TDA7240 Distortion at low volumes

scwhiteley · 24th June 2010, 09:19 PM

Howdy,

I recently built a few amps using TDA7240 ICs. I used the circuit design from the spec sheet. They seem to work pretty well, but for some reason, when set to a very low volume, there is an audible "scratchiness" to the music. Any ideas what would cause this? I did not use shielded wires to connect the source (iPod) to the amp input. Is this the likely culprit? I'm doubting it's the volume potentiometer itself, but I'm no expert.

here's a schematic of the circuit if you'd like to take a peek:
http://circuits.datasheetdir.com/344...40A-pinout.jpg

Thanks for all the help!

guitar89 · 26th October 2011, 08:36 AM

haha, its a old thread. I'm also building this chip amplifier X.x
Of course using shielded wire helps, but the noise is at same volume at all condition. The "scratchiness" you mention, is it variable as the volume of music ? or same all the time ?

picowallspeaker · 26th October 2011, 01:24 PM

Did you put local decoupling caps near the supply pins ( minimum 1000 µF ) ?

AndrewT · 26th October 2011, 01:48 PM

Local decoupling suggested by most manufacturers never approaches 1000uF (1mF).

Why should the 7240 be different?

picowallspeaker · 26th October 2011, 01:55 PM

Sorry , I read '7294'....

tanfplayer · 26th October 2011, 02:16 PM

sorry ,I also read '7294'...

24th June 2010, 09:19 PM	#1
scwhiteley diyAudio Member Join Date: Mar 2010 Location: Missoula, Montana	TDA7240 Distortion at low volumes Howdy, I recently built a few amps using TDA7240 ICs. I used the circuit design from the spec sheet. They seem to work pretty well, but for some reason, when set to a very low volume, there is an audible "scratchiness" to the music. Any ideas what would cause this? I did not use shielded wires to connect the source (iPod) to the amp input. Is this the likely culprit? I'm doubting it's the volume potentiometer itself, but I'm no expert. here's a schematic of the circuit if you'd like to take a peek: http://circuits.datasheetdir.com/344...40A-pinout.jpg Thanks for all the help!

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26th October 2011, 08:36 AM	#2
guitar89 diyAudio Member Join Date: Dec 2010 Location: Malaysia, Selangor	haha, its a old thread. I'm also building this chip amplifier X.x Of course using shielded wire helps, but the noise is at same volume at all condition. The "scratchiness" you mention, is it variable as the volume of music ? or same all the time ?

26th October 2011, 01:24 PM	#3
picowallspeaker diyAudio Member Join Date: Apr 2007	Did you put local decoupling caps near the supply pins ( minimum 1000 µF ) ?

26th October 2011, 01:48 PM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Local decoupling suggested by most manufacturers never approaches 1000uF (1mF). Why should the 7240 be different?

26th October 2011, 01:55 PM	#5
picowallspeaker diyAudio Member Join Date: Apr 2007	Sorry , I read '7294'....

26th October 2011, 02:16 PM	#6
tanfplayer diyAudio Member Join Date: Oct 2011 Location: china	sorry ,I also read '7294'...