There are a lot of factors that go into making a great wireless belt-pack transmitter. There are considerations of frequency range, transmitting power and range, battery consumption, physical size, sound quality, durability, and the usual killer: how it handles the dreaded moisture. The MM400c by Letrosonics nails just about every one of these considerations. It’s a small, powerful and watertight pack.

Recently winning the Live Design Product of the Year Award in the microphone category, the MM400c uses a Digital Hybrid Wireless design that amazingly combines a 24-bit digital audio system with an analog FM system. This hybrid approach brings the benefits of the digital and analog world together. You get the range and transmitting power of an analog FM system with the pure and superior sound of a digital system. More specifically, there’s 100mW RF output power (which is a lot!) for extended operating range operating on a traditional FM wireless link. At the same time, using the digital domain, Lectrosonics has deployed a DSP controlled, dual-envelope limiter that handles input peaks like a pro, allowing for overall higher gain settings, which increases your signal-to-noise ratio, thus delivering cleaner sound, without the usual analog compandor artifacts. There are also many other smart circuitry related features in this pack--too many to note really, but I encourage you to check them out.

Okay, so great sound, great power, great range. Check. But have you seen this thing? It looks like it was made for combat. The MM400c means business. All of this goodness is housed in a noncorrosive, rugged, machined aluminum enclosure, and it’s quite small, coming in at 3.03" x 2 x 0.69" and 3.6 ounce, not as small as a Sennheiser SK5212 but quite close.

It lacks any kind of sexy LCD screen and instead has multiple metal caps that you unscrew to access the controls. Each metal cap has a sealed O-ring that keeps water out of the pack. The company says it can handle "extreme" moisture and temperature environments, and I believe it. It is also interesting that the manual talks a lot about doing things (changing the battery, etc) when the pack is dry, as if they assume it will be wet fairly often. The only visual feedback is via three green and red LEDs: one for the battery status and two for minimal information on the audio level from the microphones.

Putting The MM400C To Use


You select you frequency by unscrewing a cap that releases a cover, exposing a pair of rotary switches. Any pack can be set to an impressive 256 frequencies, each in 100kHz steps over a 25.5MHz range. That’s some serious flexibility. The unit is powered with one AA battery, which is inserted by unscrewing the largest metal cap, which sticks off the bottom of the pack a little. Using a lithium battery, Lectrosonics claims a 5.5 hour battery life. Lithium is recommend, as duration drops sharply with a NiMH battery (4.5 hours) or an alkaline battery (a measly 1.5 hours). The unit is powered on and off by an interesting magnetic switch that eliminates the requirement of a physical connection between the switch control and the actual switch mechanism, which keeps this unit water-tight. However, since Lectrosonics shows you how to replace this switch in the manual, I imagine it’s somewhat easy to lose.

On the top of the transmitter, there’s a permanently attached antenna and a audio level knob (ie, gain). Clearly, if that knob changes either by accident or on purpose, you’ll be thrown a curve ball at front of house. Other manufacturers go to great efforts to conceal this secret knob. The microphone element connects using a 2.5mm Microjack.

The MM400c is designed to work with the Lectrosonics 400 series receivers, which are all Digital Hybrid receivers. However the MM400C unit is backward compatible and, using the Compatibility Mode, you can configure the transmitter to work with the 200 and 100 Series of Lectrosonics receivers, as well as some receivers from other manufacturers.

The MM400c is a tough nut. I don’t know if it makes complete sense to specify as a regular old mic pack, but any time water is in your production design, I’d demand an MM400c and watch it go into combat.