[Phil Allison[_4_]]

Sean B wrote:

Hello,

Has anyone ever seen a schematic for one of these mics? Just wondering
what kind of circuit approach they use. Since it's transformerless,
it would seem it can't be that different from the Schoeps circuit.


** The natural companion pre-amp device for a condenser mic capsule is a *triode* vacuum tube, which must be sited as close to the capsule as practical to minimise wiring capacitance associated with the tube's grid. Doing this also brings a source of plate voltage close at hand needed to bias the capsule with something between 60 and 100VDC. Tube mics have separate mains powered PSUs with low current at over 100VDC and a suitable heater supply.

This bulky set up was the norm from the 1940s until JFET mics arrived, eliminating the triode, and which could be fully powered by any desk or adaptor box that supplied 48V phantom. In order to drive a useful length of mic cable, a small impedance matching transformer was still fitted to the mic's handle by most makers.

However, Schoeps designers realised even this component could be eliminated with significant advantages in performance and at lower cost, by replacing it with a pair of NPN transistors operating as emitter followers - having more bandwidth, less LF distortion, low output impedance and NO sensitivity to magnetic hum fields.




..... Phil