This amplifier was a sort of - I need to build something - outburst after 5 years of, well, life....

I love diecast boxes... and all the sockets are nice and accessible... It can run on its bottom like this or on its back so it looks like a big amp, with a blank front.

This amp is about as simple as I could get a way with. It has a mosfet (IRF9640/640) push-pull class A output stage with a temp sensing trani to do temperature compensation. (The bias is only stable on these things if you run them at about one amp standing current, a bit hot for me!) the input stage runs off a voltage doubler and is smoothed by a series mosfet to about 60 volts. The two pairs of ECC88s are running in parallel, at about 4mA anode current each, to get the anode impedance down. These run in to a 1:1 single ended transformer wound by Stevens and billington for some thing else. I had terrible problems with hum pick up in the transformers, and ended up turning them round so that they cancel out the hum field of the toroid. I had to add about 10dBs of feedback to make it bareable. This also smooths out the very un flat frequency responce of the tranys. The heaters are all running in series from the positive rail, ~ 26 volts.

I like this amplifer, it is warm and fun and is very flattering to normal hi fi gear. It brings out the goodness they posses, and smooths over the wrinkles. It is always nice to listen to, with fat bass, clean mids and shiny clear treble. Some of these qualities are improved with out feedback at the expense of others.

As the Mrs says, it sings to you.