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spherayoham 20th June 2011 02:03 AM

Help with headphone jack to mp4 player
Hi everyone. I'm novice and was wondering to place a headphone jack to my mp4 player speaker outs so the speakers turn off when I plug in my 32-ohms headphones.

After installing the hiss and the slight distortion in the middle and higher frequencies are really striking with headphones. (which were already slightly audible on the internal speakers but that didn't bother me before)

The bass and the stereo image is ok and the sound of the speakers didn't change after the modification. The mp4's output is 2x2.5watts at 4ohms. Any suggestions to eliminate the distortion?

Thank you for any help!

spherayoham 22nd June 2011 02:52 AM

Hi again. I tested it more... with different music the built in speaker sounds nice, but the midrange is still distorted when listening with headphones, especially on dynamic and louder parts of the songs.

I searched thru the net for hours and I figured out that some resistors(?) may be needed to the + poles of the headphone jack to compensate the impedance difference. I don't mind if the mp4 player will be not that loud anymore or will be just half as loud with its speakers.. Can you help me which ones should I try out (how many ohms, how many watts) or how can I calculate them and should I wire them parallel or in series?

BIG thank you for any suggestion! :usd:

spherayoham 25th June 2011 03:00 AM

I was wondering why did I get no answer or suggestion as I read many many forum replies in much more complicated issues here, but anyway after 14 hours of experimenting I finally found out something. I write down my experiences, maybe it will be useful for someone some day. Please forgive my english as I stopped learning 8 years ago but I try to explain you as good as I can.

I made sure for myself the audible sound difference between the earphones and speakers was NOT because of quality difference because I tried 16ohm low volume earbuds with still good frequency response and the sound was more terrible distorted even on lowest volume. So the load was too much.

I bought many resistors and tested the sound with many kinds of music. The best was for me a 470ohm resistor per channel in series. (1Kohm was too much as the digital amp somehow turned the sound into mono or the sound was too dry in stereo. With 333ohms the hiss and the bad sound came back.) So the hiss is gone now and although some distortion is still there (why? I don't know) in dynamic sound parts, the sound is better now.

But the internal speakers sounded too quiet using the resistors and as a novice I didn't want to mess with a switch. So I wired the cables directly to my new installed jack socket without any resistor - I created a simple "speaker out".
Then I made a speaker "de-amplifier" box wich begins with a male jack cable (to the "speaker out"), continues with the 470ohm resistors per channel in the box and ends with a female jack socket to my headhones. So 50% volume of the mp4 player is enough for indoor use with using the de-amp box. Without the box it was already too loud (and dangerous) on 10% for headphones.

So I eliminated the hiss and some distortion plus I saved the original volume of the internal speakers. I could also connect other speakers to the new installed output now if I wanted. :cheerful:

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