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individual speaker sections. In Passive Bi-Amplification mode, each channel can deliver 150 Watts under 8 Ohms.
By adding a second input board, the A1.5 provides the following additional operating modes:
Stereo mode: In stereo mode, each amplification stage is driven by its dedicated input board and the amplifier operates
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as a standard stereo power amplifier. Feedback and gain settings are replicated on both channels of amplification and
the A1.5 can deliver up to 2x 150 Watts under 8 Ohms. It is the configuration used when a single A1.5 drives a pair of
speakers.
Active bi-amplification mode: As per stereo mode, active bi-amp mode links each amplification stage to its dedicated
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input board. Feedback and gain can however be adjusted individually for each channel in order to best match the
requirements of each driver. An active external crossover, usually fitted between the preamplifier (such as the CH
Precision's L1) and the A1.5, is generally used to split the signal into different frequency bands. In the Active Bi-
Amplification mode, each A1.5 can deliver up to 2x 150 Watts under 8 Ohms.
1.1.2 Feedback control
One of CH range of power amplifier's most unique feature is its user controllable feedback. This feature provides control over the
ratio between global and local feedback applied in the A1.5's amplification stage. Global feedback takes a portion of the output
signal after the power stage and feeds it back to the input of the amplifier. This ensures a very low output impedance and low
distortion figures. Local feedback, on the other hand, does not include the output stage and lets the latter operate in open loop
mode. This favors small signal details and timing. As a rule of thumb, a higher ratio of global feedback is preferred for grip and
control in the low frequencies whereas a lower ratio is preferred for speed and details in the high frequencies. This rule is however
not absolute as each speaker and crossover are different and we highly recommend to experiment to find the best match with the
connected loudspeakers, especially if the A1.5 is driving a complete full bandwidth loudspeaker. In multi-amplification systems,
different feedback settings are commonly used for the various loudspeaker sections opening a whole new level of performance.
We recommend to start with pure local feedback and increase the global feedback until the bass are tight enough to your personal
taste. Feedback settings can be adjusted on the fly from the A1.5's front panel or from the CH Control app.
1.1.3 Gain control
The A1.5 provides an integrated gain control with a 24 dB range in 0.5 dB steps. This gain control allows an optimal matching of
the speaker sensitivity, room size, and preamplifier output level. In multi-amplification systems it can be used to match the
sensitivity of the individual speaker sections. Gain can be adjusted on the fly from the A1.5's front panel or from the CH Control
app.
1.1.4 ExactBias
The A1.5 features an advanced bias control circuitry called ExactBias that not only Counteracts the effect of slow temperature
variations, but also accurately takes into account all the dynamic aspects induced by transients in the musical content.
Rev 1.0
A1.5 User Manual
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