- Written by John E. Johnson, Jr.
- Published on 15 May 2014
The Design of the OPPO HA-1 Headphone Amplifier
I never expected to place on my end table, a headphone amplifier whose output stage is biased into Pure Class A operation, using fully balanced discrete circuitry with no global negative feedback, and priced in the kilobuck range.
The front panel has an input and screen mode selector, an LCD display, volume control, balanced and unbalanced headphone jacks, on/off button, and a USB jack for iPods, iPads, and iPhones.
The rear panel has RCA and XLR analog inputs, RCA and XLR analog preamplifier outputs, and digital coaxial, XLR, Toslink optical, and USB DAC (computer) inputs, plus a Bluetooth antenna (for use with an app that works with your iPod, iPad, or iPhone).
The inside of the chassis is shown below. You can see there is no room to spare. A nice sized transformer and plenty of capacitance (this helps with the deep bass).
The grille (vent) on the top of the HA-1 gets very hot during use, due to the Class A bias. Don't set anything on the HA-1 that would cover this grille.
The IR remote control is small, and fits comfortably in the hand. It is very thin and elegant.