Pre-amps are the hardest part to get right in system matching and have caused more anxiety than any other component. Over the years I’ve tried several commercial and DIY designs ranging from tubes, op-amps and discrete. All exhibited some issues such as too coloured, too sterile, too much gain, over blown, veiled.
A passive pre using only the potentiometer provided the clarity and transparency required but passives can lose dynamics and roll off if the impedance matching is not perfect (which is very difficult to achieve). Enter the Burson Buffer which was trialled with a 10K Alps Blue Velvet. Finally it all clicked together with the transparency required, the dynamics were restored and no roll offs. To simplify the setup, I used the Burson Buffer modules inside the pre case and wired in after the potentiometer. All it does is provide the impedance matching and allows the signal to flow unimpeded to give very neutral sonics with a high level of transparency.
Great value and have recently bought a second Burson Buffer to go between a CD player and a ChipAmp.