Output Buffer/Attenuator?

[the_random_hero]

I'm playing with a dual IC distortion at the moment and I have half a dual op-amp left. I was thinking that, instead of the usual volume controls, I could use a inverting stage to vary the gain from something like 2.5 (just as a booster) all the way down to zero. Now, I'm assuming I should be using a log pot for this? The first way I thought of doing this was to have R1 as 10K and Rf as 25K, giving me about the figures I want, but how much of the pots taper is useable below 10K (unity)? Am I just taking the long and complicated way to do something when I could just use a simple pot?

[GibsonGM]

I'd try it with a simple pot (from the junk box, y'know....) and see how it works, and then if it seems to need more control or a different taper I'd mess with the pot value/taper or tapering resistors....make it rough, then fine tune it )

[David]

I'm playing with a dual IC distortion at the moment and I have half a dual op-amp left. I was thinking that, instead of the usual volume controls, I could use a inverting stage to vary the gain from something like 2.5 (just as a booster) all the way down to zero. Now, I'm assuming I should be using a log pot for this? The first way I thought of doing this was to have R1 as 10K and Rf as 25K, giving me about the figures I want, but how much of the pots taper is useable below 10K (unity)? Am I just taking the long and complicated way to do something when I could just use a simple pot?

GEOFEX.  Adjusticator.  RG.  'Nuff said.

[~arph]

I read today http://www.eng.yale.edu/ee-labs/morse/compo/sloa058.pdf That many opamps become unstable when used at less than unity gain.
The mentioned link also provides what they (texas instruments) think is the correct way to attenuate. (sub R3 for a linear pot say 100k)
Their circuit can easily be adapted to boost as well by increasing the feedback resistor.

[Processaurus]

You can make a nicer volume control than a traditional log pot volume control with a linear pot and tapering resistor, like in this article, and follow it with a fixed, non-inverting gain stage of 2.5x.  Then the phase isn't flipped, the output impedance is still low.

[Mark Hammer]

The advantage of setting the second stage for a fixed gain and following it with a volume pot is that the inverting stage can include a feedback cap to control hiss or otherwise shape the tone.  Any tone shaping achieved in the gain stage will then generally hold across all output levels.  In one placed a cap and a variable resistance in the feedback loop of an inverting stage, then the high-end rolloff would change as you reduce the gain/resistance.  I can envisage situations where you might well want that to happen, but I suspect in most instances the opposite would be true.

[the_random_hero]

I'm playing with a dual IC distortion at the moment and I have half a dual op-amp left. I was thinking that, instead of the usual volume controls, I could use a inverting stage to vary the gain from something like 2.5 (just as a booster) all the way down to zero. Now, I'm assuming I should be using a log pot for this? The first way I thought of doing this was to have R1 as 10K and Rf as 25K, giving me about the figures I want, but how much of the pots taper is useable below 10K (unity)? Am I just taking the long and complicated way to do something when I could just use a simple pot?

GEOFEX.  Adjusticator.  RG.  'Nuff said.

Wow, that's exactly what I was looking for. I'm considering scaling this pedal down a bit (I think the current draw will be too high from running off a MAX1044 if I use two NE5332's) to only include one gain stage and the Adjusticator.