Digital Reference DRC100 Drum mic
Digital Reference DRC100 Drum mic
Digital Reference DRC100
Monday, June 21, 2021
The Digital Reference DRC100 drum overhead mic is a small electret condenser with an unusual circuit. It’s basically a 3-wire electret capsule with built-in FET wired as a “Linkwitz” source follower. The body is solid and well finished. The circuit board is well laid out and constructed. The mic is not very sensitive, as expected for a drum mic to avoid overloading the mic preamp. No audible hiss or hum. It does the job and looks like it will last. It’s 48V phantom powered.
The main precaution with the circuit is the high 6.8K output impedance which means long mic cables will cause high frequency loss. The output is single ended and semi-impedance balanced, so hum pickup in short cables shouldn’t be a problem, but these aren’t the mics of choice for long snakes to a house mixing console. OTOH, they come as part of a 7-mic drum kit that sells for $199.99, so you probably won’t see them at a big stadium anyway.
So, generalities aside, what’s inside these heavy little lipsticks anyway?
Here’s photos and a sketch of the circuit.
The board has no amplification, only parts to adapt a capsule designed to run from a 3V battery to run from 48V phantom power.
The 3 wires from the capsule are ground and source and drain from the FET. The FET is used as a source follower with no voltage gain and output impedance approximately equal to the 6.8K load resistor, R3. ZD2 protects the source from power on / off surges. Electrolytic capacitors E1 & E2 couple the signal to pin 2 of the XLR connector.
The drain is connected to 2.6V DC supplied from pin 2 via CR1, a constant current reference of about 1 mA, regulated by 2.6V zener ZD1, and filtered by R4, C1, & E3.
R1 and E4 provide a ground reference and some impedance balance to pin 3 of the XLR. So the circuit is simple though it uses a fair number of parts. Not bad for the price.
The capsule is cardioid, with pretty good rear rejection. It sounds normal, which is good. I haven’t actually used the mics on drums, since I bought them primarily as body donors. :-) I have no doubt you could make a fine recording of a drum set with these, given a talented drummer to work with.