as much as 20 dB hotter than the vocal, which also attests to the openness of the signal path. Vocals sounded clear and natural, without any sibilance or muddiness. I felt that the mics really sounded their best through this preamp. Since the entire mic's response and dynamics are so evenly reproduced, you may even find you can get more uses out of the mics in your collection.

So how do rock drums sound through the Moon? Drum room mic'ed with a pair of ribbons about 6 ft out from the kit provided a very realistic and punchy image. The roll-off of the ribbons and the wide open bottom of the Moon combined to make a huge sound that could be compressed and tailored to fit the production very well. Hi-hat, which I find particularly difficult to record without becoming "splatty," sounded great with both SDC and ribbon mics; and applying shelving EQ didn't add as much phasey mush to the hat as I typically experience. Again, that attests to the full frequency response and headroom of the Moon.

My favorite application of the Moon was on acoustic guitar. Auditioning mics while using the Moon preamp was almost as much fun as recording the actual performance. Differences between supposedly matched microphones were apparent and I wound up using a combination of large-diaphragm, small-diaphragm, and ribbon mics on one particular album that really made the production shine. Again, the recordings felt very alive and well-balanced. I find acoustic guitar unforgiving when applying EQ, but these recordings took EQ, especially the airy high- frequency boosts, very well.

The Moon 3500MP belongs to a league of audio equipment that few studios can access. The audio reproduction reflects the no-compromise circuit design and build quality, and the price reflects this as well. Other preamps at this sonic level are similarly priced, so I wouldn't say this unit is overpriced, but be prepared for sticker shock. To add some perspective, Moon's audiophile monoblock power amps cost as much as $40,000! No matter what, you do owe it to yourself to audition a preamp on this level to see what's missing from your microphone's signal path.