Author Topic: Conversion of audio amp's AC coupled output to DC coupled output  (Read 1316 times)

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Online ricko_ukTopic starter

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Hi,
I want to modify the output of an audio amplifier I got from Amazon so that it has a DC component (doesn't matter how much, as long as the AC signal says above GND.

With reference to the attached picture, it looks like the output is differential. The IC is hidden under the heatsink but in the description it says it uses "TI TPA3116 and NE5532" (here's a link to the datasheet for the power stage one: https://www.ti.com/lit/ds/symlink/tpa3118d2.pdf?ts=1593702988078&ref_url=https%253A%252F%252Fwww.google.com%252F )

Would I be able to achieve what mentioned above by just shorting out the two caps?

I assume that would work if it was a single ended output but not sure about the differential output.

If my suggested solution doesn't work with the differential output configuration, can you offer any quick and simple suggestion to achieve that quickly and simply without having to build a new circuit?

(SIDE NOTE: at the back there are a couple of switches which allow to select one of 4 gains for the amplifier)

Thank you
« Last Edit: July 02, 2020, 03:19:27 pm by ricko_uk »
 

Offline TheMG

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Re: Conversion of audio amp's AC coupled output to DC coupled output
« Reply #1 on: July 02, 2020, 06:33:37 pm »
The capacitor is going to be in parallel with the output, not in series with it. It works together with the inductor to form a low pass filter rejecting the high frequency switching of the class D amplifier and only letting the audio pass through.

The amplifier output is in effect already DC-coupled, and the differential output makes it possible to avoid DC at the speaker while using a single power supply rail.

The TPA3116 also has integral DC protection, which will shut down the amplifier if DC is detected at the output.

Unfortunately, this is just the wrong IC for the job. About the only way you're going to do what you want is to float the entire power supply above ground potential (for example, the GND of the amplifier is actually +12V, and the VCC is at +24V, so you have 12V supplying the amplifier but the output always has 12V of DC on it). Such an approach would require of course a more complex power supply setup and will also require the input signal's ground to be DC isolated (by use of a transformer or capacitors), not a very practical approach.
« Last Edit: July 02, 2020, 06:36:41 pm by TheMG »
 
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Offline NiHaoMike

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Re: Conversion of audio amp's AC coupled output to DC coupled output
« Reply #2 on: July 03, 2020, 01:18:25 am »
Check one side of the differential output to ground - it's going to be about half the supply voltage.
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Offline tooki

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Re: Conversion of audio amp's AC coupled output to DC coupled output
« Reply #3 on: July 04, 2020, 05:55:19 am »
Why would you want a DC offset on a speaker amp? (And if you’re not using it to drive speakers, then why did you get a speaker amp?)
 


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