CSR8645 high pitch noise

Avantu

Member
2019-10-09 7:41 pm
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.
 
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.
 
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.
 
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I know this is a bit old but I had similar issues in the past and the best advice is to use a separate supply for the module. Running all on the same supply will generate the noise. You could try to filter some with a CRC setup at highr voltage and then drop to 5V but requires a lot of trial and error. Every time I had this setup I just added a small 5v/1a board from a phone charger and had no issues.