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…