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Class D Switching Power Amplifiers and Power D/A conversion

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix
SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix
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Old 28th June 2016, 12:58 AM   #1
doctormord is offline doctormord  Germany
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Default SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix

In addition to this thread:

http://www.diyaudio.com/forums/class...-any-good.html

I just bought one of these boards to measure how they'll do and got a v2.2.

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix-sanwu_tpa3116_csr8635_v2-2_1_1024-jpg

Sticking down a heatsink like this is rather useless. Anyway, cleaning the snot off:

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix-sanwu_tpa3116_csr8635_v2-2_2_1600-jpg

Listening to this amp reveals a slight "hiss" of HF/RF interference when having a stream connected and muted or having quiet passages in the music/sound.

From the other thread:

Quote:
Originally Posted by MosMike View Post
I have the same board since december and it is a disappointment in several aspects:
1) poor connectivity
2) hiss
3) unresponsive buttons
4) loud beeps when pairing and pushing buttons
5) no sound until a button is pressed

maybe you were lucky to receive a "first run" board
Point 2 is fixed now.

As the noise is independent from the CSR's digital volume level, the hiss is suspected to come from the link between the CSR8635 module and the TPA3116 itself and/or most likely from the power supply design.

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix-sanwu_tpa3116_csr8635_v2-2_4_1600-jpg

Sanwu decided to do a Differential 2 Single-Ended Conversion to feed the TPA3116, why ever, as shown here

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix-sanwu_tpa3116_csr8635_v2-2_4_orig_1600-jpg

Having a direct differential link is all it needs to be dead quiet, so more hiss/noise.

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix-sanwu_tpa3116_csr8635_v2-2_4_noisefix-jpg

The populated coupling caps are 4.7uF in 0603, most likely X5R 6.3V, so with 32dB gain and 15k input impedance, the f3 frequency will be at 2.3Hz. Changing them for 1uF X7R would give 10.6Hz, still low enough for normal listening.

Another benefit is the now lowered quiescent current.

Before the mod:
Idle without Link (aka TPA3116 shut down): 20mA
Connected to a device and lowest volume level: 50mA

After the mod:
Idle without Link (aka TPA3116 shut down): 15mA
Connected to a device and lowest volume level: 45mA
Attached Images
File Type: jpg SANWU_TPA3116_CSR8635_V2.2_1_1024.jpg (151.6 KB, 3283 views)
File Type: jpg SANWU_TPA3116_CSR8635_V2.2_2_1600.jpg (403.4 KB, 3271 views)
File Type: jpg SANWU_TPA3116_CSR8635_V2.2_4_1600.jpg (431.6 KB, 3137 views)
File Type: jpg SANWU_TPA3116_CSR8635_V2.2_4_Orig_1600.jpg (432.9 KB, 3117 views)
File Type: jpg SANWU_TPA3116_CSR8635_V2.2_4_NoiseFix.jpg (477.8 KB, 3136 views)

Last edited by doctormord; 28th June 2016 at 01:23 AM.
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Old 28th June 2016, 07:35 PM   #2
easp is offline easp
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Nice, thanks for sharing the analysis and the solution!
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Old 28th June 2016, 07:59 PM   #3
doctormord is offline doctormord  Germany
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Quote:
Having a direct differential link is all it needs to be dead quiet, so more hiss/noise.
should be "no more hiss/noise".
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Old 28th June 2016, 10:48 PM   #4
xrk971 is offline xrk971  United States
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SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix
Do you have a photo showing how you made the connections?
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Old 28th June 2016, 11:06 PM   #5
doctormord is offline doctormord  Germany
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Default SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix

Its just 4 wires from one end of the caps to the pad near the amp pins. I'll post a pic later. Pad connection is like shown on the last picture with the yellow lines, start/end of the line is on the corresponding pad.

Last edited by doctormord; 28th June 2016 at 11:10 PM.
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Old 28th June 2016, 11:27 PM   #6
xrk971 is offline xrk971  United States
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SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix
Did you pull off the offending parts first?

They did the differential input to reduce common mode noise or maybe prevent BT buzzing sound? I did not hear BT buzzing sound with this amp - and don't recall a hiss problem either. It's been a while since I listened though.

Last edited by xrk971; 28th June 2016 at 11:31 PM.
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Old 28th June 2016, 11:40 PM   #7
doctormord is offline doctormord  Germany
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Default SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix

I pulled down the series resistors and the caps in front of the 3116 ic. While this is enough to decouple the 5532 from the signal path, all parts shown with an "x" aren't needed anymore.

The amp is much much quieter now compared to the Diff2SE solution. (There's some small residuals left coming from the 32dB setting. I can hear that from 10cm in front of the tweeters which are high efficient. Before you could hear from ~2 meters. Ymmv as the speakers used to test are ~96dB/W/m,the mig/high is like ~100dB/W/m. (Bass + Mid are AlNiCo magnets)

Last edited by doctormord; 28th June 2016 at 11:42 PM.
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Old 29th June 2016, 12:45 PM   #8
doctormord is offline doctormord  Germany
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Like so:

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix-sanwu_tpa3116_csr8635_v2-2_5_noisefix_1600-jpg
Attached Images
File Type: jpg SANWU_TPA3116_CSR8635_V2.2_5_NoiseFix_1600.JPG (352.2 KB, 2982 views)
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Old 29th June 2016, 01:55 PM   #9
doctormord is offline doctormord  Germany
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If you want to keep your "Common-Mode-Noise-Filter" you can alternatively change those 4x 75k resistors (753) to 22k to bring the gain of the stage down from 10.5dB to 0dB. Maybe this would be already enough reduction to satisfy the demands. (I'd prefer the differential only connection.)

Last edited by doctormord; 29th June 2016 at 02:02 PM.
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Old 29th June 2016, 02:35 PM   #10
doctormord is offline doctormord  Germany
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In direct comparison, the "SANWU TDA7492P + CSR8635" is much noisier.

The interstage section is nearly the same, beside the switched line-input:

SANWU TPA3116 + CSR8635 Bluetooth 4.0 - Noise Fix-sanwu_tda7492p_csr8635_v3-2_3_1600-jpg

Due to the layout, the RF is coupling into the audio path via the 3.5mm connector. This get really worse when having a cable connected and there's a device coupled via Bluetooth. Beside the RF-noise the TDA7492P is noisier on high gain settings than the TPA3116. It would have been better to make use of the internal ADC of the CSR8635.


Also this board doesn't switch of the TDA7492P when idling and features Power-On/Off Plop.
Attached Images
File Type: jpg SANWU_TDA7492P_CSR8635_V3.2_1_1600.jpg (399.8 KB, 365 views)
File Type: jpg SANWU_TDA7492P_CSR8635_V3.2_2_1024.jpg (117.7 KB, 305 views)
File Type: jpg SANWU_TDA7492P_CSR8635_V3.2_3_1600.jpg (376.0 KB, 3612 views)

Last edited by doctormord; 29th June 2016 at 02:37 PM.
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