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Class D Switching Power Amplifiers and Power D/A conversion

Nobsound / Douk / Fosi TPA3116 2.1 Amp Gain
Nobsound / Douk / Fosi TPA3116 2.1 Amp Gain
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Old 20th February 2019, 03:03 PM   #1
von Ah is offline von Ah  United States
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Default Nobsound / Douk / Fosi TPA3116 2.1 Amp Gain

I picked up the Fosi version of this finished 2.1 amp (black case). It sounds pretty good compared to the Sanwu TPA3118 2.1 board I've had for a while. It appears to be the same board as the Nobsound branded amp.

I like the extra available controls compared to other 2.1 amps, but like most, the gain is set too high for my tastes.

In the attached stock pictures of the internal board, can anyone identify where I might be able to change the gain by removing/changing a resistor (or two for the two TPA ICs)?

Alternatively, if I use a 12V SMPS instead of 20V, could that help, in theory?

Thanks for any suggestions!
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File Type: jpg 71QC2Ose9gL._SL1000_1024x1024@2x.jpg (147.8 KB, 121 views)
File Type: jpg 613FxIUMbUL._SL1000_1024x1024@2x.jpg (69.9 KB, 120 views)
File Type: jpg s-l1600.jpg (209.6 KB, 116 views)

Last edited by von Ah; 20th February 2019 at 04:12 PM.
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Old 21st February 2019, 07:27 PM   #2
Khron is offline Khron  Finland
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http://www.ti.com/lit/ds/symlink/tpa3116d2-q1.pdf

As per the datasheet linked above, specifically section 7.3.1 on pages 10-11, the pair of resistors connected between GVDD (pin 7), Gain/Slv (pin 8) and ground controls the gain.

Best case scenario, one of the chips is set as "master" and the other to "slave".

Now, despite what some might say, i'd argue that the exact values of the resistors are irrelevant (provided they're kept in the 10k-100k range); what's more important is the voltage at their midpoint, as far as the gain-setting-detection circuitry in the chip is concerned.

Those stock photos aren't too revealing. Any chance you could remove the heatsink on your board? Some of the relevant resistors may be hiding under it (assuming they didn't place some of them on the bottom - doubtful, since that would mean extra expense, and there's plenty of space on the top).
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Old 22nd February 2019, 04:06 AM   #3
von Ah is offline von Ah  United States
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Thanks, Khron. I'll get a pic of the area around the chips without the heat sink.
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Old 23rd February 2019, 02:41 AM   #4
von Ah is offline von Ah  United States
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Here are pictures of the actual unit.
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Old 23rd February 2019, 03:05 AM   #5
Khron is offline Khron  Finland
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Looks like they're both set as "master" - slightly less than ideal, but if you haven't noticed any problems, that's not an issue.

Removing those two "104"-marked resistors (next to the "10k" silkscreen markings, next to the "473"-marked ones) will drop the gain from 32dB to the minimum of 20dB.
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Old 23rd February 2019, 03:26 AM   #6
von Ah is offline von Ah  United States
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Excellent! Just to confirm, I can just remove these (circled in magenta)?

That's easy. Thanks a bunch!
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Old 23rd February 2019, 02:22 PM   #7
Khron is offline Khron  Finland
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Exactly.

If you can be bothered, you can remove just one at a time, so you can compare the before/after.
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