Yes, I've already built one.
What do you advise me to put between the output of the circuit and a recording device in this case?
Creation CK12 capsule and power supply question
- Thread starter Putchy
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Look for the opa Alice project.
With a good jfet input op- amp you do not need a separate jfet device.
This example has been discussed on these forums, created by member rogs.
https://www.opic.jp137.com/
It might be worth making a distinction that is not always obvious to everyone. The signal from a condenser capsule is both incredibly high impedance and low level.
Generally speaking, the “headamp,” or circuit built into the microphone converts the high impedance to low impedance, but doesn’t net much gain. Often, this is done by amplifying the signal with an active device, and then”throwing away” that gain with a step-down transformer to decrease the impedance. It can also be done with an active impedance-converting circuit. In either case though, the resulting signal, while lower impedance, is still “mic level,” as opposed to the “line level” that a recording device would expect to see.
That’s the point of a microphone preamp - to convert the low mic level to line level (while maintaining low impedance).
In order to record sound using a condenser capsule, you need both.
Generally speaking, the “headamp,” or circuit built into the microphone converts the high impedance to low impedance, but doesn’t net much gain. Often, this is done by amplifying the signal with an active device, and then”throwing away” that gain with a step-down transformer to decrease the impedance. It can also be done with an active impedance-converting circuit. In either case though, the resulting signal, while lower impedance, is still “mic level,” as opposed to the “line level” that a recording device would expect to see.
That’s the point of a microphone preamp - to convert the low mic level to line level (while maintaining low impedance).
In order to record sound using a condenser capsule, you need both.
micolas
Well-known member
The condenser capsule does not provide small signal.
@kingkorg measured very high capsule output levels.
https://groupdiy.com/threads/all-opamp-mic-design-no-fet-at-first-stage.62636/post-1138844
It produces that kind of voltage into high impedance. It cannot produce high level into low impedance.
micolas
Well-known member
The condenser capsule produces a signal at high impedance. But NOT a small signal.
The impedance converter transforms it into a low impedance signal. Its input (and not only) must be able to handle this level of signal.
That's what I said.
Distortions are mainly determined by the electronic circuit which is put in difficulty by this important signal, NOT small.
The main limiting factor of the max SPL supported by the microphone in the real world is the electronic circuit. That's why we limit the signal provided by the capsule, reducing the polarization voltage of the capsule or using a capacitive pad, or acoustically by positioning it with respect to the source, etc.
Nobody said that.
The meaning was probably lost somewhere in the semantics.
The word “level” is maybe the problem here. To me, a capsule producing say, 20Vpp into 1G of impedance is not high level (it’s less than 0.2 milliwatts RMS). “Line level” is more than 10 times higher (over 2.5 milliwatts assuming a 600 ohm load). Plus, capsules only produce voltages like that on huge transients. The average voltage is closer to 1Vpp, which is 0.0005 milliwatts RMS into 1G.
I know that this is all semantics, but it’s important. No one is going to be able to plug a condenser capsule directly into a line input and get a usable sound, even if the input impedance where really high.
I know that this is all semantics, but it’s important. No one is going to be able to plug a condenser capsule directly into a line input and get a usable sound, even if the input impedance where really high.
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micolas
Well-known member
Then we both agree.
The word "level" was the source of the misunderstandings. It needs to be defined more specifically. On the other hand, huge transients are part of real life.
Personally, I consider the level delivered by the capsule signal high, in relation to what follows it in the audio chain. (eg I wish the 87 topology could handle some aspects better)
I think we now agree that we are saying the same thing.
