op-amp to drive +/-10V analog servo from old +/-5V controller

[Doddy]

If you're driving a single servo (I don't know the interface to these, but I'm going off your post) - and the drive is +/-10v wrt a common ground, then you need only one non-inverting amplifier.

Capacitors - pick a couple of 100nF ceramic capacitors and locate them close to the op-amp, between positive&ground, and between negative&ground.

Regarding which op-amp - how quickly will the signal change?, the one you originally picked had, I think, a gain/bandwidth product of a pretty miserly 75kHz, but if the signal is just driving an axis then I that'd be absolutely fine. If it was driving a spindle then it should still okay given the low gain you're looking at.

[AndrewMawson]

Also the gain is only 2 (ratio of feed back resistor to input resistor) so the needed gain / bandwidth is fairly modest as well

[Robin Hewitt]

I don't think we need worry about the slew rate

[paulus.v]

I have selected some of the available op-amps but I cannot decide. I dunno why are so many of them...

They are ordered by price with the expensive first: LM301; LT1001CN8; LF442CN; NJM4580; BA15218; LF356N; UA747-14P; MC33078P; NE5534N; LM318N08; NJM4580L.

I do not get how I use only one op-amp if I have +5V and -5V input and I need +10V and -10V output? I see in the schematic only one input and one output plus ground.

[Doddy]

This goes back to my previous reply where I presented an assumption that your servo only needs a signal, variable from -10V to +10v with respect to a common ground. So, one signal, capable of any voltage between -10V..+10V. For that, a single Op-Amp, the output of which is connected to the servo, and the other servo input connected to ground.

It's possible, though without any literature we have no means to corroborate, that the servo requires a differential drive - with one signal increasing from 0..+10V, whilst the other input decreases from 0..-10V, in which case you certainly would need 2 op-amps, or a specialised op-amp that provides the differential drive. Such a signalling regime is good for noise immunity.

Can you offer any of the literature that you have for the servo just so we can be certain of the advice offered?

[paulus.v]

Yes, my bad. There is one signal +/-10V and ground.

[paulus.v]

Now the question is how accurate will be the 0V, where the motor should stand still... Some chips have some sort of balance but don't understand what it is for.

[Doddy]

Yes some op amps allow you to set precisely the 0v offset voltage, but not the original op amp that you specified. These are used when precision is required, and it's unclear whether you will need this or not. If in doubt code an op amp that supports this and reference the data sheet for how to use it (a common use is a potentiometer between the balance pins with the wiper connected to -V, but that's not due for all opamps

[paulus.v]

Yes some op amps allow you to set precisely the 0v offset voltage, but not the original op amp that you specified. These are used when precision is required, and it's unclear whether you will need this or not. If in doubt code an op amp that supports this and reference the data sheet for how to use it (a common use is a potentiometer between the balance pins with the wiper connected to -V, but that's not due for all opamps

I have linked to a dozen op-amps in a previous post. Please point me out one of them if you have the time. I need a robust one.

The 0V is important as the positive voltage will turn the motor in one direction and the negative in the other so at 0V it should stand still. But I could filter out a "dead zone" from the drive settings if necessary.

[paulus.v]

Capacitors - pick a couple of 100nF ceramic capacitors and locate them close to the op-amp, between positive&ground, and between negative&ground.

Should I put the capacitors between the power supply pos/neg and ground or between pos/neg and ground op-amp input?