Microphone Parts RA-23
Multi-Pattern Condenser Microphone
The RA-23 is a dual-pattern FET condenser that was sold as a DIY microphone kit. It has since been repackaged and renamed for the type of capsule included; the new versions (as of 2015) are called the S-47, S-12, and S-87.
The kit includes a transformerless circuit based on the Schoeps CMC-5. The two PCBs are made in the USA. The components include matched capacitors, specially selected and pre-biased Siliconix J305 JFET, low-noise Hitachi output transistors (also matched), and precision resistors.
The PCBs were designed to fit easily with the enclosed body, which is aluminum (anodized in black), with a tapered grille made of 2 layers of brass mesh. The use of two layers of different-gauge mesh offers a good compromise between plosive protection (in which more layers are beneficial), resonance reduction (ditto), and minimization of sonic reflections (in which fewer layers, and a more open weave would be preferred).
Any of 5 large-diaphragm capsules can be selected, including K47, K67, and CK-12 types. The capsule choice affects sensitivity and frequency response, but in all cases the sensitivity would be at least 27mV/Pa (and possibly as high as 45mV/Pa), and self-noise would be below 13dBA.
The polar pattern switch on the PCB removes the capsule’s rear diaphragm from the circuit entirely when in “True Cardioid” mode; this raises the sensitivity of the mic by ~4dB in Cardioid as compared to Omni.
The kit includes: microphone chassis and body, capsule mount, capsule, PCBs (unpopulated), all components necessary to build the circuit, US-made silver/teflon hookup wire, and a zippered storage pouch.
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The mic was released in 2014.
Specifications
| Pickup Patterns | Pads & Filters |
|---|---|
|
Omnidirectional
(23 mV/Pa; 20 - 20,000 Hz) Cardioid (27 mV/Pa; 20 - 20,000 Hz) |
|
| Capsule Dimensions | Impedance | SPL/Noise |
|---|---|---|
| Diaphragm diameter: 26mm Capsule diameter: 34mm Diaphragm gauge: 3 microns |
n/a |
| Weight | Length | Max Diameter | Interface(s) |
|---|---|---|---|
| 290g (10.23oz) | 184mm (7.24'') | 50mm (1.97'') |
|
| Power Specifications |
|---|
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