These Calrec small diaphragm condenser microphones have been kicking around in the workshop for several years. They sound nice but the noise floor was always too high to be of much use, and they also need a specific power supply rather than standard 48V phantom. And they are difficult to service because the high impedance section of the circuit board is potted in what looks like epoxy resin – including an electrolytic capacitor. If anything goes bad in there then it is near impossible to replace.

Consequently these never got used and nobody wanted to buy them.

I decided to hack them and my approach to these was to do a full rebuild using a new circuit board from Russell Technologies. The new circuit is based on designs by Okatava and Schoeps, and is a simple two stage transformerless design. It works well with the Calrec capsules and sounds nice and full without being overly bright.

A couple of things to note. The connection to the capsule is made by a copper spring, This needs to be removed from the old circuit board, cleaned and soldered onto the new board. The rear of the capsule should also be cleaned to remove any oxidation.

Top – New circuit board with spring and locking ring..

Secondly, there is an internal locking ring which holds the circuit in place. This is expanded using a grub screw. This ring needs to be re-used here to ensure a little compression of the spring and good contact with the capsule back plate.

Xaudia can offer this as a repair upgrade service. Please get in touch if you need further information.