The preamp must feed the highpass filter, not the A to D converter.
The filter must feed a buffer opamp that feeds the A to D converter.

2V peak-to-peak needs a current of 20mA which is barely possible from an opamp. Let the filter feed its own resistors and feed a buffer opamp that drives the A to D converter.

 

Hi Audioguru,

Thanks.

 

I completely forgot,

 

the AD8531 is very powerful but its max allowed supply is only 6v. Its output goes from +0.1V to +4.75V into 50 ohms when it has a 5V supply

You forgot to calculate the value of C7. With 0.1uF it cuts the output power into 50 ohms in half at 32kHz. If you use 0.47uF then almost the full output power at 35kHz goes to the 50 ohms load.

 

Do you think this one is pretty good?

http://www.ti.com/lit/ds/symlink/lm7321.pdfseems to give enough output current if I have +12V for the +Vs and the -Vs at GND and bias the amp input at 6V.

 

Do you think this one is pretty good?

http://www.ti.com/lit/ds/symlink/lm7321.pdf

The LM7321 seems to give enough output current if I have +12V for the +Vs and the -Vs at GND and bias the amp input at 6V.

Don't you want the maximum input to the A to D converter to be +5V?
Since its input is 50 ohms then Ohm's Law calculates a current of 100mA which is impossible to source from that opamp.

 

Thanks Audioguru,

 

1V into 50 ohms is only 20mA that most opamps can supply.
How will you limit the signal to only 1V peak?

Are you sure that the A to D converter can handle a negative input because most do not.

 

Thanks Audioguru.


The A/D channel can handle a negative voltage and I had tested this. I remember reading for that particular board that there is an internal buffer that adds about a 2V bias for AC coupled signals.

probably too weak to give 20mA without a buffer right?

 

seems to have just under 20mA source and sink capability

 

To increase the output current you can connect TL082 in parallel.

 

To increase the output current you can connect both opamps of a TL082 in parallel.

But each opamp needs a resistor in series with its output so they equally share the current.

 

is this a better approach

 

Two opamps in parallel each need a series output resistor so that they share the current equally. The resistors reduce the total output current and change the voltage gain.

 

Thanks,
i will think about it

 

Data has rectangular waves where distortion does not matter. Then you can use tantalum coupling capacitors for their small size.

 

amps that drive speakers.

 

For a 50 ohm load then use 22 ohm resistors. The output level of the opamps must be a little higher to make up for the voltage loss.

 

Thanks Audioguru. With 22 ohm resistors the voltage output from the op amps need to be 1.44 volts to get 1 volt into the 50 ohm input for the A/D channel.

 

I'm considering making an additional version