Preamp topology regarding placement of Pot

[dine1967]

Iam not qualified enough in the electronics field so I put this question to the fellow fourm members. I have built a preamp P88 from ESP which is essentially an opamp-pot- opamp. The gain settings can be altered as desired. According to Rod, the pot in the middle need not be of very high quality as it doesn't contribute to the sonics due to the opamp ahead of it in the circuit.
I have seen most of the preamp designs here and commercially where there is pot at the input (usually) and some designs where there is pot in the output. So whats the advantage one gains by having the pot at the input followed by a buffer/ opamp? Isn't it advantageous to have the input buffered followed by pot ? Any thoughts in this matter would be greatly appreciated.
Iam asking this as I wish to upgrade my preamp and specifically looking towards building a opa637+buf634 preamp.
thanks,
Dinesh

[Gopher]

The first opamp acts a high impedance buffer to prevent the source being loaded by too low a value of pot, thereby creating distortion. Without the second buffer the output impedance of teh preamp will depend on the value of the pot and can be quite high. Together with the capacitance of any interconnect cable to teh power amp, this high output impedance can roll off the treble and affect the sound.

You can just use a pot without either buffer (passive preamp) but you might get variable results and sonics depending on your source drive capability and power amp input impedance as well as on the interconnect cable.

I would suggest you get rid of the first buffer and go for an actively buffered pot.