I'm itching for a new project. I'm thinking about building the audio amplifier project presented in the AAC experiments (http://www.allaboutcircuits.com/vol_6/chpt_6/10.html). I have a couple of questions, though...

1. If you've built one, did it perform as expected?
2. Would this be a good way for my wife to use her iPod without headphones?
3. The crossover distortion is a concern...how bad are we talkin' here?

Thanks.

 

I checked it out, and there's one thing I just don't understand. Shouldn't there be a diode and resistor on the top side of that circuit as well? Like this?

The comment on the page doesn't do a good job in explaining why there is only one diode there.

I use one diode to provide a 0.7 volt bias voltage for the push-pull pair. This is not enough to eliminate the "dead" signal zone, but it reduces it by at least 50%:

Apart from that, the circuit looks fine and should function fine. Give it a shot!

TheComet

 

1. Depends upon what you mean by "expected". It's an interesting project to learn the basics of a small audio amp, but its performance is likely just mediocre.
2. I wouldn't recommend it for that purpose.
3. Likely noticeable in the sound, particularly at low signal levels. If you use two diodes as TheComet suggested, making it into a Class AB amp, the bias current through the output transistors could become excessive.

If you want something that sounds good, I recommend using an IC audio amp. They are relatively simple to use and have good performance. If you are going to operate from a battery you might want to consider some of the Class-D (switching) amps available, such as from TI, that are much more efficient then Class B or AB amps.

 

Build it on a solderless breadboard then you can try it out first. The only issue would be the TO-220 transistors which probably need a heat sink and won't snap into the board. You can use 3-pin molex jacks such as these for a poor man's socket:
http://www.allelectronics.com/make-a-store/item/CON-243/3-PIN-CONNECTOR-W/HEADER-0.1/1.html

That said, I haven't tried this setup so I can't answer to the sonic quality. It's probably not going to sound like a Bose home theater system.

 

It is good to thermally couple the diodes to the output transistors.

 

Build it on a solderless breadboard then you can try it out first. The only issue would be the TO-220 transistors which probably need a heat sink and won't snap into the board. You can use 3-pin molex jacks such as these for a poor man's socket:
http://www.allelectronics.com/make-a-store/item/CON-243/3-PIN-CONNECTOR-W/HEADER-0.1/1.html

That said, I haven't tried this setup so I can't answer to the sonic quality. It's probably not going to sound like a Bose home theater system.

Nice idea, thanks!

 

If you want something that sounds good, I recommend using an IC audio amp. They are relatively simple to use and have good performance. If you are going to operate from a battery you might want to consider some of the Class-D (switching) amps available, such as from TI, that are much more efficient then Class B or AB amps.

I was planning on going with a battery. The biggest downside to the circuit was the need for negative voltage and such...large...voltage requirements. Swinging rail to rail +12/-12 is a heck of a feat for battery needs. I was wondering how heavy four 6V cells would be, LOL.

I thought the TL082 was an audio amp, but I'm looking again now and it seems to be a general duel op amp. I guess my reading comprehension needs some serious work.

Any suggestions as to a circuit using an audio IC that would run on a single supply using one or two 9V batteries AND sounded good enough for the wife to listen to her iPod?

 

This could be difficult. This is to drive speakers and not headphones/earbuds, right? A 9V battery has a typical "intended" current drain of about 15mA. If you're driving an 8Ω speaker, that would represent an "allowed" voltage of no more than 0.12V RMS. That would definitely not give you the Bose home theater volume you may be looking for If you remember the 80s when boom boxes were popular, those usually ran off 6-8 D or C cell batteries. 8 C cell batteries would give you 12V at a total "intended" current drain of 800mA which would be the equivalent of driving an 8Ω speaker at 6.4V RMS and would allow for 5.12W of power (or 2.6W/channel). Also, a single C cell battery has more than 10X the lifespan of a 9V when drawing the same current.

Here is some source data:
http://www.techlib.com/reference/batteries.html

 

This could be difficult. This is to drive speakers and not headphones/earbuds, right? A 9V battery has a typical "intended" current drain of about 15mA. If you're driving an 8Ω speaker, that would represent an "allowed" voltage of no more than 0.12V RMS. That would definitely not give you the Bose home theater volume you may be looking for If you remember the 80s when boom boxes were popular, those usually ran off 6-8 D or C cell batteries. 8 C cell batteries would give you 12V at a total "intended" current drain of 800mA which would be the equivalent of driving an 8Ω speaker at 6.4V RMS and would allow for 5.12W of power (or 2.6W/channel). Also, a single C cell battery has more than 10X the lifespan of a 9V when drawing the same current.

Here is some source data:
http://www.techlib.com/reference/batteries.html

I'm not looking for super-high quality. I'm thinking more along the lines of powered PC speakers. This is just a tinker project. I'm only going with one speaker (will combine stereo inputs to mono) and if the battery life is only four or five hours, that's OK. I do stuff like this to learn - and - to see if I can do it without letting the magic smoke out of the box.

If there's another way, or if anybody has a better circuit (using the TL082 or generic transistors) I'd be glad to try it.

 

My main point was that the 9V battery probably wouldn't last anywhere near 4-5 hours at a reasonable volume.

Here are a couple links to an LM386 amplifier circuit:
http://www.eleccircuit.com/amplifier-audio-small-to-use-with-9v-battery-operated/

http://tymkrs.tumblr.com/post/6490006992/lm386-audio-amplifier-lessons-learned

 

My main point was that the 9V battery probably wouldn't last anywhere near 4-5 hours at a reasonable volume.

Here are a couple links to an LM386 amplifier circuit:
http://www.eleccircuit.com/amplifier-audio-small-to-use-with-9v-battery-operated/

http://tymkrs.tumblr.com/post/6490006992/lm386-audio-amplifier-lessons-learned

Ahh, gotcha. I guess I'll keep looking, then. I might build that Class B amp just to see how it sounds and also for the experience. Thanks for the links.

 

Make sure you post your results!

 

Make sure you post your results!

Will do. I'm still looking for alternates. Considering, at the moment, using two 9V batteries and a floating ground for the Class B. It may not work, but hey, we learn through failure just as well as we learn through success.

 

Companies like Texas Instruments (www.ti.com) and National Semiconductor (now part of Texas Instruments) make a variety of low-power audio output devices. For example the National Semiconductor "Boomer" series. These perform a lot better than the ancient LM386 and are available in stereo versions.

Do a search on Digikey or Mouser to get an idea of what options are available.