SE Electronics Z3300a

[Emmathom]

I'm gonna measure again and note each mic in each configuration & before & after each modification...
For the modified one I have the values before biasing the Fet > I will measure now (SA1015 emitter, Fet drain & source, etc)
For the original one I also have the values before biasing the Fet...

 

[Emmathom]

After re-Biasing how did the tonal character of the modified microphone compare to that of the stock microphone?

As I told you I use the Edirol for measuring voltages and don't analysis for the moment the caracter of the sound...
It's a pretty tuff job for me considering my lack of experience in DIY mics so I can't do everything at the same time.
For real sound tests I will use my Presonus, certainly with my tube pre, but the mics must be "technicaly operationals" before that step

I make sure that voltages are ok, that there is no hum or strange behavior in my headphones, that all the patterns and low-cut are ok... That's my first step for now

 

[micolas]

As I told you I use the Edirol for measuring voltages and don't analysis for the moment the caracter of the sound...
It's a pretty tuff job for me considering my lack of experience in DIY mics so I can't do everything at the same time.
For real sound tests I will use my Presonus, certainly with my tube pre, but the mics must be "technicaly operationals" before that step

I make sure that voltages are ok, that there is no hum or strange behavior in my headphones, that all the patterns and low-cut are ok... That's my first step for now

OK.
Do not rush, work calmly, rationally, systematically, organized.
Most mistakes are made when we are in a hurry, we are excited. We make mistakes in objective assessment, reasoning, logic, in practice.

 

[Emmathom]

Sorry, but I ask one more time :

I come back to the subject of the SC1100: the source decoupling capacitor, 22uF, it passes the negative half-waves of the signal there, right? as for the decoupling capacitor of a tube's cathode... right ?
So the quality of this capacitor is important (in my tube assemblies, when I need to decouple, I always choose Elna Silmic II)

 

[micolas]

Sorry, but I ask one more time :

I come back to the subject of the SC1100: the source decoupling capacitor, 22uF, it passes the negative half-waves of the signal there, right? as for the decoupling capacitor of a tube's cathode... right ?
So the quality of this capacitor is important (in my tube assemblies, when I need to decouple, I always choose Elna Silmic II)

You like to transfer experiences related to tubes to the case of jFETs.

Depending on the topology, the jFET has a certain behavior.
The source decoupling capacitor influences the quality, noise, low frequencies, gain of the circuit, distorsion. They must be of the best quality, with losses, esr, etc., as good as possible.
I would really prefer instead of electrolytic, one without polarity (but it is huge) or bipolar. But nowadays there are high-quality electrolytic capacitors, so in real life we don't have to worry anymore.
https://www.tropicalfishvintage.com/blog/2020/4/18/on-cathode-bypass-capacitors

 

[Emmathom]

I can see by your link (and what you told me earlier) that you are a guitar amplifier addict ! maybe guitarist too... ?
A MKP of 22uF ??? why not in a mic housed in a barrel of beer donor-body
More seriously, I can put a 22uF Nichicon Muse BP as I put one on the signal path 4,7uF

 

[micolas]

I can see by your link (and what you told me earlier) that you are a guitar amplifier addict ! maybe guitarist too... ?
A MKP of 22uF ??? why not in a mic housed in a barrel of beer donor-body
More seriously, I can put a 22uF Nichicon Muse BP as I put one on the signal path 4,7uF

(Yes, I'm a guitarist )
I checked the voltages in the stock SC1100, with a Phantom without load of 46.8v, they are quite close to the values in green, and quite different from your stock SC1100 at 44v. As I said, it varies quite a lot, depending on the dispersion of the component parameters.

 

[Emmathom]

By the way, could you please tell me a same "protocole" for scope test on my tube pre ?
- connect smartphone output (thru 100nF - 1uF MKP) after the mic transformer
- connect the tube pre output in the USB sound card line input
- measure with REW's scope as I did for the mics
???

 

[micolas]

By the way, could you please tell me a same "protocole" for scope test on my tube pre ?
- connect smartphone output (thru 100nF - 1uF MKP) after the mic transformer
- connect the tube pre output in the USB sound card line input
- measure with REW's scope as I did for the mics
???

So you want to convert tube saturation to jFET clarity?
Do you give up all the character, the color of the tube?
I sometimes adjust the jFET's Bias to distort a bit faster to simulate the richer tube sound.

 

[micolas]

Hi @Emmathom
Did you manage to make measurements in the modified and the stock microphone?
Have you ever replaced the capsule with k47?

 

[Emmathom]

No, as I told you, I go step by step...
This afternoon I will get 2 x 22uF Muse BP with a friend so I'll put them on the 2 mics. I will also put Muse BP 4,7uF on original mic. I've already changed the two 470uF 25v for Panasonic 35v on both mics...

