This mini amplifier
is based on the Thomson Type TEA2025. In this 16-pin DIL device hides a stereo
amplifier that with a supply voltage of 9 V will provide 1watt output per
channel into a 4-ohm loudspeaker. At full output, the input sensitivity is
about 25 mVpp. If this is too sensitive, a resistor R may be connected between
pin 6 and C7 and between pin 11and C2. The sensitivity then becomes (25+ Y2R)
mV, provided R> 1k. Furthermore, the supply voltage may lie between 3 V and
12 V. The operation of the IC cannot be discussed here, but for those
interested its internal circuit diagram is reproduced in Fig.
The Type TDA1521 from Valvo/Mullard is an integrated HiFi stereo
power amplifier designed for mains fed applications such as stereo TV. The
device works optimally when fed from a ± 16V supply, and delivers a maximum
output power of 2 x 12W into 8 ohm. The gain of the amplifiers is fixed internally at 30
dB with a spread of 0.2 dB to ensure optimum gain balance between the channels.
A special feature of the chip is its built-in mute circuit, which 
