Recently I designed my first amplifier PCB using TPA3116, and using ne5532 as pre-amp.
I would like to design the amp in such way that it can operate at wider voltage range depending on the power supply, say 7-20Vdc. But for now, let's say this PCB is designed for 12V supply.
I know that on op-amps, their characteristics stand out better with higher voltage dual-rail DC supply, like +-16Vdc. But since it's the very first time for me to design such PCB, I played safe and didn't went such high voltage, and I chose the approach to make a +-7.5Vdc using a regulated switch mode DC-DC boost converter, the related schematics and board layout are attached to this thread.
My problem is that the preamp is constantly providing a 1MHz clean-looking sine wave with 1V peak-to-peak at the output. And coincidentally, it is also the switching frequency of the boost converter. This cause a very audible noise from the speakers. And if I remove the preamps, the output of TPA3116 is still noisy which I believe it is also caused by the same DC-DC boost converter.
I am looking for the solution to this problem. It could be my bad schematic, board layout, or actually me choosing the wrong approach from the start.
Please let me know how to solve this problem. Thanks a lot.
I would like to design the amp in such way that it can operate at wider voltage range depending on the power supply, say 7-20Vdc. But for now, let's say this PCB is designed for 12V supply.
I know that on op-amps, their characteristics stand out better with higher voltage dual-rail DC supply, like +-16Vdc. But since it's the very first time for me to design such PCB, I played safe and didn't went such high voltage, and I chose the approach to make a +-7.5Vdc using a regulated switch mode DC-DC boost converter, the related schematics and board layout are attached to this thread.
My problem is that the preamp is constantly providing a 1MHz clean-looking sine wave with 1V peak-to-peak at the output. And coincidentally, it is also the switching frequency of the boost converter. This cause a very audible noise from the speakers. And if I remove the preamps, the output of TPA3116 is still noisy which I believe it is also caused by the same DC-DC boost converter.
I am looking for the solution to this problem. It could be my bad schematic, board layout, or actually me choosing the wrong approach from the start.
Please let me know how to solve this problem. Thanks a lot.
Attachments
R13 and R14 are extremely high impedance - they are supposed to be setting the virtual ground and need to be either low impedance, or buffered with another opamp. Try 1k and 1k for R13/14 and add 100uF across C33/C34 so the virtual ground is properly stiff across the audio band. The rest of the circuitry is relying on this circuit node...
Did you follow the datasheet layout for the MT3608 to the letter? Its wise to do so, switchers are very fussy.
Did you follow the datasheet layout for the MT3608 to the letter? Its wise to do so, switchers are very fussy.
@Mark Tillotson I will try replace R13 and R14 with lower values. I chose 100kOhm because it is only for generating the reference voltage to feed into the input of the preamps, where there will be no current flow considering the high input impedance of op-amps. There is no other connection to this node from the rest of the components.
In MT3608 datasheet, they dont even have an example layout lol, I simply followed the guides and did my own layout, perhaps choosing another chip could be wise. I tried measure the noise of the output with an oscilloscope, on both the switching output, and the voltage regulator output. The converter outputs 16.8Vdc with 100mV peak to peak noise, the waveform is clean and purely the charging and discharging of the capacitors. After the voltage regulator, it outputs 15Vdc, and I couldnt measure the noise with my equipment.
In MT3608 datasheet, they dont even have an example layout lol, I simply followed the guides and did my own layout, perhaps choosing another chip could be wise. I tried measure the noise of the output with an oscilloscope, on both the switching output, and the voltage regulator output. The converter outputs 16.8Vdc with 100mV peak to peak noise, the waveform is clean and purely the charging and discharging of the capacitors. After the voltage regulator, it outputs 15Vdc, and I couldnt measure the noise with my equipment.