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Class D Switching Power Amplifiers and Power D/A conversion

TDA8954th btL amplifier
TDA8954th btL amplifier
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Old 26th April 2021, 06:21 PM   #71
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
@ponyta,
You have done well and tell us important information.
When the amplifier is not connected to a source or the input is short-circuited, there is no noise. Thus, it seems not to be the amplifier power supply in itself that causes the problem.
When you use a source but stop the music playing, you clearly hear hum. Thus, the hum origins from the connection with the source OR, if you use a smartphone as source, the smartphone disables the headphone output when you stop the music in order to save battery.
First test for you to do is to connect your smartphone as source, without being connected to a charger, and play music from the smartphone while you slowly reduce the volume on the smartphone to zero (don't press stop or pause). This way the headphone output is not disabled. Do you still hear hum-noise?

Last edited by FauxFrench; 26th April 2021 at 06:25 PM.
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Old 28th April 2021, 12:50 PM   #72
john_lenfr is offline john_lenfr  France
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Join Date: Jun 2005
Location: France
Hi FauxFrench, finaly changed my plan and re use an old hypex ucd180.

Tda stay in the box for now.

If ponita arrived at something good maybe I will test to modify the module.
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Old 4th May 2021, 03:56 AM   #73
ponyta is offline ponyta
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Join Date: Dec 2019
Thank you FauxFrench!
I did connect my board with a smartphone, play music, adjust volume to 0, and there no hum.
But whenever my hand touches the phone or the wire. I heard the hum, it is loud and sensitive even I come nearby the wire, not touch it.

Back with my subwoofer filter preamp circuit, I try with a different amplifier board (mono class a/b run 1pair a1943-c5200 transistors), it doesn't hum at all
(my preamp board quite similar here: NE5532 Bộ Lọc Thong Thấp Ban Loa Sieu Trầm Am Lượng Ban Module Khuếch Đại 9 15V Lọc Mo đun|Integrated Circuits| - AliExpress)
Reading tda8954 datasheet have some info, so I think maybe mass connect both 2 boards could fix that 50hz background hum.
(GDN mass connect, ground shield... etc I don't know what exactly it is or how to do. I'm so amateur, really need help).
ah, I am sorry for replying late, so busy with the living thing.
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Old 4th May 2021, 07:33 AM   #74
ponyta is offline ponyta
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Join Date: Dec 2019
I use a 24-0-24 transformer for tda8954 board and another 15-0-15 transformer for preamp filter board
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Old 4th May 2021, 11:06 AM   #75
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
@ponyta
Is your TDA8954TH amplifier mounted in a metallic cabinet? Your pre-amplifier also? Do you have some loose zener-diodes?
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Old 5th May 2021, 10:55 AM   #76
ponyta is offline ponyta
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Join Date: Dec 2019
No, I just connected the boards together, all on the wooden tabletop:

A-preamp board
B-TDA8594 btl board
C-Mono A/B amp board

B, C run a 24-0-24V power supply and no hum when no input, A run a different dual 15Vs

A+C--> no hum
A+B--> hum

I just thought about floating input in tda 8954 datasheet
A and C have 0v as (-) sound in signal so just connect signal wire and they are grounded together
but B is BTL, I don't know whether sound signal (-) (0v in A) can be wired to 0v in B to fix hum??
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