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Return to Blog3 Watt HI-FI Stereo Amplifier
Posted Jan 25, 2012 at 11:50 am
Figure 1
Tr1 and Tr2 transistors functions as direct coupled voltage amplifiers. R6 resistor, D1 and D2 diodes determine the standby current of complement driver stage (Tr3/Tr4) and output stage (Tr5/Tr6). C3, C5, C6 and R3 help keeping stability. Amplifier’s input sensitivity is 400mA at 4 ohm load and 12V supply and 600mV at 8 ohm load and 17V supply.
Gain can be increased by decreasing R4 value but it is not recommended because of increasing distortion.
Speaker’s ground must be connected directly to the ground of supply stage and must be kept away from the circuit.
Separate supply connections must be applied to the supply connection points.
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2 years ago: This could be very handy and portable, can it be supplied with batteries?
2 years ago: The circuit is just a standard complementary coupled output transformerless amplifier. But the 2N1613 for Tr5 and Tr6 are way too low a power to handle this much output power, even with a heatsink. They should be replaced with something that can handle the current and power, which are mounted on a heatsink. I would use TIP31, or at minimum BD135.
If someone wants to run this off batteries, they had better use rechargeables, because two of these (stereo) will quickly discharge a small battery.
2 years ago: I just noticed a glaring error. There is a connection point between D1 and D2. IIRC, there is not supposed to be any connection there - the diodes are only connected to each other.
2 years ago: I just checked the datasheet for the 2N1613 output transistors. They are good for only 0.8 watt each. These are too low a power and might be able to handle a 16 ohm speaker, will probably overheat with a 8 ohm speaker, and will probably burn out on a 4 ohm speaker. They should be replaced with some transistors on a heatsink. I good choice might be the TIP-31.
2 years ago: hi watson, were you able to make the circuit work? please post your modifications and thanks in advance!