The mighty BUF-03.
A proper and very good preamplifier DO NOT have his own mark on the sistem at all.The best comparing is a single wire but.....there is a few issues....
With an excellent simple Circuit and a very good Powersupply, this Preamp has the potential to sound truly stunning. However, I believe that the Parts-Quality and Implementation makes a HUGE contribution to the sound.
A buffer is a unique device; among its many characteristics are an extremely high input impedance, an extremely low output impedance, hyper-fast signal-handling speed, and the ability to source a goodly amount of current.
These devices are often called on to drive ultra-high-frequency video signals over great lengths of coax in 75 ohm circuits, and needless to say, a good buffer wets its pants with laughter at the thought of carrying mere audio signals; to call these devices "overkill" for audio would be an understatement!
But I happen to LOVE overkill, and so I began rifling through every data book I could get my hands on, looking for a suitable buffer. After listening to many promising units, I finally settled on the Precision Monolithics BUF-03. Offering a voltage gain of unity, this little FET-input, metal-can buffer boasts some pretty scary specs: 250V/µs slew rate; 63MHz bandwidth; 70mA peak current drive capability; an input impedance of 500 trillohms (5 x 10 (footnote 11) ohms!); and an output impedance of only 2 ohms! Not long after I decided upon the BUF-03, I learned that Kinergetics uses it for the output stage of their KCD-40 CD player.
By placing the BUF on the output of the attenuator, I achieved both of my original design goals: it lowered the output impedance to a couple of ohms, and since the BUF's own input impedance is so insanely high, it freed me up to go to a higher-value attenuator, thus raising the input impedance of the preamp.
Of all the different pots I tried, the best-sounding was the high-grade japanese TKD 2P65.It's build extremly well and very very precise.
Another good candidate can be Penny & Gilles and I'll stay away from so called "audiophile" Alps ,etc.
I also use Elma input switch,well know for high quality stuff.
I attach copper heatsinks to the little BUF-03s, as these class-A buffers run real hot.
The result is amaizing.