OPTIONS
Option: HP 700 with stepped attenuator
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Option: HP 700 with stepped attenuator
The volume control is an important component of a preamplifier. The demands placed on the controls
are very high. The control range must encompass at least the range of 1:3000 (or 1:0.00033) to
ensure fine adjustment appropriate for human hearing.
At the same time, the channel deviation within this range must not exceed 1 dB. The transfer re-
sistance should remain constant during and after adjustment to prevent control noises. Rotary con-
trols with a resistance track sensed by a slide meet these requirements to a large extent with our
strict selection, but spring-guided sensing of the resistance track can result in undesired resonance
effects that negatively affect the transfer resistance and impair the signal in the micro range. As a
result of this design, the frequency bandwidth, i.e. the speed, may also be limited, depending on the
control setting.
The control concept can only be improved with a stepped attenuator. In this complex process, the
resistance track is reproduced by a series circuit consisting of individual resistors. The stepped at-
tenuator now senses the connecting points of the resistor ladder. The advantages of this solution are
obvious: thanks to the low-tolerance fixed resistors, the channel tolerance across the entire control
range remains under 0.1 dB. The hard gold plated contacts on the switch have an extremely low
transfer resistance and thus do not generate micro-fluctuations in the signal level caused by me-
chanical resonances.
The switch has 47 settings. This uncommonly high number of settings allows for finely incremented,
reproducible volume adjustment.
To eliminate the effect of the control, or the control setting, on the bandwidth, the stepped attenuator
– as in the balance controls – is frequency-compensated. Equipped with this unique switching layout,
the OCTAVE stepped attenuator functions as an ideal control. The sound characteristics are constant
across the entire control range, while the center position also remains stable across the entire range
thanks to the negligible channel tolerance. The sound pattern gains depth and the finest subtleties
are audible in the layers of sound.
However, as a result of the mechanical design of the stepped attenuator, the switch positions
cannot be controlled using the remote control
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