Studio Projects C3 Circuit Upgrade Kit
This circuit mod kit will give your Studio Projects C3 the same frequency response curve as a $3300 Neumann U87 -- although with fuller bass! Better still, the high-frequency response of the circuit is adjustable, so you can dial in as much filtering/attenuation as you like.
Linear Circuit, No More
The Studio Projects C3 is nicely built, but in our opinion is too brightly voiced for many sources. It's great for sources that need to cut through a dense mix, but can be fatiguing, especially when layered.
We have created an add-on EQ circuit that reproduces the corrective high-frequency attenuation built into the Neumann U87. It gives the C3 a sound very very close to that of a U87, although with fuller low-frequency response.
The kit includes additional upgrades as well, to reduce microphonics, lower the mic's self-noise, and increase sensitivity.
Here is a frequency sweep showing the response of the C1 circuit (which is substantially the same as the C3's). This is not an acoustic test of the microphone, but an electronic test of the circuit by itself. The stock circuit is rolled off in the low bass, but linear out beyond 20kHz. This is a poor match for the K67 capsule, which can be thin in the bass but hyped in the 8-12kHz range.
The green trace shows the modified circuit: flat in the lowest bass frequencies, but rolled off above 1kHz. This is exactly the sort of complementary EQ that the K67 capsule needs and expects. This is called "preemphasis/deemphasis;" the capsule pre-emphasizes high frequency information, and the circuit attenuates it. The Neumann U87 uses precisely this same approach, with the same HF rolloff seen here.
What's in the box?
The new EQ circuit is housed on a US-made, custom PCB. You'll also get a pair of significantly upgraded, US-made signal capacitors, plus a handful of other components.
You will not need to change the C3's capsule for this mod. It is a very nice K67 type.
(If you have already changed the capsule for our RK-87 or RK-12 types, you could still use this mod kit. If you have installed a K47 capsule, we do not recommend this mod kit, as the circuit mod would cause the microphone to be too dark-sounding.)
We recorded a U87 Ai and a modded C1 side by side. The audio tracks are practically indistinguishable. Listen via the MP3 players embedded below.
Here's a frequency analysis of these two audio tracks. The response of the two mics is nearly identical above 80Hz. Below 80Hz, the modded C1 has better response. (If you don't want the lows, just switch on the mic's high-pass filter.)
Note: the graph above is not a sweep test of either microphone, but an averaged frequency response of the voice recordings included below. The point of the graph is that the U87 Ai and modded C1 capture almost exactly the same frequencies (above 80Hz).