rding?
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I'm sorry for contributing to "mess" here and thank you, Raimund and
John, for correcting me.
I meant to talk of electrets (microphone elements) in general and
fet's in general, (like 2sk170) but included EM172 e.t.c. which do
not have fet=B4s "in general" but more complex circuits.
Primo spec'a are not very accurate, on the other hand they are
usually poorer than actual data.
I get -6db (+/- 0,5db) when adding a 3,6k resistor over the output of
John's battery box.
Klas.
At 12:27 2012-12-30, you wrote:
> > An electret like EM172 is not a complete circuit. It has a very high
> > open circuit impedance, on the other hand it doesn't work, so it is
> > not relevant to talk about "impedance".
> > To make it work, a resistor is needed between the drain of the FET
> > and + of the battery and
>
>I agree
>
> > then the circuit gets the same (approx.)
> > output impedance as the resistor! So John's circuit will have a
> > output impedance of approx. 6.8k.
>
>Hmmm, the output impedance of the complete circuit it created by
>both that 6.8 k ohms resistor AND the impedance between the "GND"
>and "HOT" pads of the capsule. That impedance is the sum of the
>internal source resistor and the source-drain impedance of the
>internal transistor, which is deterimed by the operating point of
>the FET (which in turn is determined by many different variables
>such as the supply voltage and both the source and drain resistors.
>In any case, the output impedance of the entire electret mic circuit
>should always be significantly lower than the drain resistor (less
>than 6.8k in this example).
>
> > As the input impedance of the LS-11 is only 2k, it means that less
> > than 1/4 of the signal level remains.
>
>I would guess it would be a bit more because the mic output
>impedance is less than 6.8k (maybe half of that).
>
> > Raimund:
> > 1/ What do we know about the LS-11 input impedance with and without
> > plug in power?
>
>No, I never cared out that.
>
> > 2/ Do we know that it is a resistor?
>
>Yes, I think that it is a simple resistor. If I remeber correctly,
>someone already created an Excel spreadsheet on that for a number of
>different recorders, but I can't find it at the moement.
>
> > Also: When reading the specs of electret microphones, you have to
> > have a look at the "test-circuit" diagram. If Primo says that a
> > EM-172 has an "output impedance" of 2.4k, it is because they have
> > used 2.4k in the test circuit.
>
>The EM172 specification
>(http://www.frogloggers.com/Documents/EM172.pdf?cat=3D13&en=3D1)
>provides this information:
>
>"Impedance : 2.4 k=C6=92=C2=B6 }30 " at 1 kHz (RL3.9 k=C6=92=C2=B6)"
>
>As far as I understand it, it just means that they used a 3.9 k
>resistor (and a supply voltage of 5 V) in their test circuit that
>results in a output impedance of the test circuit of only 2.4k.
>
>Regards,
>Raimund
>
>
>
>
>------------------------------------
>
>"While a picture is worth a thousand words, a
>sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause=
.
>
>Yahoo! Groups Links
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
website: www.telinga.com
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