Audio amplifier help

[Liamjames193]

I tinker with small class d amp chips. I'm currently working on a MIX2052 chip 8 pin. Google shows only 1 schematic. Built amp. Amp clips at higher volumes. Does anyone know what filters I can try or any other way to eliminate the clipping? I am using a 4 ohm 3 watt speaker with a 2200maH 3.7 volt li-ion battery.

 

[Nigel Goodwin]

'Higher volumes' is meaningless, what actual level does it clip at? - if it's only fed from 1 x 3.7V, and it's bridged, then maximum output is only 7.4V p-p less losses in the chip. Which is going to be less than 1.7W in 4 ohms.

Any amplifier is going to clip if you try and get more out of it than it can provide.

 

[Liamjames193]

I am rather new to building amps and have no real education. Only being self taught online and through books I've been able to afford. I am using 5 volts. Max is 5.5volts. Does the same with 3.7 volts. Does the same with different speakers. It used to sound louder when I first built it. But when I went to package it, that's when it started clipping. I've tried all new components and I can't figure it out. I will be back Sunday night. I'm going out of town. Thanks in advance for all your help.

 

[Nigel Goodwin]

If you can borrow a scope you can measure what level it's clipping at, or take it to somewhere where you can use a scope (school, college, friend?).

 

[audioguru]

The datasheet is written only in Chinese, but in English it says, "3.9 Whats, 5.5V supply, 4 ohms load, 10% (horrible clipping) distortion".
A graph on the datasheet shows it beginning to clip at 0.7W into 4 ohms when the battery is 3.6V, but 1.2W when the battery is fully charged at 4.2V.

Sure you can filter away the distortion, if you filter away all the audio.

 

[unclejed613]

it clips because you are trying do drive the output past the power supply rails. AG is right, a power specification measured at 10% distortion is a bogus measurement. the proper way to measure it is a hair below clipping, which is where most hi-fi manufacturers measure the output power.

 

[Liamjames193]

Thanks for all the replies. I'm sorry it takes me so long to get back online as I am frequently away from the internet for a couple days at times. Also, I am relaying most of these messages for my brother who is incarcerated. He has email but not internet. I'm able to see him on his phone at his state prison, but he can't send anything. But I am able to re-draw any schematics he shows me. I am really trying to help him. I appreciate all your help. So this chip really isn't a good chip? It's weird as he said it sounded great when he put it together initially in its testing stage. But when he went to actually package it, using the exact same caps and resistors it started clipping.

This is his schematic that he setup. The speaker and IC chip both came from a Bluetooth speaker. The speaker is a 4ohm 8 Watt speaker. Maybe he's doing it wrong? Any suggestions? Thanks again for your input. And for putting up with this newbie electronic guru. He does not have access to any real test equipment other then a multimeter.

 

[audioguru]

The circuit is connected correctly but the low value (0.1uF) of the capacitors into the 33k input resistors cuts low frequencies.
The supply voltage and speaker impedance determine the maximum output power before clipping. Into a 4 ohm speaker a supply of 3.7V gives 0.8W and a supply of 5.0V gives 2.2W. 2.2W sounds only a little louder than 0.8W. 8W sounds twice as loud as 0.8W.

Maybe the original speaker was larger (more sensitive) than the speaker now.

 

[Liamjames193]

He is currently using the original speaker that came with the device. He's also tried larger and smaller speakers and the clipping seems to be at the same level on the volume dial. It seems to clip more with a lot of bass. What size input caps would you recommend for me to try?

 

[audioguru]

The amplifier causes clipping, the speaker doesn't. If the speaker is more sensitive then the volume control can be turned down.
An amplifier output produces clipping distortion when its input level is too high for the low maximum output power of the amplifier.
A "lot of bass" is an input level that is too high for the low maximum output power of the amplifier.
If the amplifier produced much more maximum output power and if the speaker can produce very low frequencies then the 0.1uF capacitors that feed the 33k resistors and therefore cutting frequencies below 48.5Hz could be increased to 0.22uF and therefore would produce frequencies down to 22Hz.

 

[unclejed613]

so, 2.8V of output swing is about 1V RMS out of the amplifier. that means the current through the speaker is 500mA, so with a 2.8V power supply you have 0.5W of audio. with a 5V supply, you have about 1.8V RMS out of the amplifier, which will give 900mA through the speaker, yielding 1.6W from the speaker.