Shure PG42 microphone

[LevinGuitar]

Expected to find Takstar internals and capsule but instead it's a 797 made. Flat circuit, bright capsule... but the dome is nice.
Haven't traced the circuit but since it have one of the "output" 22uf cap connected to ground on its negative lead, maybe it's something in the Behringer B1 way. -50v polarization on diaphragm, backplate connected to ground. 2N5457 fet, 470pf imput cap. Easy to rewire the capsule to skip that imput cap and gain 4.5v on polarization. Lower noise than the new B2 btw.

 

[kingkorg]

I keep wondering if there's some hidden reasoning behind using worst possible coupling cap for the capsule-gate connection. I don't think it's just cost cutting.

 

[k brown]

And aren't those carbon film resistors on the output?

Is it made in China?

 

[Khron]

And aren't those carbon film resistors on the output?

Axial inductors

 

[LevinGuitar]

I have traced the circuit and had a hard time understanding how to draw NPN transistors, so some of them are surely wrong, please be welcome to correct me. Q7 and D1 even not sure if are NPN or PNP.

The -15db pad engages a voltage divider.

Warning: the schemo will hurt your eyes, open at your own risk!
If someone is no nice to redraw it in a proper way it would be great.

 

[Khron]

Warning: the schemo will hurt your eyes, open at your own risk!
If someone is no nice to redraw it in a proper way it would be great.

C15 definitely does NOT have both ends connected to R18 (it would defeat the whole point of C15).

Q7 and D1 even not sure if are NPN or PNP.

D1 is more likely a double diode, hence the "D" prefix, get it?

Do the transistors have any visible markings? 2-3 letters and/or numbers...

 

[LevinGuitar]

C15 definitely does NOT have both ends connected to R18 (it would defeat the whole point of C15).



D1 is more likely a double diode, hence the "D" prefix, get it?

Do the transistors have any visible markings? 2-3 letters and/or numbers...

C15 is connected in parallel with R18. I have triple checked it.

Great about the diode

Q4: G1
Q3/Q5: 6D
Q6/Q7: 2L

 

[Khron]

C15 is connected in paralell with R18. I have triple checked it.

Visually (removed the C15 from the board), or..?

G1 might be MMBT5551, NPN
6D could be MMBF5457, N-channel JFET (makes sense, they're both wired as constant current sources)
2L may well be MMBT5401, PNP

 

[LevinGuitar]

Checked for continuity (less than 1R) on both sides as with rest of components

 

[Khron]

Checked for continuity (less than 1R)

For how long? It would take a while for 22uF to charge, with the microamps the resistance measurement current source in your meter can provide...

Take a 100uF cap and measure continuity across it, and see how long your meter beeps for, until the cap charges up enough to stop drawing current and start "showing resistance"...

 

[LevinGuitar]

They both are connected in parallel