>
> 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 circuits
> 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 into
> 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 fin=
e.
>
> On the second cable I put another acoustic guitar into one side, and the
> 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 guitar.
>
> 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
>
>
>
Is the keyboard battery powered or line powered? (I'm thinking ground loop)

-Denny
--=20
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