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Old 10th September 2011, 11:24 AM   #21
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Hey that runoffgroove site is fantastic!

As for that circuit could I don't have such a transistor, so.. :-) then again, could i substitute that part with a simple inv amp built with a 741 (I happen to have many)?

If its not good please I'm very interested to understand the reasons

Thanks everyone for bearing with my crazy questions, I do appreciate your answers and patience :-)
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Old 10th September 2011, 11:26 AM   #22
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by xchip View Post
thanks for the pointers guys! I've been using op amps to amplify small signals and feed them into a scope but never drove a speaker, this was my first naive attempt.

So the 741 is bad because of its high output impedance and low output current... if I stack one 741 on top of another wouldn't I get double output current and half output impedance?

gaetan: So what makes an opamp a good candidate for audio? Just output current and low output impedance?
"Stacking" opamps... have a look at this (link in first post). So yes it can be done but you need a lot to make it worthwhile.
Doug Selfs NE5532 Power Amp. Thoughts anyone !

The term opamp generally refers to low power devices. There are dedicated "power opamps" that have a huge following. Check out the "Chip amp" forum on here.
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All you need for your 741 is add a couple of high gain transistors and a simple bias network to drive a speaker... great for learning.
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Old 10th September 2011, 01:56 PM   #23
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Quote:
All you need for your 741 is add a couple of high gain transistors and a simple bias network to drive a speaker... great for learning.
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Old 10th September 2011, 04:21 PM   #24
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hehe, I'm glad that the idea of stacking amps was not that crazy :-)

So do you think I could use a couple of 2n2222 after the 741 to drive a speaker?

I'll try to get a nice biasing and try it out in the simulator, the whole point is to learn!
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Old 10th September 2011, 04:29 PM   #25
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If you count the higher impedance headphones (>=100ohms) as speakers.
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Old 10th September 2011, 04:58 PM   #26
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Just a question regarding the use of ua741 in a power supply, would the modern versions like lm471 be less noisy, or superior to the ones form the 80's?
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Old 10th September 2011, 05:32 PM   #27
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by xchip View Post
hehe, I'm glad that the idea of stacking amps was not that crazy :-)

So do you think I could use a couple of 2n2222 after the 741 to drive a speaker?

I'll try to get a nice biasing and try it out in the simulator, the whole point is to learn!
This is the starting point... an NPN and PNP power transistor such as a TIP41 and TIP42

The output of the opamp goes to the transistor bases as shown.

Whatever feedback nework you had connected to pin 6 (opamp output) now moves to the emitters of the transistors.

With any DC coupled amp like this and particularly as you are learning it's imperative that the speaker be protected. That means checking the output of the amp is at zero volts DC with no signal and perhaps adding a couple of back to back electroylitics to prevent damage if a fault or mishap occurs.

Edit... the grey line is the feedback network, missed the resistor out drawing it
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Old 10th September 2011, 05:37 PM   #28
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digits: likely they are better quality but whether you will see that on the output depends a lot on the circuit topology and layout.
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Old 10th September 2011, 06:30 PM   #29
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Thanks, I want to upgrade my signal generator, which is quite old and has lots of old IC's from back in the day when I was at school in the 80's and early nineties.
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Old 10th September 2011, 09:03 PM   #30
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Quote:
Originally Posted by xchip View Post
thanks for the pointers guys! I've been using op amps to amplify small signals and feed them into a scope but never drove a speaker, this was my first naive attempt.

So the 741 is bad because of its high output impedance and low output current... if I stack one 741 on top of another wouldn't I get double output current and half output impedance?

gaetan: So what makes an opamp a good candidate for audio? Just output current and low output impedance?
Hello xchip

The741 are bad also because it have a very low slew rate of .5 v/us , that's too slow and it cause slew induced distortions, and that opamp do have a low gain bandwidth.

A good opamp should have a low thd, a good gain bandwidth and a high slew rate, the LM5532 and LM5534 do have arround a slew rate of 9 v/us

Bye

Gaetan

Last edited by gaetan8888; 10th September 2011 at 09:12 PM.
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