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Tpa3118/tda7498 Ground loop
Tpa3118/tda7498 Ground loop
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Old 3rd December 2017, 04:54 PM   #1
godslayer is offline godslayer  India
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Default Tpa3118/tda7498 Ground loop

Hi,

I have a simple transformer based supply from 16 and 22v center tapped transformer.

16v for tpa3118 and 22v for tda7498.

The common ground is taken at center tap.

Each rail has 10000uf capacitors.

The amps have very slight interference which goes away when you connect either of them to the output and it becomes dead silent.

However as soon as soon as i connect their inputs to output on the same soundcard(soundblaster x-fi pro 5.1 on l/r and c/sub) on different ports, there is a very loud persistent hum on the speakers. This remains once usb is disconnected completely or connected. Somehow something inside the sound card is causing hum between the two amps.


I have tried adding diodes to ground but doesnt work.

Can someone enlighten please?
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Old 7th December 2017, 02:28 AM   #2
DUG is offline DUG  Canada
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Could you draw a schematic of your hookup?

I am not sure why you need a centre tap because neither amplifier needs a negative supply.
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Old 7th December 2017, 05:38 AM   #3
godslayer is offline godslayer  India
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Quote:
Originally Posted by DUG View Post
Could you draw a schematic of your hookup?

I am not sure why you need a centre tap because neither amplifier needs a negative supply.
Hi dug,

I am using it as it had it with me.

Here is the schematic.

Click the image to open in full size.

EDIT- **NOTICED THE WRONG POLARITY OF THE LOWER CAP, ITS OK IN THE CIRCUIT**
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Old 7th December 2017, 12:44 PM   #4
DUG is offline DUG  Canada
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The transformer seems strange...a centre tap with different voltages on each side.

You have half-wave rectified the AC, using basically two diodes in series.

This will produce a lot of ripple in the supply.

It would have been better if the 16V and 22V windings were separate.
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Old 7th December 2017, 03:06 PM   #5
godslayer is offline godslayer  India
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Quote:
Originally Posted by DUG View Post
The transformer seems strange...a centre tap with different voltages on each side.

You have half-wave rectified the AC, using basically two diodes in series.

This will produce a lot of ripple in the supply.

It would have been better if the 16V and 22V windings were separate.
I have tried this setup but the capacitors were heating like crazy for unknown reasons.
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Old 7th December 2017, 03:08 PM   #6
Khron is offline Khron  Finland
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A photo of the actual (ie. real-life) setup might help clear up things...
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