SE Electronics Z3300a

[Emmathom]

The best symetry is with R source 1KΩ...
109dB / H2 65dB / H3 50dB and a peak at 50Hz (must be a ground pb since the mic is opened)

Fet D 14v / S 0,45v

Now I must measure all voltages but with Presonus 48v...

 

[micolas]

Did you BIAS it through the mic output transformer?

 

[Emmathom]

Did you BIAS it through the mic output transformer?

Yes

 

[micolas]

As I said before, a compromise must be made between the best symmetry, the lowest H2 harmonic and the highest level up to limitation, distortion.
The subjective factor of the audition also comes into play in the adjustment, the sound you like more.
The 2nd harmonic seems a bit big to me, but if everything went through the transformer (it can be a transformer harmonic) then the BIAS is quite conservative, safe.
A few volts are obtained directly after the jFET.
Anyway, the interface and the software are not calibrated.
Don't lower Rsource too much, (I think around 1.7...1.9 seemed to be ok)

 

[micolas]

Have you tested how they sound?

 

[micolas]

even the symmetry can be affected by the transformer

 

[Emmathom]

Have you tested how they sound?

Here the values with Presonus 48v
Sound tests to come...

 

[micolas]

if you manage to buy the digital oscilloscope I was talking about you will be able to do jFET BIAS under optimal conditions

 

[Emmathom]

I ask for the third time (maybe) : what voltage do I read on my scope ? (I calibrate the Edirol in REW)
When it's written 2v scale, is it +1v / -1v or +2v / -2v ???

 

[micolas]

Here the values with Presonus 48v
Sound tests to come...

Mod's R source is too small and the jFET drain current too high.

 

[Emmathom]

Mod's R source is too small and the jFET drain current too high.

It's the value (1KΩ) where the symetrical is optimum : should I up it ? 1,5KΩ or 1,8KΩ ?

 

[micolas]

I ask for the third time (maybe) : what voltage do I read on my scope ? (I calibrate the Edirol in REW)
When it's written 2v scale, is it +1v / -1v or +2v / -2v ???

is that what the REW reads at the mic output?
It's not real, the interface is not calibrated.
(2v/div > 4Vpp ? Or 10Vpp?)

 

[Emmathom]

is that what the REW reads at the mic output?
It's not real, the interface is not calibrated.
2v/div > 4Vpp

As REW asked, I looped teh Edirol line out into the line in (symetrical jacks) and the soft did his work...

 

[micolas]

It's the value (1KΩ) where the symetrical is optimum : should I up it ? 1,5KΩ or 1,8KΩ ?

I remember a previous value of 1.7..1.8k which sounded good

 

[micolas]

do some sound tests
"If it sounds good, it's good!"

 

[micolas]

As REW asked, I looped teh Edirol line out into the line in (symetrical jacks) and the soft did his work...

i understand
But the transformer confuses us
has the effect of self-induction, hysteresis, compression, harmonics, phase shifts, frequency attenuation, frequency resonances, etc.
Anyway so far so good.
You will make fine adjustments when you can

 

[Emmathom]

quick sound test (and a little visual analysis)
- the 2 mics sound equal in term of sound (and they sound not bad at all)
- the ORIG has 1,7db more gain than the MOD in Cardio / only 0,6dB in omni
the MOD makes a bump noise when changing patterns > the ORIG don't
- when looking at the wave form (zoomed in) I can see that now the MOD has a bit more pos. than neg. > Fet R source too low ?

 

[micolas]

quick sound test (and a little visual analysis)
- the 2 mics sound equal in term of sound (and they sound not bad at all)
- the ORIG has 1,7db more gain than the MOD in Cardio / only 0,6dB in omni
the MOD makes a bump noise when changing patterns > the ORIG don't
- when looking at the wave form (zoomed in) I can see that now the MOD has a bit more pos. than neg. > Fet R source too low ?

matched pair microphones can have a tolerance of +/- 1.5dB (or even more)

 

[Emmathom]

I could replace the R source for the jfet to run with less current : which value ? It seems that the MOD body is a little bit warm than the ORIG body (as I can feel with my fingers) but it's really so little warmth, just a tiny difference

 

[micolas]

I have between 4...7 microphones of the same model, from
Studio Projects, B2-pro, B1, t.bone, Rode, fame etc.
They all sound different (sound and volume) and measure differently in all points.
Basically, I do NOT have a matched pair