Dr.EM
New Member
I'm trying a simplified version on breadboard, just the free running ADC connected up as shown with the op-amp input and DAC output. The op-amp uses a higher supply and 1/2 supply is used as artificial ground. It's not going very well, here are my observations:
When I switch it on, there is a lot of noise on the power rails (supplied by 317 regs). Around 2v-pp. It is high frequency and is present even if I remove power to the ADC, so is somehow caused by the op-amp? It has a bypass cap.
The same noise exists at the output. It becomes much larger when I connect my mixer to the output.
The ADC outputs seem to do what they should, though at the wrong times. With no sound input, they have a lot of activity (probably because the noise which is also present at its input?). They do change with a signal applied, I have attached the noise at the output followed by the noise with an input signal and you should be able to hear it a little.
The input signal is audable at the output even with the ADC outputs disconnected!? It is quite clear if I attach the ADC analogue ground to the 1/2 supply artificial ground. It is less clear with it at actual ground, but I can hear more of the digital signal (as in the attached mp3). I really don't know where it should go, why are there seperate analogue and digital grounds? How can they possibly be seperate? I think this is the cause of the problems.
Vref2 is unconnected. Should it go somewhere?
Any ideas?
When I switch it on, there is a lot of noise on the power rails (supplied by 317 regs). Around 2v-pp. It is high frequency and is present even if I remove power to the ADC, so is somehow caused by the op-amp? It has a bypass cap.
The same noise exists at the output. It becomes much larger when I connect my mixer to the output.
The ADC outputs seem to do what they should, though at the wrong times. With no sound input, they have a lot of activity (probably because the noise which is also present at its input?). They do change with a signal applied, I have attached the noise at the output followed by the noise with an input signal and you should be able to hear it a little.
The input signal is audable at the output even with the ADC outputs disconnected!? It is quite clear if I attach the ADC analogue ground to the 1/2 supply artificial ground. It is less clear with it at actual ground, but I can hear more of the digital signal (as in the attached mp3). I really don't know where it should go, why are there seperate analogue and digital grounds? How can they possibly be seperate? I think this is the cause of the problems.
Vref2 is unconnected. Should it go somewhere?
Any ideas?