Boombox line in noise

[kobilica]

Hello, I have a problem with Hitachi TRK-3D7 Boombox cassete player.

I want to hook up an mp3 on it, well I did and it works. But it only works when I click REC on cassete player, and well, on standby there is coming out quite noticeable noise. How can I get rid of this ****? I don't know much about sound electricity but I know much about electricity. So any suggestions, do I have to ground anything, cut anything...? Thanks...!

[kobilica]

Also let me mention, when I catched one clear AM station on radio that is inside boombox, there was no noise present. The sound was superb. Can't comment about FM radio, because it is detuned/broken and doesn't catch any station clearly.

So I really think it's not issue with amplifier. :s

[kobilica]

cmon any idea? Would it be possible to wire mp3 directly into amplifier?

[sofaspud]

How do you have the mp3 player connected to the boombox? Through line-in jacks on the back? Or external mic jacks? You've provided little to work with.

[kobilica]

Through line-in jacks on the back.

[Buckapound]

It sounds like the shield may not be connected, either in the cable or at one of the jacks. What kind of noise is it? Have you tried a different cable?. Swapped left and right?

[kobilica]

Even if I disconnect it the noise is still there. It is present at all frequencies, even if I raise only low or only high in EQ (equalizer), the noise is still there. The noise is nothing like speckling or cracking, it's just that constant noise, not very special in any way (like pitching, modulating or anything in anyway), and it is quite noticeable when nothing plays.

[sofaspud]

Yes, it would be possible to wire "directly" to the amp. Your boombox likely contains a chip amp(s). The big problems are that your boombox is not in good working condition to start with, and there are filters/splitters involved to deliver the required signals for the particular speaker configuration. You'd probably have better success with a signal generator and patience than continue with this current diy forum path.
Or maybe you could just disconnect the cassette capstan motor power lead and use that REC button.

[kobilica]

Well, It does contain chip amp. Also, I did disconnected oscilloscope. Well, I will try to find right signal with oscilloscope, one per time . Thanks for your help!

[sofaspud]

I'd try breaking the circuit at the source selector and feeding a signal at that point to see if it plays cleanly. If it does, there's your mp3 hookup.