New Music Monday: Warm Audio WA-MPX Microphone Preamp

Old Ampex 351 tape machines have been sought out for many years not so much for their tape aspects but for their warm sounding microphone preamps. While most other vintage pieces have been cloned already, the 351 preamps have not been – at least until now. Warm Audio has introduced its version of the preamp with its new WA-MPX.

The WA-MPX is a tube mic preamp consisting of three tubes – two 12AX7’s and a 12AU7. The inclusion of a third tube in the circuit is an interesting change from the original Ampex circuit in that it now provides up to 90dB of gain, which is plenty for ribbon mics or a low-sensitivity SM7B. It also includes custom-wound CineMag transformers, which are essential for capturing close to the original sound.

Interesting Controls

There are three main controls on the front panel – an Input Select control where you can select either Mic, Line or Instrument; a large rotary Preamplifier Gain control; and a rotary Output Level control. Between the input and output control sits a large analog VU meter.

There are a series of 7 front panel switches, and that’s where things get interesting. On the top row sits the +48V phantom power switch, then a High Gain switch that adds an extra 20dB to the input, and Polarity switch. The Tone switch at the end alters the input transformer impedance to add some extra color.

The bottom row starts with an instrument input jack, an 80Hz high pass filter, a 2kHz low pass filter (unusual!), and finally the Tape Saturation control that engages a discrete circuit in the signal path to add some natural compression, harmonic distortion, and focused tone filtering to emulate the sound of a tape machine running at 15IPS.

The single channel WA-MPX retails for $749 while a dual channel unit is available for $1,399. You can find out more here, or watch the video below.

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