Following the success of the OBH-11, the new OBH-21 incorporates more advanced circuitry utilizing professional standard operational amplifiers. The discrete transistor technology used in the OBH-11 has been replaced by high-grade integrated circuits providing a capability to drive different types and impedances of headphones without problem.
There are two 1/4" (6.3mm) stereo headphone jacks on the front panel of both models. the output level is regulated by the volume control on the front pane. When using the OBH-21, one source can be amplified as the headphone amplifier has only one stereo input. It has stereo phono sockets (RCA jacks) on the rear panel for input from any line-level source, along with a DC power jack. Like with all electrical appliances, the OBH-21 requires a power source. A custom power supply is provided, which must be connected to the unit via the DC inlet on the rear panel. The power supply may vary depending on country of use.
The cosmetic difference between the OBH-21 and its predecessor, the OBH-11, is striking. Featuring a 50 percent longer case, the new models have a solid 5mm brushed silver anodized aluminum front panel with black printing