M49 Alternate schematic for cardioid only

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Now i don't understand what's wrong with C2, please help me out :) i'm totally out on this one

You only posted (a part of) this schematic AFTER my first observation, so that 10nF C2 is not the issue ;)

Edit: Ah, nevermind, you deleted that schematic, but Drosselmeier corrected it...
 
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My capsule is a M7. I don't really get the role of C6 on my schematic or C1 on your microphone. :))
It creates a low pass filter. Probably to deal with RFI.
Just remove it and test the mic without... but it won't fix your low mids problem.
Did you test your M49 with various polar pattern? The frequency response will change.
 
Well, with the 100k where you originally had it (and especially with C2 connected as it was), you would have had pretty much ZERO sound. I can't say for sure how that affects the sound, but the amplitude would be virtually none.
Yes i understand, in fact i was trying redraw the schematic of my friend and i have made lots of mistake. Drawing schematic helps my analyse... R9/C7 form a low-pass filter. (More feedback for low frequencies.) I might want to keep it if i want a better low end roll off?

https://groupdiy.com/threads/m49c-circuit-details-questions.80237/

Ruud comment

I must have measurements of the M49 circuit with and without the filter active.
But I suppose they are on my old computer.
You can simply disable the low-cut filter by lifting one end of the 5M.ohm resistor.

EDIT: found it! Blue is the fixed low-cut active.

1714789846711.png
 
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Hello Guys i found these informations

I have the impression that C6 560pf plays a very important role in the midrange.
If the capsule is well balances maybe i don't need C6?

I found this information about C6 can you confirm?

o C6=100pF
▪ Cutoff frequency = fc = 1 / 2πRC
▪ fc = 40,000 Hz

o C6=220pF
▪ fc = 18,086 Hz

o SiC6=470pF
▪ fc = 8,466 Hz

o SiC6=560pF
▪ fc = 7,105 Hz

o SiC6=680pF
▪ fc = 5,851 Hz

o In conclusion, it will be necessary to test the appropriate value in practice on the prototype if we wish to correct the presence of the capsule.

▪ For treble attenuation: C6 = 470, 560 or 680pF

I found this information about R9 and C2 can you confirm?
• R9: feedback resistance between the transformer primary and the backplane to filter to suppress subsonic frequencies (1H to 20Hz).
o Subsonic frequencies (1 Hz – 20 Hz) are generally produced by earthquakes and by large organs found in churches. It is therefore more a matter of vibrations felt than heard.
o 4.7MΩthrough-metaloxide1/4W
• C2: Forms a low pass filter with resistor R9 to remove the audio signal from the transformer
o C2 = 10nF/200V (metalized polypropylene MKP)
▪ fc = 1 / 2πRC
▪ fc = 3.4 Hz
The audio signal (cutoff frequency <3.5Hz) is brought back to the input of the amplification stage
triode inverter.
 
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I have the impression that C6 560pf plays a very important role in the midrange.
If the capsule is well balances maybe i don't need C6?
I don't know how you calculated the influence of C6 on the frequency response, but if you measure the influence of this capacitor in a real M49 circuit, you will find completely different values.
In fact a value of 500 pF has hardly any influence on the highest frequencies of the M49.
 
I don't know how you calculated the influence of C6 on the frequency response, but if you measure the influence of this capacitor in a real M49 circuit, you will find completely different values.
In fact a value of 500 pF has hardly any influence on the highest frequencies of the M49.
Hello Ruud, i took off the 560pf on C6 and my M49 with the M7 sound more clear. I has changed something on the top end of the microphone. Thank you. Best regards.
 

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