Sunday, May 31, 2015

Two years or so ago I embarked on building a amplifier. I never got around to doing a proper write up so here it is! (minus the proper part)
I saw a kit on eBay and read some reviews about the LM3886, all of which were good. Decided this would be my first amplifier project.
As usual I ended up spending far more money than I had intended. It started out partly as a money saving venture, a good quality amp is expensive but DIY is cheap.
Well it's cheap when you know what you're doing.

In the end I was happy, it sounded great and I learned a lot in the process.

I had built a small tube buffer amplifier (another kit from China) which exposed me a bit to transformer/mains voltage, I asked a coworker to give me a hand wiring up the transformer which gave me a bit more confidence dealing with mains voltage.
This project however I did myself and helped increase my comfort with mains - no shocks!
Looking back at this work I am somewhat unhappy about the wiring which is pretty sloppy. I'm pretty sure I covered up the mains connectors, and I'm pretty sure I
connected a chassis ground. I know however I checked for continuity to earth ground.

In the end this amplifier ended up in the hands of my friend. I had purchased another kit to build one for
him, and well it didn't happen and I ended up giving this one away.
This was the kick I needed, my old amplifier (A $2 acquirement at a garage sale - worked great
but came no where close to the great clean sound the LM3886 produced.
I'll eventually get the photos of that new amp I built which I'm much happier build wise with.

One thing I still have not been able to figure out is the volume control.
With a loud input source the pot works great, however
it's difficult to drive the amp to it's limits as from my computer the sound-card clips before the
amp does.
I believe I need a preamp in there and as of 2015-05-29 I have ordered a few other kits to try and fill in this gap.
I highly suggest this amplifier, other than the caps I did not switch out any of the components.
Folks on have many suggestions for components to swap out.
At some point I may give it a go, but I think my speakers are now the weak link and I have no complaints
about the sound!.

I bought the transformer from the same eBay seller and s/he had shipped it all together.
So in transit one of the Capacitors was damaged. The seller was happy to replace it but being in a rush to get things underway I ordered some caps from digikey - Nichicon UFW1H103MRD - $8 a pop!
Damaged cap!
Nichicon UFW1H103MRD
Pot, I believe this is a ALPS 100k
Step attenuator I ordered - I never build it
some progress on the amp pcb
bottom of psu pcb
Bottom of the amp pcb
Power-supply PCB almost populated
All done!
Basic test using a scrap heatsink
Messy workbench!
Speaker protection board
The testing setup.
Small device that has some RCA plugs and is wired to the pot. Useful for the testing process
Getting the heat sinks mounted was a exercise in frustration Drilling the holes in took way too much effort. If only I had a drill press.
I tried to drill the other way, it sorta worked.
It all worked out in the end.
Starting to figure out how to lay everything out
IEC Connector with the integrated fuse holder
Hey not bad!
Starting to wire up everything
The embarrassing layout
Sitting open while I do tests
Close up of the IEC connector, you can see how much of a struggle I had cutting that hole. It wasn't perfect but it's on the back, so hey no one will notice!
close up of the power button
Power button switch
Speaker binding posts installed
All the components laid out on the bottom plate of the chassis
It's a mess in there....
Back of the amp with stuff connected
Turned on, look at that pretty power glow!
Hey you can see ole reliable still on the shelf!