The OBH-21 incorporates advanced circuitry utilizing high grade op-amps for signal amplification, providing the capability to drive headphones with impedances ranging from 30 to 300 Ohms without a problem. Gain (level) will be greater for lower impedance headphones.
There are two 1/4" (6.3mm) stereo headphone jacks on the front panel of both models. The matching impedance for each of these sockets is slightly different which allows for better individual matching. When using two sets of headphones, the impedance will be the same for both. The output level can be adjusted by an analogue volume potentiometer coupled to a solid metal control knob on the front panel. The OBH-21 has only one pair of stereo inputs using stereo RCA (Phono) sockets on the rear panel. To make connection to another amplifier easier, there is another pair of sockets which can patch the input signal through to another amplifier. This is especially useful if the OBH-21 is used in series with the tape loop of a pre-amp or integrated amp. It is suitable for any line level analogue source.
In common with all electrical appliances, the OBH-21 requires a power source. A custom stand-alone Creek OBH type power supply is provided that must be connected to the unit via the DC inlet on the rear panel. The mains power supply and connector plug will vary, depending on country of use. Inside the OBH-21, custom circuitry is used to convert the power supply from a single, positive rail, into a split positive and negative supply and ghosted ground. Split rail supplies provide better Common Mode Rejection Ratio (CMMR) which will improve the sound quality by increasing interference suppression and allow for DC signal coupling on the SE version.
The OBH-21 uses two high-grade NE 5534 op-amp circuits for the amplifying stage and audio grade coupling capacitors in the signal path to block DC (direct current). The SE version uses two instrument grade LM 7171 op-amp circuits but has no coupling capacitors from the signal path to achieve DC coupling from input to output, for better sound quality. Like the Classic and Destiny amplifiers; it uses a custom Creek DC servo loop to eliminate any trace of DC from the output.
The OBH-21 can also be used in conjunction with other Creek OBH series products, such as Phono pre-amplifiers or the passive pre-amplifier. Furthermore, it can also function with a stand-alone pre-amplifier or integrated amplifier, connected in the tape loop.