Yes, C12 is part of the filter, D7, D8 are just for the opamp's input protection.
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The external supply +/- would need to reference the same ground as the op amp. If he's using the supply for the NS-OPS, he'll already have a +/- 15V supply referenced to the same ground built into it. Too bad the rail mosfets are bypassed.
Those diode are between the + input and ground, not the - input.
Those diode are between the + input and ground, not the - input.
That appears to be a mistake I had not noticed. The input protection diodes should be between +IN and -IN.
Now does that make a difference to start up behaviour?
separate +/-15v to offset controller
No, this solution just hides the problem.
What i mean.
Amplifier's offset start from about 400mV if the separate power supply start up about 12'' before the main power supply.
Amplifier's ofsset start from 3 volt when separate power supply start up about 5'' before the main power supply.
To my point of view this act exactly as when common power supply was used.
Another find is that offset is 3v when i forgot to startup the separate offset controller power supply.
No, this solution just hides the problem.
What i mean.
Amplifier's offset start from about 400mV if the separate power supply start up about 12'' before the main power supply.
Amplifier's ofsset start from 3 volt when separate power supply start up about 5'' before the main power supply.
To my point of view this act exactly as when common power supply was used.
Another find is that offset is 3v when i forgot to startup the separate offset controller power supply.
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What you can try to clear the situation - remove the opamp and ground the output pin, where the opamp's output was, to ground. Start it up and see the offset behaviour. I think, it will start from 3V. Then we know what to do
Hi Valery,i will try your suggestion tomorrow.What you can try to clear the situation - remove the opamp and ground the output pin, where the opamp's output was, to ground. Start it up and see the offset behaviour. I think, it will start from 3V. Then we know what to do
Thanks.
Yes you are right,start up from 4v and stay here.What you can try to clear the situation - remove the opamp and ground the output pin, where the opamp's output was, to ground. Start it up and see the offset behaviour. I think, it will start from 3V. Then we know what to do
It may be caused by the difference in input LTP's base currents due to significant difference in base-to-ground resistors' values.
It would not be a problem if the input devices would be the jFETs or the tube triodes, but is a problem with BJTs.
For a test, we can insert an electrolytic capacitor in series with NFB resistor, placed between the -IN and the signal ground.
It would not be a problem if the input devices would be the jFETs or the tube triodes, but is a problem with BJTs.
For a test, we can insert an electrolytic capacitor in series with NFB resistor, placed between the -IN and the signal ground.
But the base current is of the order of 6uA. That was confirmed some while ago and confirmed that the LTP was reasonably in balance (just within that tolerance of ±10%).
6uA across 22k is only 132mV.
changing one side to 11k only creates a difference of 66mV. That very approximately should become the new output offset.
6uA across 22k is only 132mV.
changing one side to 11k only creates a difference of 66mV. That very approximately should become the new output offset.