in order to quantify the effects that my modifications had on the performance, i used some bash scripts and gnuplot to compare the spice simulation results of the two designs. needless to say, i was quite pleased to see that gain, headroom, frequency response and phase response were all improved. :) (trust me, i don't claim to be the first one to make these changes, but the circuit feels more like my baby now, if that makes any sense...) the comparison results, in pdf format:

the case construction was started once i had laid final plans for the circuit board layout. i first used a band saw to cut a rough block (approx 4.5"x3"x1.75") down to approximate size and then i used a shell cutter to precision mill the block to 3.5"x2.0"x1.5". i drilled through-holes for the phone jacks (3/8" dia.) and dc power jack (7/16" dia.) and then made through-holes for the side-panel mounting screws using a #25 bit. the mounting holes were then tapped for #10-24 screws. on the top and bottom of the case, i drilled out TO-220 mounting holes using a #25 bit and then, using a 1/4" endmill, milled out room for the screw heads to fit flush with the case walls. finally, i hollowed out the interior of the block using a 3/8" dia. end-mill.

mounting the circuit boards inside the case was tricky, since electrical isolation was required. the boards were secured by two stainless steel #6-32 hex head machine screws through the two TO-220 packaged components, with mica insulators underneath them and a nylon nut above them, ensuring isolation. a section of teflon tubing was also cut to thread onto the screws between the screw threads and the TO-220 tabs, and the mounting holes of each TO-220 component were widened with #19 drill bits in a vise. the conductive traces on the bottoms of the circuit boards were isolated from the case with spray-on conformal coating.

the mirrored finish on the aluminum was achieved by first using 600, 1500, and 2000 grit wet sanding paper under a faucet, with a sandal for a sanding block, and then applying a white polishing compound until the part was shiny. :) i was able to pick up the above supplies and terry cloths for polishing from a local autozone, and the finish, as is visible in the photographs, is quite spectacular.

finally, the wooden sides were cut from a stock 0.5" thickness red oak board using a table saw, and then sanded down to the precise dimensions of the aluminum housing. before finishing, through-holes for mounting were drilled into the wood using a #3 bit and countersinked. i milled a 0.2"-deep recess into the inside of each wood panel with a 3/16" endmill. i then applied a first coat of stain to the wooden panels before filling the pores of the oak in with minwax filler and applying the final coats of (minwax cherry) stain. green adhesive felt feet were added to the undersides of the wood panels to keep the aluminum chassis section off the table surface for better cooling.

the power supply enclosure was a bit trickier, as more parts were used in the final case. three 1/4"-thick aluminum blocks were cut to rough size and endmilled to 1.15"x3" (1) and 5.25"x3" (2). eight mounting holes in each top and bottom face were made using a #3 drill and a 5/16" endmill for the #10-24 screw heads which would be used. the same tools were used to mill a pocket for an M5 bolt to mount the toroidal trafo to the bottom panel. vent holes were milled using a 1/8" endmill in the top panel. the small aluminum block was drilled to hold the TO-3 voltage regulator such that it is isolated from the other two aluminum panels. wood side panels were cut and mitered to dimensions required to form the outer walls of the case. both materials were finished using the same techniques used on the amplifier case.