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PreSonus MP20 Microphone Preamp

PreSonus' MP20 stereo microphone preamp has the same basic electronics, features and sonic character as the M80, putting it a notch or two above many of its competitors.

When PreSonus introduced the M80 eight-channel mic preamp, it raised some eyebrows with its combination of sonic quality and features. PreSonus’ MP20 stereo microphone preamp has the same basic electronics, features and sonic character as the M80, putting it a notch or two above many of its competitors.
Product PointsApplications: Studio recording; live sound

Key Features:Class A discrete circuitry; transformer-coupled design; stereo mix bus; IDSS warmth control; front-panel instrument inputs; headphone output; balanced inserts

Price: $650

Contact: PreSonus at 800-750-0323 .


+ High-quality, versatile sound

+ Stereo mix bus

+ Headphone output

+ Balanced inserts


– No switchable output level

– No dedicated 1/4-inch outputs

The Score: A great-sounding mic preamp with features and flexibility that exceed its price.

The MP20 ($650) offers two channels of preamplification, each consisting of a Class A discrete input buffer, twin-servo gain stage and high-quality audio transformer. By changing the current through the transformer, the MP20’s IDSS control allows variable generation of even-order harmonics. The ear usually hears this as a thickening or warming of the sound.

Each channel of the MP20 offers a variable gain control (10 dB to 60 dB gain), IDSS control, phase invert, phantom power, pad and 80 Hz high-pass filter. A L/R switch assigns the input to the MP20’s stereo mix bus and a constant-power pan knob sweeps each input across the stereo bus.

The MP20’s metering consists of 12 LEDs; 0 dB sits in the middle, with green LEDs spanning the range from -24 dB to +24 dB. Its peak indicator sits at a generous +28 dB. Each button on the MP20 glows when engaged, as does the large, round power button on the unit’s right side. The MP20’s numerous lights, classy blue brushed-aluminum faceplate and chrome knobs add up to a very nice-looking piece of gear.

The MP20 is well-equipped in the area of inputs and outputs. In addition to the individual channel XLR inputs and outputs, the PreSonus has a pair of instrument inputs on the front panel. Also on the front surface is a stereo headphone output that monitors the stereo bus. A knob controls level to the headphones and the MP20 puts out enough juice to drive even inefficient, high-impedance phones to strong levels.

A real surprise on a preamp at this price range is a TRS balanced insert for each channel – one usually feels lucky to get unbalanced inserts on such a product. For patching in a compressor or other processor(s), balanced inserts are the way to go. Since the MP20 has no 1/4-inch outputs, the insert send serves this purpose as well. The insert returns can be used to return a line-level source to the stereo bus.

Unlike the M80 (which uses a large, external power supply), the MP20 has an onboard power supply. Noise performance around 60 Hz may suffer a few dB for this decision, but the convenience factor is undeniable. Internal power supply or not, I doubt many recordists at this level will gripe about the MP20’s -94 dB noise floor.

I poked around inside the MP20 a bit, and was impressed with the quality of construction. I could see no “oops” leads hand-soldered to any circuit board and the innards revealed that plenty of care went into its design.


Like the M80, the MP20 has a focused and punchy sound. It doesn’t have a particularly treble-heavy output, nor is it as fat and full sounding as others. With IDSS all the way down, the MP20 has a nicely balanced sound with a solid midrange response. I described the M80 as almost tough-sounding (PAR, 8/99, p. 38) and the same holds true for the MP20.

The preamp’s IDSS circuit changes its sonic character dramatically. The increase in even harmonics takes some of the sheen off the MP20’s sound and lowers the perceived level a bit. Boost the gain to compensate and the end result is a fuller, darker sound. With the MP20’s IDSS control at 100 percent, the preamp’s sound is considerably less detailed and open. Transients also take a hit, which makes for a smoother, less dynamic sound (an improvement in most cases).

The IDSS circuit lets the MP20 cover a broad range of the middle ground between ultrapure on one side and colored or thick-sounding on the other. With IDSS all the way down, the MP20 gives you sound nearly as accurate as some much pricier solid-state designs. Wind the IDSS up near the top of its range and the MP20 takes on a loose, somewhat dark character often associated with a tube preamp working up a sweat. This chameleon-like nature of the MP20 is a real plus – it’s like getting several preamps in one.

Does the MP20’s IDSS circuit allow it to nail the sound of a thick tube preamp? I wanted to answer this question, so I did a head-to-head comparison between the MP20 and a high-quality ($2,500) tube preamp. With its IDSS control at about 75 percent, the MP20’s sound was quite similar to that of the tube preamp. At 100 percent, the MP20 was actually darker. The MP20 didn’t quite generate the large, rich sound that the tube preamp did, but it came as close as I’ve heard from a solid-state design.

What the IDSS control does for a mic it also does for instruments. It was nice to be able to dial away some of the brittleness of a direct electric guitar or piezo acoustic pickup. The pseudo-compression of the IDSS circuit also helps the track sit in the mix, which was beneficial for direct electric, acoustic and bass guitars.

On the control front, the MP20 gets two big thumbs up. Knobs are arranged logically and have ample room to breathe. Switches are clearly labeled, and their bright LEDs clearly indicate their settings. The MP20’s metering is greatly improved over the M80, which lacks resolution around 0 dB. The MP20 offers LEDs at 2, 4, 8, 16 and 24 dB above and below the 0 dB marker.

The MP20’s stereo mix bus is a thoughtful, handy feature. Being able to pan a pair of mics through the stereo field can give live recording engineers a bit more control over their sound. Studio recordists can sum top and bottom snare mics to mono, blend an acoustic guitar’s direct pickup and microphone, or dream up any number of other uses for the stereo bus. Even if used for nothing more than monitoring, it’s a nice touch.

There isn’t much I didn’t like about the MP20. I do wish it had dedicated 1/4-inch outputs in addition to the 1/4-inch insert jacks. Switchable output levels (-10 dBV and +4 dBu) would be appreciated when interfacing the MP20 with some types of gear. Even these complaints are minor in the face of all the MP20 does so well.


I wouldn’t just recommend the MP20 to folks shopping for an affordable microphone preamp – I’d also pitch it to those with as much as $2,000 to spend. I’ve tested more expensive stereo preamps that didn’t have the sonic quality, tonal flexibility or thoughtful features of the MP20.

It looks like PreSonus has another winner on their hands.