Amplifier question

[zesla]

Hello.

I have made an amplifier out of LM3875 IC.
When I put the ground pin of the speaker to the ground trace of the circuit the distortion appears at one places on the ground trace but it does not apears at other places of the ground trace when I change the ground wire of the speaker!

Can somebody tells me the reall reason? I my self am thinking of ground loops but the ground trace on the circuit is robost enough... so?

Thank in advance

 

[Nigel Goodwin]

Try posting a picture of how you've built it - but layout on these amplifier chips is pretty critical.

 

[zesla]

Try posting a picture of how you've built it - but layout on these amplifier chips is pretty critical.

Thanks Nigel, Sorry I have no pic right now.

How to learn to design a proper layout??

Is a software like Protel able to detect the proper layout for a circuit?

Thanks

 

[ljcox]

Protel won't do that for you - that is your job.

The Gnd line must be laid out so that the high currents do not pass through the same tracks as the input currents.

I drew that attached circuit for someone else recently to make that very point.

He has programmed the PIC to generate a Ding/Dong doorbell sound.

 

[crutschow]

Page 15 of the National LM3875 data sheet discusses layout, ground loop, and stability issues. Have you read that? If not, why not?

 

[ljcox]

Also have a look at this

LM3875 PCB Layout - diyAudio