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Old 24th June 2010, 09:19 PM   #1
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Default 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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Old 26th October 2011, 08:36 AM   #2
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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 ?
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Old 26th October 2011, 01:24 PM   #3
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Did you put local decoupling caps near the supply pins ( minimum 1000 F ) ?
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Old 26th October 2011, 01:48 PM   #4
AndrewT is offline AndrewT  Scotland
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Local decoupling suggested by most manufacturers never approaches 1000uF (1mF).

Why should the 7240 be different?
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regards Andrew T.
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Old 26th October 2011, 01:55 PM   #5
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Sorry , I read '7294'....
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Old 26th October 2011, 02:16 PM   #6
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sorry ,I also read '7294'...
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