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Amplifier sharing same GND as LINE IN

batata004

Member
Joined
Jul 15, 2021
Messages
14
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Location
State of Santa Catarina - Brazil
I have a digital piano with LINE OUT. I also have a mini amplifier named "pam8610" (cheap and very common) which has LINE IN. I have 2 power supplies, each one with 12V and 5A. When I connect each power supply to each device (one power supply to the piano and the other power supply to the mini amplifier) everything works just fine: when I play the piano the sound goes to the mini amplifier and then goes to the speaker.

HOWEVER, when I connect both devices (piano and mini amplifier) to the same power supply while keeping the LINE connected, my piano turns off immediatly, something is really wrong. If I disconnect the LINE and use the same power supply, no problem happens (but of course no sound is produced because the LINE is not connected).

Using a multimeter, I discovered that the GND of the LINE OUT is the same GND of the power supply (continuity test in the multimeter). I dont know if this is common practice, but for some reason my piano provides the LINE OUT with the same GND of the power supply. So, when I use the same power supply to power the mini amplifier and when I connect the LINE, some kind of short is happening. Using 2 separated power supplies, everything works fine.

Do you guys have any idea how can I fix this or what is going on?

IMPORTANT: I am pretty sure I am not overloading the power supply, because my piano turns off even without playing any sound... as soon as I connect the power supply to the mini amplifier, the problem happens.
 
In well designed units:
a] the audio circuit common is connected to the metal chassis
b] the DC supply common is connected to the chassis
c] a RCA unbalanced LINE out (or in) common (shell) is connected to the chassis

* * * * * * * * *
matbe one of your units does not treat either DC supply lead as common.
 
I think the GND paths are all connected right... Maybe it's not common sharing the same power supply accross amps and pianos or line out devices? But I still cant understand what is causing this...
 
I have a digital piano with LINE OUT. I also have a mini amplifier named "pam8610" (cheap and very common) which has LINE IN. I have 2 power supplies, each one with 12V and 5A. When I connect each power supply to each device (one power supply to the piano and the other power supply to the mini amplifier) everything works just fine: when I play the piano the sound goes to the mini amplifier and then goes to the speaker.

HOWEVER, when I connect both devices (piano and mini amplifier) to the same power supply while keeping the LINE connected, my piano turns off immediatly, something is really wrong. If I disconnect the LINE and use the same power supply, no problem happens (but of course no sound is produced because the LINE is not connected).

Using a multimeter, I discovered that the GND of the LINE OUT is the same GND of the power supply (continuity test in the multimeter). I dont know if this is common practice, but for some reason my piano provides the LINE OUT with the same GND of the power supply. So, when I use the same power supply to power the mini amplifier and when I connect the LINE, some kind of short is happening. Using 2 separated power supplies, everything works fine.

Do you guys have any idea how can I fix this or what is going on?

IMPORTANT: I am pretty sure I am not overloading the power supply, because my piano turns off even without playing any sound... as soon as I connect the power supply to the mini amplifier, the problem happens.
how do you plug one power supply into two devices?
 
Power supply is probably supposed to be floating for one of the devices in order for the device to derive a split rail supply.
 
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