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?
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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@imhififan you are right, the GND of the power supply pin on the mini amplifier is connected to the GND of the LINE IN - there is continuity when using multmeter. @imhififan I only have ceramic capacitors and eletrolytic ones at hand now, but I will try to buy the bipolar one that you said. Just to make it clear: I should take the signal wire that leaves my piano (Line out) connect it on one leg of the capacitor and the other leg I must connect to the singal line input of the mini amplifier. Is that right? @erik_squires and @yoyoyaya I am pretty sure the problem is not current, because the problem happens even when I have no speakers attached to the mini amplifier. Also, the power supply is 5A which is plenty for the piano (which uses no more than 1A) and for the mini amplifier (which should use way less than 1A without speakers). @jasonbourne52 I would like to be able to use only one power supply, and at least understand what is the problem! |
@imhififan I did what you said and it worked!!!!!!! UHULL!!! Using just one power supply, everything worked. However now I have lots of humming/noise on the speaker connected to the mini amplifier.
I didnt have a 2uF bipolar capacitor, so I took 2x 4.7uF electrolytic capacitors and connected them in series with the GND of the line in and line out. I did this:
GND of LINE OUT of piano -> positive leg of capacitor (1) -> capacitor (1) -> negative leg of capacitor (1) -> negative leg of capacitor (2) -> capacitor (2) -> positive leg of capacitor (2) -> GND of LINE IN of mini amplifier.
Is this correct? Any idea how I can reduce the humming? |
@imhififan I will try your suggestion of leaving the negative leg open, but if I do that, the circuit will be open! In the image below you can see how I connected the capacitors. I connected then in series on the GND line... if I leave any leg of the capacitors open, the circuit will be open. Am I doing something wrong? Thanks for your attention!
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