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svart · 26th February 2009

True.

I was thinking in terms of changing effective input impedances over gain range if you use the volume-pot-in-feedback style. Tweaking for S/N and clipping is fine assuming that you aren't tweaking during actual usage.

I suppose in most BJT opamps this isn't a *big* deal but if sensitive circuits designed around Jfet opamps are used, this could be a bad thing. I just don't like changing a circuit's operation over some range as well as the obvious need for tightly matched(read expensive) pots.

My idea was to gain first, then attentuate. In RF land this is required for good S/N to begin with. The secondary buffer was just to have an easily available driver for the following circuit or to drive a bus but is not required by any means.

But after re-reading his description, I initially thought that he was using the pot as the actual feedback resistor. Maybe I'm mistaken and he meant use the pot as the shunt resistor in a voltage divider feedback network? This would be acceptable.

26th February 2009	#124
svart Gear addict Joined: Dec 2006 Location: Atlanta Posts: 472	True. I was thinking in terms of changing effective input impedances over gain range if you use the volume-pot-in-feedback style. Tweaking for S/N and clipping is fine assuming that you aren't tweaking during actual usage. I suppose in most BJT opamps this isn't a big deal but if sensitive circuits designed around Jfet opamps are used, this could be a bad thing. I just don't like changing a circuit's operation over some range as well as the obvious need for tightly matched(read expensive) pots. My idea was to gain first, then attentuate. In RF land this is required for good S/N to begin with. The secondary buffer was just to have an easily available driver for the following circuit or to drive a bus but is not required by any means. But after re-reading his description, I initially thought that he was using the pot as the actual feedback resistor. Maybe I'm mistaken and he meant use the pot as the shunt resistor in a voltage divider feedback network? This would be acceptable.