Can I replace the first input resistor (56k) with a variable resistor (50k) to adjust the volume?

If by "variable resistor" you mean a potentiometer connected appropriately, then yes. Simply making that resistor variable won't work.
Several noise generating high-value resistors in that design, not going to be as quiet as it could be, especially with carbon film.
Using a combination of carbon film and metal film in the feedback network means some distortion is guaranteed by design - best to use metal film throughout.
Not sure of the wisdom of using an attenuation network on the input when you could have just selected the correct gain with the feedback network in the first place.
Using a combination of carbon film and metal film in the feedback network means some distortion is guaranteed by design - best to use metal film throughout.
Not sure of the wisdom of using an attenuation network on the input when you could have just selected the correct gain with the feedback network in the first place.
Yes, but use only a 10k log volume pot.
It will not work well with higher pot values (unless it is a linear pot),
as the 22k input resistor will load down the pot wiper and alter the taper.
Don't use carbon resistors in the feedback loop (or elsewhere), only metal film types.
It will not work well with higher pot values (unless it is a linear pot),
as the 22k input resistor will load down the pot wiper and alter the taper.
Don't use carbon resistors in the feedback loop (or elsewhere), only metal film types.
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