Test
A commonly used fet.ic was used.
1/
a/ Drain was led to input, Sorce to ground and a 60pf condensor was a
dummy mike AC shorting the gate to ground.
b/ A 1 mv 500 Hz sinus tone was injected at the Gate.
c/ The LS-10 gain control was set so that the meters showed -12 db,
between 5 and 6.
d/ The tone was removed and a 30 sec recording was made.
PIP voltage was 3 v unloaded and 2,7 when the Fet's Drain was connected.
2/
a/ PIP vwas "off" at the LS-10
b/ Drain was connected to input via a 220n condensor.
c/ Drain was also connected to a 2.2 kohms resistor giving 2,7v at
the drain from 3 V batteries.
d/ A 1 mV sinus tone was injected at the gate. Now the gain of the
LS-10 had to be increased to get to -12 db, as the 2,2 kOhms is a
heavier load (lower input impedance) compared to the current
generator. For -12 db, the wheel had to be set to between 6 and 7.
A new 30 sec recording was done.
No difference in noise can be seen or heard between the two measurements..
Klas.
At 20:41 2009-07-05, you wrote:
>Hi Klas,
>
>Yes, I agree that an original FET with a capacitor instead of the
>mic capsule might be an even better dummy load as a simple
>termination resistor. However, when you then switch off the PIP, the
>input would no longer be terminated (the FET output would then be at
>a high impedance state). Though, I'm not sure whether this would
>make any difference because the input impedance of the microphone
>input is probably already in the same range as the output impedance
>of a PIP microphone.
>
>Raimund
>
> >
> > Tonight I will connect one of those fet-IC's commonly used and a 60
> > pf condensor from gate to ground instead of a mike capsule, all put
> > in a screening tube.
> > Then it would be appropriate only to switch pip on and off..?
> > Agree?
> >
> > Klas
>
>
>
>
>------------------------------------
>
>"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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