zimmer@calvin.stanford.edu (Andrew Zimmerman) (02/17/91)
First:
I seem to be having problems with the audio on my stereo. I think that
the guy in the next Apartment is trying to jam my audio. So, does anyone
have a circuit to filter out the EM source? :-) :-)
Seriously:
I would like to mix the outputs of a CD player, a computer, and a
radio and feed the signal to a pair of headphones. Radio Shack does
have such a unit, but it is more then I want to spend, and all of the
jacks are wrong, etc. So, I would like to build one.
So, does anyone know of a good source for a schematic for a 3-4
channel stereo mixer?
The mono mixers I have seen just use a simple op-amp circuit. But, I
was curious about the stereo systems. Do they use one potentiometer to
control both channels, or do the slide pots control two resistors?
Same question applies to a balance control. Actually, I am more
interested in the answer to these couple of questions then in getting
a schematic.
Thanks for your help,
Andrew
zimmer@calvin.stanford.edusmithj@hpsad.HP.COM (Jim Smith) (02/20/91)
Andrew Zimmerman writes: ==== was curious about the stereo systems. Do they use one potentiometer to control both channels, or do the slide pots control two resistors? Same question applies to a balance control. Actually, I am more ==== Actually, most mixers use two pots with two sliders. But for your application,typically one control would control two resistors. Stereo volume control pots are pretty common, last time I checked Radio Shack sold a 100k version. Although a balance control can be implemented with a single pot element, most of them that I've seen use dual pot elements, with opposite tapers. Actually, there is a balance pot taper, where the resistance of one side decreases to zero from one end to the center of rotation, then the resistance of the other side begins to increase. Again, last time I checked, Radio Shack sold such a beast. For your application, a simple summing opamp circuit in each channel should do fine. Any linear applications handbook (like National's or Signetic's) should have a decent schematic. Bells and whistles you could add include buffer amps on each input and an input trim on each input to match the levels of all the inputs at any particular fader setting. One thing to be aware of is that if you want to feed a phonograph to it, you will need to put a phono preamp circuit ahead of the mixer. Last time I built a mixer, I had trouble finding appropriate slide pots (with more than a 1.25 inch throw and a decent feel and the right taper) and ended up using rotary pots (ala Radio Shack). It does the job... Good luck! ----------------------------------------------------------------------------- | Jim Smith | e-mail: smithj@hpsad.HP.COM | | Firmware/Software/Kludges | Telnet: 794-4632 | | HP Signal Analysis Division | AT&T: (707) 794-4632 | | 1212 Valley House Dr. | HPDesk: Jim M Smith/HP5300/I0 | | Rohnert Park, CA 94928-4999 | HP Mailstop: 2LR-D | | Everybody wants a rock to wind a piece of string around. - TMBG | -----------------------------------------------------------------------------