DIY mixer - use diodes to prevent input potentiometers influencing each other

Question

I've builded a simple amplifier (just stereo audio in, two speaker outs) and I'm building a mixer for it.

There are some audio inputs, which goes through stereo potentiometers (volume for each input) and then all into main potentiometer (master volume). It looks like this:

EDIT: The schematics is wrong. To wiper is connected output, not ground. To resistive strips is connected ground and input.

But when I connected, I find out how stupid this is. The potentiometers are influecing each other, so when I lower one of the outputs by turning potentiometer, other inputs's volume's are also lowered. I tried to solve this by putting diode after each potentiometer, before the wire are joined, but this extremely lowered audio quality (the speakers were just buzzing the melody).

How to solve this? Is there any diode made for audio?

And my second problem is, I have mono wireless microphone with mono outpout (output from lm741 based preamplifier) and I want to make it stereo, but if I will connect the output to both L a R signals and joining them, as far as I know, the stereo inputs will no longer be stereo.

How to make mono signal (one input) playing on both, L a R signals, without destroying the stereo on other inputs?

Thanks.

Answer 1

You need a simple mixer circuit based on the summing amplifier.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Stereo mixer basic schema.

As Brian Drummand says, you need a virtual earth mixer. Here's the basic schematic showing how to handle the mono input.

This diagram does not show power-supply and capacitors. You'll find details in a web search.

Answer 2

As the circuit is drawn, you are grounding the wiper of the potentiometers. This is wrong. To wire a potentiometer as a potential divider, you need to connect the input to one end of the track, ground to the other end of the track, and the output to the wiper.

As wired, you are dragging the outputs down to ground. Which is why the pots are affecting one another.

Answer 3

The active circuit as shown by @transistor is certainly the preferred method. But if for some reason you need a PASSIVE solution, then a circuit like this is typical....