SE Electronics Z3300a

[Emmathom]

Hi
So, first of all, the microphones were out of phase: this is now corrected.
But even taken separately, one sounded "lighter" than the other... The 47nf was indeed connected...

This morning, re-biasing the 2 microphones by removing R10. I found much closer values for the source R : 1.8KΩ and 1.5KΩ.
There are still small voltage variations between the 2 microphones but they are now much closer in terms of level (+/- 1dB) and flow of sound. However, something new appeared: the positive alternation of the sinusoid of the signal now takes over the negative by a small amount...
I think they are now operational and ready for a recording test as they are before exchanging the capsules for Arienne K47-flat.
Attached are various files to support my remarks.

 

[micolas]

Hi
So, first of all, the microphones were out of phase: this is now corrected.
But even taken separately, one sounded "lighter" than the other... The 47nf was indeed connected...

This morning, re-biasing the 2 microphones by removing R10. I found much closer values for the source R : 1.8KΩ and 1.5KΩ.
There are still small voltage variations between the 2 microphones but they are now much closer in terms of level (+/- 1dB) and flow of sound. However, something new appeared: the positive alternation of the sinusoid of the signal now takes over the negative by a small amount...
I think they are now operational and ready for a recording test as they are before exchanging the capsules for Arienne K47-flat.
Attached are various files to support my remarks.

 

[micolas]

Hi
So, first of all, the microphones were out of phase: this is now corrected.
But even taken separately, one sounded "lighter" than the other... The 47nf was indeed connected...

This morning, re-biasing the 2 microphones by removing R10. I found much closer values for the source R : 1.8KΩ and 1.5KΩ.
There are still small voltage variations between the 2 microphones but they are now much closer in terms of level (+/- 1dB) and flow of sound. However, something new appeared: the positive alternation of the sinusoid of the signal now takes over the negative by a small amount...
I think they are now operational and ready for a recording test as they are before exchanging the capsules for Arienne K47-flat.
Attached are various files to support my remarks.

The polarization voltages of the capsules must be equal. In DC/DC In series with the zener diode, add one or two small LEDs, blue or green, to increase the stabilized voltage with which the oscillator is powered. Reduce the DC/DC supply resistor a little (without removing it from the board, put another parallel resistor of 47...100k over it, until you get the desired result, i.e. slightly higher stabilized voltage for the oscillator, so equal polarization voltages in both microphones)
*
If you have to compensate the voltage after R5 4.7k (because DC/DC will consume more), then you reduce its value to have the same voltage in both microphones after it.
You leave it in the circuit and put a resistance of 22...47k or as needed in parallel over it.
*
Adjust the BIAS until the half-sinusoids are equal, even if it decreases the microphone headroom. In order to get overdrive, distortion, in effects pedals, I used to connect two LEDs of different colors (therefore with different limiting voltages) in anti-parallel connection to make asymmetric clipping. In the Marshall ValveState amplifier I used this method for overdrive.
*
Repeat BIAS for both microphones several times, note the values of VR and perform listening tests each time.
Then average and make a decision. It's a compromise between technically correct and subjective personal preference for sound.

 

[Emmathom]

The video is interesting... but I've not got all his equipments (dynamic signal analyser for SNR for ex.) and he knows cery well how to use them (what is not my case).
As same for me he got more H3 than H2... I noticed also that he kept R10 (3KΩ) and "plays" with R9 to find 750Ω so the finished value is 750Ω + 3KΩ (I'm far from that value with 1,5KΩ or 1,8KΩ in a unique R).
Keeping R10 means that the 1GΩ does not connect to ground : so what's the best way ? playing with R9 + R10 fixed or playing with a total R ?

Back to my case, when I scoped the signal the sine wave equally distored pos. & neg. when I increased the level so I thought it was good. If I read correctly my signal is 2Vpp without clipping...

 

[Emmathom]

The polarization voltages of the capsules must be equal. In DC/DC In series with the zener diode, add one or two small LEDs, blue or green, to increase the stabilized voltage with which the oscillator is powered. Reduce the DC/DC supply resistor a little (without removing it from the board, put another parallel resistor of 47...100k over it, until you get the desired result, i.e. slightly higher stabilized voltage for the oscillator, so equal polarization voltages in both microphones)

Wich zener ? there are 6 of them on the polarisation board... Wich R is the supply R ? R15 ?

If you have to compensate the voltage after R5 4.7k (because DC/DC will consume more), then you reduce its value to have the same voltage in both microphones after it.
You leave it in the circuit and put a resistance of 22...47k or as needed in parallel over it.

Ok

 

[micolas]

I noticed also that he kept R10 (3KΩ) and "plays" with R9 to find 750Ω so the finished value is 750Ω + 3KΩ (I'm far from that value with 1,5KΩ or 1,8KΩ in a unique R).
Keeping R10 means that the 1GΩ does not connect to ground : so what's the best way ? playing with R9 + R10 fixed or playing with a total R ?

R10=0 ohm

I explained to you many times that the stock, Chinese scheme put R10 to make a kind of self-Bias. Be able to use almost any Jfet, without manual BIAS, individually, for each mic.
Lower performance is achieved, but time and profit matters.