The next step after that, will be to change the transformer on the original (which will not be original anymore)
And then test it thru scope with 1kHz and look at how the Fet is biased : if it needs biasing, I will do with a RV to find the good value and place a fixed R (like I did on the other one)

After all that is done, I will record a audio file test with the mics as they are
And last, I will change the 2 capsules and record the same audio file in the same conditions

 

[Emmathom]

Hi
I worked on the microphones today...
I changed the transformer on the original SC1100, the 47nF and 10nF capas for wima mkp, the 22uF source for Muse BP and the 4.7uF for Muse BP too, as in the modified version. Both have now same capacitors.
Now the original is called Orig-mod and the full modified Mod.

I took the opportunity to bias the Fet (Orig-mod) and I think I'm starting to understand REW. First I calibrate the sound card.
I noted the measurements of the 2 microphones and they are quite close except for the jfet source voltage.
The values of the Mod are from yesterday and those of the Orig-mod have been made today.
I think I didn't bias well the Mod because I have less level on the Mod (-3dB) compared to the Orig-mod but above all, when listening, I have less presence and bass. The sound is more "fine" and less "powerful".
We can see on the audio files recorded in my DAW that the Mod has more neg. alternance than pos. but the Orig-mod seems to be perfectly balanced...
We can also see on the spectrum file (shape in red) that the 3rd harmonic and 50Hz are quite present (Orig-mod)

 

[micolas]

Hi
I worked on the microphones today...
I changed the transformer on the original SC1100, the 47nF and 10nF capas for wima mkp, the 22uF source for Muse BP and the 4.7uF for Muse BP too, as in the modified version. Both have now same capacitors.
Now the original is called Orig-mod and the full modified Mod.

I took the opportunity to bias the Fet (Orig-mod) and I think I'm starting to understand REW. First I calibrate the sound card.
I noted the measurements of the 2 microphones and they are quite close except for the jfet source voltage.
The values of the Mod are from yesterday and those of the Orig-mod have been made today.
I think I didn't bias well the Mod because I have less level on the Mod (-3dB) compared to the Orig-mod but above all, when listening, I have less presence and bass. The sound is more "fine" and less "powerful".
We can see on the audio files recorded in my DAW that the Mod has more neg. alternance than pos. but the Orig-mod seems to be perfectly balanced...
We can also see on the spectrum file (shape in red) that the 3rd harmonic and 50Hz are quite present (Orig-mod)

If you want to do BIAS correctly, put R9 a VR=15..25K and you have to make R10=O ohm

 

[micolas]

@Emmathom
You must also include the polarization voltages of the capsules in the measurements
*
It seems that there are quite large differences between the jFETS parameters
*
Differences also appear in DC/DC (voltages at R15 are quite different)
*
I hope you measured all the components you put in

 

[Emmathom]

If you want to do BIAS correctly, put R9 a VR=15..25K and you have to make R10=O ohm

Hum... so I replace R9 by a VR (to find the right value > will place the right fixed approched value after) and put "a string" at R10 (shunt) ?

 

[Emmathom]

@Emmathom
You must also include the polarization voltages of the capsules in the measurements

I will ok...

It seems that there are quite large differences between the jFETS parameters
*
Differences also appear in DC/DC (voltages at R15 are quite different)
*
I hope you measured all the components you put in

I put only new capacitors
The fets and the bjt were already there...
In the Mod one I took the transistors from the original board and soldered them on my "bread-board"

 

[micolas]

I will ok...

I put only new capacitors
The fets and the bjt were already there...
In the Mod one I took the transistors from the original board and soldered them on my "bread-board"

The two microphones were not bought simultaneously, as a matched pair, they are from different batches, all components have +/- tolerances

 

[micolas]

Hum... so I replace R9 by a VR (to find the right value > will place the right fixed approched value after) and put "a string" at R10 (shunt) ?

Yes. The correct circuit (which will bias properly) does not contain R10
Only after the correct BIAS-ing in both microphones, you will replace the VR with fixed resistors.
The important thing is to make them as correct as possible, according to your taste. You can equalize the volume differences in post processing.

 

[Emmathom]

Yes. The correct circuit (which will bias properly) does not contain R10
Only after the correct BIAS-ing in both microphones, you will replace the VR with fixed resistors.
The important thing is to make them as correct as possible, according to your taste. You can equalize the volume differences in post processing.

Yes but in this way, the 1GΩ after the 1nF goes straight to ground.
I did took off R10 at first time and it brought me lots of gain but unbalanced sine wave (more neg. than pos)
But Micolas you didn't comment my values... about the H3 peak, the 1kHz sine wave in the scope (4vpp ?)... how can I go further if I don't get observations on what I do... ?

 

[micolas]

I put only new capacitors

Did you measure the new capacitors to be identical?
The ones on the source can affect the gain and the response at low frequencies (and the coupling ones influence the passband)
*
The bias voltage of the capsule affects the sensitivity and to some extent the tone.