Will adding an input volume control mess with input impedance?

[lowvolt]

If an input volume pot is installed on a simple circuit (or I guess any circuit), y'know just a simple voltage divider type volume pot setup right off the input jack, will it goof with input impedance enough to matter?

How about with a circuit that has a buffered input (Tube Screamer perhaps)?

And while we're at it, how about an output level control, same setup, just a simple voltage divider type pot control.

If "yes" to either input or output, is it best to use a very high value for the pot?  Such as a 1m pot for the input volume control?  Or would it even matter?

Thank you. 

[gcme93]

A volume pot like that after the input buffer should be fine. The buffer is has an extremely high input resistance, and a very low output resistance so will negate the changes a volume pot makes.

[R.G.]

Correct. If you put a pot after the input jack, it will always lower the input impedance. Whether it lowers it a lot or only trivially depends on the existing input impedance value. But it will always lower it.

If there is a buffer, in general the buffer makes the volume control's lower impedance not matter to the driving signal from the input.

Very high value pots have their own problems, not least of which is that they can cause frequency losses in the high end from parasitic capacitance.

[Keppy]

If the circuit already has, say, a 1M pulldown resistor, you could replace that with a 1M pot without messing with the input impedance too badly. I think.

[lowvolt]

A volume pot like that after the input buffer should be fine. The buffer is has an extremely high input resistance, and a very low output resistance so will negate the changes a volume pot makes.

I should have been more clear ... mount the pot right off of the input jack.  I'm aware that putting it after a buffer would be of little consequence, but how about before a buffered circuit?

AND

If I were to elect to use an input level control (like maybe with an unbuffered compressor to prevent hot pickups from clipping it) what is *rule of thumb* acceptable for a value of the pot used?

Thanks for all the helpful replies!  Certainly helpful! 

[lowvolt]

If the circuit already has, say, a 1M pulldown resistor, you could replace that with a 1M pot without messing with the input impedance too badly. I think.

The only issue I can see there is when the input pot is maxed out then you have no pulldown happening.

[lowvolt]

......If there is a buffer, in general the buffer makes the volume control's lower impedance not matter to the driving signal from the input. ....

This makes a lot of sense.  The buffer will ~correct~ the crappy impedance of the pot all by itself.

So using an input level control either before or after an input buffer won't have much negative consequence on things (as far as loading down the input source), do I have that right?

[Keppy]

If the circuit already has, say, a 1M pulldown resistor, you could replace that with a 1M pot without messing with the input impedance too badly. I think.

The only issue I can see there is when the input pot is maxed out then you have no pulldown happening.

Wrong. When maxed, the 1M pot then functions the same as the 1M pulldown resistor which it replaced in this hypothetical scenario. Any variance to the input impedance would only happen as the pot gets turned down, at which point part of that 1M impedance goes from being in parallel to the impedance of the components following the pot to being in series with them, while the component that remains parallel gets smaller and smaller.

In other words, when maxed, the pot has the same effect as the pulldown resistor. When turned down, things begin to change, but not too badly. I think.