What is a tube microphone?

Electrical signals produced by the capacitor in a mic capsule are tiny, and they need to be amplified before they can be sent down a cable to the rest of your gear. This onboard amplification inside a mic’s body is called a head amplifier or head amp.  

The primary component of any head amp is the amplifier itself, which can be based on a vacuum tube or a Field Effect Transistor (FET). They do the same job, but in very different ways. 

A tube or triode has three conductors inside. When the tube heats up, electrons start to flow through the vacuum in the tube, from the cathode to the anode, while the grid sits in between them, watching the tiny signal coming from the capsule. 

As electrons flow through the grid on their way from the cathode to the anode, the grid modulates the flow, turning it into a greatly amplified low-impedance version of the grid signal that’s ready to send down the cable. 

Click here, if you want to learn more about how a microphone works. 

That magic difference between tube and FET can be heard when you push the head amp by putting the mic up close to a sound source.

A tube creates extra harmonics – even harmonics that the human ear perceives as euphonious (a fancy word meaning ‘nice-sounding’). The signal gently compresses, too, which sounds awesome. 

Tube mics are great in certain applications, but beware of elevating them to the status of icons or assuming they’re all hype and no substance.

As always, you need to know the sound of your mics, and be able to match them to an application for the best results, rather than rely on what everybody knows. Remember: if it sounds good, it is good. 

If you're looking for a high-end tube microphone for your studio, you can check out the LEWITT PURE TUBE.