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'[EE]: Stereo to mono mixer'
2004\04\11@201019 by Tal

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Hi All

Can anyone help me resolving this problem:

I want to connect a stereo signal (audio) and convert it to mono, BUT keep
the stereo inputs separate for use in other equipment.
is it possible?

I was thinking using a fast oscillator (~100Khz) and a 4066 bilateral
switches but it looks overkill. can you think about a simple solution?

Thanks

Tal

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2004\04\11@202717 by John Tserkezis

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Tal wrote:

> I want to connect a stereo signal (audio) and convert it to mono, BUT keep
> the stereo inputs separate for use in other equipment.
> is it possible?
>
> I was thinking using a fast oscillator (~100Khz) and a 4066 bilateral
> switches but it looks overkill. can you think about a simple solution?

 Buffer the two stereo inputs, and then mix them in the traditional manner.

(excuse the ascii text)

          |\
Left -----| >---/\/\/\---|
          |/             |
                         +----- Output
          |\             |
Right ----| >---/\/\/\---|
          |/

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2004\04\11@205451 by SavanaPics

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Although very basic, this may be  a starting point

http://www.richmond.infi.net/~allenk/techref/splitter.html

Eddie Turner, kc4awz

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2004\04\11@205623 by Rick C.

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If you want something simple and passive, just use two 10k resistors and a 1k
resistor. Connect a 10 k resistor to each of the stereo outputs. Tie the two
other ends of the 10k's together and to a 1k to ground. The junction of the
three resistors is your mono (summed) audio. There should be enough level at
this point to drive the next stage. If not, raise the 1k to 4k7. If still not
enough, raise it to 10k or leave it out completely. The only reason for
putting it there is to "possibly" prevent left-right bleedover which may not
be a problem depending upon the output impedance of the stereo jacks.
Rick

Tal wrote:

{Quote hidden}

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2004\04\11@223456 by PicDude

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On Sunday 11 April 2004 08:09 pm, Tal scribbled:
> Hi All
>
> Can anyone help me resolving this problem:
>
> I want to connect a stereo signal (audio) and convert it to mono, BUT keep
> the stereo inputs separate for use in other equipment.
> is it possible?
>
> I was thinking using a fast oscillator (~100Khz) and a 4066 bilateral
> switches but it looks overkill. can you think about a simple solution?
>
> Thanks
>
> Tal

Not sure what you intend to do with the oscillator, but if I understand this request correctly, it sounds similar to getting a mono-output for a subwoofer.  You should just be able to tap off each of the stereo signals and send those to a high-impedance op-amp (so you don't really affect the original signals).  Then mix the op-amp outputs to get a mono signal.

Cheers,
-Neil.

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2004\04\11@235349 by Harold Hallikainen

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A purely passive mixer would just be a couple resistors in series between
left and right. Take the mono sum from the junction. When you take a
number of equal resistors and tie them to a common point, the voltage at
the junction is the average of the input voltages. So, if you have two
(Left and Right) the voltage at the junction is (L+R)/2 . This is assuming
ideal voltage sources (zero ohm sources) and infinite resistance on the
load connected to the junction.

However, if the voltage sources are not zero ohm sources, there will be
crosstalk between the channels. The crosstalk level would be related to
the ratio of the summing resistors to the source resistance.

Crosstalk can be eliminated by using a zero ohm summer. Instead of just
taking the output off the junction of the two resistors, drive an op amp
current to voltage converter. If the input resistors are 10k, connect them
to the inverting input of the op amp. The non-inverting input is grounded.
Put a 10k (for unity gain) resistor between the output and the
non-inverting input of the op amp. The output will be -(L+R) . The -
indicates the phase is reversed (this is an inverting summing amp).

A reduction in crosstalk can be achieved using the passive circuit by
adding a low resistance resistor to ground between the two summing
resistors. However, as crosstalk is reduced by reducing the resistor
value, output voltage is also reduced.

Years ago, when I worked in a radio station, we had a mixer made by GE
that used a passive summer followed a high gain amplifier. The network
came in on phone lines (this was before satellite network distribution).
So, I put the network on the cue channel as I waited to join the network.
I also would cue up records on the cue channel. Turns out there was
crosstalk so the other stations in town running the network ended up
broadcasting my records being cued.

Good luck!

Harold



{Quote hidden}

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2004\04\12@014949 by David Duffy

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Harold Hallikainen wrote:

{Quote hidden}

I think you meant put the resistor between the output and inverting input.
David...

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2004\04\12@055320 by Tal

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Hello and thanks for the help

To many times I do the same error and ask a question with some lack in
details.

I have a stereo satellite receiver and a stereo TV and a mono video
cassette, so I want to be able to enjoy watching/listening in stereo but
record in mono but have both L+R lines. I never do that before and it look
to me if I use 2 resistor in series to join the stereo I will destroy the
stereo signal.

I know when you want to separate a dc sources or join them you can use a
diode/s but in this case it looked to me to distorted and not acceptable. so
AC signal give you an headache... furthermore you don't want to kill the
sound.

I think I will adopt the buffer idea and try it.

Thank you all for you help!

Tal

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2004\04\12@072018 by Rick C.

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We that have responded understand your dilema. You will not destroy your
discrete stereo with the passive resistor method. The stereo output impedances,
are typically 10k although I believe they are a good bit lower. I repeat, you
will *not* mar the quality of the stereo. That's the reason for the resistors.
They passively sum the audio together. The resistor to ground simply provides a
low mono impedance that reduces crosstalk. I do what you are trying to do in
many instances at home and at the radio station I engineer at.

Use the following:
http://www.pic101.com/pix/MIX.GIF

Rick

Tal wrote:

{Quote hidden}

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2004\04\12@073059 by Tal

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Thanks Rick

I just emphasize it. to be clear.

Tal

-----Original Message-----
From: pic microcontroller discussion list [.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]On
Behalf Of Rick C.
Sent: Monday, April 12, 2004 1:20 PM
To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subject: Re: [EE]: Stereo to mono mixer


We that have responded understand your dilema. You will not destroy your
discrete stereo with the passive resistor method. The stereo output
impedances,
are typically 10k although I believe they are a good bit lower. I repeat,
you
will *not* mar the quality of the stereo. That's the reason for the
resistors.
They passively sum the audio together. The resistor to ground simply
provides a
low mono impedance that reduces crosstalk. I do what you are trying to do in
many instances at home and at the radio station I engineer at.

Use the following:
http://www.pic101.com/pix/MIX.GIF

Rick

Tal wrote:

{Quote hidden}

so
{Quote hidden}

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2004\04\12@112559 by Harold Hallikainen

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>
> I think you meant put the resistor between the output and inverting input.
> David...
>


Oops! Right you are! Audio just sounds wonderful after going through a
schmitt trigger!

Harold



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