first build problems

[gimpchop]

Hi just put together my first chip amp it is built on a pcb board i purchased from km tech (from ebay) with new parts purchased from cpc farnel. I've double checked all joints are soldered correctly and components are in the correct place but i cant get any sound from it i've tried a few power supplies but i get nothing. I attached a few pic just incase anything jumps out to you.thanks for looking

 

[Puffin]

What power supply are you using? I assume you have a split rail supply?

 

[gimpchop]

I was using a laptop psu rated a 19v

 

[Puffin]

Ah, a laptop supply is normally a single +/- supply.

You need a +/0v/- supply like this (see pic)

 

[gimpchop]

Ahh ok thanks. is there any way of testing even for a short tim without needing to make that circuit?

 

[Puffin]

Not to my knowledge. I would be careful about connecting it again in case you cause any damage.

You can make a split rail supply by using 2 single rail supplies, so if you have another identical laptop psu you can join the + of one to the - of the other to provide the 0v )(voltage reference) and you then have + 0v - Have a read up on split rail supplies.

 

[gimpchop]

OK I will have a good read up about them thanks for the quick. replies.

 

[Mark Whitney]

You should not use the amp without a heatsink on the LM3886. Not the reason that is doesn't work though.

 

[john blackburn]

Good reading on safe power supply building Building a Gainclone chip amp power supply.

 

[Kshishtoff]

You can try that schematic, but for your own risk and only for cheking. It must work.
If the chip is not broken for connecting power supply only to one rail. And be sure to use a heatsink.

 

[Kshishtoff]

Have you alredy tried that variant of connection? And if so, do not try my previous advice.

 

[Mark Whitney]

Don't do that, it will not work.

1. The LM3886 has an under voltage protection. +-10V is to low.
2. Depending on the used RMute the IC will not switch on.
3. Two capacitors in series will not split the voltage into two identical parts. The rails will swing between 0V and 20V depending on the current demand of each rail.

 

[tomchr]

You can try that schematic, but for your own risk and only for cheking. It must work.

You can't use two capacitors in series to create a split supply or a ground reference.

If OP has two laptop bricks and their outputs are galvanically isolated from the mains inputs (not all of them are), they can be connected in series to form ±19 V. That'd be plenty for an LM3886.

Do note that not all laptop supplies like to have their outputs connected in series. Some shut down if you try that, which the leaves you back at the single supply situation you currently have.

Tom

 

[tomchr]

Have you alredy tried that variant of connection? And if so, do not try my previous advice.

That connection leaves the ground pin of the LM3886 floating, which means the internal biasing circuit for the input stage and mute does not have a reference.

If you want to run the LM3886 on a single supply you have to change the circuit rather dramatically as shown in attached image (from the LM3886 data sheet).

Tom

 

[Kshishtoff]

I did not do it myself, but I heard that it's possible connect power for a short time for checking. If it's wrong, then I apologize.