Are there any source-follower-only condenser mics?

[midwayfair]

There are a couple old tube condensers that are cathode follower-only, an AKG and a Sony at least.

I've never seen a FET mic with a source follower circuit. Seems like it would be a way to use a low-ratio transformer, even 1:1, which could be tiny and cheap.

Is anyone aware of one that I could take a gander at?

And would there be any major drawbacks or benefits to doing so? The two big ones I can think of is that maybe the variable Gm of a FET would make it a bad idea, or the power filtering required to keep the voltage high would mean very large capacitors.

The other issue I can think of is that you're limited to the headroom of the FET at its gate, but that seems like an issue with a voltage amplifier, and you don't have the headroom of the whole circuit to contend with like you do with a voltage amplifier setup.

 

[Matador]

If memory serves, the Aurycle microphone is a simple JFET into a PNP BJT follower, with a low(ish) ratio transformer.

 

[Khron]

Pretty much all(?) the Chinese transformer-coupled solid-state mics use the JFET + PNP combo, precisely in order to get away with a lower-ratio transformer.

Apex 480, sE2200A, CAD GXL 3000, MXL 2001, MXL V67 etc.

 

[Dylan W]

I think he's asking about a single JFET follower as impedance converter.

I didn't know the answer either, but a quick google turns up the C37A's brother, the C37-FET.

http://www.coutant.org/sonyc37fet/c37fet.pdf

Not sure about the transformer ratio. It may be in that PDF.

 

[midwayfair]

Indeed, I was looking for something that might have used the JFET ONLY as a source follower, a single-transistor sort of deal. The Sony fits that bill, so thanks Dylan! The transformer has multiple windings but it would make sense if one of them is 1:1 as 250Ohms doesn't seem out of the question for the FET's source. (Also, it looks like it's using the taps on the Xfo for the low cut.)

I have a feeling that the unpredictable nature of a JFET's output impedance might be off-putting, but this was more curiosity than anything.