The Creek OBH-21 headphone amplifier eliminates the need to use a full sized integrated amplifier to boost the audio signal when only headphones are used. An average output level CD player or tuner can be connected directly to the input of the headphone amplifier. This is much more convenient and can improve performance for headphone listening compared with larger integrated amplifiers.

The OBH-21 incorporates advanced circuitry utilising 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. 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 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-Uni 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.  Split-rail supplies can provide better Common Mode Rejection Ratio (CMMR) which will improve the sound quality by reducing interference.
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 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 or pre-amp output.

The OBH-21SE is a higher grade version of the standard OBH-21. Higher grade components and additional circuitry are used to produce a better performance. The main differences between the 21 and SE are as follows:-

Volume potentiometer type:-
OBH21 is fitted with a 16mm carbon film pot.
OBH21SE is fitted with a 27mm plastic film pot.

Amplifier circuitry:-
The OBH21 uses 2 x NE 5532.
OBH21SE uses 2 x LM 7171.

Signal coupling:-
OBH-21 is AC coupled using audio grade caps.
OBH-21SE is DC coupled and offset voltages are controlled by a custom DC servo circuit.

Input socket type:-
OBH-21, Nickel pressed metal.
OBH-21SE, Gold pressed metal.

• Output Power >10mW
• Suitable Headphone Impedance Range 30 Ohms to 300 Ohms
• Higher impedance headphones will work but the output level will be reduced proportionally.
• Frequency Response 10Hz to 50kHz +/- 1dB
• Total Harmonic Distortion <0.01% @ 1kHz
• Signal To Noise Ratio >70dB
• Power Supply Requirement Creek UBH-Uni, (24V DC, 15W)
• Power Consumption <3Watts in operation,
• <1 W in standby
• Weight 3kg