Mix 2 balanced signals to 1 input

Archived from groups: rec.audio.pro (More info?)

Problem:

My SAAB 9-5 has balanced signal inputs on the amps and I need to mix
the signal from the factory stereo with the sound from my carputer. I
simply want full signal level for both sources so I can listen to a CD
on the stereo at the same time as getting instructions from the
computer navigation system. If I want to listen to mp3's on the
computer I simply turns down volume for the stereo and vice versa.

Questions:

What is my best option? Buy an external soundcard (usb/firewire) with
XLR, or get some kind of converters for my 1/8 unbalanced output to
balanced output?

How can I mix the two balanced outputs together into the amp? Is it ok
to just wire them together???

Thanks for any input on this!

Regards,
Henrik

Archived from groups: rec.audio.pro (More info?)

"Henrik" <henrikolofsson@yahoo.se> wrote in message
news:7030d3aa.0505030738.2d22dee9@posting.google.com...
> Problem:
>
> My SAAB 9-5 has balanced signal inputs on the amps and I need to mix
> the signal from the factory stereo with the sound from my carputer. I
> simply want full signal level for both sources so I can listen to a CD
> on the stereo at the same time as getting instructions from the
> computer navigation system. If I want to listen to mp3's on the
> computer I simply turns down volume for the stereo and vice versa.
>
> Questions:
>
> What is my best option? Buy an external soundcard (usb/firewire) with
> XLR, or get some kind of converters for my 1/8 unbalanced output to
> balanced output?
>
> How can I mix the two balanced outputs together into the amp? Is it ok
> to just wire them together???


No, you need a mixer. If I understand correctly, you want to mix a balanced
stereo signal from your car stereo system with the unbalanced mono signal
from the car computer. If you don't need a mixer with separate volume
controls for each source, a passive resistor network will do. The resulting
mixed signal will be slightly lower than the respective source signals, but
it's a simple and cheap solution.

Predrag



> Thanks for any input on this!
>
> Regards,
> Henrik

Archived from groups: rec.audio.pro (More info?)

"Henrik" <henrikolofsson@yahoo.se> wrote in message
news:7030d3aa.0505061339.52d084b7@posting.google.com...
> "Predrag Trpkov" <predrag.trpkovNeSpamu@ri.htnet.hr> wrote in message
news:<d5a32i$9gj$1@ss405.t-com.hr>...
> > "Henrik" <henrikolofsson@yahoo.se> wrote in message
> > news:7030d3aa.0505030738.2d22dee9@posting.google.com...
> > > Problem:
> > >
> > > My SAAB 9-5 has balanced signal inputs on the amps and I need to mix
> > > the signal from the factory stereo with the sound from my carputer. I
> > > simply want full signal level for both sources so I can listen to a CD
> > > on the stereo at the same time as getting instructions from the
> > > computer navigation system. If I want to listen to mp3's on the
> > > computer I simply turns down volume for the stereo and vice versa.
> > >
> > > Questions:
> > >
> > > What is my best option? Buy an external soundcard (usb/firewire) with
> > > XLR, or get some kind of converters for my 1/8 unbalanced output to
> > > balanced output?
> > >
> > > How can I mix the two balanced outputs together into the amp? Is it ok
> > > to just wire them together???
> >
> >
> > No, you need a mixer. If I understand correctly, you want to mix a
balanced
> > stereo signal from your car stereo system with the unbalanced mono
signal
> > from the car computer. If you don't need a mixer with separate volume
> > controls for each source, a passive resistor network will do. The
resulting
> > mixed signal will be slightly lower than the respective source signals,
but
> > it's a simple and cheap solution.
> >
> > Predrag
> >
> >
> >
> > > Thanks for any input on this!
> > >
> > > Regards,
> > > Henrik
>
>
> Thanks for helping!
>
> Where can I find schematics for resistor networks to use in this
> project? I actually want to mix 4 channels (front + rear) from my head
> unit with the stereo sound from the computer into the 4 channel
> balanced XLR input on the factory amp. So basicly I got 4 ch XLR from
> head unit + 2 or 4 ch RCA from computer and mix them to 4 ch XLR input
> to factory amp. Hope you understand what I'm trying to do here
>
> Regards,
> Henrik


Sure, this is where you'll find the schematics:
http://www.forsselltech.com/summin [...] matics.htm

And this is a no-nonsense explanation of theory behind it:
http://www.forsselltech.com/summing%20buss.htm

The passive summing busses shown there are 8 into 1 configuration, so you
can reduce the number of inputs to suit your needs. Of course, you'll need
four of those, one for each channel.

The number of inputs should be the same for all summing busses, since it
defines the signal loss. In case of your computer, I'd simply mult left
output to the summers for both front left end rear left channels. Same for
the right output. Connect tip of the RCA connector to pin 2 of the summing
buss input and sleeve of the RCA connector to pin 3. Leave pin 1 free.

Depending on the input/output impedances of the devices you'll be
interfacing, you may need to experiment a bit with the value of the
resistors to find the optimum match.

Good luck with your project.

Predrag