Very few inline booster preamps are designed to pass phantom power — most deliberately block it — but the FetHead Phantom, which adds a fixed 18dB of gain, is one of two such products offered by Triton Audio.
I have a Tram TR50 lavalier mic with a very low output level. I was thinking about getting an inline gain booster for it, but someone told me that this kind of device was not appropriate for lav mics. Could you please offer some advice?
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SOS Technical Editor Hugh Robjohns replies: The Tram TR50 is, indeed, quite an insensitive microphone, delivering around 1.5mV/Pa (slightly less than a Shure SM57). So if your recorder or preamp struggles to provide enough gain for quiet sources an inline booster might seem a good option, but there’s an obstacle: all modern lavalier mics are electrets and need power for their internal impedance conversion circuitry. Some use an internal battery, some require ‘plug‑in power’ from a radio mic transmitter, portable recorder or laptop, and some have an XLR adaptor, which accepts professional phantom power. Very few inline boosters provide phantom (or even plug‑in) power, and most block it by design, to protect delicate ribbon microphones.
The easiest solution in your situation is to install a battery in the TR79 balanced XLR /phantom‑power adaptor that came with the Tram. With a battery installed, the mic doesn’t need phantom power, so you could use any of the familiar inline boosters which don’t pass phantom power (they all require phantom power from the preamp they’re connected to for their internal electronics, of course). Alternatively, you could use one of the few inline boosters that do pass phantom power (such as Triton’s FetHead Phantom or FetHead Broadcast), or a compact standalone phantom supply such as the ART Phantom II Pro, and connect that between the mic and (non‑powering) gain‑booster.