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How to emulate line input?

dataworx

Feb 19, 2016
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Feb 19, 2016
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I've been using a TPA3116D2 chip amplifier, with great satisfaction, for about a year. I recently added a Bluetooth module so I can play tunes off my phone or other BT source. This has proved so useful that I have no use for the line input (currently from my laptop), but if I remove the line input that connects to the system via the Bluetooth board, I get a nasty hum/buzz from the amp, so I'm seeking a solution that will substitute for or emulate the line input. The buzz also occurs if I power my laptop down with the line connected.

I measured the resistance on the line output from my laptop (which when plugged in to the Bluetooth board pretty much eliminates the hum, as long as the laptop is powered on) - it's about 32 ohms on either channel. I'm also aware that line voltage is typically anywhere from 0.3 to 2.0 volts.

Can I apply resistance and/or voltage independently to the input on the BT board to eliminate the buzz so that I can remove the physical cable? If so, how would I go about it, and what resistance and/or voltage should I test with?
 

Harald Kapp

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Nov 17, 2011
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Simply short-circuiting the line input should suffice. Make sure no output can be connected to this modified input as the short circuit may damage the output.
 

dataworx

Feb 19, 2016
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Feb 19, 2016
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Thank you Harald. So I can short L channel in and R channel in to channel common/ground?
Line in to the BT board is the middle connector on the board LN-BT02:
 

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Harald Kapp

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Yes, with no source connected to these inputs.
 

dataworx

Feb 19, 2016
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Feb 19, 2016
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Yes, with no source connected to these inputs.

Followed your instructions, the hum is now at the same level as when the input is connected directly to my laptop i.e. negligible. Thank you very much for this solution.
I assume I can leave this 'short' in place with no adverse effects?
 
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