Saturday, June 25, 2011
Shown here is the second build of the simple but good sounding preamp. In this version (MKII) two values were changed in the cuircuit which has caused a sharp drop in distortion (0.2%) and better performance from the whole preamp. Internally the build is neater and tighter. With even shorter signal path than in the previous build. The finish is beaten copper.
Again single brd. construction prevailed with no PCB. All component-2-component wiring using silver solder and wire wrap wire to connect to the pot and RCAs. An Alps Blue Velvet pot is used on the output with a solid brass black chrome knob. Any 12AU7 can be rolled to the provide different timbres and tone. The cast Al case is damped with tar/Al heavy foil and thick silicon feet fit-off this fine preamp.
Friday, June 17, 2011
This simple single stage preamp requires only a single 12AU7, a 24V wall wart and the balance of a good stereo system. The construction consists of a single board with PS at one end and a tube at the other, but how it sounds beguiles its simplicity. The tube is a 12AU7, blue velvet attenuator with 4oz solid brass knob on the output and all component-2-component wiring. No PCB to dull the sound and silver solder used throughout. Frequency repsonse is from 10hz to 130Khz (-3db points).
A small amount of negative feed back is used in a local sense. The way this is applied contributes to the excellent sonic signature. The detail, warmth and deep sound stage exceed most of the preamps I have ever built both in the tube and SS camps. This one was commissioned and will be employed in an elaborate theatre system to add warmth and detail to the centre channel. But in a 2 channel system this absurdly rudimentary preamp really shines. And now one for me.