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Old 1st Aug 2015, 11:24 pm   #1
yestertech
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Default Simple 2 into 1 Stereo Mixer requirement

I'm currently homebrewing an audio switcher, using a 'reworked' unit made by a company called Audionics
this unit employs solid state switches , one for each leg of each of the stereo balance inputs
The prototype logic section seems to function OK as a breadboard layout, now I have to try and translate it to strip board .
One additional requirement we have is to add another pair of stereo signals to the stereo output of this unit. The signal is relative to standard zero level (line up ) and the output is electronically balanced
The additional input will be gated on and off by a computer play out system so it can be permanently mixed together with the output of the Switching unit.
I'd like to keep this a simple as possible.
I could do a balanced pair resistive pad of some sort, but then it has to be followed by an amp to restore the correct level.
Alternatively, I have to build a set of balanced input amps with some sort of combiner, followed by another balanced output amp.
Another possibility is some sort of hybrid transformer with 2 in and one out, but I suspect these are neither plentiful or cheap.
Does anyone have any other ideas ?

Andy

Last edited by AC/HL; 2nd Aug 2015 at 12:33 am. Reason: As requested
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Old 2nd Aug 2015, 6:52 am   #2
Diabolical Artificer
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Default Re: Simple 2 into 1 Stereo Mixer requirement

Andy, I may have some purpose built audio switches, will let you know later when I've had a rummage.

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Old 2nd Aug 2015, 6:46 pm   #3
mhennessy
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Default Re: Simple 2 into 1 Stereo Mixer requirement

So you have a stereo, balanced output signal from the Audionics box? And you have a stereo, balanced signal from the computer?

If both signals are already balanced, there is no need to convert back into the unbalanced domain, only to convert back again to balanced.

Simply, 4 op-amp sections is all you need. The a pair 5532s will do the job. These will be Left Hot, Left Cold, Right Hot, and Right Cold.

Non-inverting inputs to ground.

10k resistors between output and inverting input.

10k resistors between Audionics and the inverting inputs.

Outputs of NE5532 sections to output connectors, via something like 51 ohms.

At this point, all you've done is inverted the outputs of the Audionics box. If absolute phase matters in this application, you can swap hot and cold signals at the output connectors.

Now, connect the computer playout system to the circuit - 10k resistors between that and the inverting inputs of the op-amps.

Of course, now we have a summing amplifier. Job done!

If the computer system is unbalanced, you can balance it by inverting each leg. Another NE5532. Very simple.

Mark
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Old 3rd Aug 2015, 6:12 am   #4
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Default Re: Simple 2 into 1 Stereo Mixer requirement

Boxes mentioned turned out to be speaker switching units Andy. Sorry my mistake, can't help, but Mark's put you on the right path. See project 94 on ESP project pages for more detail.

Andy.
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Old 3rd Aug 2015, 8:37 am   #5
yestertech
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Default Re: Simple 2 into 1 Stereo Mixer requirement

Quote:
Originally Posted by Dr Wobble View Post
See project 94 on ESP project pages for more detail.
Thanks both
Andy, not sure to what you are referring above ?

A
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Old 3rd Aug 2015, 8:55 am   #6
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Default Re: Simple 2 into 1 Stereo Mixer requirement

Here, Andy:
http://sound.westhost.com/project94.htm
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Old 3rd Aug 2015, 11:00 am   #7
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Default Re: Simple 2 into 1 Stereo Mixer requirement

Thanks Nick, that's the one.

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