Studio Projects C1 circuit mod kit: fix the high-frequency hype

Description

Is your Studio Projects C1 too bright, too hyped, too sibilant?
We have a field-proven fix: a unique circuit modification that recreates the high-frequency rolloff found in the Neumann U87.
This mod kit promises to fix the harsh, thin, dare I say metallic tone of the original Studio Projects C-1, and it does indeed deliver, 100%.
-Ray V.
Really great components and a really nice result. Warmth and output enhancement are exactly as advertised. Best instructions of any DIY kit I've ever gotten so far and I've done amps, pedals and outboard recording gear. It was fun to do as well. Highly recommended.
-Adam J.
The best detailed instructions, packing and process suggestions I have ever seen.
-Gerald T.
I did some before-and-after testing (through a Grace preamp) and what a noticeable difference! Sibilants are smooth and pleasing. I then tried replicating the "after" sound by applying EQ to the "before" sample, and all it did was darken harsh sibilance. There's no comparison. The EQ board mod literally removes the harshness at the source.
-Tom L.
The "corrective EQ," aka high-frequency de-emphasis, found in the U87 is required for the U87's capsule to sound good. The Studio Projects C1 needs that treatment too, but the C1's circuit doesn't provide it. That's where our circuit mod kit comes in: it does for the Studio Projects K67-type capsule what the Neumann U87 circuit does for Neumann's K67 capsule -- namely, it fixes the boosted top end of the frequency response.
Because the Studio Projects capsule is a pretty nice copy of the original German K67, the corrected C1 microphone (with circuit mod kit installed) sounds very, very close to a 00 U87 Ai. It sound so close, in fact, that we did an acoustic sweep test and saw how close they were. The modified C1 (total cost: 0 plus 1 hour of time for the modification) versus a brand-new U87 Ai (total cost: 00), delivered near-identical results.
We did a swept sine-wave test using a custom calibrated acoustic test rig. The resulting graph can be seen in the images section of this page.
What it shows is that the stock C1 (orange line) has a boosted response between 5kHz and 12kHz. The peak is at 12kHz, where the C1 is at +6dB. What you see in that line is the reason the stock C1 sounds bright, peaky, and hyped.
In contrast, the U87 Ai (purple line) is within about 1.5dB of flat response, up to 12kHz.
Now look at the modified C1's trace (green line): it is nearly identical to the U87 Ai, although the C1 has better bass response below 100Hz, and more "air" at 15-20kHz.
Compatibility
This circuit mod kit is compatible with all 3 known versions of the Studio Projects C1:
The original "797 Audio" cobranded C1 with no switches
The "797 Audio" cobranded C1 with a single combined pad/filter switch
The later Studio Projects "Red Badge" C1 with separate pad and filter switches
The circuit mod kit includes parts and instructions for all 3 versions of the microphone.
We make a version of this kit for the Studio Projects C3; inquire for details. It is a different kit than the C1 kit. Please don't buy the C1 kit for your C3.
We do not have a circuit mod kit for the LSD2; our C1/C3 EQ mod circuit board won't fit inside the LSD2 case.
What's included
Here's what you get:
Custom, made-in-USA circuit board for our proprietary EQ circuitry
hand-picked components, including US-made polypropylene signal capacitors, imported Wima film capacitors, high-quality NP0 ceramic capacitors (used in the DC circuit, not the audio circuit), low-noise 1% 50ppm Dale resistors, etc.
US-made, mil-spec silver/Teflon hookup wire (pre-cut, with ends stripped and tinned)
30-page DIY instruction manual that leads you step-by-step through the mod process with color photographs at every stage
Results
We're on our third run of PCBs, and third printing of the DIY manual. This is one of our best-selling circuit mod kits, with hundreds of happy customers.
Difficulty Level
This is a DIY electronics kit; you will need to solder in order to install this. You will populate a small circuit board (~10 components), then remove between 4 and 8 components from the C1's audio PCB. Then connect the new circuit board using the included wires.
If you have never soldered before, we recommend practicing your soldering skills first. This kit is not difficult, and the instructions are excellent. But if you cannot confidently form good solder joints, we recommend either practicing that first, or enlisting the help of a friend to complete this kit.
Typical build time for this kit: less than 2 hours.