Thursday, May 23, 2019

"LeManja" - Hybrid Tube and chip headphone amp

LeManja comprises a tube front-end and a chip backend. The tube section is a 4SU universal design so that any 12A?7 tube can be rolled with no bias adjustments required. The chip, which drives the headphones, is a PT2308. It is a dedicated very low distortion headphone driver. Generally you would require an input cap for the chip but by keeping the Alps blue velvet pot at the front of the tube I could use the tube section's ploy output caps to block DC. This means there is only two caps in the signal path. Two mutually exclusive inputs are on the back with a four pin socket for the three exernal DC volatges and common earth.  

The PS is external and has a choked (Hammond 5H) triple Pi HT filter. The last cap at the ceramic socket for the tube is a 4uf PIO and snubbed. The tube here is a new Tung Sol 12AX7 gold pin. DC is supplied for the filaments and a separate DC 30V source for the chip. The chip max voltage is 7V so a 6V reg. holds the voltage to the chip. All caps on the chip veri-board are LESR types. A 24VAC 1A wall wart provides the initial power from the mains. All audio path wiring is via silver plated fine single strand copper wire.

The amp is absolutely dead quiet. The back ground is completely black causing all music to standout 3D style with amazing dynamics. The chassis is a Hammond Wood Cheek and is sprayed black with Epoxy Enamel paint first, an etching primer for an outstanding finish. The wood cheeks are treated with a ceda oil.