 

[Emmathom]

R10=0 ohm

I explained to you many times that the stock, Chinese scheme put R10 to make a kind of self-Bias. Be able to use almost any Jfet, without manual BIAS, individually, for each mic.
Lower performance is achieved, but time and profit matters.

I know I know... ! but in the video you sent me the guy keeps R10 and modify R9 so that's why I asked you what's the best way to do ? (he could have taken this R10 off... but he doesen't)

 

[Emmathom]

Looking at these values we can see that :
- with more voltage on P2 & P3 Mod has less volatge than Orig-mod before R5 4,7KΩ
- after R5 the Orig-mod has 670mV more than the Mod : is it so important ? if yes I will level up by 0,67v
- SA1015 emitter are quite the same for the 2 mics before & after re-biasing
- D & S K170 voltages are quite the same for both mics
- the main differences are on the polar board, at R15 (DC In) and at caps. polar voltages (which I must increase according to your advice)

 

[micolas]

Wich R is the supply R ? R15 ?

No. R13
*
Leave zenner alone
(4 diodes are normal, for voltage multiplication)
*
Reduce the resistor R13 27k as follows:
Put another 75...150k resistor in parallel over it in the circuit and measure the new polarization voltages, to be equal to those of the good microphone.

 

[micolas]

I know I know... ! but in the video you sent me the guy keeps R10 and modify R9 so that's why I asked you what's the best way to do ? (he could have taken this R10 off... but he doesen't)

U87

 

[micolas]

Looking at these values we can see that :
- with more voltage on P2 & P3 Mod has less volatge than Orig-mod before R5 4,7KΩ
- after R5 the Orig-mod has 670mV more than the Mod : is it so important ? if yes I will level up by 0,67v

- the main differences are on the polar board, at R15 (DC In) and at caps. polar voltages (which I must increase according to your advice)

The polarization voltages of the capsules must be equal.
The voltages after R5 must be equal.

 

[Emmathom]

The polarization voltages of the capsules must be equal.
The voltages after R5 must be equal.

Ok I will "work" on R5 (try 4,7KΩ // 50KΩ-RV) and R13 (try 27KΩ // 100KΩ-RV) no 150K in stock

What about the jfets biasing values you read and the signal wave from the scope ?

 

[micolas]

What about the jfets biasing values you read and the signal wave from the scope ?

When you have equal capsule polarization voltages for both microphones and equal voltages after R5, you will make re-bias and measurements.
Then we analyze.
The important thing is that you understood the process, the concept.

 

[micolas]

Zenner diodes D1 and D2 are connected in series to form a higher voltage Zenner D1+D2, of appropriate value for the circuit (lower voltage zenners have less noise)
*
First deal with DC/DC so that both microphones have the same polarization capsule voltages.
*
After that you change the voltage after R5.
*
Both PCBs consume from Phantom so they are interdependent, it is possible to redo these procedures several times.

 

[micolas]

Did you manage to get the polarization voltage of the capsule +/- 57v by reducing the value of R13?

 

[Emmathom]

Did you manage to get the polarization voltage of the capsule +/- 57v by reducing the value of R13?

some friends have come to visit me : will work tomorrow morning...
but I clearly understood your guidelines every changed parameter will modify another...

 

[Emmathom]

Hi
I just put 100KΩ VR in // with R13... and I had to go down, down, down R value to get (only) 54,43v at caps. polar. compared to 57v on the Orig-mod.
When I desolder the VR what was my surprise to read 1Ω !!!
As I checked, R14 (27KΩ) is in serie with R13 (27KΩ) so now the total amount is 27KΩ (27KΩ + 1Ω) > which means that I could "play" on the 2 resistors to begin with something like 10KΩ + 10KΩ or so...
here are the values... (I've inverted the table so now the latest values go from left to the older ones to the right)

 

[micolas]

Hi
I just put 100KΩ VR in // with R13... and I had to go down, down, down R value to get (only) 54,43v at caps. polar. compared to 57v on the Orig-mod.
When I desolder the VR what was my surprise to read 1Ω !!!
As I checked, R14 (27KΩ) is in serie with R13 (27KΩ) so now the total amount is 27KΩ (27KΩ + 1Ω) > which means that I could "play" on the 2 resistors to begin with something like 10KΩ + 10KΩ or so...
here are the values... (I've inverted the table so now the latest values go from left to the older ones to the right)

Leave R13 0...3.3k.
Zenner diodes D1 and D2 are connected in series.
It seems that their total stabilization voltage is lower than the original microphone. De-solder the end of D1 and D2 from the point where they make the connection.
Insert a 3mm red LED in series with them, respecting the polarity (the LED will increase the stabilized voltage by approximately 1.4...1.6v, depending on the current through them)
It measures the polarization voltage of the capsule.

 

[micolas]

Zenner diodes D1 and D2 are connected in series.

Insert a 3mm red LED in series with them, respecting the polarity (the LED will increase the stabilized voltage by approximately 1.4...1.6v, depending on the current through them)
It measures the polarization voltage of the capsule.

if you reverse the polarity of the LED then the total stabilized voltage will decrease with that of the LED
(LEDs of other colors, green, blue, etc., have a higher stabilization voltage)

 

[Emmathom]

D2 gives 17,20v
D2 + D1 give 25,85v
(Mod mic)