I am building a phono pre-amp and i was toying with the idea of running it from the 18v DC supply in the turntable, which i have done a transformer swap on. Then I can just install it in there without using a new power supply.
So I built one of those capacitor and voltage divider virtual split rail.
I was testing - i have a +15-0-15 supply that makes this work fine. So I realize I'll have to isolate inputs and output earth with coupling capacitors. I did that and the phono signal still passes through and gets amplified.
Then I'm trying to run this NE5532 with this virtual power - using one of the rails as an input of 0v 15v - it measures (pos)7.5-0-7.5(neg) which connected up with the circuit and i've isolated the inputs/ouputs - linking their earth ... but now earth/0v is floating. So basically that kills the signal. Since they are isolated with coupling caps I thought, ok then I'll use the 0v that is actually now the negative rail for the pre-amp but its 0v otherwise as the 0v/ground and then i should have my input signal basically as before. Since 0v was ground before and it worked.
Doesn't work. Looking at the data sheet the NE5532 wants 5-15v +/- as min to max +ve and -ve supply. So I've got 7.5, should be enough to function.
My working circuit has 100 ohm current limiting resistors on the +ve/-ve supply of the op-amp which I do because it is one thing (along with bypass caps) that helps make it stable. Earlier I built unstable pre-amps and I copied this idea ... but maybe at this voltage that is a problem? I still have to test it like that ... but any ideas or circuit examples of how this kind of power supply changes a circuit and keeps the virtual ground isolated? Thanks - and sure, just link to another thread if I'm just repeating history.
So I built one of those capacitor and voltage divider virtual split rail.
I was testing - i have a +15-0-15 supply that makes this work fine. So I realize I'll have to isolate inputs and output earth with coupling capacitors. I did that and the phono signal still passes through and gets amplified.
Then I'm trying to run this NE5532 with this virtual power - using one of the rails as an input of 0v 15v - it measures (pos)7.5-0-7.5(neg) which connected up with the circuit and i've isolated the inputs/ouputs - linking their earth ... but now earth/0v is floating. So basically that kills the signal. Since they are isolated with coupling caps I thought, ok then I'll use the 0v that is actually now the negative rail for the pre-amp but its 0v otherwise as the 0v/ground and then i should have my input signal basically as before. Since 0v was ground before and it worked.
Doesn't work. Looking at the data sheet the NE5532 wants 5-15v +/- as min to max +ve and -ve supply. So I've got 7.5, should be enough to function.
My working circuit has 100 ohm current limiting resistors on the +ve/-ve supply of the op-amp which I do because it is one thing (along with bypass caps) that helps make it stable. Earlier I built unstable pre-amps and I copied this idea ... but maybe at this voltage that is a problem? I still have to test it like that ... but any ideas or circuit examples of how this kind of power supply changes a circuit and keeps the virtual ground isolated? Thanks - and sure, just link to another thread if I'm just repeating history.
Yes - like that. That part seems to work with 1000uF caps for supply reservoir and 1k resistors for voltage divider. 0.1uf seems to just be there as a nicety.
I have made that part ... but the isolation and the op-amp, the signal ground isolation ... i just wondered if anyone had dealt with this with a pre-amp using this kind of power supply? Maybe in writing it i'm answering my own question - i still have to try a few more things like removing current limit resistors with lower voltage.
I have made that part ... but the isolation and the op-amp, the signal ground isolation ... i just wondered if anyone had dealt with this with a pre-amp using this kind of power supply? Maybe in writing it i'm answering my own question - i still have to try a few more things like removing current limit resistors with lower voltage.