Very Basic Question re: combining two signals

[liam]

Hi,

I have a quick question which hopefully has a really simple answer. I would like to combine two signals to run into one amp and wondered if you could just combine them as in 1. or if you have to put in diodes such as in . and if you have to add diodes does this at all impact sound quality.

1.
input 1 --------------\
                           output
input 2 ---------------/

2.
input 1 ------|->|----\
                            output
input 2 ------|->|----/


by the way this, |->|, is supposed to be a diode and the rest of the lines are wires.

Cheers
Liam

[R.G.]

I have a quick question which hopefully has a really simple answer. I would like to combine two signals to run into one amp and wondered if you could just combine them as in 1. or if you have to put in diodes such as in . and if you have to add diodes does this at all impact sound quality.

1.
input 1 --------------\
                           output
input 2 ---------------/

2.
input 1 ------|->|----\
                            output
input 2 ------|->|----/

The first one might work, depending on the signal sources. It's much better to insert resistors in series in the two wires. That keeps the two signal sources from "shorting out" each other.

The second one will not work at all for small signals, and will introduce distortion for big signals.

[GibsonGM]

Take a look at the schematic for an amp....look for how the two 68K (usually) resistors are used. That's a good way to mix signals passively.  Of course, you could always use an opamp, and get great input/output impedance to boot!