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.
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.
It depends on what you call GND. Most of the time the mass/secondary side of PSU ground is called GND or Audio GND. That Audio GND is of course connected to the PSU GND. Common practice or you would not have signal and return.
Now there's a thing called PE. Then things start to become more complicated. It is often called "ground" or "earth" as well....
And there is the phenomenon that the loudspeakers are used "floating" so the "-" of the loudspeaker outputs should not be connected to GND. This is also often misunderstood as "-" is ground right?1 Well it is not in this case with PAM8610. The wires "+" and "-" of each output should just go to the loudspeakers and nowhere else.
I think it is best when you show pictures , a simple drawing and some brand names and type numbers. What is the problem of using 2 power supplies? When stuff works OK you could leave it like that, it is technically better as well.
Now there's a thing called PE. Then things start to become more complicated. It is often called "ground" or "earth" as well....
And there is the phenomenon that the loudspeakers are used "floating" so the "-" of the loudspeaker outputs should not be connected to GND. This is also often misunderstood as "-" is ground right?1 Well it is not in this case with PAM8610. The wires "+" and "-" of each output should just go to the loudspeakers and nowhere else.
I think it is best when you show pictures , a simple drawing and some brand names and type numbers. What is the problem of using 2 power supplies? When stuff works OK you could leave it like that, it is technically better as well.
Last edited:
Try add a capacitor on the amplifier line-in negative side.
The negative of line-in should not connect to ground, it is a differential Input stage.
That depends on the PAM8610 board. Most have 2 caps (so also one in the negative input but then going to GND) and are used unbalanced.
Since you already established that the two grounds are connected, that cannot be the problem.
It seems that connecting the two supply outputs together is the issue.
But I can't imagine what it would be, but that's probably the limitation of my imagination ;-)
Jan
It seems that connecting the two supply outputs together is the issue.
But I can't imagine what it would be, but that's probably the limitation of my imagination ;-)
Jan
I double checked right now, I disconnected the mini amplifier from everything (PSU and line in cable) and the GND of the line in is connected to GND of PSU (0 ohm resistance).
@chrisng from what you say, I think your suggestion of using a capacitor is to isolate the signal right? I just didnt understand how should I connect the capacitor... I should connect it in series with the line input GND? If so, which leg of the capacitor should point to line input ? The negative or the positive leg of the capacitor?
@chrisng from what you say, I think your suggestion of using a capacitor is to isolate the signal right? I just didnt understand how should I connect the capacitor... I should connect it in series with the line input GND? If so, which leg of the capacitor should point to line input ? The negative or the positive leg of the capacitor?
If that is the case, my suggestion might not works!
However, I think it's worth trying, the capacitor should be bipolar.
If you don't have a bipolar cap, you can use two electrolytic caps in series
"-"+"+"-" to form a bipolar cap, two 2.2uF cap in series will give you 1.1uF.
@chrisng
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. Image below. Do you know why I am having lots of noise? Thanks!
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. Image below. Do you know why I am having lots of noise? Thanks!
Mono or stereo Line Out ?
If it's a Mono Line out, connect only the tip to both L&R amps inputs. Sleeve goes to amp GND.
@MAAC0 your suggestion looks really nice, but I think I should not connect the Sleeve to GND right? If I connect Sleeve to GND the problem will still happens because, as I said previously, there is continuity between GND (from the power supply) and GND (from the line out). But you got me thinking: what if I leave the Sleeve unconnected? Just connect the tip (signal) and connect the power suplly. Do you think it could damage anything?
I don't think it could damage anything, the worst case scenario there's no audio signal pass-thru.
If utilize the capacitor works, maybe you can try a transformer isolator instead of capacitor to eliminate humming/noise.
Portable Stereo Ground Loop Isolator
