Simple circuit

[Godsend]

Im not a very good engineer yet... But I am looking to design or find something for use on my pc set up. I have three 1/8" headphone audio outputs, I am looking for something to take these 3 sources to one input.

I know I can use a simple headphone splitter but, I was thinking I could I could wire a diode into each line then use it.
Would this work?
What is the output voltage of most computer sound cards so I can get the right diode for the system?

Please help

 

[felixc]

Your circuit would not work.

Your sound card, or your motherboard (if it has integrated audio) normally has several possible inputs that you could use to connect your three outputs to. Check your user's manual, it usually has come CD inputs, line inputs, and AUX inputs. Besides the different names, they are the same type or input. You could then use the software mixer of the PC to balance your inputs. All you have to do is a cable between your output and the sound card input connector.

 

[logbook]

Silicon diodes take about 0.5V before they start conducting. Even then they only conduct well in one direction (rectification).

You can make a passive adder from a few resistors for single-ended signals. As a starting value you might try 47R resistors in series with each signal, with all three resistors driving into the same input. Depending on the impedance levels this may or may not do anything sensible!

 

[Godsend]

felixc: My pc has that possibility but i dont want to have my pc running when I want to watch TV et.

logbook: Can you explain the passive adder theory, and will it work in this situation?

 

[ScottyUK]

You might search on Google or in a high school text for 'op-amp mixer'. It might seem very advanced right now, but the basic principles are quite easy to understand and the most common circuits are very well documented with explanations that a beginner could follow, right through to more rigorous mathematical analysis if you have the desire to learn it.

When I first started playing with electronics, it was with simple transistor and op-amp audio circuits. I found the latter were the more predictable in behaviour given my limited understanding. Take the plunge - the components are only a pound or so and you could find a very rewarding hobby or future career.


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Start each day with a smile. Get it over with.

 

[VEBill]

"...three 1/8" headphone audio outputs..."

Normally, the only PC sound cards that would have three outputs are the 5.1 surround-sound type. If you're trying to mix these down into a single stereo input, then all you need to do is make the required setting in your sound card driver's user interface.

Somewhere in the menus will be a speaker selection screen. You simply change it from 5 speakers plus a subwoofer to two stereo speakers. Assuming that all the other related settings are correct, then the software will automatically down-mix the audio to one stereo feed.

On the off-chance that your PC is completely different than the norm, and you really do need to mix the audio, you can probably just parallel the outputs using a couple of dollar-store headphone 'splitters' (run backwards). The outputs will almost certainly have series resistors on the card and thus they probably aren't required in the mixing circuit.

Even better would be the 47R resistors mentioned by logbook. No need for any active circuitry like opamps. And diodes are right out...

 

[felixc]

You want to use your PC setup, but do not want to turn it on... please explain better. You just want to use the speakers?

 

[Godsend]

I have 3 different sources. I am not trying to combine the surround sound.

I have 3 completely different sources but my pc does allow mic inputs so i could input to the mic's and output the sound essentially mixing it in the computer. But I dont want my pc on all the time that I want to use the speakers.

I found a stereo headphone mixer at radio shack for $40 and may use that to mix the sound together and then output it to the speakers.

 

[VEBill]

Sorry for not understanding - I guess I was confused when you asked, "What is the output voltage of most computer sound cards...?"

Sounds like you're on the right track with the RS headphone mixer.