Question about input impedance into blended input capacitors

[Derringer]

There's a circuit that look like this at the input.
My thinking is that the blending pot is so large because the designer expects the user to plug a guitar directly into it ... that and this design allows for less parts.

The rest of my thinking goes, if I decide to buffer the input with something like a non-inverting tl072, would I be able to drop the blending pot down to something like 50K and have things still sound the same?

I'm going to breadboard it and see when I get a moment, but I like to learn from you all as well.

thanks

[Gus]

I would make a spice model of the circuit and the guitar and cable and try different values
Then model it with a opamp before it

Here is something I posted in the past that might help you with a spice model

[Derringer]

Cool, but I haven't learned spice yet. One of these days.

Thanks Gus.

[merlinb]

Cool, but I haven't learned spice yet. One of these days.

Don't forget Tina-TI. It's a lot easier to use than Spice. Hardly any learning curve.
http://www.ti.com/tool/tina-ti

[anotherjim]

If you make that tone pot smaller, you'll only succeed in reducing the operating range - since it's a variable resistor, not a potentiometer. In this case, reducing the bass cut range.

Changing to a low impedance source will mean reducing both input caps anyway.

Without Spice, use a filter design tool for CR high pass. Calculate the input impedance - 68k//220k for the R and try a value that represents the direct path cap and the tone pot on max (start with 4.7nF) and see what the corner freq is. Then try a C value that represents both caps in parallel (pot at min) to see what change that makes to the corner freq. This method assumes you have a low enough source impedance (such as op-amp) that won't change the filter freq.

The value of the tone pot is a matter of how much you need to change the tone. That's a matter of taste, as whatever value it is, it will still go to zero.

My gut feeling is that you can get the new C values pretty quick by just going one size down - 3n3 & 47n?

[Derringer]

Ok, that makes sense.

I just tried it with the intended front end buffer and a 100K pot instead of 500K. I need to play it some more and A/B, but I think I like the 100K pot better. Seems to have more treble than I need on the max throw and sounds fuller in other settings. The capacitors will have to remain fixed though because I already soldered them into the board.

Merlin, I'm in the process of registering with the TI site. They seem rather serious about their programs  .
That and their page seems to be time-ing out on me a lot. So hopefully I'll have a copy of Tina TI soon.

thanks all