Upon testing today, the preamp exhibited 70dB of gain with the Baxandall passive EQ engaged (a big source of volume loss). That's a milestone, but yesterday the preamp was oscillating when I turned up the volume too much. Fixed that as well. Just needed more shielded wire inside. Also, the noise is practically non-existent. The tone is pretty good and probably even awesome by most standards, but I would like it to be a little less colorful and a bit more perfect. Unfortunately, that will come at a price. Todays tests were conducted with no negative feedback in the signal path. By employing some negative feedback I'll be able to get the preamp sounding less colorful and more pristine, but at the cost of gain. Its completely variable and can be adjusted to taste, but I fear that it will dip into the 60dB range or lower once I have it sounding the way I really want it to sound. I'm trying my hardest to avoid having 3 tubes per channel - it currently has two. That extra tube per channel would require a much more expensive power supply, the extra pair of tubes, and additional resistors, caps, wire, labor, etc. I really don't want to see this thing escalate into ultra expensive land. In the end I will do whatever is necessary to get it sounding exactly the way I want... and I am damn picky. Tomorrow I will dial in some negative feedback to taste and hope the overall gain of the preamp stays at or above 60dB. Fingers crossed.
About the Author
Mike Congilosi II, Inventor/Engineer