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HEADPHONE AMPLIFIERS
Creek headphone amplifiers eliminate the need to use a full size amplifier
for boosting the power when only headphones are used. An average output
level CD player or tuner can be connected directly to the input of the
headphone amplifier.
Creeks OBH-21 & OBH-21SE incorporate advanced circuitry utilising
professional standard operational amplifiers. The discrete transistor
technology used in earlier model Creek headphone amplifiers has been
replaced by high-grade integrated circuits providing a capability to drive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 panel. 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, together with a DC power jack. In common 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 (2.1mm positive centre pin power jack) on the rear panel.
The power supply may vary depending on country of use.
The SE version features internally advanced circuitry to split the power supply from a single positive to
a split positive/negative supply, which allows circuits to be DC coupled and to eliminate capacitors.
Higher grade components are used in the SE version. It also features two pairs of stereo Phono sockets
(RCA jacks) on the rear panel for input from any line level source and chain linking to another product
in a tape loop circuit. The DC power jack for connection to a custom OBH high-grade power supply
adaptor is also located on the rear panel.
The OBH-21 can also be used in conjunction with other Creek OBH series products. It also functions
with a stand-alone pre-amplifier or integrated amplifier without headphone output, connected in the
tape loop.
PHONO PREAMPLIFIERS With modern amplifiers expected to cater for so many new devices, the Phono capability has frequently
been one of the features to disappear. Creek Audio has always been aware of the benefits of vinyl - that
is why it continues to provide a number of Phono stage options.
The OBH-15 Phono pre-amp can drive long cables, due to its low output impedance. It has combined
the high quality discrete semiconductor circuitry of the earlier Creek OBH-8 and OBH-9 input and gain
stages, and added improved open loop gain by cascading them, prior to the selector switch and combined
passive RIAA circuit.
Separate Burr-Brown professional grade low-noise op-amps are used for each channel to buffer the
output signal and provide a very low impedance drive to any pre-amp or integrated amplifier. The OBH-
15 can switch from moving magnet to moving coil cartridges, via a simple push button on the rear panel.
As the OBH-15 has two input circuits, optimised for each type of cartridge it allows for the connection of two
turntables. A high gain MC version, for low output MC cartridges, is available to order. The OBH-15 has a
built-in high performance power supply regulator circuit which makes it immune from power supply
f luctuations so, it can be used with the unregulated OBH-1 6 Watt power supply. It will sound better with the
regulated 12 Watt OBH-2, which is available as an option.
Internally, the OBH-15 has been built to the highest standards using a
glass-fibre double sided, plated through hole PCB and very high-grade
components. The OBH-15 looks the part too! Designed to complement the
Creek range of amplifiers, tuners and CD players, the OBH range features an
impressive 4mm thick solid aluminium front panel in a silver finish. The
remainder of the 150mm deep extruded aluminium case is painted black, so
the product all but disappears.
The function of the OBH-18 is to boost the level and correct the frequency
response of a low level signal coming from a moving magnet phono pick-up on a
conventional turntable. The signal required by most modern amplifiers is
described as being 'LINE' level, which is, in technical terms, between 200 and 500
milli-Volts with a f lat frequency response. Unless your amplifier has a specific
'Phono' or Disc input, the level will be too low and the frequency response will
be wrong. The OBH-18 is designed to boost the signal and introduce an
R.I.A.A. frequency response characteristic.
PASSIVE PREAMPLIFIER
The function of the Creek OBH-22 passive pre-amplifier is to provide input
selection and volume adjustment to a Hi-Fi system from an armchair, via
infra-red remote control. The unit can also be controlled directly from the
front panel.
The OBH-22 consists of a high quality motorised volume potentiometer, and
two stereo relays which select the desired input plus tape output, together with
a muting relay that can short the signals to ground. A built-in micro-controller decodes the infra-red signals
transmitted by the handset and translates them into commands which activate the motorised potentiometer
and the muting and input selection relays. After each operation, the micro-controller turns itself off to avoid
any possibility of interfering with the main music signal. LED's are used to indicate the status and mode of
operation.
The OBH-22 is purely passive and does not introduce any gain or distortion into the signal path. It is
therefore suitable to be used as a control pre-amplifier, provided the sensitivity of the power amplifier that is
being used is high enough to be driven directly from the source. i.e. CD player or tuner etc.
The volume control can be operated manually at any time, whether the OBH-22 is powered or not, but
without power only Line 1 can be utilised.
