Audio Amplifier with multiple outputs

Other Hardware General Electronics
1

Hiya,

I have been doing streaming on Twitch.tv and use an audio mixer to pull together a number of audio sources. The problem I am running into is I need a number of the input sources, as well as a number of the outputs from the mixer, to each split off to other devices (headphones, SD audio recorder, speakers, PC audio input, PC audio output, Mac audio input and output).

I can look up the schematics for an audio amplifier online no problem, but my question is about where the amplifier IC should be when it comes to multiple outputs. should there be a single amp IC between the input and multiple outputs, or should there be an IC for each output?

2

Headphones and speakers need amplifiers. The rest of the sources and sinks are all line level and just need some kind of matrix switcher. Most of what you will probably need to do can be done with op-amps and resistors.

What's your signal flow look like? Will all inputs receive the same signal? E.g., you mentioned two computers and an SD recorder. Would they all use a main mix output, or do you need to send one source input to each? Will that source change, or is the routing pretty much fixed?

3

as well as a number of the outputs from the mixer, to each split off to other devices (headphones, SD audio recorder, speakers, PC audio input, PC audio output, Mac audio input and output).

If you don't need separate volume controls, you can simply connect the inputs of a few devices together with [u]Y-Adapters[/u] (splitters). Or, you could make a patch-bay with several RCA jacks in parallel.

The general rule is - NEVER connect OUTPUTS together. (That's what your mixer is for.)

But, it's generally OK to connect inputs together. For example, you can connect a few amplifiers to a tape player or mixer. The load impedance drops as you add more devices, so if you connect too many devices you will start to affect the signal. It depends on the output & input impedances, but I'd say 5 line-level inputs to one line-level output should be OK.

Headphones need a lower impedance output than line-level, so headphones should be connected to a headphone amplifier. On the other hand, headphone voltage is approximately line-level, so you could connect many-many line-level devices to a headphone output. (The headphone output on a laptop doubles as a line-output, but the line-out on a desktop soundcard is not always rated to drive headphones.)

If you need separate volume controls for a few devices, you can build op-amp "amplifiers" with volume controls and a maximum gain of one. These should have an input impedance of around 100K (which is generally going to mean a 100k volume control at the input of each.

PC audio input, PC audio output, Mac audio input and output).

Be careful with your signal flow... It sounds like you might be making a feedback-loop with the computer output feed-back into the computer input through the mixer.

4

macharborguy:
Hiya,

I have been doing streaming on Twitch.tv and use an audio mixer to pull together a number of audio sources. The problem I am running into is I need a number of the input sources, as well as a number of the outputs from the mixer, to each split off to other devices (headphones, SD audio recorder, speakers, PC audio input, PC audio output, Mac audio input and output).

Remove "PC audio output" and "Mac audio output" from that list, they are not inputs!

Which mixer are we talking about? Professional mixers can use line levels too high
for computer inputs (4V I think), I presume this is a small domestic one.

Generally all the line-level inputss can be driven direct from the mixer line-out,
headphones from mixer headphone amp (which in turn comes from the mixer
bus, and always has its own separate fader in a real mixer).

Is everything stereo? You might have to think about providing a balanced mono
output too if not.