?
Jules Ryckebusch:
>I can’t measure a difference and of course with the OPA1642?
>I’m already 100dB in the weeds for THD to begin with.
Jules,
How are you measuring this ?
In my experience unless the input stage differential JFET pair is fully cascoded with very little?
extra nonlinear input capacitance then every opamp I have measured using a capacitor in series?
with the + input of the opamp will show around -70 to -50 dB of distortion due to the nonlinear?
input capacitance.
The input capacitance of the OPA1642 is 8 pF
Question 1:
Did you actually measure the distortion of the OPA1642 using a series capacitor having the actual?
capacitance of a real condenser capsule ?
Question 2:
Using an electret capsule instead of a true capacitor capsule will provide a much lower source impedance?
than a true condenser capsule so the opamp distortion when fed from an electret capsule will be lower due?
to the much lower source impedance of that kind of source.
But in that case the actual distortion will be due to the scrappy single N channel JFET that buffers the electret?
capacitor and the distortion then is much higher than any kind of reasonable good opamp so the opamp distortion?
means nothing at all in that case.
The OPA1642 uses, fig 37, a source resistor of 10 kohm to measure distortion below 0,001 % @ 5V rms in a unity?
gain configuration.
Thats impressive, but I wish to see the distortion using a 22 - 33 pF capacitor so we can see what that means to?
the actual distortion using a true condenser capacitor.
Have you done this Jules ?
Thanks !
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Best regards,
Goran Finnberg
The Mastering Room AB
Goteborg
Sweden
E-mail: mastering@...
Learn from the mistakes of others, you can never live long enough to
make them all yourself.??? -?? John Luther
(\__/)
(='.'=)
(")_(") Pyret, Ranglet, Aron, VovVov, Nero, Smurfen & Pussin:RIP
