Easy Amplifier

I've been meaning to make an amplifier for the back room for a long time. This project finally kicked off after finding some Sony bookshelf speakers on the side of the road and the Instructables competition for hand tools only, well that's the sort of project I'm qualified for.

I had bought a Tripath amp PCB a few years ago, along with a power supply, some speaker binding posts, RCA sockets, plugs and switches ect. All of these items then got moved from box to box and finally to the back of the shed. After much searching I finally found all the bits I needed to get this project going.

Dremel - Router attachment, 3mm Cylindrical Bur & Cutting wheels

Plunge router - 45 degree bit

Mini rip saw

Cordless drill - Selection of drill bits

Bench clamps

Soldering iron

Eye glasses & ear protectors

I have had an idea for this amp design for a while and I like the way you can bend aluminum composite panel

First check the panel is square, I was hoping that I would get away with not having to square it up but it was not square (it is an off cut).

For this you can use a router or as I did my mini rip saw.

Now the real fun begins. Setting up a jig using bench clamps and a strait edge (3mm aluminum bar works well for this) at 90 degrees from the side of the sheet.

Now we nearly ready to cut our first channel. First set the height of your Dremel so it mills all but the last .5mm of panel. This isn't as hard as it sounds but you may want to try the depth out first on a off cut.

Because aluminum composite panel has a plastic core you will need to run the Dremel up and down a couple of times to clear out the melted plastic. Once done you should have a channel that is clear of debris and still have about .5mm of plastic and the aluminum outer skin still intact.

My side panels are oak off cuts and are 50mm tall so I need to allow a 50mm section which will become the front of the amp. This means I need to mill my second channel 50mm from the edge of the first channel so I can bend the panel around the oak side panels.

The last job is to trim the finished panel down to size.

VERY IMPORTANT NOTE: aluminum composite panel comes with a protective film on both sides. I took this off what will be the inside of the box before I had finished working the panel. As you can see when I cut the end of the panel down to size I scratched the paint off. Luckily it wont be seen.

I wanted as clean an enclosure as possible so I decided on only four screws to hold it together, two on the top and two on the bottom.

I also wanted the screws to be counter sunk. I haven't had a lot of success in the past with countersinking screws. With a hand drill the countersink bounces around and gives an irregular shaped hole, internet research suggests its not really possible to get a good smooth finish without a drill press.

So what to do……… Then it stuck me. I have a plunge router, so using a 45 degree bit and adjusting the plunge stop so not to go all the way through I was able to make perfect counter sunk holes for my screws.

The last thing to do was to bend the front of the enclosure around the oak side panels and screw it all together. First I screwed the oak side panels to the top panel then with these securely in place I bent the composite panel around the wood and finally screwed the bottom lip to make the top, front and sides of the box.

The bottom tray has no bending, its simply a square piece if composite panel with countersunk holes in the four corners, feet and the brackets to hold the back panel in pace.

I drew up the back panel with marks for were I wanted holes for the binding posts and RCA plugs. I then printed it out on self adhesive sheet, cut it out and stuck it down. I carefully drilled the holes and cut the square hole for the power socket using a Dremel with a cutting disk. At this point it looks a bit rough but when you add your sockets and cover the torn edges it looks pretty smooth.

With the back panel assembled its time to lay out the position of the amplifier components, not really much to say here, just mark the holes, drill add stand-offs and screw together.

Because the amp PCB had the volume pot on board I had to remove it so I could mount it on the from panel of the enclosure. Unfortunately the pot broke whilst I was desoldering, fortunately I had a spare. it was bigger and as it turned out easier to fit. I soldered lead wires to the new volume pot, soldered wires to the RCA plugs and speaker binding posts, attached wires from the mains plug to the power supply and switches.

I only wanted two switches on the front. One is to be the volume the other to be the power.

I had in my parts box two power switches the clear green I want for the power switch the black I will chop up and make into a matching volume control.

I marked out the central line of the front panel, decided were I wanted my switches and marked and center punched for drilling with a 22mm spade bit, this worked well and left a clean hole.

Next I cut up the black switch to become a volume knob, I found this particular type of switch didn't come a part.

So using a pen lid and shaping it to fit the inside of the switch and a small volume knob that fitted in the other end of the lid I was able to hot glue the assembly together to give my what I needed.

An aluminum bracket was made for the volume pot and the assemble was screwed into position.

Nearly there, last few screw to secure the whole thing together and we are done.

After all the excitement of getting it together I turned it on only to hear absolutely nothing!!!!

If any of you had noticed from the pictures I had neglected to wire the power supply to the amp, this wasn't such a big deal even though I had cleared away all my tools for the day, it was just a screw terminal and plug.

So after putting it all together for a second time, I can say I'm very pleased with how it turned out, but there is a minor change I would like to make.

I would like the green power switch to be lit when on, so I need to figure out how to get an LED in there, shouldn't be to hard.