My First LM3886 GC

[yangsmm]

When I assembly the LM3886 Power Amp, It was to find the heatsink for it. I can't make the hole for bolts. so I paid to drill the hole. and I am going to try to make upgraded power amp with LM2886. So why don't we try together?

[Edits]

Guess you also built one using the same PCB?

Yes dino, I used them as my first GC, tweaked them until broken beyond repair
And congratulation for the BT! who knows may be I was one of the judge? or one of the paticipant sitting next to you?

[Dino-Indo]

Whohoho Edits.. Many Thanks!

Now.. I'm still trying hard to remember who was sitting next to me during the Blind Test..
Also tried hard to remember who was the juror for that event..

But, I got to admit that it was fun for me to be able to participate in that blind test... truly a memorable experience.. especially for me.. a newbie DIY

[samsagaz]

Hi guys, i build this schematic, test it and dont work no sound at the output, just an HUMMM.

Can someone please check if everything are OK?

http://www.proyectosdiy.com/_tmp/sch2.pdf

Thanks in advance.

[Puffin]

Thats an LM3886 ?

[pacificblue]

Hola, Samsagaz.

The schematic shows all GND connections to have the same potential. Maybe you have produced a ground loop somewhere. Many threads in this forum deal with separate grounding for signal and power, and with star grounding concepts. If you cannot find your solution there, please post photos and/or your PCB layout.

Do you get hum with anything connected to the input? Or with the input floating? Or shorted?

Does the hum go away, if you lift GND from PE?

Do you support C2 and C3 with more capacitors outside the PCB? Or do you really only use 220µF per rail?

[samsagaz]

I get the HUM with any input, if i get it floating no HUM.

im using just 220uf per rail, the Power Supply have like 30000uf


this is the PCB Design.

http://www.proyectosdiy.com/_tmp/pcb.pdf

[Puffin]

I Should learn to look more closely "my first LM 3886GC".

Is the picture of the PCB from the top or underneath ?

From the schematic you posted it looks as though Pin 3 should be connected to pin 10, not pin 9

[pacificblue]

As far as I understand your PCB you have put the star grounding point on the PCB at the bottom of your drawing (bigger drilling), is that right?

The ground plane forms a closed loop around the PCB. You could try to interrupt it somewhere, e. g. behind the chip. At the moment you have two paths from the ground connection to Ri. A short path over the right side, and a long path over the left side running on the top over the chip to the right and then down again. You might get the hum from there.

You can check that before cutting the PCB. Lift Ri or Ci, which ever you have connected there, from the ground below IC pin 11, where it seems to be connected now, and connect Ri/Ci directly to the star point with a wire. Make sure the wire doesn't connect to the ground anywhere else. If the hum goes away, you need to cut the loop as I wrote above.

If the hum doesn't go away, you may still cut the loop and it will probably help, but then there might be some further cause for the hum.

[ionomolo]

Originally posted by samsagaz
I get the HUM with any input, if i get it floating no HUM.

im using just 220uf per rail, the Power Supply have like 30000uf


this is the PCB Design.

http://www.proyectosdiy.com/_tmp/pcb.pdf

If the hum is not present with the input floating then there is a ground loop with your source through safety earth. Try feeding it with an ipod/mp3 player (of course not connected to a computer by usb) and check there is no hum with the ipod paused (if it's switched off the output becomes high-impedance and acts like an antenna.