I've built a very basic stereo pre-amp, which is just a gain stage, followed by a cathode follower. Both stages use a 6SN7. It has weak bass, and although I haven't measured it with a spectrum analyzer, I'd swear there is a dip in the upper bass register. Frankly it just doesn't sound that great. Please take a look at the schematic and let me know if I've committed a design flaw that will just suck the life out of a pre-amp.
The gain stage is as basic as it gets (common cathode). It is biased so that it's passing 10 mA (which seems to be a popular point for the 6SN7). It is DC-coupled to a cathode follower. The potential divider between the 2 stages should only attenuate the AC signal, leaving the DC voltage the same as at the anode of the gain stage. The diode between the grid and cathode of the cathode follower is only there to protect the tube from arcing during power-up when the grid is at B+ and the cathode is at ground, and should effectively drop out of the circuit once the cathode starts conducting. This stage settles in when the grid is about 4V lower than the cathode and produces an idle current of ~10mA.
The potential divider is there because I don't really need any gain in my system, but used a gain stage on purpose to add some 2nd harmonic magic. Output voltage (AC) after the divider is ~1/4 of the input voltage.
As you can see, the power supply is fully passive CLC and CRC topology.
Here is my background with building pre-amps. About a year ago, I built an e-bay knock-off of the Jadis J200, using 12AX7s. It had beautiful velvety mid-range, crystal-clear highs, and tight bass, if not particularly strong. However I abandoned that design as it had horrible ground-loop noise that I and a pro amp building friend could never track down. We spent about a month trying to track the inject point.
For my next attempt, I decided to use an octal triode, and found a mu-follower design on the web for the 6SN7. I built it, point-to-point and it worked without a hitch (no ground-loop). It produced full, thunderous bass, so I know the 6SN7 is capable of producing low-end "umph." But the pre-amp had no magic. It was dry and clinical, and didn't get me emotionally involved in the music.
This final attempt was based on the assumption that a basic triode common-cathode gain-stage would be less linear than a mu-follower, and perhaps might give me some warm, inviting music. But it just sounds blah, and there is no low-end. Have I unintentionally created some kind of high-pass filter? Any thoughts would be appreciated.