Audio electrical noise using a TI card

bacteria · Post by **bacteria** » Tue Sep 16, 2008 10:19 pm

Linked up an MP3 player today into an audio amp (salvaged from a small PC speaker set), ran the amp from a PSone power supply (7.5v) fine, connected the power lines to a TI card to get the voltage to under 3v for the MP3 player; get a background electrical hum, which is annoying, especially on quiet tracks. Snipping the wires from the TI card and using a standard AA battery works fine for the MP3 player, so has to be electrical noise from the TI card.

Any thoughts on how to stop this noise?

APHawkes · Post by **APHawkes** » Wed Sep 17, 2008 11:06 am

Any chance that a capacitor in the line would smooth out the signal?

Rekarp · Post by **Rekarp** » Wed Sep 17, 2008 1:07 pm

Did you follow the datasheet for the card to the letter? There are reasons they have specific requirements. Most Ti cards have a input buffer cap of 100uF and an output of 100uF-220uF. You need these to smooth the on-off motion (which is more like a rectified AC current).

bacteria · Post by **bacteria** » Wed Sep 17, 2008 1:59 pm

I just used a 100uf capacitor on the TI card and a resistor to reduce the voltage. Have I missed something (if so, please advise).

I was getting the noise from both the positive and negative terminals through the MP3 player.

Interestingly, I didn't get this with my old iPod mini (before it died); perhaps the existing MP3 player is a bit sensitive??

Rekarp · Post by **Rekarp** » Wed Sep 17, 2008 2:13 pm

try a larger capacitor.

bacteria · Post by **bacteria** » Wed Sep 17, 2008 2:52 pm

Rekarp wrote:try a larger capacitor.

No problem - what do you suggest? 220uf, 470uf, 1000uf; or whatever? How will that affect which resistor I use?

nitro2k01 · Post by **nitro2k01** » Wed Sep 17, 2008 3:26 pm

Also, did you really put caps on both sides?

bacteria · Post by **bacteria** » Wed Sep 17, 2008 3:43 pm

nitro2k01 wrote:Also, did you really put caps on both sides?

?

Rekarp · Post by **Rekarp** » Wed Sep 17, 2008 3:45 pm

Caps on both input and output. I would try 220uF as thats what the specs calls for maximum. You could try a 1uF Ceramic if you have those to.

timmeh87 · Post by **timmeh87** » Wed Sep 17, 2008 9:15 pm

Try an inductor in series with the load.