Stereo problem

soundbabe · 2nd April 2010, 01:04 PM

Hello guys,

I tried to design a stereo amplifier using 2 LM3875 chips.
The power supply is a 50V transformer.
The first problem I am facing is that I have the left output audio in the right output speaker and vice versa, It is weak but considerable.
Can you tell me the reason and the soultion of the said problem please?

THANKS.

gfiandy · 2nd April 2010, 06:03 PM

Hi,

You have crosstalk, this can occur in may places and without a circuit diagram, PCB layout and photos of the actual design it will be very hard for people to help you.

The most common reason for this is shared ground(0v) returns so look for that first.

Regards,
Andrew

soundbabe · 2nd April 2010, 08:22 PM

Ok thanks for your help.
How can I trim the said problem please?
And how can I solve the shared ground problem too? Can I use bigger capacitors between ground and +/-??

soundbabe · 2nd April 2010, 08:28 PM

I have even noticed that the place of one output pins (the ground one) is important to causes or removes the humm noise I hear in the speaker, How can I find out the best place for it too?

P,S Can somebody please introduce me a schematic based upon LM3875 as an stereo Amplifier? I want to trim my design by an sample one too to remove such problems.

boholm · 4th April 2010, 05:09 PM

The data sheet of LM3875 contains a schematic:
http://www.national.com/ds/LM/LM3875.pdf
Or you can do a search on "LM3875" and get lots of information.

A suitable power supply could be this:
Power Supply for Power Amplifiers

Or this:
Solid State Power Amplifier Supply Part 1

2nd April 2010, 01:04 PM	#1
soundbabe diyAudio Member Join Date: Feb 2010	Stereo problem Hello guys, I tried to design a stereo amplifier using 2 LM3875 chips. The power supply is a 50V transformer. The first problem I am facing is that I have the left output audio in the right output speaker and vice versa, It is weak but considerable. Can you tell me the reason and the soultion of the said problem please? THANKS.

4th April 2010, 05:09 PM	#5
boholm diyAudio Member Join Date: Apr 2004 Location: Copenhagen	The data sheet of LM3875 contains a schematic: http://www.national.com/ds/LM/LM3875.pdf Or you can do a search on "LM3875" and get lots of information. A suitable power supply could be this: Power Supply for Power Amplifiers Or this: Solid State Power Amplifier Supply Part 1 __________________ Best regards Bo

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2nd April 2010, 06:03 PM	#2
gfiandy Audio Engineer diyAudio Member Join Date: Jul 2003 Location: Cambridge UK	Hi, You have crosstalk, this can occur in may places and without a circuit diagram, PCB layout and photos of the actual design it will be very hard for people to help you. The most common reason for this is shared ground(0v) returns so look for that first. Regards, Andrew

2nd April 2010, 08:22 PM	#3
soundbabe diyAudio Member Join Date: Feb 2010	Ok thanks for your help. How can I trim the said problem please? And how can I solve the shared ground problem too? Can I use bigger capacitors between ground and +/-??

2nd April 2010, 08:28 PM	#4
soundbabe diyAudio Member Join Date: Feb 2010	I have even noticed that the place of one output pins (the ground one) is important to causes or removes the humm noise I hear in the speaker, How can I find out the best place for it too? P,S Can somebody please introduce me a schematic based upon LM3875 as an stereo Amplifier? I want to trim my design by an sample one too to remove such problems.

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