Hi! I started designing the circuit below in order to acquire car audio signals to my processor over ADC channels.
I want to scale down the audio source from high level or low level signals using a slide switch.
The idea is that both low level or high level signals can be plugged into the same "RCA" connector. Then, I would use the slide switch to select from "LOW LEVEL INPUT" or "HIGH LEVEL INPUT". I could not find any schematics like this.
Case 1 - High level input expected to max 10Vrms at RCA connector. This is the CH+ and CH- from car audio radio (wires that would go to speakers).
Desired: Differential outputs INN and INP need to be scaled down from max 10Vrms input to 5Vpp output differential.
Case 2 - Low level RCA audio source expected to max 4Vrms at RCA connector. This is the signal and GND of low level RCA cable.
Desired: Differential outputs INN and INP need to be scaled down from max 4Vrms input to 5Vpp output differential.
Note: Using single supply in all op-amps adding some offset at non-inverting input.
I assembled the circuit but it isn't good at all. Circuit has noise and its bandwidth is limited from 50Hz to 17kHz only. (Expected 15Hz to 20kHz range).
Could I get some inputs and recommendation of changes to fix those issues? I see that there are some failures in the approach.
Any help is very appreciated.
Thanks.
I want to scale down the audio source from high level or low level signals using a slide switch.
The idea is that both low level or high level signals can be plugged into the same "RCA" connector. Then, I would use the slide switch to select from "LOW LEVEL INPUT" or "HIGH LEVEL INPUT". I could not find any schematics like this.
Case 1 - High level input expected to max 10Vrms at RCA connector. This is the CH+ and CH- from car audio radio (wires that would go to speakers).
Desired: Differential outputs INN and INP need to be scaled down from max 10Vrms input to 5Vpp output differential.
Case 2 - Low level RCA audio source expected to max 4Vrms at RCA connector. This is the signal and GND of low level RCA cable.
Desired: Differential outputs INN and INP need to be scaled down from max 4Vrms input to 5Vpp output differential.
Note: Using single supply in all op-amps adding some offset at non-inverting input.
I assembled the circuit but it isn't good at all. Circuit has noise and its bandwidth is limited from 50Hz to 17kHz only. (Expected 15Hz to 20kHz range).
Could I get some inputs and recommendation of changes to fix those issues? I see that there are some failures in the approach.
Any help is very appreciated.
Thanks.
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Simulation gives me around -.3dB at 20kHz from 1kHz using ideal op amps. But also around 2dB less output from the speaker level connection vs. RCA connection (using given output levels). Changing R5 to 129 ohms gets the outputs really close to equal around 4.5Vpp. I didn't sim VRef circuit.
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Have you checked the voltage at VRef to make sure it's correct before testing?@dkfan9 Do you see any other changes that improve signal quality, less noise and stability?