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Warm Audio WA-MPX – A Mix Real-World Review

In a first for the Mix Real-World Review, our reviewer finds no "cons" with a product—find out why!

Warm Audio WA-MPX
THE TAKEAWAY: “No matter how you set it, it’s a retro-vibe machine.”
COMPANY: Warm Audio •
PRICE: $749
• Versatility; authentic-sounding Tape Saturation circuit.
• Up to 90 dB of gain.
• Tone circuit adds character.
• High-pass and low-pass filters.
• Pleasing, old-school design and solid build quality.
• Excellent value.
• None.

Digital modeling of tube processors has improved significantly, but there’s nothing like actual tube hardware. Warm Audio’s single-channel WA-MPX and 2-channel WA-2MPX are affordable tube preamps that emulate the performance and sound of vintage Ampex 351 preamps from the 1950s, which were popular in recording studios during the tape era. Warm Audio sent Mix the single-channel WA-MPX for this review.

The two-rackspace unit, which is solidly built, features three tubes—two 12AX7s and a 12AU7—and custom-wound CineMag USA transformers.

Most of the I/O, including the XLR mic, TRS line inputs and outputs, and an IEC power inlet, resides on the back panel. The one exception is the front-panel instrument input.

The company designed the WA-MPX to look similar to a 351 preamp, including an aluminum faceplate, star-shaped knobs and large metal switches.

The two most prominent knobs control Preamplifier Gain and Output Level, while a smaller one switches the unit between Mic, Line and Instrument levels. A large VU meter shows the input level and can be calibrated from a front-panel calibration screw.

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Seven toggle switches clustered on the left side of the unit allow users to easily turn various preamp functions on or off—some typical, others not so much. The former group includes switches for 48V phantom power, Polarity reverse, and a high-pass filter set at 80 Hz. Among the non-standard features are a low-pass filter set at 2 kHz and a High Gain switch, which, when activated, boosts the preamp gain from 70 dB to 90 dB.

The Tone switch is similar to those found on certain other Warm preamps. It lowers the input impedance to give you a slightly more gruff-sounding result.

Another switch turns the Tape Saturation effect on and off, which Warm describes as adding “compression, harmonic distortion, and focused tone filtering to emulate the sound of tape machines running at 15 ips.” Although there’s no actual tape involved, the effect sounds excellent, whether you’re using a little or a lot. With the Tape Sat switch on, turning up the Input Gain provides more distortion.

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I recorded several lead vocal parts through the preamp using my go-to vocal mic, a Mojave Audio MA-300 tube condenser, and I got consistently full and warm-sounding results. On some of the tracks, I dialed in a bit of the unit’s Tape Saturation, which added a pleasing edge to the sound.

I also tried the WA-MPX on tambourine, acoustic guitar and mandolin, the former through the Mojave mic and the latter two miked with an Oktava MK-012 pencil condenser.

The parts I tracked clean on mandolin, and acoustic guitar had nice character. I also tried a little bit of saturation with those instruments. As long as I kept the Input Gain low (below 9 o’clock), the results were edgy and fat, but still natural. Single-note lines sounded especially good.

I also loved how the preamp sounded on DI electric guitar and bass. Dialing in just a tad of Tape Saturation warmed up my Fender Precision. Maxing out the Saturation effect added authentic-sounding distortion to my direct Telecaster. I also re-amped a couple of existing electric guitar parts through the WA-MPX with the saturation turned up high, with excellent results.

I’m highly impressed with the WA-MPX. It offers plenty of gain, and its Tone and Tape Sat circuits provide impressive sonic versatility. No matter how you set it, it’s a retro-vibe machine. What’s more, the price is surprisingly low for what you get.