The Sony C220a is a multi-pattern stereo tube microphone that was introduced by Sony in 1965. Sony reports that only 88 microphones were ever produced, each made to order. Miraculously, our studio has two of them, one will soon be available for purchase - please send us a message if you're interested.
The 220a uses a pair of medium diaphragm double-sided edge-terminated gold sputtered capsules (similar to the ones used in the C57 and C107), and two 6D-H3 tubes in a cathode follower circuit. The 6DH3 is a Japanese tube based on the AC701k developed by Sony for use in their tube microphones. Unfortunately, these tubes are extremely rare and next to impossible to find, but there are suitable replacements that only require a simple modification to the PSU to provide the correct filament voltage.
Like most stereo microphones, the C220a has one capsule mounted above the other with the top capsule on a swivel mount that can be rotated up to 270 degrees. The microphone uses a Sony CP-5 stereo PSU which houses the output audio transformers for the microphone. It has two fully-variable polar pattern adjustments - one for each capsule - as well as the same high pass and low pass controls as the CP3 and CP4 (used for the C37a, C57, C17b and C107). The CP5 has two output modes: standard L/R operation and M/S operation. In L/R mode, each capsule is sent to its own output. In M/S mode the CP5 uses a transformer-based Mid-Side matrix to output a stereo signal.
