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Feedback wanted - TV Fixed Line-out Volume Control
Feedback wanted - TV Fixed Line-out Volume Control
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Old 29th December 2017, 11:41 PM   #1
mgf897 is offline mgf897  Australia
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Default Feedback wanted - TV Fixed Line-out Volume Control

Hi All,

I recently tried to connect some external amplified speakers (PC speakers) to my Samsung TV. The sound was MUCH better but there was no way to control the volume without getting up and turning the volume knob on the speakers.

I've drawn up a schematic for a volume control board to accept the 3.5mm fixed audio line out from the TV and provide a variable line out signal to the external speakers. The micro will control the digital pots using the IR signal from the TV remote. The board will be powered by USB which is available on the back on the TV.

Concerns:
* I have no isolation on the audio, will I have problems with ground currents?
* Have I completely missed something/made an obvious mistake?

Any feedback/critique is appreciated

Thanks,

Matt
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Old 30th December 2017, 12:23 AM   #2
linuxworks is offline linuxworks  United States
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digital pots often suck for audio.

look into using the pga2311. great chip, also has zero-crossing detection which the digipot solution will never have.
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Old 30th December 2017, 12:47 AM   #3
mgf897 is offline mgf897  Australia
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Thanks for the recommendation linuxworks, zero-crossing was something I hadn't considered. The pga2311 certainly looks like it would simplify some aspects of the design
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Old 30th December 2017, 01:45 AM   #4
linuxworks is offline linuxworks  United States
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it has an onboard op-amp (buffer) for output. that's nice. still, I recommend 3 stages: prebuffering, pga chip, postbuffering.

postbuffering protects against reversing input and output jacks and blowing up the chip. plus, its nice to have to decouple the chip from the outside world.

prebuffering, since you want to give the pga chip's input a fairly low and predictable Z. an input OA can also limit the input swing that the pga sees (oa should run slightly lower in rails than pga) and that tops bad pga behavior.

(ob disc, I'm working on a pga/arduino board; you're welcome to give it a try.)
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