Can I put two inputs into and amplifier?

I have eight speakers, each with an 18 W TDA2030 mono amplifier attached (Audio Amp). These are connected in parallel to an Arduino to take a tone library output. I also want to put voice through these same speakers using a Max4466 electret microphone amp ( Microphone).

I have reservations about hooking up the Max4466 and Arduino outputs, in parallel, into the inputs of the TDA2030 amps (to achieve dual inputs) although not sure why.

Is it OK to wire them up as outlined above or is there a better way?

Without anything it's indeed NOT okay. A crude solution is to put a resistor in line with both sources. But, I say crude because the output impedance of the source gets loaded differently depending on the signal from the other source. Using an opam as audio mixer will give you better results.

lemming:
I have reservations about hooking up the Max4466 and Arduino outputs, in parallel, into the inputs of the TDA2030 amps (to achieve dual inputs) although not sure why.

Is it OK to wire them up as outlined above or is there a better way?

In general, if there are at least a few different sources (eg. from books, or reputable online electronics teaching sites etc) that demonstrate this particular configuration ------ then there's a good or fair chance it will work without issues --- without components or devices failing (getting destroyed etc).

For the configuration that you describe --- it doesn't sound like it will work. A circuit diagram will help a lot toward seeing just what you mean.

If you want to mix various audio sources, then this generally means summing the signals --- so a operational amplifier circuit in a 'summing' configuration may be what you need. A op-amp summer. It will also be handy to know the specifications of amplifiers - so that the signals to be applied to the amplifiers are at suitable levels.

I suspect you might need some gain somewhere, given the low output of that microphone amp. An opamp
summing amp can give gain as well as summing.

NO. The general rule is NEVER* connect two outputs together. The outputs are low-impedance (lower than the recommended minimum load) so the outputs essentially "short each other out". Both devices can overheat and it they are different the one with the lowest impedance will "dominate" killing the signal from the other.

It's generally OK to connect multiple inputs together (such as the 8 amplifier inputs).

The best solution is a [u]small mixer[/u], which has the added benefit of volume control(s).

[u]This page[/u] shows you how to make a passive mixer with resistors (with or without pots). A passive mixer like this will cut both signals in half (which should still give you plenty of signal to the amplifiers.)

The resistors should be high-enough in value so it doesn't "load" the source, but low-enough in value that you don't get a voltage drop to the amplifier(s). Normally, 10K is a good compromise but with 8 amplifier inputs connected in parallel (lower total input impedance) you may need to go down to 1K.

Or you can build an active mixer with an op-amp summing amplifier.

  • There is an exception with open-collector digital outputs which can make a "wired or" connection (actually NOR) Or, with tri-state logic outputs where the outputs can be disabled (high impedance state) so only one output is active at a time.