300 Watt audio Amplifier

Posted on Apr 29, 2012

For many application there's no substitute for sheer power- low efficiency speakers, outdoor sound systems, or maybe you like the full flavour of the dynamic range of a high power amp. Whatever your requirement-this super power module should fit the bill. How it works: The amplifier can be divided into three separate parts. These are : the input stage, which consists of Q1-Q9 , a high gain, low power driver; the output or power stage- witch only has a voltage gain of four but enormous power gain; and the power supply. The input stage is a complementary -differential network, each ''side'' with its own current source. Each transistor in this stage is run at a collector currant of about 0.7mA. Emitter resistors are employed to stabilize the gain and improve linearity.

300 Watt audio Amplifier
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300 Watt audio Amplifier - image 1
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The output of Q1-Q5 drives Q7 and Q9. The latter are virtually two constant-current sources run about 7mA collector current. With an input signal these ''current'' sources are modulated out of phase - the collector current of one decreases while the other increases. This configuration provides quite an amount of gain. In between the bases of these two transistors is Q8, the thermal sensing-bias transistor. The voltage across Q8 may be adjusted by TR1, thus setting the quiescent bias current for output stage. The output stage, Q10-Q11, Q13-Q14 and Q16-17, has a gain of about five, set by R44 and R28 plus R29. Diodes D4 and D6 prevent reverse biasing of Q10 and Q11 (otherwise the output would be limited). Protection of the output transistors is provided by Q12 and Q15 which monitor both current and voltage in the output transistors and bypass the base current if the limit is exceeded. Frequency stabilization provided by capacitors C6, C11, C12 and the RC networks R31/C10 plus R46/C15. Frequency response of the amplifier is set by C1 and C7 (lower limit), C6 sets the upper frequency limit. If you want use the Protection DC and Balance/Bridge circuits. All the transistors that are inside the interrupted line are placed on an aluminium corner and he screwed on a suitable heatsink. The transistors Q7,Q10,Q11, Q8, Q9, Q13,Q14,Q16 and Q17 placed on this aluminium corner, with suitable isolation from this.[ETI 4/80] >>>>>>>...

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