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Old 14th December 2013, 04:34 AM   #1
Gost22 is offline Gost22  Bolivia
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Default Audio amplifier with uA741 and 2N3055/MJ2955

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?
Thank you for your cooperation!
Attached Images
File Type: jpg SChematic-1.jpg (16.7 KB, 587 views)
File Type: jpg Schematic-N.JPG (59.2 KB, 573 views)

Last edited by Gost22; 14th December 2013 at 05:00 AM.
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Old 14th December 2013, 07:50 AM   #2
PetruV is offline PetruV  Romania
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One cannot power an opamp rated for 15v from 37v,explosion will be instant,but you can try lowering the the rails to 15v and try it so,it is a very common topology in amplifiers
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Old 14th December 2013, 08:18 AM   #3
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It has 2k actually but it's too small for 37v..should be about 7.5k
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Old 14th December 2013, 08:24 AM   #4
sajti is offline sajti  Hungary
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The 2nd schematic looks more promising, but the 3055 is not able to handle the +/-40V supply.
Generally it's very simple, and well known topology.

Sajti
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Old 14th December 2013, 08:30 AM   #5
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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.
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Old 14th December 2013, 09:09 AM   #6
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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).
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Old 14th December 2013, 09:51 AM   #7
Gost22 is offline Gost22  Bolivia
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Quote:
Originally Posted by sajti View Post
The 2nd schematic looks more promising, but the 3055 is not able to handle the +/-40V supply.
Generally it's very simple, and well known topology.

Sajti
To replace 2n3055/mj2955 with MJ15003/MJ15004?
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Old 14th December 2013, 09:57 AM   #8
Gost22 is offline Gost22  Bolivia
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Quote:
Originally Posted by franzm View Post
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).
Is it possible BD679 can be replaced with BD139 and IC LM741 be replaced with a TL071?
This schematic-NEW gave it right?
thanks!

Last edited by Gost22; 14th December 2013 at 10:27 AM.
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Old 14th December 2013, 09:57 AM   #9
sajti is offline sajti  Hungary
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Quote:
Originally Posted by Gost22 View Post
To replace 2n3055/mj2955 with MJ15003/MJ15004?
That looks OK.

Sajti
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Old 14th December 2013, 10:34 AM   #10
Gost22 is offline Gost22  Bolivia
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This schematic-NEW gave it right?
thanks!
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File Type: jpg Schematic-New.jpg (91.3 KB, 514 views)

Last edited by Gost22; 14th December 2013 at 10:38 AM.
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