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Same power supply from piano and amplifier

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?
 

batata004
erik_squires
16,355 posts
 

Have you considered that you need more current??

Current draw per device adds.  So if you have 2 x 4A devices you need a total of 8A..

jasonbourne52's avatar
jasonbourne52
2,863 posts
 

Stick with using a separate power supply to each device.

imhififan's avatar
imhififan
2,211 posts
 

I think the problem is the power supply ground of the "pam8610" should not connect to its INPUT "ground". You can use continuity test in a multimeter to confirm that.

If you using 2 separated power supplies and connect both power supply negative together, I think the piano will shout down as well.

 

 

yoyoyaya's avatar
yoyoyaya
807 posts
 

Regardless of the cause, you should be using the two power supplies. You should also check their current capacity - it should be marked on them - and use the one with the higher current capacity for the amplifier.

imhififan's avatar
imhififan
2,211 posts
 

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

If using one power supply, make sure it can handle both load.

Put a 2uF bipolar capacitor on the negative lead between LINE OUT of digital piano and LINE IN of mini amplifier, so the power supply negative (ground) will be isolated from the mini amplifier LINE IN negative.

 

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