Hi everyone!
I need to build a front-end to an ADC that can both accept a (balanced) line input, or work as a very simple microphone preamplifier.
I was thinking of using the classical three-opamp instrumentation amplifier approach (pic for reference).
However, the ADC I will be using has differential inputs, whereas the standard INA topology has a single-ended output.
My first thought was to replace the differential amplifier (U3) with a fully differential opamp to drive the ADC; then I thought, can't I just remove U3 and associated resistors at all, and drive the ADC directly from U1-U2?
I think I can see it working on paper, as gain for differential signals is still provided by U1 & U2; but I'm afraid I might be missing out on some real-world limitations or issues that could make this simpler / lower part count approach undesirable.
Any comments on this?
Also, as far as the preamp gain goes, I was thinking of implementing a stepped control with 3 or 4 steps, using relays to swap resistors in place of VR1 (I have hundreds of relays laying around...).
What would you recommend as "reasonable" gain steps? I'm planning to use this thing mostly with dynamic mics (on stage - live sound), but I might also need the occasional line input, which I guess warrants a 0dB step in there.
Thanks!
- Dave
EDIT: and I guess I managed to post this in the wrong board. Sorry guys! I guess it should be moved to the Drawing Board or something...
I need to build a front-end to an ADC that can both accept a (balanced) line input, or work as a very simple microphone preamplifier.
I was thinking of using the classical three-opamp instrumentation amplifier approach (pic for reference).
However, the ADC I will be using has differential inputs, whereas the standard INA topology has a single-ended output.
My first thought was to replace the differential amplifier (U3) with a fully differential opamp to drive the ADC; then I thought, can't I just remove U3 and associated resistors at all, and drive the ADC directly from U1-U2?
I think I can see it working on paper, as gain for differential signals is still provided by U1 & U2; but I'm afraid I might be missing out on some real-world limitations or issues that could make this simpler / lower part count approach undesirable.
Any comments on this?
Also, as far as the preamp gain goes, I was thinking of implementing a stepped control with 3 or 4 steps, using relays to swap resistors in place of VR1 (I have hundreds of relays laying around...).
What would you recommend as "reasonable" gain steps? I'm planning to use this thing mostly with dynamic mics (on stage - live sound), but I might also need the occasional line input, which I guess warrants a 0dB step in there.
Thanks!
- Dave
EDIT: and I guess I managed to post this in the wrong board. Sorry guys! I guess it should be moved to the Drawing Board or something...