OPA551: OPA551 amplification circuit sizzling sound

Please show an oscilloscope trace of the input and output signals.

hi

The input and output waveforms are shown in the following figure；

Thanks！

Hi Jeno,

Usually audible noise comes from components that have piezo-electric effects, meaning that a changing voltage will cause a small physical increase or decrease in the component's dimensions.  This is common with low-grade ceramic capacitors.  In the case I would first suspect C33 and C36.  Can you try to test the circuit with those components removed?  You'll have to adjust the DC level, to get it within the correct DC bias, hopefully this is possible.

 Regards,
Mik

Hello，

Removing C33 and C36 still produces a sizzling sound, which cannot solve the problem. Please refer to the attachment for specific testing details. Please help analyze the cause.

OPA551 AC amplifier has noise issues and debugging feedback.docx

Hi,

Ok, so both OPA551 and ALM2403, on completely different circuits, produce the sound?  

I still suspect components other than the amplifiers.  The bypass capacitors (capacitors on the power supply pins) could source significant amounts of current if the load on the amplifier is high (current on the output).  If you change the load (resistor change from 100 Ohms to 1kOhm), does the sound go away?  

Can you tell me the part numbers for the bypass capacitors?

Regards,
Mike

Hello，

The customer tested and found that the cause of the noise was caused by the filtering capacitor of the operational amplifier power supply. There are still a few questions that need to be consulted.

1. Why does the filtering capacitor of the operational amplifier power supply cause a sizzling sound;

2. Does adding only one 100nF capacitor to the operational amplifier power supply not affect the output? Will the noise increase?

3. If it is necessary to add uF level capacitors, can the capacitors be added to the far end of the operational amplifier power supply?

4. Is there any good suggestion provided?

Thanks！

Hi Jeno, 

jeno.zhang said:

1. Why does the filtering capacitor of the operational amplifier power supply cause a sizzling sound;

Mike indices in the previous reply - Usually audible noise comes from components that have piezo-electric effects, meaning that a changing voltage will cause a small physical increase or decrease in the component's dimensions.

Ceramic capacitors can sometimes exhibit audible sounds due to the piezoelectric effects present in the ceramic material. This phenomenon is often referred to as "piezoelectric audio noise" or "capacitor singing. Please keep in mind that not all ceramic capacitors exhibit audible sounds, and the effect can vary based on the capacitor's design and the application. 

jeno.zhang said:

2. Does adding only one 100nF capacitor to the operational amplifier power supply not affect the output? Will the noise increase?

The audible noises are related the capacitor use. Please read the ceramic capacitor's datasheet for your frequency operating range. If you select a different vendor or higher quality ceramic capaictors, these audible noises may disappear. Human ear is very sensitive to audible frequency range between 2kHz to 4kHz, and 2.5kHz is very close to the peak of human ear (typically human's hearing sensitivity peaked at approx. 3kHz).

jeno.zhang said:

3. If it is necessary to add uF level capacitors, can the capacitors be added to the far end of the operational amplifier power supply?

This is power application, It is good to use low ESR capacitor, such as MLCC low esr capacitor with approx. ESR = 10mΩ type. You have to check out ceramic capacitor's datasheet, make sure that it will supply peak current and transient response in the bypass cap. At the OPA551's power supply rails, the application will have DC and AC presented at the supply pins. If low ESR bypass capacitor is used, then the high frequency will be coupled directly to ground, where capacitor is a short in AC. The high uF value, lower the AC impedance. 1uF cap at 2.5kHz will have impedance of 1/sC = 1/(2*pi*2.5kHz*1uF) = 64Ω. 10uF will have impedance around 6.4Ω etc.. 

jeno.zhang said:

4. Is there any good suggestion provided?

Change to different and higher quality capacitor the bypass low ESR capacitor, use different vendor or different size or package ceramic capacitor as the bypass ceramic capacitor. The audible sound implies that the specific ceramic material has resonance frequency at approx. 2.5kHz range. It is likely that the ceramic. The vibration in the specific frequency is resulting the audible behavior. Use different vendors or high quality capacitor may solve the problem. 

Best,

Raymond 

Hello Raymond，

Thank you very much for your support！

Thanks！