Chassis for Guitar Amps

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Amp Chassis made from Aluminum

The guitar amp chassis is the metal box that holds the circuit board, transformers, vacuum tubes, switches and jacks. It is the main component to the entire amplifier. The size of your chassis box will depend on the type of circuit you are building. In other words, if you are building a simple Fender Champ, the chassis will be relatively small, but larger circuits will require a larger chassis to accommodate the extra components.

Pre-Fabricated Chassis

Chassis boxes can be purchased in pre fabricated units for certain style amps. Most have a finished front side (visible side) with precut holes for components and labeling for the controls. I’ve seen chassis boxes available on the web from $50.00 on up. Buying a pre made chassis will definitely save some time on your guitar amp project and also gives it a nice finished look.

Custom Made Chassis

In order to keep my cost down I chose to fabricate my own chassis box. Fortunately I had access to some sheet metal working tools. For my box I found a piece of scrap aluminum sheet metal that was .063” thick. I wouldn’t recommend going any thicker than .063” since that material is fairly rigid for the size of chassis box needed. Using a metal shear and a metal break, I cut and bent the piece forming three sides. The measurements were roughly 4.5” tall by 10” long and 3” deep. The face of the chassis measures three inches. The two ends of the box were covered using two additional pieces of aluminum bent and fastened to the ends with rivets. Simple pop rivets will suffice. The whole amp chassis box was mounted to the amplifier cabinet by means of two nut plates. One nut plate was installed at each end of the chassis box face. This allowed two screws to hold the chassis against the amplifier cabinet. It works out great. If you don’t have nut plates available, as most probably don’t, a simple screw and lock nut will work fine.

Alternative Chassis

Another solution is to find a box of suitable size that could be used as a chassis. Make sure the box is constructed of a conductive metal. The metal box provides a ground plane barrier to reduce electrical interference from other devices. This is a must. A guitar amp that picks up external noise will sound very bad. I will have a section on electrical interference later in the site.

Chassis Layout

To complete my amp chassis I laid out all the switches, pots and jacks into a reasonable fashion and drilled the holes to match. I used a step drill, which may be obtained at any hardware store. The transformers were mounted to the backside of the chassis. The power transformer is recessed in the chassis box and requires the chassis to be cutout to accommodate the transformer. A jigsaw with a metal blade will do fine to cut the transformer hole. The vacuum tubes are mounted to the bottom side of the chassis and were cut out using the step drill.

Component Mounting

Once all the holes are cut I mounted all the components to the chassis. The vacuum tube sockets were mounted with #4-40 screws and lock nuts. The transformers were mounted with the supplied hardware. All hardware should have some sort of locking mechanism to ensure nothing will work itself loose. Loose hardware in the guitar amp will cause rattling noise. Final assembly will be with the circuit board in place.

Electrical Shock Hazard !

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