“Input Voltage” Switch
A wide range of signal input voltages can be accommodated by each of the HD600/4’s differential-balanced inputs (200mV – 8V RMS). This wide range is split up into two sub-ranges, accessible via the “Input Voltage” switches located in each input section of the amplifier. Be aware that each input section’s “Input Voltage” switch will have to be configured, regardless of how many input cables are actually feeding the amplifier.
The “Low” position on each “Input Voltage” switch selects an input sensitivity range between 200mV and 2V. This means that the “Input Sens.” rotary control will operate within that voltage window. If you are using an aftermarket source unit, with preamp-level outputs, this is most likely the position that you will use (regardless of what voltage output capability is claimed by the source unit).
The “High” position on each “Input Voltage” switch selects an input sensitivity range between 800mV and 8V. This is for use with speaker-level outputs from source units and small amplifiers found in many OEM (factory-installed) systems. To use speaker-level sources, splice the speaker output wires of the source unit or small amplifier onto a pair of RCA plugs for each input pair
or use the JL Audio ECS Speaker Wire to RCA adaptor (XB-CLRAIC2-SW).
The output of the amplifier decreases for a given input voltage when the “Input Range” switch is placed in the “High” position. The output increases with the switch in the “Low” position. While this may sound counter- intuitive, it is correct as described.
“Input Sens.” Control
Located next to the “Input Voltage” switch in each input section is a rotary control labeled “Input Sens.”. Once the appropriate “Input Voltage” range has been selected, this control can be used to match the source unit’s output voltage to the input stage of each pair of amplifier channels for maximum clean output. