Wheatfield Audio Wheatfield Audio HA-4 Users Manual
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The HA-4 controls in detail
The Volume Control
The volume control adjusts the listening level by attenuating the signal before the
main power amplifier. By doing so it controls the overall gain of the amplifier.
The EQ controls
The three EQ controls adjust how much the level of the audio signals in each of
the three frequency ranges is boosted. The three center frequencies - 90 Hz, 2.5
kHz, and 20 kHz - were chosen to provide compensation for the frequency
response of the ear coupled to headphones, as compared to the ear listening to
speakers at a distance.
When the control is turned fully counter-clockwise, the frequency band is boosted
4 dB relative to 1 kHz. At mid-range, 8 dB of boost is provided, and fully clockwise,
12 dB. The overall gain is dropped 5 dB when the EQ is enabled, to provide
loudness equal to the bypass setting.
We suggest starting with all three controls at mid-range (8 dB), and after listening,
adjust the controls as you desire. Everyone has different ears, tastes, and
headphones, so this is purely a subjective adjustment.
The Crossfeed Selector
The crossfeed selector lets you allow some of the audio from the left and right
channels to be intermingled. This circuit attempts to duplicate the natural
crossfeed that occurs when you listen to a pair of speakers. Obviously, when
listening to speakers, your right ear can hear the left speaker (and vice versa).
To try and duplicate this effect, the signals that are crossfed are passed though
passive RC filters that provide some equalization and delay in the signal path
from one channel to the other. The equalization helps mimic the fact that
hearing is much less directional at lower frequencies than at high frequencies.
The delay simulates the time difference that it takes sound to reach the "far" ear
relative to the "near" ear.
Crossfeed can be disabled, or enabled at one of two levels, by adjusting the
crossfeed selector switch. Again, we recommend starting in the mid-range
setting, and adjusting up or off to your liking. The exception to this is for true
binaural recordings, and for digitally processed surround sound or computer
generated 3-D audio, where crossfeed should be disabled.
The Bypass switch
Pressing in the bypass switch physically routes the signals around the entire EQ
and crossfeed circuit. When in bypass mode, the amplifier is completely flat and
linear throughout the audio frequencies, and the left and right channels are
completely isolated from one another.
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