Hi Kleinstein, :-)
Thanks for your remaks!
The are manny ways to do the precharge, also automatic, but I opted for manual way.
R8 can get a higher value, but I'm going to do the first tests with 5K.
About you remark for extra imput protection 20 Ohm, maybe, i will think about it.
The second stage i tested already, and works fine.
I will certainly test the NE5532a in this position, cost is not a problem, i want quality ;-)
I've thought about it, to change the position of filters, but for the fist test i keep it this way.
There is also a peak level detector, in order to show whether the signal remains within dynamic range.
And the dynamic rage is BIG, almost -+15V
This noise measuring system main input, is for low level use, noise/hum below 1mV RMS, so that i can use my HAMEG HMO3004 to view the noise of references and low noise power supply's.
There wil be a second input, symetrical, with more gain choices.
I also thought of a 50/100 Hz notch filter, but I have a lot of experience in the measurement of small signals and do not need it now.
There is something very wrong when I measure references and the 50Hz is dominant.
That means I can go back to school and then will have to re-learn how to make a measurement setup
I welcome your comments, they make me think about some points.
The project is not finished yet, this afternoon I'm going to build on the preamp and make some first measurements.
I fixt the gain of the test setup at about 80dB.
I have just received some extra samples quad opamps to test for the first stage.
The first stage wil be dominant for the noise, and afther the first measurements I will decide witch quad opamp i wil use.
OPA4140
ADA4004-4
MAX44252
MAX44243
OPA1664
OPA4188
OPA1654
ADA4077-4 (lower bandwith)
LT1885
LT1679A lot of testing to do, low and high impedance source (10 Ohm and say 1K source impadance)
It wil keep me of the streets of Amsterdam
Kind regarts,
Blackodg