What’s Inside a USB Mic? Can it be Modded?
What’s Inside a USB Mic? Can it be Modded?
USB Mic Teardown
Sunday, June 30, 2024
I bought this microphone because it was cheap and it looked like it might make a good donor body for a mic with a couple of switches on the front panel. But before ripping it apart, let’s see if it works, what the circuit looks like, and whether there’s anything mod-able.
In the box is the mic, a USB A to B cable, and a manual which reads like it was translated to English by Google. Notably missing is any sort of stand, shock mount, or mounting clip. You’ll have to supply an AKG shock mount or a universal type. The dark blue metallic paint looks nice.
Plugging the mic into my Mac laptop, a blue LED comes on inside the mic, and it appears as a mono input source and a stereo output in the Audio MIDI Setup control panel. It works at 16 bits and 48KHz only. “CD Quality” in other words. Pressing the knob mutes the mic, and the LED changes to red. The LED also changes color if you mute and unmute the mic from an audio app or the computer keyboard.
The mic requires a USB host, a computer, iPad, or smart phone to work. Just giving it power from a USB power bank doesn’t work. No sound even in headphones plugged directly into the mic. When connected to a host, the built-in headphone amplifier has a direct connection without latency to the mic at all times, mixed with audio from the computer. Monitoring from the computer can produce weird echoes due to driver and app latency, and is best avoided. Fortunately, that’s the default in most apps.
Voice pickup is crisp and easy to understand. There is an effective foam pop filter inside the grille. The pattern is directional, and noise pickup from the rear is minimal. As supplied, it’s a better mic than the one built into most computers for Zoom conferences and the like because you can place it where it sounds best, close to your mouth, assuming you have a suitable stand.
I was afraid it might sound like some of the BM800 mics with cheap USB sound cards. It doesn’t. Digital noise is well filtered, there is a proper headphone driver circuit, and a low noise op-amp mic preamp built in. It does hum when your hand comes near the volume control or plastic front panel if your body isn’t grounded to the mic or computer. So let’s look inside.
Capsule
16mm cardioid electret without internal FET
Circuit Board
24C02 EEPROM
2K serial memory
(unmarked chip)
Probably CMedia
CM108B
USB CODEC
USB connection
MAJOR COMPONENTS ON CIRCUIT BOARD
LMV721 Op-Amp
low noise 5V operation
2SK596 JFET
on other side of printed circuit board
Mic volume control
on other side of printed circuit board
Dual Op-Amp
headphone amplifier
CIRCUIT BLOCK DIAGRAM
What can we do to improve this mic? It’s well designed for the low cost parts employed. I replaced the 16mm capsule with a 25mm CM012 electret which sounds better for my voice, and added a jumper wire from the case of the volume control to ground on the PCB. That helped with hum pickup. Not much else can be modded. There are USB mics built around fancier CODEC chips with multiple higher sampling rates and greater bit depths, but those are completely different circuits.