discman car conexion digital noise

[mbahi]

Hellow , i am new in this forum , best regards to all members.

My problem is the next :

I have in my car a Denon Car cassete receiver . I buy a cd discman player aiwa XP-234 for connect to it . It works okey .

But , i have the problem with the batterys ( it agotates ) . I self made one dc car adaptor 12-5v converter with a tipical 7805 IC with 470 uF capacitors and 0,1f capacitors .

The problem is , when i conect de power supply to the discman , i heard over the music , very digital noise ( tipical of the circuits of control of the motors of the transport of the laser head , etc. ) .

With batterys , any problem

I revised groundings , etc. and etc. . i have a pionner alternator noise supresor , direct lines of the battery , etc.

What is may problem

Thanks in advance

[mbahi]

I answer myself this problem . It can be util for others.

The problem is that i was have a analog/digital ground loop in the circuit formed with the cassete player and the diskman.

When i use the diskman with bateries , this loop is broken and i don't have the digital noises , but when i put the dc adaptor 12v/5v , this loop is established and i have the noise again.

the solution :

i buy a electronic component dc/dc isolated ( more important this ) coverter 12v /5v , and the problem is solved. no digital noise with 12 car batery diskman powered .

this component is from Newport components part : nml 1205s, but they have a full line of voltages and power.

Thanks