Please help me identifiy and optimize this mic circuit

[Mellowmusic]

Hello there!

I got hold of this microphone, which originally seems to have been a Fame SKEC 002/w.
Further research led to the "Apex 420", but the PCB looks totally different and I haven't found any more information about this mic.
Has anyone here ever seen this PCB before and can help me?

The capsule has been changed to a Peluso CEK 89 at some point. Sounds kind of harsh once you sing louder and the circuit seems to distort quite early. I can't tell if other parts in the circuit got replaced.

Some values I can identify:
Both transistors are A1015 GR01
C5 and C7: 07L 474
C8: nothing soldered in (?)
C6: 226 1G+
I can try to decipher more of the values, if needed.

Any help or pointers in the right direction is appreciated very much!

Best regards and thanks in advance,
Mellowmusic

 

[Khron]

Soldering looks pretty much factory, so it's likely no further mods were done.

JFET might use rebiasing though - no trimpot in sight, so you're at the mercy of (loose) manufacturing tolerances.

 

[daschnoz]

Hitting the google with "E257309 circuit board" led me here:
https://productiq.ulprospector.com/en/profile/204859/zpmv8.e257309?term=ul&page=1623

I don't have an account, so I can't dig any deeper in that page. Hell, what was returned might be a hair dryer for all I know... but it is a positive hit on what looks to be a UL number of some type from the circuit board (based on the symbol that it's directly next to).

Try throwing some of the other numbers on the board into google. It might return something useful.