Car audio LM3886 + SMPS on single sided board

[rwaudio]

I finally have the first version built, tested, and working beautifully. There are a few changes and upgrades to be made, I should add a snubber, and move a few things slightly for easier assembly.

The board is single sided, single layer with NO JUMPERS. It was milled/drilled on a cnc router. The smps is based on the SG3525 to make a very simple power supply. The transformer was hand wound on an F140-77 core and operates at around 52khz. There are 4 LM3886's in a parallel setup (2 pairs) to form a 2 channel amplifier that puts out either 60x2 @ 4 ohms and 120x2 @ 2 ohms, with 28v rails or 100x2 @ 4 ohms (not 2 ohm stable) using 35v rails. A small preamp board is also in the works to allow bridging and gain adjustment. There is a solid 4.1" x 0.75" x 1.5" aluminum block in the center used as a heatsink, which also attaches to the enclosure to create a large enough heatsink, a fan might also be required because of the very small size.

It is designed to fit inside the common hammond 1455 enclosure (don't have the exact number handy).

I'd like to release the g-code and artwork for others to make this simple amp at home once everything is perfect. It could be easily etched/milled at home and used to create small good sounding car audio amplifiers. I may even make boards available including some of the harder to find parts, like the toroid, power terminals, magnet wire etc.

Any tips or questions are welcome

[rwaudio]

Another pic.

[rwaudio]

yet another.

[rwaudio]

last one

[AndrewT]

Originally posted by rwaudio
There is a solid 4.1" x 0.75" x 1.5" aluminum block in the center used as a heatsink, which also attaches to the enclosure to create a large enough heatsink, a fan might also be required because of the very small size.

nice PCB, nicely packaged arrangement.
Fan to cool might not be enough. This is going to run very hot in the open and in a car will probably cut out on temperature protection.

[ashok]

What semiconductors ( chip, fet's, rectifier ) have you used in the smps ?

[rwaudio]

AndrewT
Yes it runs a bit warm on the bench, not too hot to touch, but hotter than any other chipamp I've built, there will be a 3"x8"x0.125" aluminum spacer between the block and the enclosure, they will all be screwed together and I'll use heatsink compound so here's hoping I can't fry eggs on it. I had originally designed it to use a copper block in the center and copper spacer, but I had these on hand. And copper is getting expensive these days.

ashok
I'm using the SG3525 unregulated at 52khz running 2 IRF540's per phase (I had these on hand, but will probably switch to something with a lower rds on later) rectifiers are MUR1620CT and MUR1620CTR

[rajudp]

Can u provide the schematic and pcb files please

[rwaudio]

I'll be happy to post the schematics and artwork for the board as soon as I know things are perfect, I don't want anyone to build the amp if there are any issues, I'm also finishing up the preamp stage with differential input etc.

After some bench testing using a 1.5" square fan and the amp hooked up to a 2.66ohm bridged load (below rated load) the amp in enclosure but without thermal grease, ranged from barely warm to warm (not hot) to the touch between idle and 1/3 power. I'll have to do some torture testing to see how hot it gets at full power, into rated load or lower. And how much ambient temperature changes affect it's cooling. I just need a higher current power supply for that testing. But sofar at room temp of about 25 deg C it actually runs much cooler than both the alpine cd player and power supply I was using for testing.

[Redshift187]

Are you checking the temperature of the enclosure/heatsink, or the chip? Because the heatsink won't warm up much if there isn't good contact, especially without paste.