I don't know what mixer he has, but both of mine are stereo mixers.=20
One is 6 stereo channels or 12 mono
 channels, and the other one is 8 stereo channels or 16 mono channels.=20
Using the pan control, you can move
 virtually any channel to either the left or right output, or any point
in between.  They were designed to
 allow stereo signals to be input conveniently, but also, to allow
single ended inputs to be utilized too.
=20
 Of course, you could always use each stereo pair as one by either
feeding both left and right input with
 the same signal, or just leave either the left or right channel
unconnected, using only half of the stereo
 pair.  But leaving an input unconnected is asking for problems.=20


 Regards,

 Jim

> -------- Original Message --------
> Subject: Re: [TECH] Audio Mixer MixUp
> From: Oli Glaser <oli.glaser@talktalk.net>
> Date: Tue, May 24, 2011 9:49 am
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
>=20
>=20
> On 24/05/2011 14:42, Mark E. Skeels wrote:
> > A puzzle for you.
> >
> > I recently had occasion to attach 3 acoustic guitars and a Yamaha
> > keyboard through balanced mic cables into a Yamaha mixer.
> >
> > The acoustic guitars all have internal battery-powered preamps and 1/4"
> > Phone plug outputs, which are very common.
> >
> > I split each of two balanced mic channels into two single ended circuit=
s
> > each using one side of the balanced circuit with ground common. At the
> > mixer end I split the signals out to 1/4" single ended and ran them int=
o
> > the line inputs.
> >
> > (Yes, I know they are line inputs. The channels have preamp level boost
> > pots and the sound was fine with no significant hum. Yes, I also know
> > about direct boxes.)
> >
> > On the first cable I connected two acoustic guitars. This worked just f=
ine.
> >
> > On the second cable I put another acoustic guitar into one side, and th=
e
> > Yamaha keyboard into the other.
> >
> > My fatal mistake was that I never hooked them up at the same time until
> > shortly before the actual performance.
> >
> > Well, with both sources hooked up, I could get no signal from the guita=
r.
> >
> > In the process of troubleshooting, I swapped everything in the circuit.
> > Finally, I happened to pull the connection to the keyboard and the
> > guitar channel sprang into life.
> >
> > At present, all I can think of is that the keyboard imparted some DC
> > offset to it's channel which confused the mixer's input somehow.
> >
> > I'll get back to it in a couple of weeks and try to figure out what
> > actually happened..
> >
> > Any ideas what might have happened here?
> >
> > Thanks,
> > Mark
> >
> >
>=20
> I'm guessing the keyboard output impedance might be low, and the guitar=20
> output a lot higher (I know they have a small preamp built in but I=20
> think it will still be higher) so it's getting attenuated severely when=20
> you mix them together. I would check the output impedances of both to=20
> make sure anyway.
> Why are you splitting the inputs anyway? Do you not have enough channels=
=20
> on the mixer?
>=20
>=20
>=20
>=20
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