LAB10 Audio Amplifier Project

lineup · 8th January 2006, 10:54 PM

This is an experimental and easy build audio amplifier.
You can make changes and improvements in several ways.
The possibilities are endless!

Amplifier Details in this PDF:
LAB10 Audio Amplifier
More info at this website:
http://www.engga.uwo.ca/ece241b/

Attachment shows the basic circuit for
LAB10 Audio Amplifier

jaycee · 9th January 2006, 08:13 AM

The op-amp follower is a pretty common idea. They make quite good headphone amps too

peranders · 10th January 2006, 11:02 AM

Quote:

Originally posted by lineup
You can make changes and improvements in several ways.
The possibilities are endless!

.... sure! 741 as input stage isn't very exciting. LM358 is possibly even worse but almost every other opamp is better

baggins · 10th January 2006, 02:34 PM

I used to make guitar practice amps using 741,s into h/phones they worked great you could over drive them into clipping distortion for effects if you wanted.
There was a better alternative with 2 amps in the 8 leg package I think
it was a 1448 I used these to make a disco console coupled to 125
watt amplifier modules from greenweld electronics it all worked successfully they are simple and reliable devices.

regarding Darlingtons Sony use them in multiples in the output stages of their home cinema amplifiers -Sanken 2448 & 1620

carlosfm · 10th January 2006, 11:44 PM

The feedback of the op-amp should be connected to the output of the power amp.
No coupling caps (C1/C3) needed, and use a fet input op-amp, non inverting.
Some small changes to that circuit would make it perform better.

Bazukaz · 16th February 2006, 11:10 PM

Won't this amp run into thermal runaway ? I think emitter resistors are missing.

lineup · 16th February 2006, 11:25 PM

Quote:

Originally posted by Bazukaz
Won't this amp run into thermal runaway ? I think emitter resistors are missing.

In fact this is a true Class B amp.
there is no bias in output stage ( or very very little )

'bias voltage' is set by 3 diodes ~3x0.6 = 1.8 volt

but to turn two Darlingtons on, we need, more than 4 Base-Emitter drops

normal turn on for one darlington is something like 1.0V
in this case we need a bias voltage of ~ 2.0 volt to turn two darlingtons

So 3x0.6V = 1.8V is not enough

destroyer X · 17th February 2006, 09:38 PM

I love those simple circuits....this 741 is very famous, and was used since the seventies...it is nice.

thanks

Carlos

rinox · 22nd February 2006, 03:34 PM

741

LF351: Jfet Input

Check the pinout, i think it' s not the same.
By the way, it's a good newbie project.

lineup · 22nd February 2006, 03:41 PM

Quote:

Originally posted by rinox
OP741, uA741
Check the pinout, i think it' s not the same.
By the way, it's a good newbie project.

Pinout is standard for single Op-amp.
+input - pin3
-input - pin2
+Volt - pin7
-Volt - pin4
Output - pin6

We should not use uA741 for audio anymore.

Good replacement for uA741 could be:
NE5534
TL071
OPA134
AD797

10th January 2006, 02:34 PM	#4
baggins diyAudio Member Join Date: Jan 2006 Location: haverfordwest,pembrokeshire	op amps & darlingtons I used to make guitar practice amps using 741,s into h/phones they worked great you could over drive them into clipping distortion for effects if you wanted. There was a better alternative with 2 amps in the 8 leg package I think it was a 1448 I used these to make a disco console coupled to 125 watt amplifier modules from greenweld electronics it all worked successfully they are simple and reliable devices. regarding Darlingtons Sony use them in multiples in the output stages of their home cinema amplifiers -Sanken 2448 & 1620 __________________ heretics are sometimes right

17th February 2006, 09:38 PM	#8
destroyer X diyAudio Member Join Date: Feb 2004 Location: Recife - Brasil Northeast	Lovely amplifier Line up..thank you to show it to me I love those simple circuits....this 741 is very famous, and was used since the seventies...it is nice. thanks Carlos __________________ Try to build an amplifier folks ... it is pure adrenaline!.. when not work first time, then becomes a nice challenge...and we usually overcome the trouble... and we feel very well to be mastering the machine.

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9th January 2006, 08:13 AM	#2
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	The op-amp follower is a pretty common idea. They make quite good headphone amps too

10th January 2006, 11:44 PM	#5
carlosfm Banned Join Date: Mar 2003 Location: Lisbon, Portugal	The feedback of the op-amp should be connected to the output of the power amp. No coupling caps (C1/C3) needed, and use a fet input op-amp, non inverting. Some small changes to that circuit would make it perform better.

16th February 2006, 11:10 PM	#6
Bazukaz diyAudio Member Join Date: Nov 2005 Location: Vilnius	Won't this amp run into thermal runaway ? I think emitter resistors are missing.

22nd February 2006, 03:34 PM	#9
rinox diyAudio Member Join Date: Oct 2004	741 LF351: Jfet Input Check the pinout, i think it' s not the same. By the way, it's a good newbie project.

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