[SOLVED] Hum noise on LM386 output

[Sm.r.Tadayoni]

Hi My Friends...

I have a circuit with LM386 Amplifier to amp the signal of VS1003 Left and Right channels.

The question is, when i put the headphone cable (example iPhone 4) to the output stage, i dont hear any noise, but when i use another headphone (iPhone 5S) i hear noise of "Hum-Hum-Hum-...". Probably for the old headphone the sensitivity is low and the noise couldnt hear, but for the new headphone the sensitivity is high and the noise will be there on output. So how can i reduce this noise?

I used a USB Charger for Power Supply.

 

[BradtheRad]

Increased load can cause increased ripple on a power supply. Is your USB charger designed to run audio equipment? Or only to charge batteries? Then it may not be filtered sufficiently for your needs.

It could help if you add a smoothing capacitor across the power terminals of your 386. For suitable values try 50-500 uF.

 

[Audioguru]

The datasheet for the LM386 amplifier shows a "Bypass" pin #7. A graph shows that a 10uF capacitor from pin 7 to ground (pin 4) reduces power supply hum by -40dB and 50uF reduces power supply hum by -50dB.

 

[Sm.r.Tadayoni]

Thanks for your replies. The problem solved with your help.

Increased load can cause increased ripple on a power supply. Is your USB charger designed to run audio equipment? Or only to charge batteries? Then it may not be filtered sufficiently for your needs.

It could help if you add a smoothing capacitor across the power terminals of your 386. For suitable values try 50-500 uF.

I used battery charger. This charger is poor but i used some filter to regulate it.

The datasheet for the LM386 amplifier shows a "Bypass" pin #7. A graph shows that a 10uF capacitor from pin 7 to ground (pin 4) reduces power supply hum by -40dB and 50uF reduces power supply hum by -50dB.

I didn't use this bypass capacitor. When i used it the noise reduced in large scale.

Thank you alot...