LM4766 silent or it give distortion

Lukas Marek

Other Parts Discussed in Thread: LM4766, TPA3116D2

Hello,

I use the LM4766 in single supply mode. For that I use Figure 6 as a bridged amp (Figure 5) in the datasheet.

The resistor RSN and the capacitor CSN left out.

My problem is, the output works very silent (maybe the Spike protection). If I paste the 22uF (Ci) into the ciruit, the output give distortion on the same settings. I can only set the input voltage down so I make a low noise.

If I don't paste Ci, the distortion is less.

In both cases the sound is very silent. Should I change Rf?

over 4 years ago

0 Xiaolin Qin over 4 years ago

TI__Expert 6295 points

Hello Marek,

for figure6 optional components, what you select for your setup? do you use TI EVM run test?

regards

Linda

0 Lukas Marek over 4 years ago in reply to Xiaolin Qin

Prodigy 110 points

Hello Linda,

whether I use optional components or not, the LM4766 work silent.

what is TI EVM run test?

regards

Lukas

0 Luis Fernandes de Pina over 4 years ago in reply to Lukas Marek

TI__Genius 14640 points

Hello Lukas,

Can you post your schematic for clarity. Also can you see what the current flowing through Rm/your mute pins when you don't see audio.

Best Regards,

Luis

0 Lukas Marek over 4 years ago in reply to Luis Fernandes de Pina

Prodigy 110 points

Here is my schematic. I have already replace the BC547 with 2N3904 with the right polarity.

X5-2 is for +24V and X5-1 for 0V (GND)

0 Yanming Gong over 4 years ago in reply to Lukas Marek

TI__Mastermind 19480 points

Hello Marek,

Rf is feedback resistance to provide AC gain and Ci is feedback capacitor which ensures unity gain at DC. Ri and Ci also create RC filter.

You can change Rf and Ci to adjust the gain setting.

Since LM4766 is old device, I suggest you can consider new generation device TPA3116D2 for new design, you can get more technical support.

Regards,

Derek

0 Lukas Marek over 4 years ago in reply to Yanming Gong

Prodigy 110 points

Hello Derek,

if I use my frequenz generator and Oszilloskope I can listen a silent beep from the LM4766 and the voltage breaks in to 23,5V. Is that a malfunction? If I used the Ci (for one input to compare) the output didn't work better.

If I disable S1 [JP1 in my picture] (for Rm), the beep is not available anymore (or very very silent), but my output show me a direct current from my supply voltage.

0 Yanming Gong over 4 years ago in reply to Lukas Marek

TI__Mastermind 19480 points

Hi Lukas,

According to your description, I think there would be OC fault happened.

I suggest you can decrease Rf to reduce the gain setting.

Regards.

Derek

0 Lukas Marek over 4 years ago in reply to Yanming Gong

Prodigy 110 points

Hi Derek,

I have decreased the Rf to 12kOhm. I measure the output with an oszi and the gain isn't evenly. It is doing a sharp step from 0V to +12/-12V (with the input frequency) on the output. In this case I can hearing a beep (maybe from the frequency).

Regards,

Lukas

0 Yanming Gong over 4 years ago in reply to Lukas Marek

TI__Mastermind 19480 points

Hi Lukas,

So it works well now?

Regards,

Derek

0 Lukas Marek over 4 years ago in reply to Yanming Gong

Prodigy 110 points

Hi Derek,

no, because I can listen a beep from the LM4766 if my input amplitude is high enough. Should the gain nearly linear to the input?

Regards,

Lukas

0 Yanming Gong over 4 years ago in reply to Lukas Marek

TI__Mastermind 19480 points

Hi Lukas,

I suggest you check the output and input waveform. I think the output may be clipped.

Regards,

Derek

0 Lukas Marek over 4 years ago in reply to Yanming Gong

Prodigy 110 points

Hi Derek,

yes I have a square wave voltage on my output, but the gain isn't linear to my input.

It may be the circuit have an error? I used the same from the datasheet (Figure 6), but the circuit "OC".

With a normal OPV the gain is usually linear to my input, but with the LM4766 the circuit it start at 1V/pp (input) increase the output to +/- 12V. It still the same at higher input amplitude.

My supply voltage is +24V.

Regards,

Lukas

0 Yanming Gong over 4 years ago in reply to Lukas Marek

TI__Mastermind 19480 points

Hi Lukas,

What's the load impedance? 2ohm or 4ohm?

The gain setting is related to the Rf and Ri resistor, if the 2 resistors are fixed, I think the gain setting variation is very small.

Device limits the output current to approximately 4.0APK, so please monitor the output current when issue happened.

The schematic looks fine, I did not find obvious error.

Regards,

Derek

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LM4766 silent or it give distortion