Ev re20 - restoration and modification

After my chinese Schoeps circuit mic mod:
http://www.groupdiy.com/index.php?topic=51824.0

I couldn't help to futher examine my archaic RE20.It's old and crackling and without filters...without filters, it has no bottom end.and the high end is hissing for unknown reason.

So I reinstalled filters.This bring the low bass back.See this link below:
http://www.gearslutz.com/board/so-much-gear-so-little-time/371862-diy-re20-filter-replacement-step-step-photos.html

And cleaned the capsule.The hissing is gone.

but I still don't very happy with it's top end.So I installed two 47uh inductors on the out put of the mic.

Listen to the samples(change .jpg to .mp3).

Note 1:beware that you could adjust the high end response by changing the angle of the mic.At first I didn't aware of it and overdid my mod.

Note 2：you could diy your filters with 20ppi porous filter cotton.I happened to have it which i used as my computer fan filters.

re20 ad.mp3

RE20_Engineering_Data_Sheet

Mmmm.... 47 µH at 20 KHz. gives a reactance of:

2 * Pi * 20 * 103 * 47 * 10-6 =  5,9 Ohms in series with the output...

Times two (inductors in both wires) = 11,8 Ohms. At lower frequencies even less!
Does that really make a difference? (When the amplifier input is 2 K.Ohms or more?)
Sounds like 'psychoacoustic'  ;D (Or am I wrong?)

Trust me!
If you don't believe me ,I recorded samples alone the way.

Inductors also have saturation effects.

It's like a transfomer.It doesn't just transfor voltage.It saturats and distords the sound at the same time.

Don't get me wrong, I am happy to hear that it works for you!
But I am still sceptical about the coil saturation.
The (resistor style) chokes I have here, are rated 150 mA.
But there is almost no voltage (millivolts!) at the output of the microphone, and also no current.
So I doubt if core saturation will be an issue.
Besides that, I would hate the idea that distortion was build into the microphone deliberately!
OK, it will do something with the phase of the signal.
But again, I'm happy when you're happy with the result!

RuudNL said:

Don't get me wrong, I am happy to hear that it works for you!
But I am still sceptical about the coil saturation.
The (resistor style) chokes I have here, are rated 150 mA.
But there is almost no voltage (millivolts!) at the output of the microphone, and also no current.
So I doubt if core saturation will be an issue.
Besides that, I would hate the idea that distortion was build into the microphone deliberately!
OK, it will do something with the phase of the signal.
But again, I'm happy when you're happy with the result!

Click to expand...

There is a simple way to test the effect of inductors and any other subtle effects.Just connect a much larger reading component,say 1000uh,see if you can tell the difference.

Thanks for all your tips and thoughts.

I just spoke to Patty @ Bosch and they are going to send me an RE20 foam kit. The whole kit is only $11, shipping is $10. They still have a $25 minimum on parts, but  Patty let me skate since it was so close!

here are updated Bosch/EV part numbers as of March 2014, with the old numbers

F01U 264975 ( replaces 78233-windscreen and 78230-acoustic filter  )
F01U 153540 ( 78232-rear foam )
F01U 110421 (78231-pop filter )

Steve