using valve.
http://www.geocities.com/TimesSquare/1965/project.html
DIY high power MOSFET amplifier 200W rms into 8 ohms OR 350W rms into 4 ohms.
http://users.swing.be/edwinpaij/ampli_mosfet.htm
http://www.aaroncake.net/circuits/mixer1.htm
Based on LM386. The circuit amplifies the input signal by 20X. A gain of 200X can be obtained by connecting a 10uF capacitor between pins 1 and 8.
http://www.reprise.com/host/circuits/lm386.asp
amplifier with 382W to 8 ohms power rating, can drive speakers at 2-16 ohms range.
http://www.ptt.yu/korisnici/s/r/srmarkovic/poweramp.htm
used the same type of N-channel FET as the output transistor. With an N-channel FET the current generator and the output transistor will have the same characteristics according to thermal behavior and distortion.
http://www.tanker.se/lidstrom/eng/zeni.htm
another very simple audio preamp to build. all parts should be available at your very local electronics shop.
http://www.reconnsworld.com/audio_singleicpreamp.html
This elevon mixer is designed to be used in transmitters which use an encoder IC. (NOT Flip Flop stages).
http://www.uoguelph.ca/~antoon/gadgets/mixer.htm