Leach Amp Chassis

Building the chassis may seem to be an unusual first step, but this actually makes the whole process a lot easier. The reason I recommend you building the chassis first is that the PCBs and the heatsink don't have any components atteched to them yet and this makes them much easier to work with. I chose to build my chassis out of MDF, traditionally an amplifier chassis is built out of aluminum or steel, but I don't have much experience with metal work and no real desire to learn at this time. The MDF was quick and easy to work with and produced a chassis I like very much. Lets get down to the basic design.

As you can see from the design the chassis is made of 1/2" MDF with the exception of the back panel which is made of 1/8" hard board. This design can very easily be made from one 2'x4' sheet of 1/2" MDF and one 2'x2' sheet of 1/8" hard board which can be purchased from Home Depot for about $9. I used a jigsaw and drill with 1/4" bit to create the openings in the back panel. The 1/2" pieces of MDF were glued and clamped together first, then the 1/8" hard board back panel was glued and clamped in place. I modified the back panel before gluing it into place, but your could probably do this after gluing it. The top panel was made to be removable, so obviously this piece was not glued into place. After all the chassis pieces had been glued I positioned the top panel and carefully drilled pilot holes through the top panel and into the side walls for the four screws wood screws that would hold the top panel in place. Then I took a larger drill bit and drilled recesses so that the heads of the screws would be sunken into the top panel. Normal wood screws 1" in length are used to hold the top panel in place. A 13/16" hole was then drilled in the center of the front panel, this is where the power switch will be mounted. I knew that I wanted to finish the chassis with paint, so I went ahead and filled the seams with wood putty so they could be sanded later.

Now it's time to drill holes on the inside of the chassis so that the amplifier components can be mounted. First, a 3/8" hold should be drilled in the horizontal center of the bottom panel 3 1/4" away from the front panel (this is for monting the toroidal transformer). Next you should take your two blank Leach Amp PCBs and lay them down flat on the bottom panel. Center them along the back panel horizontally spacing them about 1/4" to 1/2" away from the back panel. Now carefully mark the four mounting holes of each PCB (these are the large holes in the corners of the PCBs) onto the bottom panel, you should mark eight holes total. Now drill these markings about 1/4" deep with a 1/8" drill bit. If you already have your nylon standoffs you can glue them into these eight holes now (I used a polyurethane based glue called "Gorilla Glue") or you should wait until later.

You should also take this time to drill the mounting holes in your heatsink. I did it by placing the chassis face down on a table and then centering the heatsink on the back panel horizonally while spacing is 1/2" away from the bottom of the back panel. Then you can begin drilling holes for the mounting bolts through the heatsink and then through the back panel with a 3/32" drill bit (thats just under and 1/8"). I chose to drill my holes through the last valley in the heatsink, each about 1" away from the edges. I do not recommend you drilling the holes anywhere else. Throughout this process it may help to reference the pictures of the finished amplifier to get picutres of exactly where and how all of the components will be mounted.

Once you've applied your desired finish for the chassis you can add the 4 rubber feet by simply gluing them to the bottom, I used the Gorilla Glue here as well.