Multi-Pattern Condenser Mic U87AI DIY Kit K870 Capsule

Multi-Pattern Condenser Mic DIY Kit 34mm K870 Capsule U87AI Circuit

Specification :

Frequency Response: 20Hz – 20kHz
Polar Patterns: Cardioid / Figure-8 / Omni-directional
Sensitivity: 28mV/Pa (Cardioid) / 22mV/Pa (Figure-8) / 20mV/Pa (Omni)
Output Impedance: 200Ω
S/N Ratio: 80dB
Max SPL: 116dB
Power Supply: 48V Phantom Power
Output Connector: 3-pin XLR
Dimensions: 250mm (L) x 46mm (W)
Weight: 0.76kg

Feature:

This DIY kit features a sleek beige elongated body design with electroplating and baking paint finish, offering excellent durability and wear resistance. The circuit references the classic U87AI design with dual PCB layout, supporting three polar patterns switchable via micro switch: Cardioid, Figure-8, and Omni-directional. It also includes a low-cut filter switch.
Circuit Features:
Dual PCB design: One board provides +60V and -60V bias voltage for the capacitor capsule
2N3819 transistor amplifies the capsule signal and drives the nickel alloy transformer for final output to 3-pin XLR
U-type nickel alloy output transformer for warm, natural tone
High-temperature resistant wiring and precision micro switches
Capsule Specifications:
Model: K870 reference design
Type: 34mm pressure gradient sensor, DC bias type
Diameter: 34mm, Thickness: 13mm
Four-wire double-sided gold-sputtered design
Wide frequency response, high SPL handling, and excellent sensitivity for accurate sound reproduction

Packing:

1pc body

1set un-assembled circuit

1pc capsule

Application:

Professional studio recording, vocal and instrument recording, live sound capture, live streaming, and home recording.

Attention:

PCB A and PCB B are connected by three wires.
The U-type transformer is secured with copper wire — do not pull the transformer wires forcefully. Refer to the wiring diagram: T1 connects to black wire, T2 to yellow, T3 to black, T4 to white.
Raise the height of inductors L1 and L2 during assembly.
The two black wires from the capacitor capsule should be shorted together.
Solder the micro switch quickly to avoid heat damage. The 3-position pattern switch has an orientation notch that must face downward.
Important: Do not touch the capacitor capsule with bare hands. Do not clean with alcohol.

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