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CSR8645 high pitch noise
CSR8645 high pitch noise
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Old 20th November 2019, 01:27 PM   #1
Avantu is offline Avantu
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Join Date: Oct 2019
Default CSR8645 high pitch noise

Hi!

I'm building myself stereo amplifier based on TDA7292 and CSR8645. My problem is that when i connect bluetooth module to amplifier there is very loud high pitch noise, similar to modem or data transfer. I power everything by IRM-60-24 and use LM317Ts to step down voltage for bluetooth and other periferials such as opamp LME47920. Once i tried lab power supply with 3 independent outputs, 24V for amplifier, 5V for transistor to activate amplifier and 3.3V for bluetooth and it was playing fine. But when i try to connect everything with IRM it is horrible. What can i do? Would it be better if i just connect 18650 battery to bluetooth? But i wanted it to run entirely on IRM-60-24 and idk what to do. Even when i used IRM only for amplifier and arduino or nucleo for 3.3 and 5V lines there was the same problem. Do you have any ideas? The sound doesn't have to be perfect at all, i just want to remove noise as cheaply and easy as possible, this whole thing is more like experiment than proper audio system.
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Old 20th November 2019, 06:00 PM   #2
Mark Tillotson is offline Mark Tillotson
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Join Date: May 2018
Location: Cambridge UK
Sounds like a beat note between the SMPS's switching frequency and the Bluetooth unit's DAC sample rate. When such a beat note ends up in the audio range it will be very obvious - the solution is to change one of the frequencies (try a different PSU?). Alternatively aggressive filtering may be needed to knock down one or both ultrasonic notes.
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Old 21st November 2019, 09:14 AM   #3
Avantu is offline Avantu
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Join Date: Oct 2019
I have tried laptop power supply and lab power supply with no better results. (arduino and nucleo also as I mentioned before.) Maybe problem is somewhere else?
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Old 23rd November 2019, 01:48 PM   #4
Markw4 is offline Markw4  United States
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Join Date: Jul 2016
Location: California
Switching power supplies can make some RF noise, both conducted and radiated. Hard to say much based on the information you have provided so far.

When you say you hook up a blue tooth module does that mean it is the only available input device and its output is routed to the amplifier at all times, or can you switch to another input device while blue tooth is still powered up? The idea would be to try to figure out if the noise is coupled through the power supply, if the blue tooth module needs more power filtering when powered from an smps, or what. Many different possible things might be wrong, and we know nothing about the details of what you have done.

If you want to post clear, close-up, high-resolution pictures of your design, and a schematic too, then maybe people here will have a better idea of what the problem might be.

Last edited by Markw4; 23rd November 2019 at 01:51 PM.
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