solid state audio

Attached is the PCB schematic for an audio amp based around national’s overture series. I designed and built this to suit a B&O beogram purchased when I had v. little coinage. The pad layout was created under circad, on a little old laptap running windmills 95. I was at a conference in Monterrey CA at the time (2004), and the bucolic scenery was too much to resist; I mostly sat on the beach drinking it all in, knocking this design together. There was a neat record shop which appeared to be the last bastion of the counterculture popular in Monterrey during the sixties. I picked up several LP’s including rare garage rock and was regaled by the owner’s tales of hearing Dylan back in the day.

I sampled out the 56W overture model from national; if you’re not familiar with this, engineers etc can get free samples from manufacturers, try it sometime. I also included a phono stage based around the LM833, to perform the RIAA equalization. This is of course necessary since the freq response of LP playback is not flat, so as to counteract deleterious mechanical issues. You could of course forgo this stage for a rather weird aural experience.

All you need to know is contained in the National tech note on the LM833 and overture, including supporting discrete components. I also include in the circuit a mixer/balance IC and notch filter for 50Hz. Thankfully I didn’t need to utilize the latter, the hum left when I eliminated all the ground loops; don’t forget to tie the ground of your LP to the amp & connect voltages to the right rails. The speaker(s) I built from pine to suit, which has a lower resonance than a hardwood like oak and to my mind the sound is richer, more mellow. The speakers (bose) and cross overs were bought online from allelectronics.com for pennies.

In the works 2009 is a tube amp…

main board PCB art

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concrete counter

We’re nearing the end of an almost total restoration of our ~1860 house. It’s gigantic with many beautiful details but some aspects needed severe TLC, including the kitchen. We tore back ~100 years worth of previous alterations to expose bricks, uncovering large windows which had been boarded up(!). In order to work in some modern industrial design features whilst working with the rustic nature of the room, we struck upon using concrete for a large center island, referring to Cheng’s book for inspiration.

I decided to experiment a little, straying from the designs within the book, largely due to the weight issue. For instance a 2″ by 7′x3′ slab suitable for the island would be something like 600lbs and given the nature of the old joists, I didn’t fancing loading the floor to that degree. So for my design, I settled on a 2.5″x 2.5″ overhang, and used a blank to remove some of the volume; the majority of the counter is 1.5″ thick. I used quickrete mix with fibreglass in the hopes of reducing the threat of cracking given the thin slab.

Pictured is some of the detail of the mould, including water run off, fashioned from tin sheet and lumber, filled with car body filler. I made the corners by heating acrylic in a conventional oven on 250F for 5-10 mins and dropped them in the sink corners to capture the shape before cooling. Along the underside of the mold are 3″ strips of pine, ripped up on the table saw and screwed and glued edgewise to the mould back to keep it true. I used threaded re-bar with coupling nuts within the overhang for extra support, given that there is some cantilever action at the (unsupported) eatery end of the island. The sink is undermounted, for an undulating surface finish… more photos of the kitchen in ..er.. ‘photos’