Andrey "Spirit" Builds a Low-Cost, High-Performance Studio Mic — and Releases It for Free
Featuring an open source "slightly cursed" pre-amp, this condenser microphone is claimed to deliver "perfect" results for under $100.
Semi-pseudonymous engineer Andrey "Spirit" has eschewed high-cost off-the-shelf condenser microphones in favor of building his own — and has released the resulting design under a permissive open source license for all to build.
"I've always wanted a nice studio microphone, but all of the ones I was considering were too expensive," Spirit explains of the project. "So I made my own, including a somewhat cursed preamplifier schematic. It's fully open source, and costs less than $100 to build!"
Designed for a higher sensitivity than dynamic microphones, condenser microphones can be pricy — and the more affordable ones can lack in quality. Spirit's design, then, aims to approach the lower end with cost but higher end in performance — using a cloned condenser capsule in a low-cost microphone shell with a custom pre-amp board.
"The microphone build uses a clone RK12/CK12 capsule ($40-50 on Aliexpress/Ebay/etc, search for 'edge terminated capsule'), a U87 donor body ($15-30, also Aliexpress, search term 'U87 mic'), and a custom preamp board($20-30)," Spirit explains. "The board is very simple, yet high performance — it uses a dual FET input op-amp in a single package to both convert the capsule's impedance and provide a differential signal, while the bias is provided by a slightly cursed hex Schmitt trigger inverter charge pump."
The resulting microphone is, in Spirit's words, "perfect," with very little self-noise and a high dynamic range. The audio signal also comes through cleanly — "you get exactly what the capsule sees on the XLR connector," Spirit explains. "Pretty much none of this is really original and has been done dozens of times (i.e. DJJules/Sound Sleuth over at Instructables, whose circuit I took inspiration from), I just put my own twist on it."
The project files and assembly instructions are available on Spirit's GitHub repository under the permissive MIT license. "If you want to build it, go ahead," Spirit writes. "If you want to sell it, also go ahead, but just mention this [repository] or something."