Hello Wonderful people.
I would be very grateful for thoughts on this. I've built one of the level adjust circuits from Doug self's book. I'm getting, I've got a +/-17vDC supply but am getting - or + 17vDC on pin 1 the buffer output. Here's my schematic
I really thought I'd finally nailed this, after endless oscillation problems. Having read a bit I think it is going to be a input offset voltage problem? Leading to saturation at one of the rails? Which I believe is a problem of the feedback network and bias current? Apolgies if I'm making a mess of this.
Self uses the NE 5532, wonder if I'm using the wrong op amp (had several LM4562's lying around)
I don't get that same output vDC at pin 7
Peace and Love
Pat
I would be very grateful for thoughts on this. I've built one of the level adjust circuits from Doug self's book. I'm getting, I've got a +/-17vDC supply but am getting - or + 17vDC on pin 1 the buffer output. Here's my schematic
I really thought I'd finally nailed this, after endless oscillation problems. Having read a bit I think it is going to be a input offset voltage problem? Leading to saturation at one of the rails? Which I believe is a problem of the feedback network and bias current? Apolgies if I'm making a mess of this.
Self uses the NE 5532, wonder if I'm using the wrong op amp (had several LM4562's lying around)
I don't get that same output vDC at pin 7
Peace and Love
Pat
Should there be a resistor in parallel with C26? C5 means there is no path to set the DC OP of the circuit, so U1A integrator will drift to one of the rails. That problem isn’t related to your op-amp choice.
Thanks both. Was advised by someone to put 100pF caps in the loop to reduce oscillations. Can it contribute to the DC problem though?
Self states that C5 is there to stop DC arriving on the trim pot.
Would adding a resistor in U1A feedback loop and then one to ground help? I could make it a v low gain amp rather than a buffer, could then tinker with gain of U1B to compensate?
Self states that C5 is there to stop DC arriving on the trim pot.
Would adding a resistor in U1A feedback loop and then one to ground help? I could make it a v low gain amp rather than a buffer, could then tinker with gain of U1B to compensate?
Of course, the opamp output will just swing to one of the rails without DC feedback.
That circuit appeared in the Precision Preamp in 1996. It a classic text book circuit that works well.
thanjks mooly, wire link installed and problem fixed. think i thought the 100pF replaced the wire link, lesson learned!