I wanted to talk about the Sony C37A.
I have a pair, and the bass response is totally different in one than the other, so I started taking them apart to check the component values, to make sure they are matched, and are as the schematic calls for. What I realized is that it's a totally different implementation from most European mics of that vintage, and we never really discuss the mic. I thought it would be interesting to get into.
First thing that sticks out to me is the edge terminated capsule. It's different than the most well known Euro edge terminated capsule of the day, the CK12, in a few obvious ways. First, notice this beveled edge on the membrane, and the space between the outer ring and the back plate.
The network of through holes on the backplate looks very different from typical Euro capsules, as well.
And then to really set itself apart, there is a screw that lets the user choose between cardioid and omni, or "unidirectional" and "nondirectional," as their manual puts it. I can't see the mechanism employed. I'm assuming it is physically manipulating something in the backplate, but I can't see what it's doing. If anybody knows how it works, please do tell.
It employs a 6AU6 tube. Maybe Oliver can tell us if anybody was making these with specs that would have met Teutonic standards for microphones. I just found 5 NOS JAN versions on eBay for $25. Wish me luck!
The other departure from Euro mics is locating the transformer in the PSU. I know Altec used this approach in some of their mics. Does increasing the distance from the tube to the transformer increase the mic's noise? Is there a reason they weren't doing this in Vienna or Berlin? However, this also gives them the ability to use a HUGE transformer (with the sony label on top) and rather large capacitors.
And then there is a switch attached to the coupling cap that adds either one or two more in series, to act as a hi pass filter. You can see that switch here on the schematic. Maybe one of you designers can talk about the pros and cons of this method. (You can also see the the 6X4 recifier tube in the above pic, and below is the primary coupling cap in the .5