If your source has a high quality volume control (as with a few DACs that change volume by adjusting the reference voltage), you can achieve the impedance and power supply benefits mentioned earlier using a high quality, unity gain, buffer, which I believe is similar to what @grannyring‘s well-regarded The Truth preamp is doing, although The Truth provides the volume control too using photo cells. Pass is correct about having sufficient gain in our sources but he also recognized the sonic benefits of an active stage, which is why he designed his B1 buffer. SMc’s VRE-1 is another excellent unity gain line stage (with volume control). Tortuga Audio’s tube preamp buffer is another buffer option (no volume control) at a lower price.
