Studio Projects C1 Circuit Upgrade Kit

$49.00 $89.70

This circuit mod kit will give your Studio Projects C1 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.

Features & Benefits

  • Makes your C1 sound very close to a U87...
  • ...but with better low-frequency response.
  • Reduce microphonics.
  • Raise output level and sensitivity.
  • Reduce self-noise.
  • Save the cost of a new capsule!

About the C1

The Studio Projects C1 has always had a good reputation, for good reason. It has a very nice capsule, is solidly built, and uses generally decent components.

But it has a problem, one that is ironically shared by so many imported condensers: it is too brightly voiced. It uses a linear* transformerless circuit (based on the Schoeps design), and a K67 capsule that expects corrective EQ in the circuitry. The resulting mic can sound nice on certain sources, if you need to capture a lot of high frequency information to help a source cut through a mix.

But on too many sources, the C1 is just too bright and peaky. The capsule has a boosted top end, which the circuit does not correct. The result is an over-bright and fatiguing sound. On solo acoustic guitar or voice, the mic becomes sharp and sibilant.

*(We use the term "linear" to indicate that the circuit does not provide high-frequency corrective EQ, such as the K67 capsule expects. But the C1 circuit is really only linear above 80Hz; it is rolled off in the low bass frequencies, even when the high-pass filter is disabled.)

We have come up with an adjustable EQ circuit to correct this fault. In fact, we've reproduced the EQ curve of the Neumann U87. The modified circuit will behave just like the U87, although with fuller low-frequency response.

The kit includes additional upgrades as well, which we've included to reduce microphonics, lower the mic's self-noise, and increase sensitivity.

Here is a frequency sweep showing the circuit's response. 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.

C1 Circuit Sweep

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 C1'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.)

Audio Sample

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.)

Modified C1 vs U87 Frequency Graph

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).


The C1 mod kit that we stock in the UK warehouse contains documentation and parts for both the older "797 Audio" C1 and the newer "Red Badge" C1.

If your C1 has no switches, the circuit mod kit can be installed, but you would have to work from simple text instructions, because we do not have detailed full-color documentation for the no-switch version of the C1 microphone.

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