car + mp3 + powersupply + noise HELP!

[Fenris]

Hi there! I'm an electrical engineering student, and currently i have a problem in my car, some time ago i installed a majestic amplifier so that i would be able to use my mp3 player in my car, i built a custom speaker switch so that I'm able to still use my car cd-player when I'm not useing my mp3, now everything works a charm till recently i decided to power the mp3 player via a voltage regulater i built, the voltage regulator (used an lm317 + capacitors) works fine its a VERY clean (checked it with a CRO too) 1.495V output (mp3 works with 1.5V) now when i used it to power up my mp3 player i got noise as soon as the mp3 player switched on, the noise is a constant huxx and high pitched at times too!! whist it works great on the 1.5 battery! i tried checking the power-supply + mp3 player with my home speaker amplifier and it worked fine!! recently i even added an L7800 to stabilize more the input voltage before adjusting to 1.459. so I'm guessing that the problem is either in a variable voltage from the car batt (which i checked and its a clean 13.04V) or else my car amplifier lacks a suitable input filter??? any help??!!

[ante]

Hi Fenris,

Welcome to our forum.

I think you have a ground problem here, maybe the regulator ground and the audio ground are not the same.

[Fenris]

Thanks for the welcome Ante!

Well i didn't actually think of that, but the car's earth is the -ve batt terminal, and i took power directly from the battery for testing.  ???  could you please explain ur point in more detail please!!

Just for the sake of completness the amplifier has 2 power in lines, 1 is just used for identifing the key in igintion, the othe is the power drain, and the other is ground! i didnt avtually ground the boy of the amplifier as i asuumed it would be internally grounded, the amplifer is fed via its low signal input by the mp3 player wish on batt works perfectly but when i use my PS added a noise factor, the PS takes power from batt + and -.  I really cannot figure the problem  :(

[audioguru]

You need to ground the MP3 player and its power supply at the amplifier, not at the battery.

[Sukhbinder]

Hi fenris, i would like to know that are u using a USB type MP3 player. Keep in mind that most such players donot have the audio output ground and power supply ground as the same. In such USB type of MP3 players the voltage from a 1.5 volt battery is stepped up by a DC/DC converter. If it has different colour selection for the screen then it is a step up type because u cannot drive a blue or green or even a red led from a 1.5v source. u may have to open up the player for finding the correct ground terminal. just chek for the continuity between the audio ground and the battery ground. if its not there u have a DC/DC converter based player

[Fenris]

Hey Sukhbinder thanks for your reply, the screen is an lcd and it doesn't chage colour, and it isn't backlight eather. but il do a continuity check as you suggested!! THANKS!!!  ;D

Hey audioguru, i think you could have a point there!, could you be more specific please?

I had tried powering up the mp3 player ps from the same ground and 12V the amplifer uses but i still got noise! what do you mean exectly please??

could i try useing dual ground?? I mean use the batts + & - to power the PS, and then ground the audio shield out of the mp3 at the amplifier ground???

You guys are really great!!! Thanks for your time!!!!!!  :D

[audioguru]

The amplifier, power supply and MP3 player's audio output cable's shield should all be grounded at a single point. Maybe your power supply is coupling 12V noise to the input of the amplifier through the audio cable's shield. Try connecting the power supply's ground to the amplifier's ground and to the MP3 player for power. Then connect the MP3 player's audio output cable's shield only at the amplifier, disconnected at the MP3 player.

[Sukhbinder]

Glad to help u fenris. i have a USB MP3 player which is made in taiwan. it has a backlit LCD display which changes colour using a blue, red, and green leds. Mine has a built in lithium ion battery which can be charged from USB port of any computer or an iPod type travel charger. the later charges it in 1-2 hrs to full capacity. i get about 10 hrs from a single charge. I've hooked up mine to my car stereo using the headphone jack to the radio section as my sets tuner is not functional. it sure saves me lot on CDs and cassettes. no skipping and no dust problem, totally solid state. i think the manufacturers should look to this as a good new feature. Just carry ur music in a USB Flash drive, connect to the player and play. what more my mp3 player even suuports document files  like any common USB drive for a computer. In addition to it it has a FM tuner with presets, voice recording via its inbuilt mic or from the FM. what else can u ak for. I've seen the single battery type MP3 players and i opened one to see a small DC-DC converter in it.  the rechargable type are a bit expensive but u surely save in the long run. u may check out the site of sony who have launched new USB MP3 players with capacities of 512MB and 1GB. They by the name of SONY BEAN. the site says that u charge it for 3 min and get 3hrs of playback and 50 hr playback on a full charge.... Quite high end battery technology. By the way  i have a 256MB and a 512MB player. ;)

[Fenris]

ok Thanks audioguru!!!! I"ll try that!!! it makes sense too  :) you guys really have some expreience!! i totally neglected that option!

Hey Sukhbinder My mp3 player is a Thomson, it has 256MB internal and an mmc slot i use a 512 MB card, i use it as  a pendrive too its really handy and sinice its migration in my car i only use the car cd-player when its batt is flat thus the PS  hehe, i think i know your mp3 player model and its really cool :D.

I'll let you know hoe the shielding test goes!!! wish you a good day!!