basic buffer quickie.

Just a quickie to be sure..
When adding a unity gain op-amp buffer after a pot, do I need an extra ground reference R close to the op-amp input, or is it sufficient to rely on the pot resistance to ground to serve the purpose?
As I cannot get suitable log pots here (seriously, it's deepest mexico) I'm loading the pot by putting a 10k R to ground in parallel with wiper to ground. So there'll always be at least 10k to ground before the op-amp input. Does this sound ok?
Any thoughts so I can rest easy, and avoid ordering a few more resistors? Thanks. jeth

There are fault conditions where you might want that additional R to ground, but strictly speaking you don't need it unless, as you are already doing, you want the specific loading effect to change the characteristic of the pot.

If you had the log pot to begin with you might still want a largish R to ground in addition, so that in the event the wiper of the pot became intermittently open, the op amp would still have a ground reference and not have its input and output go sailing off to some extreme voltage.

Another consideration about buffers after pots: if the buffer has much input bias current, you will get a fair amount of noise when you operate the pot. If you are using an FET input op amp you can typically get away with direct coupling, but bipolars can benefit from a.c. coupling---cap between wiper and opamp input, resistor to ground from opamp input to ground for d.c. reference. In your case that resistor could be your 10k for approximating the taper you want. Make the C large enough so it doesn't limit your low-frequency response.

Many thanks for the reply. I appreciate the extra information, obviously the question screamed noob at you. Great to ask for an answer and learn something else as a bonus. I've read before about coupling caps and pot noise, but didn't really know when it applied..Now I do.

Once again my parts choice is restricted by my location, the only really viable chips I can get my hands on happen to be TL072. As they're FET input I guess I can risk direct coupling and save myself another trip to the parts store..or would you suggest including them as a precaution anyway?

[quote author="jeth"]
Once again my parts choice is restricted by my location, the only really viable chips I can get my hands on happen to be TL072. As they're FET input I guess I can risk direct coupling and save myself another trip to the parts store..or would you suggest including them as a precaution anyway?[/quote]

An 072 should not be a problem with direct coupling.