LM3886 Schematics + PCB

[gootee]

Originally Posted by batteryman

.
But I never said 'Schematic' you did and this means changing the circuit.

I said 'PCB layout' - this means altering the track routing NOT the schematic.

Small changes in the pcb design are not audible.
BM

batteryman,

How can you even try to argue? I quoted your post #101 directly.

You said both "layout" and "schematic":

Here's what I quoted from your post:

"The pcb layout is not critical for audio circuits so there won't be any loss of quality if the schematic is not the same as the datasheet."

Also, I disagree with your new statement, because "small changes in PCB design" can be quite audible.

I've said things that made less sense than those, here. But when it's pointed out, I usually try to say something like "Oops! Sorry!". However, if you genuinely disagree, then that's where the fun starts, here (and where things can be learned)!

Anyway, I didn't make that post to attack you! I did it for the benefit of those who might read this thread. (OK, maybe I'm a bit of a stickler about accuracy. But I believe it's important. And I quickly learned, here, the hard way, that we all should be prepared to have to defend what we post, which tends to make us think harder about its accuracy before hitting the Submit button, which isn't a bad thing.)

No worries. Carry on.

Cheers,

Tom

[paranoid06]

Hello apexaudio!
I really appreciate all your work and research.
Thanks for posting your work on this forum!!

I have built this module according to your PCB and installed the correct parts on it.
The PSU is 24-0-24V/5A Trafo with 4700uF/50V Capacitors 85 degree types.
When I try to power up the circuit, there is only hum from the speakers... I am using the amp on a 8 ohm load.
I also checked for shorted PCB traces. But everything is fine.
I have used metal film resistors and box type capacitors for the build to induce the least noise.
But this is something else...! The IC gets hot as soon as I switch the amp on.
Is it that there are shorted traces? Or the IC is bad?

Regards

[udailey]

The back of the IC can not touch metal if that metal is grounded. If you have insulated the back of the chip then you need to also make sure that there is no bolt touching the tab of the chip. Turn it off and use your multimeter to see if you have any resistance/short between ground and chip tab.

[paranoid06]

Originally Posted by udailey

The back of the IC can not touch metal if that metal is grounded. If you have insulated the back of the chip then you need to also make sure that there is no bolt touching the tab of the chip. Turn it off and use your multimeter to see if you have any resistance/short between ground and chip tab.

My IC is a full plastic one..
It does not have a tab!

Regards!

[udailey]

Then get a wire and put an alligator clip on each end. Attach one end to earth ground and the other end should then touch signal ground, then speaker ground, then the 0V ground from the secondary side of the transformers. Listen while you do this. Often if its not a cold solder joint you can find the grounding problem this way. Also try one alligator on signal ground then touch all the other grounds then try one alligator 0V and one Earth.
Uriah

[paranoid06]

Tried doing that too....But there is no change in the output....only hum...And the IC gets really very hot within 3-4 seconds...I think thats a bad IC....
What say guys?

[AndrewT]

Para,
did you test the wiring of your transformer?
Did you test your PSU?
Did you test the amplifier for output offset?
Did you just connect everything up to your speaker and hope for the best/worst?

[paranoid06]

Originally Posted by AndrewT

Para,
did you test the wiring of your transformer?
Did you test your PSU?
Did you test the amplifier for output offset?
Did you just connect everything up to your speaker and hope for the best/worst?

The transformer wiring seems to be fine according to me.
The signal ground, transformer's middle wire (ground) and the amplifier ground are soldered to each other.
I use a 35A Bridge. The power supply seems to be fine too.
I am just scared to check the DC Offset!! The IC turns so very hot as soon as it is connected even though it is on an heatsink! I just expect that it will burn!
So I'm kinda scared too!!

I still don't know what the problem is! I also checked for shorted traces.
But I din't find any!

I'm confused!!

[AndrewT]

Looks like you are saying that you just banged it all together and hoped for the worst, "because it looked right" !!!!!

[udailey]

Time for pictures.