The new HA12 headphone amplifier is the result of a custom headphone amp built for a customer, and this version is now offered for anyone interested.
This circuit design has several refinements for hi-end performance. This includes include a tube rectified and choke filtered high voltage power supply,
with regulation for the signal amplifier. The filament supply has 18800 uF of capacitance for very low noise and ripple.
Uses two EL84 output tubes, one 12AX7 preamp tube, and one 6CA4 rectifier tube.
The output signal is transformer coupled to a pair of low-Z (32-100 ohm) and hi-Z (200-600 ohm) headphone outputs.
The result is more similar to products in the $1000-1500 range
There are two inputs, and dual mono gain/balance attenuators, followed by your choice of an ALPs RK27 volume control or a 21 step precision volume attenuator.
The high voltage to the 12AX7 signal amplifier is regulated for very low noise and separation from the power amp output.
The signal thru the EL84 output tube goes thru a high quality polypropylene film capacitor to the impedance matching output transformer
Frequency response is measured to be flat from 10Hz to 40KHz. Output power is meaured to be 500mw into 32 ohms and 60mw into 300 ohms, equivilent to a 2 watt amplifier into 8 ohms.
the basic PCB board kit with parts (no chassis, no tubes, no transformers) is $249 including shipping inside USA
a complete kit of all parts to build is $790 including shipping inside USA
assembled, tested, ready to use HA12 headphone amp, $999 including shipping inside USA