This design started out as request from an audio nut friend. It uses an EF86 as a pre-amp, a 12AX7 as the phase splitter and a pair of Sovtek 6550A beam power pentodes in a class AB output stage. The design makes about 40-50W into 8 ohms, with a THD figure of under 0.5% from 100Hz - 20kHz. Distortion is a little higher below 100Hz due to the output transformers - which are a little under sized due to my friends (and my) budget. A toriodal power transformer was utlized to keep hum noise low. Besides typical left and right level controls, I added a contour control that effectively tilts the frequency response "up" (meaning a bit brighter) or "down" (meaning a bit warmer) centered around 600Hz.
The sound of this amplifier is simply stunning! I'm a skeptic when it comes to audio voodoo magic - but listening some CD's through this amplifier (NAD 1130 pre-amp and my home made ETON clone speakers) revealed stuff I'd never heard before. My wife actually walked in the room thinking I had a friend over because she heard the individual background vocalists so clearly! I'm not going to burden this page with too many words...if you build or buy this amplifier you'll absolutely love it! It has become the one I listen with most often.
Contact me at geoff@bandonelectronics.com if your're interested in this amplifier. I liked it so much I decided not to give it to my friend after all - I built him another one!