If you want build hi-fi power amplifier about 30watt to 50Watt or 75 watt. Recommend use TDA2050 below, builds by the integrated circuit and PCB layout.
The simple low voltage preamplifier circuit for headphone with tone control that use 1.5V X 2.The transistors as main. For MP3 player or other small source.
This is Active bass boost circuit with PCB layout using IC-741 or LF351 op-amp as low frequency filter circuit diagram ,Select frequency by change RC only.
This is 2 watts + 2 watts Stereo small LM386 amplifier x3 ICs. It is cheap and easy to builds for BCL amplifier,mobile,MP3 player using 6V battery (AA x 4)
Simple audio noise filter circuit for receiver, stereo radio station.Because the stereo system is splits signals-to-noise ratio (S/N), it use simple parts
This is Low noise microphone preamplifier circuit using IC-NE5532, M5218P. Simple circuits but high quality balance-Unbalance Input for dynamic microphone
This is 27MHz CB radio amplifier circuit projects with PCB about 2-3W using V-MOS FET, also use FM range as as the RF amplifier circuit