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Old 4th September 2007, 10:39 PM   #1
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Question Distributed Amplifier questions

I've done some searching here and on the internet, but I could not find any useful schematics/answers for a distributed audio amplifier for about 6 outputs.

My idea was to have one input or two switchable inputs and then have one op amp to drive the 6 outputs, each with an individual volume pot, and one bypass switch to use only one output to drive some speakers. And then fit this package into a box that is small enough to travel with it.

After some reading on the subject on this forum I realized I might need one op amp for each output, which one would be the most appropriate, one op amp to power them all or one for each output?

My intention is to use one/two 9V batteries (depending on the requirements of the op amp(s)). Will this do it or is more juice needed?

Also what kind of resistors should I use to produce the required gain?

I know it sounds quite noobish, but I know at least something about electronics (and how to put them together), but I haven't been too much into audio electronics so I find it easier to ask about it than making something that doesn't work the way I want

Looking forward to get some answers on my questions and some feedback/input on my project.

Thx for the help
Islandstone

And if it is really neccessary to clarify it, yes I'm talking about stereo audio
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Old 5th September 2007, 01:47 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
a portable six channel amplifier for stereo.
You have confused me.
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regards Andrew T.
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Old 5th September 2007, 08:47 PM   #3
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lol thought I described it well enough

I'm talking about one stereo audio amplifier with 1 or 2 inputs, and 6 outputs.

That made more sense?
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Old 6th September 2007, 03:56 PM   #4
gootee is offline gootee  United States
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Hi Islandstone,

You have not given nearly-enough information.

What will the outputs be driving?

What devices will supply the input signals?

You will probably need to know at least the range of the input voltage level. And knowing the output impedances of the input-providing devices would help.

You will need to know the impedances of the devices that will be connected to the outputs.

Forgetting about speakers for the moment, you will probably want a separate dual amplifier for each output. Dual opamps should work, if the impedances of the loads are high-enough. But keep in mind that most opamps can supply very little power, and might get very hot if asked to supply anything near their maximum rated power. You might want to poke around at ti.com, national.com, analog.com, and linear.com. TI and National, at least, should both have Datasheets and/or Application Notes with circuits for the amplifiers you need.

9V Batteries? This will likely be your biggest problem. I guess it all depends on what you will be driving, with the outputs. If it will be something like very-high-impedance headphones, you might have a chance. Do some searches for "headphone amplifier", and "headphone impedance". Find out how much current each stereo amplifier might draw, at an average listening level. Multiply that by the number of amplifiers to get the total current. Find out how many milliamp-hours your batteries have in them. Divide that by your total milliamps to see how long the batteries might last.

Speakers? I would have to guess that one or two 9V batteries will be sufficient for only very small, low-power speakers, for any reasonable battery lifespan.

You might want to do some battery shopping. If there are acceptable larger batteries, preferably with higher voltages (up to, say, 18v, but 12v would probably be OK), the job will be much easier, and the results much better. Maybe you could find some common consumer item's re-chargeable battery pack that is cheap.

You should also consider making it be able to use "shore power", whenever it might be available, e.g. a "wall-wart" or an automotive adapter. And that might mean that it will be easier to use a "single supply" type of amplifier design, rather than having both positive and negative voltages, unless you use either a switchmode power supply (SMPS) to derive an equal opposite-polarity voltage, or use a "rail splitter" to derive opposite polarities at half the original voltage, each.

Good luck!

- Tom Gootee

http://www.fullnet.com/~tomg/index.html
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