audio distribution circuit

[john3]

Hi,

I would like to build a circuit to distribute a stereo audio feed to multiple sets of speakers, for a "multi-zone" home audio system. I would like to use digital switches and control the system with a computer eventually (on/off and volume for each set of speakers). The stereo feed could be digital or analog, and does not need to be extremely high quality. What would be the best way to do this? Which amplifiers should I use? Are there amplifiers with multiple outputs available, or do I use one discrete amplifier for each set of speakers?

Thanks very much for any suggestions!

 

[john3]

Could I use a series of LM386, using the same audio signal to feed into all of them? Would I need to isolate the LM386's from each other?

 

[jiripolivka]

In the good old days, people fed their stereo signals into a pair of power amplifiers driving a pair of speakers. No switching needed, and each power amplifier had a potentiometer for volume control.
Next, people wanted to feed the stereo pair of signals into "front" and "rear" pair of speakers. The simple way is to connect both speaker pairs in parallel to the power amplifiers. Who wanted to "move" the music source, used four power amplifiers with separate volume controls.

Nowadays people want to do the same but using a computer. So learn how to switch your signals from it: thousands of transistors in your PC are needed to drive a pair or two of analog switches like 4066 or 4016.
To control the volume in two, four, etc. audio channels, find "digital potentiometers" e.g. made by Analog Devices or Maxim. In their data sheets you will find the details of their serial control.

Check some car radios; some have all you would wish ready to use, but not controlled by your PC- they have their internal PCs in the box.

I would better use my time in enjoying the "analog" music with manual volume controls, instead of wasting it in designing a digital multi-processor, and all the software.

 

[john3]

Thanks, jiripolivka. Sorry, my desciption is not very clear. My question is really: how do I send a stereo audio signal from the computer (or any device) to multiple sets of speakers? What audio amplifier would be best? Is it easiest to send the signal to multiple amps in series, using a common power supply?

(The bit about switching and volume control I would implement separately, possibly through a parallel port or local network. Also, perhaps there is a chip that will take a digital audio signal and convert it to analog (and amplify) it? As you can see, I don't know very much about audio circuits.)

 

[jiripolivka]

Thanks, jiripolivka. Sorry, my desciption is not very clear. My question is really: how do I send a stereo audio signal from the computer (or any device) to multiple sets of speakers? What audio amplifier would be best? Is it easiest to send the signal to multiple amps in series, using a common power supply?

(The bit about switching and volume control I would implement separately, possibly through a parallel port or local network. Also, perhaps there is a chip that will take a digital audio signal and convert it to analog (and amplify) it? As you can see, I don't know very much about audio circuits.)

If your task is so simple, then you can use the LM386 to feed each of speakers with ~ 0.5 W audio, through a volume-control potentiometer. There are many other good audio amplifiers, often sold as kits (Ramseykits, All Electronics, elexp.com) some with more than one watt of audio output. At MCM electronics I saw nice tiny 20W audio power amps.
The only task then would be to use simple resistor dividers from computer audio output(s) to each amplifier input(s). Volume control is either built in such amplifiers, or, you can use 10 kOhm audio taper potentiometers for it.
As I mentioned, for computer-controlled switching, 4066 or 4016 ICs are analog switches controllable by TTL inputs. To replace the ordinary potentiometers, there is a selection of digital ones; details in their data sheets.

Concerning the DC power supply, most of the above mentioned amplifiers use 12 VDC. A good idea is to get a good "large" power supply capable of several amperes of current, and with DC blocking capacitors of 4000 uF or more. Often you can expect some audible interference due to ground loops, etc. A good idea is to try connecting all devices including audio output jack shield to a common ground. As laptops and PCs use switching power supplies, you may need a filter to reject unwanted sounds. In my case, to listen audio CDs and DVDs from my laptop on a larger TV display with stereo speakers, hum and high-pitch sounds forced me to use small audio transformers to break the ground loop. Expect some experiments to achieve good results.

You may search suppliers of "professional" audio systems. For much more money you could possibly find almost perfect system ready for anything. Ground loop problems are sometimes solved by using optical fiber or balanced transformers. Start with simple devices and gradually try to use more complex devices.

 

[john3]

Great, thank you very much. Yes, it is a simple idea, but like you suggest, it can get more complicated with ground loop interference and such. I will look for some suitable amps and begin with simpler components and grounding them as you describe. It doesn't seem complicated; I don't know why more companies don't offer this kind of audio distribution system. Of course, if I make it myself, I can adapt it and add to it as I like. Thanks again, we newbs just need a bit of guidance to get started.