GT convertible mics

pucho812 · May 24, 2005

Bump ...

Gus · May 24, 2005

The capsule looks like the ones in the 33s and 44 I have.

The circuit looks to be the Schoeps circuit I see 4 ceramic SMDs C4 is the only number I can read the cap on the left of one of the electro caps looks like the other cap both might go to the two pnp bases. (.1uf?)

The two bottom (.022uf?) look to be the RF filter caps.

pucho812 · May 25, 2005

yeah no writing on the caps so out comes the trusty fluke. :grin:

dam gus your good. Caps measure out to said values. :thumb:

I am still wondering about the 30pF cap on the back. some friends of mine picked up some of the same mics and I looked them over. out of 5 total including my 2 only 2 have the 30pF cap but all have the 1000pF ceramic. I am thinking that 30pF should go as some have them and some don't.

Rossi · May 25, 2005

The 1000 pf is essential to the circuit, that's the capsule to FET cap. Many mics have it, and usually it's on the back of the board. The extra cap is unusual. It may be a simple low pass to suppress HF crap. From what I can tell from the pix, it looks like signal to ground. Is it?

Gus · May 25, 2005

The S circuit might have to much gain for the capsule voltage used and therefore the signal out. The schoeps schematic circuit I have seen uses a .47uf cap Drain to capsule voltage(feedback or feedfoward?) to reduce the gain. +3 -2 jumper section blue dot etc...

being a china microphone it is a pad cap a bandaid fix to a copy and not a real design. FWIW I have seen this in other china SD microphones.

Any good mods to that circuit might not fit. Look at the 603 threads for ideas.

pucho812 · May 25, 2005

Look at the 603 threads for ideas.

Yeah IMO the circuit seems similar to the 603. being how some mics do not have the 30pF cap need to a/b between one with and one without depending which one sounds better it may have to go... I will read the 603 threads and look for some ideas. Updates will be soon.