SE Electronics Z3300a

[Emmathom]

Ok, for what I am concerned, I'm about to leave this "voltage part" and go now for Fet biasing... ?

 

[micolas]

Did you not put Monacor in both microphones?

 

[Emmathom]

Did you not put Monacor in both microphones?

yes That's the reason why I called the original Orig-mod (only because of the transformer Monacor and except that everything is original in it)
SORRY NO : R10 has been taken of so now Fet R source is 1,8KΩ (instead of 1,8K + 3K)

 

[micolas]

maybe, but I'm not going to operate on the Orig-mod

Orig-Mod
does it have a Monacor transformer?
Let's name them
Orig. and Mod

 

[Emmathom]

Orig-Mod
does it have a Monacor transformer?
Let's name them
Orig. and Mod

Both have Monacor (and R10 taken of)

 

[micolas]

okay
make jFET BIAS in each mic

 

[Emmathom]

ORIG Fet biasing has already been done...
The audio level has been set (samrtphone output) just before the Mic In Edirol begins to clip

 

[Emmathom]

And... I can't do the biasing with the Presonus because it's installed not closed to my Mac so I have to use Edirol... or I got to move my Mac and all my stuff to the Presonus... but in that case the values will be different from the ORIG that have been done on the Edirol

 

[micolas]

Correct jFET BIAS:
The largest amplitude without limitation, distortion,
Equal half-sinusoids
For each microphone you will probably find a different optimal source resistor and differences between the maximum input voltages and distortion.

 

[Emmathom]

the spectrum of 1kHz at 105dB of the ORIG

 

[Emmathom]

is it 2vpp or 4vpp ?
is this level correct with you ?

 

[micolas]

If you do jFET BIAS on Edirol, when using Presonus, you will have more headroom until distortion
Make the sine wave symmetrical!

 

[Emmathom]

If you do jFET BIAS on Edirol, when using Presonus, you will have more headroom until distortion
Make the sine wave symmetrical!

I think they are! (on the last pict I posted)

 

[Emmathom]

If you do jFET BIAS on Edirol, when using Presonus, you will have more headroom until distortion
Make the sine wave symmetrical!

Do I use Edirol or Presonus ?

 

[micolas]

Do I use Edirol or Presonus ?

for audio tests you will use Presonus.
Edirol is an entry-level compromise for portability and convenience.

 

[Emmathom]

Ok for Edirol...
So I replace the 1,8KΩ installed by a VR10KΩ pre-settled at... 2KΩ ? and I bias more or less depend on the scope, right ?
Do I connect my 10nF (from smartphone) after the 1nF, direct on Jfet gate ?

 

[micolas]

Ok for Edirol...
So I replace the 1,8KΩ installed by a VR10KΩ pre-settled at... 2KΩ ? and I bias more or less depend on the scope, right ?
Do I connect my 10nF (from smartphone) after the 1nF, direct on Jfet gate ?

set VR to 10k and analyze how the values vary

 

[micolas]

I expected the Rsource value to be 3.9...5.6k, but for the K170 it seems to be lower.
I am used to the 2N3819, new from Central Semiconductor

 

[micolas]

I expected the Rsource value to be 3.9...5.6k, but for the K170 it seems to be lower.
I am used to the 2N3819, new from Central Semiconductor

It's correct because on
R8=20k you have a voltage drop of about 5v,
i.e. a current of 0.25mA,
close to U87.

 

[Emmathom]

before going any further, I measured with the R 1.8KΩ in place and I noticed certain things...
to prevent the Mic input of the sound card from saturating (there is a clip-LED) I have to lower the output of the smartphone quite a bit (even with gain pot. full CCW) , but it still shows me 105dB input level in REW so I think it's a decent level (?)
since I don't have a good grasp of REW, what I see in the sine-wave represents 2.5 squares at the top and 2.5 squares at the bottom of 0v: what is the peak-to-peak voltage that I measure?
when it says 2v on the scale, is it +2v <> -2v or is it +1v <> -1v?
and what do you think of the tension oI get ? whether it is 2Vpp or 4Vpp
the spectrum analysis of 1kHz / of pink-noise / the sine wave with 1kHz