Ela M251 schematic question.

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Jazzy_Pidjay

Well-known member
Joined
Jun 7, 2004
Messages
370
Location
Paris (FRANCE)
Hi !

I'm on building a ElaM251 "clone"

and when i look at the schematic one thing seems
strange to me.

In the microphone part, there's a 100pF between Tube Plate
& Ground !!
Just before the 3,2uF blocking cap which run the signal through
the transformer !

If i understand, this cap with small value, will "cut" alternative
signal to the ground !!!!
So this cap cut "sound" before the blocking cap ???

Seems to be very strange idea ?? what i don't understand ?

Why this cap ??

http://www.geocities.com/SiliconValley/Peaks/5212/1534_2c.pdf

elam250_2.jpg


THanks :thumb:
 
:thumb:
ok !!!!!!

So Mica or Styroflex ? one is better for that ? equal ?


Just another one :

In the C12 there's a 1000pF between backplate of the capsule
and tube grid.

But there's nothing in the Ela M251

And there's one in the G7...


This one is for what ? Why some designs have and some not. ?
 
Yes i begin to understand the circuit topology
but some point are obscur.

--- a 1000pf like the one between Backplate & Grid
can "erase" the DC. i think it's there for that.
But i'm not sure. And i'm not sure to understand
why some mic works without this DC and some with this DC
if the DC is the reason of the presence of this cap.


--- And for the Mica or Styroflex ? egal ?
one have better HF properties ?

--- TDSL say Ra = 25kOhms for the 6072
why calculate the corner freq, with 50k ?
any tips ?

Thanks a lot
 
Another question :

Concerning the Cathode (Resistor + Cap)

On the G7, 1,8kOhms total resistance is formed
with a 1,6k and 220 resistors, with the capacitor
only between the 1,6k legs...

On the ElaM251, the same resistance value 1,8kOhm
but the capacitor is directly connected between Cathode
and ground.

Why in the Jakob design, there's a 220 resistor
before the capacitor ?


Concerning the value...
there's also a big difference, 20µF against 100µF
What is the effect of the capacitor value here ?

I wanna try a BlackGate BG-N, for the ElaM
is there's a problem using a non-polarised capacitor
for the Cathode ?


any link or documentation about microphone design is welcome.

thanks you. :thumb:
 
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