Audio amplifier with uA741 and 2N3055/MJ2955

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Gost22

Gost22

Banned
Joined 2012
Hi all!
Does anyone has made ​​amplifiers under this schematic?
Is this is a good schematic (circuit) and should make some changes for the power supply for the Ucc=+/-40V?
Is this Schematic-N is better?;):confused:
Thank you for your cooperation!
 

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aardvarkash10

aardvarkash10

Member
Joined 2007
cant vouch for the rest of the circuit, but I can say that with the supply to the opamp regulated as shown, its not going to explode at all, and if the zener is suitably rated the 2k resistor is fine. Ohms law if you want proof, but 25 volts across a 2k resistor is going to generate around 1/3 of a watt of heat. Smoke is an unlikely result.
 
F

franzm

Member
Joined 2010
According to the datasheet the 741 is internally compensated for unity-gain and pin 8 is not connected. So the 10pF capacitor is useless.
Its slew-rate is also on the low side (0,5 - 0,7V/µs). This gives an over-all slew-rate of max. 5V/µs. A NE5534 (with those 10pF or more) will give better results.
The second schematic should have better thermal stability but the component values of the bias-spreader are not correct (BD689 is a Darlington, VR1 should be placed in the B-E branch).
 
Gost22

Gost22

Banned
Joined 2012
franzm said:
According to the datasheet the 741 is internally compensated for unity-gain and pin 8 is not connected. So the 10pF capacitor is useless.
Its slew-rate is also on the low side (0,5 - 0,7V/µs). This gives an over-all slew-rate of max. 5V/µs. A NE5534 (with those 10pF or more) will give better results.
The second schematic should have better thermal stability but the component values of the bias-spreader are not correct (BD689 is a Darlington, VR1 should be placed in the B-E branch).
Click to expand...
Is it possible BD679 can be replaced with BD139 and IC LM741 be replaced with a TL071?:confused::(
This schematic-NEW gave it right?
thanks!
 
Last edited:
CBS240

CBS240

Member
Joined 2005
Since the output stage is a feedback pair (common emitter) then the op amp is not responsible for the voltage gain. A lower voltage source for the op amp is required and will not affect the limit of the output voltage swing. Sure the resistor's current drops out the voltage but at the instant of power up, destructive voltage could possibly occur across the op amp. It is just good practice and good for reliability in electronics that devices, especially BJTs are not subject to Vceo breakdown voltages as it reduces the life expectancy significantly.:)
 
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