Hello all, just registered, great forum! Guess I'll jump right in. I want to build a compact stereo mixer that can mix the stereo headphone output from the intercom system from a TV camera and mix it with the stereo headphone output of my iPhone, (so I can shoot a show and simultaneously listen to MP3's or use my phone). I will be listening to the mixer with the camera intercoms headphones (which have a 60 ohm speaker in each ear). In the future I would also like to build a circuit that lets me use the headsets mic with the phone as well as the intercom, but first things first.

So, I am good at building things, and I can solder, but I know little about circuits. I did find a few mixer circuits that looked like they may be close to my needs but my lack of knowledge is holding me back. I don't know if I need to modify the plans somehow since my sources may not be typical, or if that even matters.

So would something like this work?

 

I believe this general design will work, although you should specify which op-amp you're planning on using so the experts here can comment. You should also address how you plan to power it.

I'd consider dropping the L-R panning pots. Good pots are the most expensive part of many DIY builds, and IMHO you don't need stereo panning. But you WILL want to control the volume of the different sources, maybe at the sources.

 

Thanks for guidance wayneh, on to the details...

you should specify which op-amp you're planning on using so the experts here can comment.

I will definitely need help on this one, I have no idea what I need. I prefer higher quality (within reason) over low buget, if that is important here.

You should also address how you plan to power it.

I'm glad you mentioned that because I was having trouble just understanding where the power ties in in this mixer. I was thinking of using a 9v battery if that is possible.

Good pots are the most expensive part of many DIY builds...

I would like to have decent pots. How can I tell which pots are of higher quality? Again, I lean toward quality over cost. Is there a brand I should go with, or am I looking for a particular spec?

But you WILL want to control the volume of the different sources...

Which brings up another question. Do I need to include an amplifier circuit after the mixer? Or in other words, will I experience any loss of volume from the mixer? I work with many different cameras from job to job and sometimes the intercom will have a lower volume than I prefer, even when maxed, so I just want to make sure I am not any worse off if that is the case.

 

Which brings up another question. Do I need to include an amplifier circuit after the mixer? Or in other words, will I experience any loss of volume from the mixer?

The op-amp in the circuit is an amplifier, and will use battery power to apply gain (amplification) to the signal. That gain is something you can adjust. You could get away with a single master volume, adjust it for your quietest source, and then adjust your other sources down. But if you want you can add pots to adjust each source at the inputs. That's how a commercial mixer would do it.

A 9v battery will work, but they have limited life compared to, say, AAs. If you don't mind replacing it, I think it would be OK. Using two of them may also simplify your design, because you won't have to establish a virtual ground. Your diagram doesn't show it, but I believe the op-amp is meant to be powered by a split supply, for instance +9v and -9v.