[Scott Dorsey]

Jay Ts wrote:
On Thu, 12 Jun 2014, Scott Dorsey wrote:
The Primo specs can be believed, and the reason why the quiet ones are
quiet is mostly because they use a conventional FET with external
biasing resistors rather than using a "FET-IC" with diodes fabricated on
the surface to act as bias resistors.

That's probably a 2SK596, and I've been reading the datatsheets for it.

There are more modern ones than that, and the Chinese are making some very,
very inexpensive ones, but the 2SK596 is a classic one.

I was very suspicious of the "resistor" that the manufacturers show in
the schematic, and guessed that they were using reverse leakage current
from diodes to bias the gate. But I haven't found any confirmation of
that idea. Scott, are you sure that's what's going on?

Most IC processes use diodes as resistors. Part of what made the Analog
Devices op-amps so much better than their monolithic competitors back in
the seventies was that they could actually make real resistors on chip.

I was trying different things with the CUI capsule, and the 2SK596 in it
did not respond as any jFETs I'm used to using. I was disappointed by it.

You'll find a similar device inside the Panasonic capsules, etc.

Anyway, I'm really interested in the Primo products now, and I hope I can
get them to sell me a few! The datasheets suggest that *maybe* they can
be made into pretty nice small-diaphragm mics, and I'll have to build up
a few to try them and learn how good they can be. There won't be any DPA
or Schoeps killers coming out of this, but maybe some decent, much lower
cost and useful microphones.

The Primo capsules are used by a lot of mid-range microphone vendors.
As are the Panasonics for that matter.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."