By Mark Goldenberg

The Sunnaudio Custom Shop MS-2 stereo preamp (from $775.00) is an all-analog, two-channel unit designed for use on stage or in the studio. Along with versatile inputs and output routing, two independent channels with boost function, phantom power, and post and pre inserts for each channel, the MS-2 boasts a unique feature: a dedicated mid-side decoder function, which allows the user to mix an internal guitar mic with the direct pickup signal, creating a beautifully wide stereo effect that is, quite frankly, addictive.

The Layout and Features
The compact (5.7″ x 4.7″ x 2.7″) MS-2 is solidly built and can run on its internal battery, via phantom power, or with a 9.6v power supply. My review unit came with a power supply and an experimenter’s kit: a temporary-mount internal microphone, which I needed to audition the mid-side decoder function. The two channels are basically identical, except that the second one has a 9–12 volt DC mic power switch. Each channel has top-mounted volume, and bass and treble cut/boost knobs. Underneath those are smaller controls for a 20Hz–200Hz high pass filter; boost capable of 7db of gain; a mid-cut/boost control; and a mid-frequency control, which can range either from 1k–2.5k, or 300hz–1k, switchable via a small side-mounted push button.

There are two large footswitches. One, labeled Signal, engages or disengages the device and has multiple functionality, determined by the settings on a Signal Mode dipswitch, allowing the user to configure the preamp according to the desired use of the pedal. The other is the on/off switch for the global boost function. When engaged, the boost circuit can be assigned to either or both channels via a second dipswitch on the front panel, the amount of boost determined at each channel by way of the individual channel’s boost gain pot.


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The settings here can be used to turn post inserts on or off, on one or both channels, in pretty much any combination one might need. When the Signal switch is engaged, the HPF knob is illuminated in bright green, and the boost gain pot is blue when the boost is on—a cool feature for stage use. There is a small green light in the center of the top panel that lets you know the unit is receiving power, and two small buttons: one for switching on the mid-side effect and the other for enabling mono mode. Each channel’s side panel has a 1/4-inch input, the mid frequency range button, one dipswitch for added presence and another to change the input impedance, and two 1/4-inch TRS jacks for pre and post channel insertion. On the back panel are output jacks for each channel, either balanced +4 or unbalanced -10 1/4-inch jacks.

Tones for Days
Extreme flexibility is the name of the game here, and even though there are many options and tons of controls, I found the MS-2 to be well laid out, easy to understand and use, and just darn fun to fool around with. To test it, I used my Collings 001 Mh, fitted with a Trance Audio Amulet pickup/preamp system. Just for grins, I also ran my Danocaster T-type electric guitar through it.

I connected the MS-2 to my UAD Apollo interface with no effects or processing, monitoring everything with my trusty Mackie HR824 speakers. I began by plugging my Collings directly into the Apollo, fed into the MS-2. The engaged preamp did not add any noise that I could perceive. I tried adding some treble, and that really added some nice sparkle to the amulet. I fooled around with the bass and treble controls adding and cutting frequencies. The MS-2 was very musical-sounding, even at extreme settings. The mid feature was really effective, as was the HPF, and the boost was ample enough to irritate a front-of-house guy.


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I tried the pre and post inserts with a Chase Bliss Dark World reverb pedal and a Chase Bliss Warped Vinyl. Things were super quiet, with no insertion loss that I could discern. Finally, I installed the temporary mic with the included sticky tape. It took me just a couple of minutes to find a spot that worked for me, but once engaged it sounded beautiful. With the pickup added I had a lot of fun adjusting the EQ on both channels. I didn’t hear any phase problems between the two channels, but I thought since this box does everything else so well a phase reversal switch might be great.

The real magic of the MS-2 happens when the mid-side decoder gets kicked in and you pan the outputs hard left and right. The effect was mesmerizing—very three-dimensional, beyond realistic, venturing into almost chorusing. With reverb engaged and headphones on I went deep down the rabbit hole and almost didn’t come back.

The Bottom Line
The Sunnaudio MS-2 is an extremely high-quality preamp with superb flexibility and awesome functionality. With the delicious mid-side decoder effect, this preamp exists in its own universe and is certainly worth considering if you’re looking to elevate the sound of your acoustic guitar. sunnaudio.com