Monday, January 17, 2011
JFET phono preamp-in a chocolate box
I was never completely happy with my phono preamps weather tube or OPAMP base. I made the Boozhoundlabs two stage jFET "Le Pacific" style preamp. Once more I went for the vero-brd. Also, though I wanted to build it with the Russian PIO military caps I did not have some of the values I wanted. I opt for a build using high voltage (630V) brown polypropylene caps.
The cct. brd. above uses pure silver 1mm earth links, 2SK170 BL jFETs and silver based solder. Low ESR 220uf caps (snubbed) sit across a decoupled V+ rail and a single 10,000uf caps (snubbed) feed the V+ through a 1ohm resistor (a La Pass). Currently running under 27V of lithium batteries.
Ferrite beads sit across both the ground and hot wire to the cct. brd. from the input Also the PS input has ferrite beads also. No shielded wire is used (I don't like it) but the input wiring is heavily twisted, hot wire and ground. See previous post for chocolate box enclosure.