RT-SM01 and RT-SM02 - PCBs for Schoeps-type circuits.

The RT-SM01 and RT-SM02 are two variants of a PCB for the circuit of the well-known Schoeps topology. They can be used for electret microphone capsules without an internal FET. With the addition of a polarising voltage generator it is suitable for use with conventional (non-electret) capsules. They are also suitable for building and experimenting with Scott Helmke's "Alice" design.

Please see RT-GB01 if you require polarising voltage generators.

Here is Scott Helmke's Alice page.

The RT-SM01 pcb is 15 x 87 mm, and will fit easily in 22mm copper tubing and in many hand-held microphone bodies.

The RT-SM02 pcb is 30 x 50 mm with fixing centres at 26 x 47 mm, 2mm dia. This variant can de fitted to most wider-bodied microphones. It is not designed to fit a particular mic body, but most will have enough room for it.


These designs can also be used for capsules with an internal FET (with or without the Linkwitz mod), by simply leaving out the on-board FET and connecting appropriately. Instructions for this are supplied with each order.

However, please consider RT-EM01 which is recommended for capsules with internal FET.

RT-SM01 pcb.
Price £6.50 with free p&p in UK. £3.50 p&p for ROW.
RT-SM02 pcb.
Price £6.50 with free p&p in UK. £3.50 p&p for ROW.
RT-SM02 assembly.
Click image for pdf
Making a vocal mic using this pcb. Crude example, but works very well. Start with a dynamic mic with failed capsule.
Filling the switch hole with Milliput epoxy resin.
Paint black.
The pcb is held in place with foam wedges. Simple but effective.
Electret capsule is mounted on rubber support on a foam disc.
This Canford mic is likely a rebadged Chinese item. It works but has a noise problem. The capsule however is very nice, I suspect it is an upgrade to the original capsule. I decided it was an ideal candidate for an SM02 and GB02.
Here you can see the original circuit. It looks like some sort of Neumann style ripoff with an output transformer.
I have put the boards in rather crudely, just a couple of wires soldered to the side supports and some of my favourite foam jammed in. This was a rush job for a recording and will be re-done.

Here you can also see how easy it is to make mistakes when you are in a rush. The capsule is connected wrongly. And I designed the thing so I should know better.

Here is a view from the GB02 side, showing the capsule connected properly.

The capsule is good quality and it is centre-terminated, so I took the risk of cranking the polarising voltage up to nearly 80V. It paid off, the mic is very quiet and sensitive and sounds nice.

The Egyptian god Thoth is often depicted messing about with an SM01.
Customer photos. This looks nice.
Many thanks to Bernard Loffet