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Impedance matching

Ned

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I am interfacing PCM5100A audio DAC which is 2.1 Vrms (Ground Center), Stereo line output load (1K ohm, nominal 10K ohm) to a mixer stage audio channel that is 500 ohm input.
I am using only a single output (mono) channel from the DAC and the DAC output is connected, per its application note, to a 470 ohm resistor and 2.2nF cap (RC).

Having only basic knowledge with impedance matching; Does the 470 ohm resistor in series with the DAC output increase the input impedance to near 1k? Hence, testing this in practice is working without attenuation.

Or should I consider adding a simple op-amp; not to amplify the signal, but to lower the output impedance? Any advice on the op-amp and its schematics is highly appreciated.

Thanks
Ned
 

DVDdoug

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We don't impedance match with modern audio... It was a thing back in the days of audio transformers & tubes...

You want a low impedance source driving a higher impedance load.

to a mixer stage audio channel that is 500 ohm input.
The microphone inputs might be 500 Ohms but line inputs should be 10K or more. Microphone signals are also millivolts so a mic input is "wrong" for your DAC output.

Just for a different example, an amplifier with an 8-Ohm output is rated for use with 8-Ohm (or higher) speakers but it has an internal source impedance of less than 1 Ohm. The ratio of load impedance to output impedance is the "damping factor". Sometimes you'll see a spec for that and higher is better (up to the point to where it's high enough that it doesn't matter).
 
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Ned

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You want a low impedance source driving a higher impedance load.

Thanks for the reply.

To achieve this then do I need to lower the 1K min load line output of the DAC to at least 500 ohm or lower?
The mixer input is Line input marked only as 500 ohms input impedance.
 

DonR

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Ideally, you want a unity-gain op-amp buffer after the DAC and before the mixer. Infinite (or close enough) input impedance with a sub-50 ohm (usually under 1) output impedance.
 

sarumbear

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I am interfacing PCM5100A audio DAC which is 2.1 Vrms (Ground Center), Stereo line output load (1K ohm, nominal 10K ohm) to a mixer stage audio channel that is 500 ohm input.
Are you sure that your mixer’s line input has such a low input impedance?
 
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Ned

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Ideally, you want a unity-gain op-amp buffer after the DAC and before the mixer. Infinite (or close enough) input impedance with a sub-50 ohm (usually under 1) output impedance.
A voltage follower and a mechanism to limit the current.

Are you sure that your mixer’s line input has such a low input impedance?

Yes, its a custom 8 channel line inputs that clearly marked for 500 ohm input and then it outputs the mixed signals to a 500 ohm impedance headphones.
 

DonR

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A voltage follower and a mechanism to limit the current.
Yes, even a 50-ohm resistor on the output would be enough to limit the current in the event of a short circuit and you would still have only a 50-ohm output impedance.
 
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