I will mesure the capsule capacitance and calculate so :OK. It wasn't clear.
IIUW the piece of schemo is a mod of an original, so the 27pF value is about random.
capsule-capa*(5,5-1) = C in pF
For -15dB > x0,18 > 1/0,18 = 5,5
I will mesure the capsule capacitance and calculate so :OK. It wasn't clear.
IIUW the piece of schemo is a mod of an original, so the 27pF value is about random.
It's not how it works.I will mesure the capsule capacitance and calculate so :
capsule-capa*(5,5-1) = C in pF
For -15dB > x0,18 > 1/0,18 = 5,5
Thanks guys for your brains here!It's not how it works.
Your calculation would be correct for a capacitor across the capsule, but not for a charge amp.
The input circuit goes from a non NFB common source stage to a voltage-to-current NFB type.
It may be possible to calculate - with a precision of ca. -50/+100% though - but it's typically the kind of things you adjust by trial-and-error.
Anyway, I'm not sure the value of 15dB is optimum.
Let your ears (and soldering iron) do the work.
Which value would you begin with for a significient attenuation ?Anyway, I'm not sure the value of 15dB is optimum.
Let your ears (and soldering iron) do the work.
The 2 Tx out were changed for Monacor LTR110
We didn't entirely designed this circuit at all : we just remove one resistor (R4 / 3KΩ) and try to bias the jfet correctly and that was all.
The actual gain will be limited by the drain-gate capacitance (i.e. Miller effect) but this is very nonlinear (depends a lot on drain-gate voltage), so expect lots of distortion.
Much more simple Indeed !Just realised I forgot a few somethings to simplify and improve the circuit...
View attachment 132381
Thor
To where we are now, why not change K170 for a more appropriate Jfet ?
Ok will try your schem. as it is drawn...The the charge amp no longer works, not enough open loop gain.
Here the point is to make minimal and mostly subtractive changes and get a better result. Quick fix, minimal effort.
If we want a to design a competent solid state microphone, that is a whole other ballgame.
Thor
Ok will try your schem. as it is drawn...
Almost.@thor.zmt
cascode Jfets ?
I vote for mo bettaIf we do that, why go polish on a solid piece of excrement (polish a turd) or Tuna Fish, if we can do mo betta?
like a J304 which has a VGS(off) from -2v to -6v ? or (again) a J113 ?Almost.
Gate to lower FET source.
And use a higher pinchoff voltage FET for upper. But we are exiting "reuse existing PCB and stuff" and redesign.
like a J304 which has a VGS(off) from -2v to -6v ? or (again) a J113 ?
a new pcb will be created from a perf-board (6cmx4cm seems a good option for mic bodies and it's a standard size)
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