Some questions about the Sony C37a - mics with cathode follower

[Tim Campbell]

I’m hoping one day I’ll buy a Flea 251 then. I have to admit my Barbaric 251-inspired mic with a CT12, GE 6072 5-Star, and AMI T14 in a 460 body with an “upgraded” headbasket is my least favorite Barbaric mic on vocals; not much body and very ess-y.

Haven’t played with it much at all. It’s always been “nope” in session and I need to move fast to something else. Haven’t even tried a different tube yet.

It is hard to say why that could be. If it is one of my capsules that no one has altered in any way you are always welcome to send it to me.

 

[Recording Engineer]

It is hard to say why that could be. If it is one of my capsules that no one has altered in any way you are always welcome to send it to me.

It is, but that’ll probably be one of the last things I’ll look toward when I haven’t looked at anything else still. I just may take you up on that if I eventually end up getting there. Thank you.

 

[rock soderstrom]

Another mic with a cathode follower impedance converter - I updated the list.

Sony C17b

Schematics for mic and PSU.


Photos are from this source

 

[KrIVIUM2323]

Very interesting, what the hell are all those diodes doing in the input section? Capsule polarization and grid resistor substitute?

Edit: The designer liked diodes, the cathode biasing is also done with diodes.

View attachment 107039

The diodes in the grid portion of the circuit are there to prevent arcing of tube until circuit is fully warmed up and stabilized.
If wisely selected the diode voltage reference can be very quiet which is a must when connected to cathode, here they bypassed the diode string whith capacitor for this very reason ( the one between cf cathode and ccs anode).
This is a nice example of 'modern' design approach to cf imho. Thank you sharing it.

 

[KrIVIUM2323]

And yes after looking at it further 2 of the diodes strings in the grid circuit replace the grid R. It's clever.

After all a diode is some basic ccs and as such act as a very high impedance with stable V drop.