Dear All,

I recently ripped apart an old Sony Stereo system I had. I also just built a new computer, but I have no speakers for it. Although the Sony system is pretty old, I'm sure the speakers are of decent quality. I am hoping to build my own amplifier system and hook the speakers up to my computer.

I plan to connect the audio out of my computer to my amplifier by using either a male-male 3.5mm jack (like those used in aux inputs), or a 3.5mm to RCA cable. Not sure if one is better than the other, but they both look to do the same thing.

I'm only looking for a simple amp, with an on/off and volume/gain control (using a potentiometer). I've attached the PDF of the Sony speaker. It says that the stereo system outputs 2.3W to each speaker (3.2Ω). I'm also hoping to re-use the amplifier inside the stereo system. Although I've read 2.3W is very little for a speaker, and I'm sure there are better amplifiers out there nowadays, I want to give it a try and see how the speakers sound. If they are horrible, then I will re-design it with better a better amplifier. Everything will be run off 9V.

I am planning to build the simple amplifier shown here:
http://www.electronica.ro/audio/LA4597.shtml

This looks similar to what is inside the Sony stereo system as well. I'm curious as to whether I need a pre-amplifier, and where I would put a potentiometer for volume/gain control. I'm also curious as to what type of amplifier this is (Class A, B, AB, D?) and if this amplifier sucks...why? Would it be possible to choose better cap values in order to make this amplifier better? I don't really know how to perform those calculations.

Ideally, I'd like something small like this: http://www.8audio-mall.com/servlet/the-490/Tripath-TA2024-Stereo-Power/Detail. I am by no means an audiophile, so I don't need or want something amazing. As long as it does not sound horrible, I will be OK with it. I usually use my headset anyways, but thought it would be a cool little project.

Thanks,
Philip

 

Oh, I was also wondering if I could cut the ends off old headphones for testing purposes. That is, plug the 3.5mm headphone into the audio out and use the left & right terminated wires as my inputs for the amplifier so I can do some tests on a breadboard. Is this possible?

Thanks!

 

Oh, I was also wondering if I could cut the ends off old headphones for testing purposes. That is, plug the 3.5mm headphone into the audio out and use the left & right terminated wires as my inputs for the amplifier so I can do some tests on a breadboard. Is this possible?

Thanks!

That would probably work, especially if you start with the headphone volume very low and only turn it up when you can hear whether you're causing clipping, as the headphone output will be able to overpower the line-in inputs. It'd be better to use a line-out signal from a cheap CD player or such.

 

Thanks Wayneh,

I'll most likely be using the audio-out from my PC...from what I understand, this isn't the same as a headphone out right? I'm curious as to why the quality of a headphone out is worse than a line-out of a CD player or a audio out from a PC.

I was planning to use a headphone cable just like you would a 3.5mm stereo mini phone plug to dual RCA jack stereo cable (http://www.ramelectronics.net/howto-pc-audio.ep. I'm not sure if that works though...

Do you happen to have any suggestions on where to put a volume potentiometer, or what class of amplifier this is? I'll probably be putting it together this weekend.

Thanks!

 

I'll most likely be using the audio-out from my PC...from what I understand, this isn't the same as a headphone out right?

Right, as long as "audio out" means something meant to connect to an amplifier, not out to headphones. The former is "line out" (look it up) and that has a lower peak-to-peak voltage (will not cause clipping) and a higher impedance.

I'm curious as to why the quality of a headphone out is worse than a line-out of a CD player or a audio out from a PC.

It's not about quality so much as in matching the output and input, like choosing the right gear on your bicycle.

I was planning to use a headphone cable just like you would a 3.5mm stereo mini phone plug to dual RCA jack stereo cable

.That'll probably be OK, but the difference with headphone cable is that it's usually not shielded (because it's a low impedance path!). Audio line cables should be shielded to avoid electromagnetic interference, particularly 60 cycle hum.
Volume control is a pre-amp function. Beyond that I'm not the person to help you with amp design.