SE Electronics Z3300a

[Emmathom]

This is the waveform of audio I recorded yesterday with the modified mic
and same part with the original one

 

[micolas]

you don't have to look for a specific voltage source. They all differ. The jFETs differ from one to another.
The BIAS must be adjusted for maximum amplification, without distortion and with equal positive and negative half-sine

 

[Emmathom]

I will record a Fs like 400Hz > a nice and clean sine to look at it...

 

[micolas]

I will record a Fs like 400Hz > a nice and clean sine to look at it...

Non.
do you have android phone?
on the android phone install the application

Frequency Sound Generator

https://play.google.com/store/apps/details?id=com.finestandroid.soundgenerator

 

[micolas]

I mean from emitter trhu C4 (4uF) it's the signal + out

4 is in the secondary.

 

[Emmathom]

4 is in the secondary.

Yes ! 1 to audio signal out / 8 to ground & XLR 1 / 4 to XLR 2 / 5 to XLR 3

 

[micolas]

1.
Connect the microphone to the sound card. In your DAW you have an oscilloscope or you install an Osciloscope plugin.
You replace the capsule with a capacitor of 60...70 pF.
You inject a 1kHZ signal through a 470...1000pF capacitor into the C8/R12 junction, from the phone. You increase the injected signal until the sinusoid starts to limit, to clip.
Adjust the VR until the limitation disappears and the sine wave is again symmetrical and perfect. Increase the volume of the injected signal again and repeat the procedure. Make sure that the + and - branches of the sinusoid are symmetrical, limit at the same level.
Repeat the procedure until you can no longer stop limiting, but limit symmetrically.
Reduce the volume of the input signal until the limitation disappears. The sinusoid must be symmetrical, perfect.
2. Another more unscientific method.
It injects complex music with many frequencies at the same point. Listen in studio headphones. Turn up the volume until you hear distortion. Adjust the VR until it sounds clean. Increase the input volume further and repeat the procedure, several times, until the VR can no longer be adjusted to hear clearly without distortion.
Do all this in small steps, patiently and carefully.
You can disconnect the output (drain) of jFET from capacitors C5 C6

 

[micolas]

If you do not have an android phone, with the frequency generator application installed, record a file of several minutes of 1kHz, sinusoidal, at high volume, -1dB, clean, without distortion. And injects signal from the laptop.

 

[Emmathom]

1.
Connect the microphone to the sound card. In your DAW you have an oscilloscope or you install an Osciloscope plugin.
You replace the capsule with a capacitor of 60...70 pF.
You inject a 1kHZ signal through a 470...1000pF capacitor into the C8/R12 junction, from the phone. You increase the injected signal until the sinusoid starts to limit, to clip.
Adjust the VR until the limitation disappears and the sine wave is again symmetrical and perfect. Increase the volume of the injected signal again and repeat the procedure. Make sure that the + and - branches of the sinusoid are symmetrical, limit at the same level.
Repeat the procedure until you can no longer stop limiting, but limit symmetrically.
Reduce the volume of the input signal until the limitation disappears. The sinusoid must be symmetrical, perfect.

You can disconnect the output (drain) of jFET from capacitors C5 C6

Ok thank you for "the procedure" (I had alreday a tone generator on my smartphone)
I have 47pF in stock (no 60 > 70pF)
So I inject a signal R12/C8 trhu a 680pF or 1000pF

You can disconnect the output (drain) of jFET from capacitors C5 C6 : You mean I go straight from drain to SA1015 base without capa ?

 

[micolas]

Ok thank you for "the procedure" (I had alreday a tone generator on my smartphone)
I have 47pF in stock (no 60 > 70pF)
So I inject a signal R12/C8 trhu a 680pF or 1000pF

You can disconnect the output (drain) of jFET from capacitors C5 C6 : You mean I go straight from drain to SA1015 base without capa ?

sorry, I was thinking of the oscilloscope method connected immediately after the jFET.
Ignore this with capacitors decoupling.

 

[micolas]

Ok thank you for "the procedure" (I had alreday a tone generator on my smartphone)

the one I recommended delivers a very high, clean, undistorted output level,
against others.

 

[Emmathom]

sorry, I was thinking of the oscilloscope method connected immediately after the jFET.
Ignore this with capacitors decoupling.

Hum... so 1kHz signal thru 680pF to R12/C8 junction ? (caps disconnected of course)

PS : I have a mini-jack stéréo (wired in asymetrical) with already 2,2uF soldered ? Is it Ok ?

 

[micolas]

Hum... so 1kHz signal thru 680pF to R12/C8 junction ? (caps disconnected of course

the capsule is replaced with a capacitor, 47pF, if that's all you have.

 

[micolas]

Hum... so 1kHz signal thru 680pF to R12/C8 junction ? (caps disconnected of course)

PS : I have a mini-jack stéréo (wired in asymetrical) with already 2,2uF soldered ? Is it Ok ?

collects the output signal from the small jack only from one channel, L or R

 

[micolas]

PS : I have a mini-jack stéréo (wired in asymetrical) with already 2,2uF soldered ? Is it Ok ?

It's ok

 

[Emmathom]

collects the output signal from the small jack only from one channel, L or R

I just had a look : it's only left signal that is connected (I did that for purpose but forget about it)

 

[micolas]

I just had a look : it's only left signal that is connected (I did that for purpose but forget about it)

if you sum L+R, phase distortions appear, comb filter effect, etc
You will NOT have a pure sine wave anymore

 

[micolas]

When you order something on Ali, you must get an all-in-one multi-tester/oscilloscope/generator
https://a.aliexpress.com/_EylESMd
You can't DIY without it

 

[Emmathom]

Hi Micolas, like yesterday, it's late again... 19h30 > I'm going back to my family...
Anyway this has been a good day for the SC1100 project because I finaly made it working !
I think I'm gonna put the original Tr back before biasing the Fet because you told me it was a good quality one and also because I'd like the 2 mics to sound the same... and then I will bias the 2 mics as your "protocle"

 

[Emmathom]

When you order something on Ali, you must get an all-in-one multi-tester/oscilloscope/generator
https://a.aliexpress.com/_EylESMd

Yes my friend had just bought the same one from Ali ! but I never used a scope in my entire life... maybe it's not so complicated to learn how to use it ?
(I put one item "in my basket" )