Thank you Mooly for always being here and keep giving me advices (Y)
So, since I'm a beginner, I didn't really understand in practise what you mean with the PSRR and that it's the only way that the output can be degraded via noise on the rail. Is this something I can change by changing the schematic diagram and its components?
So, since I'm a beginner, I didn't really understand in practise what you mean with the PSRR and that it's the only way that the output can be degraded via noise on the rail. Is this something I can change by changing the schematic diagram and its components?
PSRR is the means by which noise and any variation in rail voltage can influence the output of an amplifier.
If you take an opamp circuit and make for example the 9 volt rail into a varying voltage (say a squarewave that changes between 8v and 10 volt) then the opamp circuit should reject that unwanted supply variation and no disturbance or trace of it should be seen at the opamp output.
In practice the rejection is high at lower frequencies but worsens rapidly at higher ones (like from a switching supply). This means noise can enter the opamp via the rail.
So you can only improve on that by improving the filtering to opamp supply pins.
Noise from switching supplies tends to be both high frequency and spiky in nature and that makes it very difficult to remove.
If you take an opamp circuit and make for example the 9 volt rail into a varying voltage (say a squarewave that changes between 8v and 10 volt) then the opamp circuit should reject that unwanted supply variation and no disturbance or trace of it should be seen at the opamp output.
In practice the rejection is high at lower frequencies but worsens rapidly at higher ones (like from a switching supply). This means noise can enter the opamp via the rail.
So you can only improve on that by improving the filtering to opamp supply pins.
Noise from switching supplies tends to be both high frequency and spiky in nature and that makes it very difficult to remove.
great, thank you!
So with the circuit I have (in the image I posted), I get a peak around 10 000 Hz which is really disturbing. Do any of you know how to filter this signal?
I already have a RC low-pass filter, with a cut off at around 3.5 Hz, so I thought that this peak would be removed by the filter, but no.
So now my question is if the noise comes from the OP-amp or something else in the circuit .... Is there a way of splitting the resistor values so that I get less noise? Or do you think it could be due to something else?
Have a good weekend everyone!
So with the circuit I have (in the image I posted), I get a peak around 10 000 Hz which is really disturbing. Do any of you know how to filter this signal?
I already have a RC low-pass filter, with a cut off at around 3.5 Hz, so I thought that this peak would be removed by the filter, but no.
So now my question is if the noise comes from the OP-amp or something else in the circuit .... Is there a way of splitting the resistor values so that I get less noise? Or do you think it could be due to something else?
Have a good weekend everyone!
A couple of things you could try for curiosity:
1/ With the circuit making the noise you could see if adding further load to the supply changes anything. The opamp draws only a few milliamps so try adding say 330 or 470 ohm across the supply pins. Does the noise change?
2/ This might sound a bit crazy but get the circuit powered up and making the noise and then switch off, disconnect the + feed from the power bank and now power the circuit up via a normal battery.
Do you still get the noise?
Do you get the noise if you now add a load to the power bank? Try the 330 or 470 ohm across its output but leave the positive lead isolated from the preamp. Just leave the negative connected from the power bank.
1/ With the circuit making the noise you could see if adding further load to the supply changes anything. The opamp draws only a few milliamps so try adding say 330 or 470 ohm across the supply pins. Does the noise change?
2/ This might sound a bit crazy but get the circuit powered up and making the noise and then switch off, disconnect the + feed from the power bank and now power the circuit up via a normal battery.
Do you still get the noise?
Do you get the noise if you now add a load to the power bank? Try the 330 or 470 ohm across its output but leave the positive lead isolated from the preamp. Just leave the negative connected from the power bank.
The 330ohm would load the power supply and that should get it to produce the noisy rail (now across the 330 ohm). Connecting the negative only would couple the powerbank to the preamp.
It was just for curiosity to see if the noise was still present or not
