Problems with LM3886 chip amp

[TasKitas]

Hello everyone

I was trying to build LM3886 amplifier and can't figure it out how to make it work. I tried t ofollow the guide on circuitbasics. A Complete Guide to Design and Build a Hi-Fi LM3886 Amplifier - Circuit Basics

I made my own pcb (LM3886 - Album on Imgur) according to the linked image. First problem i figured is that my 12V toroid, makes to the mute circuit only 15,5 V, so instead of zener I just connected the contact with wire. Thought that should work, but nothing has changed.

When i turn on the amp for a split second i can hear some noise and then it's gone. Only other way to get some sound is to try to move the speaker contact wires (i guess it's just some noise out of moving conductor).

I guess this had happened for someone during all these years of this chip, but couldn't find anything to solve it here. Maybe someone can help me to find the solution and to make it work.
Thanks.

 

[Osvaldo de Banfield]

At first try, do the following:
Remove the speaker. Then, measure the output voltage, it must be 0 ± 30mV. Then, check the heating in the amp, perhaps it is failed. Both without loading nor signaling the amp.

 

[Mark Whitney]

I cant see where P_G and S_G are connected together.

 

[TasKitas]

I cant see where P_G and S_G are connected together.

It is connected on the power supply pcb, same way as in the guide, where positive rail of onr channel and negative of other connects to make 0V.

 

[Mark Whitney]

Perhaps some photos would help.

 

[TasKitas]

Perhaps some photos would help.

Of course, just right now i'm away.
Tomorrow i'll try what Osvaldo de Banfield have suggested and will make a better view of whole setup.

 

[adason]

On your pcb image on imgur, you have capacitors on V- incorectly positioned...

 

[Hicoco]

C5 should be 100uf not 100nf

 

[nigelwright7557]

On your pcb image on imgur, you have capacitors on V- incorectly positioned...

C8 is wrong polarity.

 

[Hicoco]

C8 is wrong polarity.

and C10 also.......

 

[TasKitas]

On your pcb image on imgur, you have capacitors on V- incorectly positioned...

Thank you for noticing it, that was the problem, it's working now. Since I'm quite fresh in electronics, I didn't realize before that if you're going for negative voltage, capacitors have to be directed with - to more negative, not ground. Now I've learned something new.

About 100nF, it was a typo in schematics, there's 100uF soldered there.

As i understand it was not working because only one rail was giving stable voltage and it was 15V, which is not enough to run the chip.

Also here's my setup (temporary for testing) LM3886 setup - Album on Imgur.
It didn't fit in the shot, but before the toroid there's lightbulb connected to the hot wire of 220V.

Thank you guys again for helping me

 

[chindman]

No heat sink on the chip! The quiescent power on the 3886 is nearly enough to burn it out, w/o a heatsink, even with the lightbulb. Don't turn this on until you have heatsink on that chip!!!

 

[adason]

That is true, you need heatsink, even for idle.
Other thing is, it you exposed electrolytic caps to opposite polarity, you should not use them, they may be damaged. Use new ones.

 

[TasKitas]

That is true, you need heatsink, even for idle.
Other thing is, it you exposed electrolytic caps to opposite polarity, you should not use them, they may be damaged. Use new ones.

Alright, thanks for advice. I've checked with my multimeter tho, it showed capacity. Also chips are with heatsink now.

 

[TasKitas]

Also I want to ask, how good quality should be the C2 and C13 capacitors. Oddly in my country there are no silvermica capacitors, that were offered in the guide.