SE Electronics Z3300a

[Emmathom]

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)
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The bias voltage of the capsule affects the sensitivity and to some extent the tone.

No I didn't measured the Muse BP 22uF nor the 4,7uF...
Does a bad-biased jfet can influence the tone ? (my lack of bass & level)
Now the 2 mics are "online" and I can notice a 4,6dB level difference

 

[micolas]

Yes but in this way, the 1GΩ after the 1nF goes straight to ground.

the 1GΩ after the 1nF must go straight to ground.

 

[micolas]

No I didn't measured the Muse BP 22uF nor the 4,7uF...
Does a bad-biased jfet can influence the tone ? (my lack of bass & level)

Yes

 

[Emmathom]

the 1GΩ after the 1nF must go straight to ground.

Ok but in the original schematic it doesn't... R10 is 3KΩ in original t.bone

 

[micolas]

Ok but in the original schematic it doesn't... R10 is 3KΩ in original t.bone

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 profit matters.

 

[micolas]

Ok but in the original schematic it doesn't... R10 is 3KΩ in original t.bone

the correct non-mutilated circuit, as in U87

 

[Emmathom]

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 profit matters.

sorry... lot of things to learn later on, to digest... and jfet are soooo specials !
https://sound-au.com/articles/jfet-design.htm

 

[micolas]

Now the 2 mics are "online" and I can notice a 4,6dB level difference

It is possible that your audio build to the second microphone on the bread-board introduces parasitic capacitances to the jFET input side, which at the huge impedance introduce signal and high frequency attenuation, just like the km84. We are talking about a few pF!

In km84. C9=15pF introduces an attenuation of -10dB!

 

[Emmathom]

I hope my audio board doesn't mess up the mic...
Anyway I will rebias the 2 mics tomorrow with a RV for R9 and no R10... and also find some good tutorials on REW to understand clearly what & how to do with this software

 

[micolas]

Now the 2 mics are "online" and I can notice a 4,6dB level difference

#27

?

Post in thread 'Two microphones as matched pair, what properties are matched?' https://groupdiy.com/threads/two-mi...hat-properties-are-matched.84151/post-1092481

 

[Emmathom]

It's not the level difference that bothers me (it can be adjust by gain at recording) but the sound difference. The Orig-mod has more body, more detail when the Mod is thin, less caracter...
Let me rebias the fet and I'll be back with (I hope) good news

 

[micolas]

It's not the level difference that bothers me (it can be adjust by gain at recording) but the sound difference. The Orig-mod has more body, more detail when the Mod is thin, less caracter...
Let me rebias the fet and I'll be back with (I hope) good news

measure the newly installed capacitors
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make identical BIASs on the graph

 

[micolas]

You can try to change the capsules between them.
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you can even swap jFETs between them
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Are transformers both wired identically?

 

[Emmathom]

You can try to change the capsules between them.

Yes I could... (I will if no update by re-biasing)

Are transformers both wired identically?

Yes in "A" mode
Have you had a look at the link about Jfets ? I found the guy's explanations very interesting...

 

[micolas]

Have you had a look at the link about Jfets ? I found the guy's explanations very interesting...

I have been following Rod Elliott (ESP) for many years

 

[micolas]

*
you can even swap jFETs between them
*

 

[Emmathom]

No... solder / de-solder /re-solder > I'm gonna ruin the boards...
I'm gonna find a solution for matching (I just read the topic > no matching mics, just as close as you can find) the 2 mics in term of sound, color, etc...
Anyway, one of the 2 I bought second-hand was "haunted" since the begining (Tr out-of-order !) so if I can't fix the problem I'll have to buy another second-hand and work on it (changing capacitors & biasing the fet). I think the "Mod" is a mic that has lived a turbulent life befor I got it...

 

[micolas]

No... solder / de-solder /re-solder > I'm gonna ruin the boards...

You can very easily change the wires of the capsule, reverse Front with Rear, maybe the front membrane has problems.

 

[micolas]

@Emmathom
Are both microphones in phase?

 

[micolas]

the Mod is thin, less caracter...

If it sounds thin check if C6=47nF is connected.