OPA1611 is a good choice in terms of low noise and distortion slew rate almost
the same as LF411.
the same as LF411.
There is one 960 ohm resistor on DOGC board. Cant find anf 960 ohm resistor. Will the closest work. Say 976 ohm, 953 ohm or 1k.
Hi viki_v2,
that value is critical, because it forms the "bridge" together with the coil and the 120pF Capacitor. I got mine from mouser: 71-RS02B960R0FE12
that value is critical, because it forms the "bridge" together with the coil and the 120pF Capacitor. I got mine from mouser: 71-RS02B960R0FE12
I would chose 976R, with a very little bit higher gain and distortions, but also little better stability.
LF411, like most opamps used for DC servos, has a JFET inputs and very low input bias current.
OPA1611, on the other hand, is bipolar input.
Input bias current can be up to 250nA, compared to 5ßpA of the former.
I would suggest the likes of OPA140, LT1792, etc.
976R // 56k will give you 959R. Close enough.
Patrick
OPA1611, on the other hand, is bipolar input.
Input bias current can be up to 250nA, compared to 5ßpA of the former.
I would suggest the likes of OPA140, LT1792, etc.
976R // 56k will give you 959R. Close enough.
Patrick
A DC servo usually deploys high impedance RC network, e.g. 1µF 1M-ohm.
A high input bias current of the opamp will create a much larger DC offset than otherwise.
A FET input opamp is usually preferred with such high impedances.
Also they results in lower noise.
Opamp?? FET vs Bipolar
DC Servos
opamp for DC servo
Patrick
A high input bias current of the opamp will create a much larger DC offset than otherwise.
A FET input opamp is usually preferred with such high impedances.
Also they results in lower noise.
Opamp?? FET vs Bipolar
DC Servos
opamp for DC servo
Patrick
Hi Patrick,
thank you very much for your explanation. So I might try a FET or JFET input opamp. In my DOGC the OPA1611 does a good job with a DC-offset of about 5...10mV
P.S. I still have some JFETs to match... did not forget it ;-)
Michael
thank you very much for your explanation. So I might try a FET or JFET input opamp. In my DOGC the OPA1611 does a good job with a DC-offset of about 5...10mV
P.S. I still have some JFETs to match... did not forget it ;-)
Michael