LM1877 poor THD tuning...

Peter Tseng

Mastermind 6650 points

Other Parts Discussed in Thread: LM1877

Dear sirs,

As customer feedback, the LM1877 THD is very poor in their system.

What can I do for customer to modify to improve the THD performance?

Thanks.

P.S. the vin is 12V

over 12 years ago

0 John Fedak over 12 years ago

TI__Expert 6715 points

Hi Peter,

That THD seems very high, but without more information I don't know what may be causing noise in their system.

How are they running this test? (what are thier inputs/load conditions?)

Do they have a screen capture of the waveform?

Regards,

~John

0 Peter Tseng over 12 years ago in reply to John Fedak

Mastermind 6650 points

Hi Sir,

The attached snapshot is only I have now.

I will discuss with customer RD while my duty on!

As the snapshot, It seems customer use speaker as output load and the USB Mic. as input device.

Just let me know if you need any furthur information.

Thanks.

0 John Fedak over 12 years ago in reply to Peter Tseng

TI__Expert 6715 points

Hi Peter,

I do not see any attachment. More than knowing just the input type, what is the signal strength of the input (in Vpp or Vrms)?

Regards,

~John

0 Peter Tseng over 12 years ago in reply to John Fedak

Mastermind 6650 points

Dear John,

Sorry for mistake! Maybe the file size is too large to paste.

Please find attached file that I cropped.

0 John Fedak over 12 years ago in reply to Peter Tseng

TI__Expert 6715 points

Hi Peter,

I should have clarified better what I was looking for. I'm looking for the output waveform from the LM1877. I believe it will be clipping substaintially with 37% THD.

With Vin at 12V, the LM1877 has a typical output of 1.3W/Channel at 10% THD (Rl = 8Ohm). What are they trying to drive the output to be? With a larger Vin, they will be able to get more power out of the LM1877.

Regards,

~John

Audio

Audio forum

LM1877 poor THD tuning...