Hello! I've been designing a new feature for my animatronics. First, the audio is being sent (via Bluetooth) to a pair of highly-directional speaker/amplifier systems. I plan on keeping the audio local to each character, as it is used as input to the servo-control subsystem for synchronized speaking and audio.
However, the other channel will be amplified locally for an internal speaker and sent to the DSA systems. One line level output will feed an amplifier and two mixers... It's not practical to split out the internal amplifier feed, but I plan on using an active splitter to feed two mixers... Each mixer will mix/balance up to four sources and transmit the audio signal to the DSA via Bluetooth. Each mixer input will come from one side of the splitter, balanced with a 10K Linear Pot.
I've researched both active splittters and mixers. I found an article on Learning Electronics for a three channel splitter. I modified the output resistor values to make it a two-channel splitter. Here is a closeup of my splitter model in LTSpice:
AAC has a thread on a mixer, but I used another circuit which is very similar as it was easier (IMHO) to modify to include the splitter. The mixer circuit is attached to this thread.
So, my circuit combining the two functions is shown below. This image is pretty tiny, so there is a .pdf and .asc file as well.
Basically, I have a couple of uncertainties.
Don dj Lutz
dj's fantasi
However, the other channel will be amplified locally for an internal speaker and sent to the DSA systems. One line level output will feed an amplifier and two mixers... It's not practical to split out the internal amplifier feed, but I plan on using an active splitter to feed two mixers... Each mixer will mix/balance up to four sources and transmit the audio signal to the DSA via Bluetooth. Each mixer input will come from one side of the splitter, balanced with a 10K Linear Pot.
I've researched both active splittters and mixers. I found an article on Learning Electronics for a three channel splitter. I modified the output resistor values to make it a two-channel splitter. Here is a closeup of my splitter model in LTSpice:
AAC has a thread on a mixer, but I used another circuit which is very similar as it was easier (IMHO) to modify to include the splitter. The mixer circuit is attached to this thread.
So, my circuit combining the two functions is shown below. This image is pretty tiny, so there is a .pdf and .asc file as well.
Basically, I have a couple of uncertainties.
- The line input is coming from a VS1053 codec. It's datasheet states clearly "do not connect to ground." But I wonder if that means ground of the VS1053 (as the audio ground is created by the chip). But if I'm connecting to another circuit, whose ground is not connected to the VS1053 supply ground, I should be ok. As long as digital ground is separate from analog ground. (I'm struggling with this concept)!
- I've adjusted the splitter resistor network. The original circuit had three outputs, each fed with an 330Ω resistor. The ratio works out to be an even 33%. But with two outputs, I changed it to 470Ω. The total resistance is close to 1KΩ in both cases and the ratios are commensurate with the number of outputs (1/3 for three outputs; 1/2 for two outputs)
- I've not figured out what to do if I only need 2 or 3 sources... Normally, I'd explicitly wire up an unused op amp. But in this case, it might be in use later, just not now. Looking at the circuit, I may be set, as there are no floating inputs. But I'm also not sure.
- And to close out, any other comments are welcome! I'm more comfortable writing code for a microprocessor than analog electronics. But this is a particularly critical project that I can't screw up.
Don dj Lutz
dj's fantasi
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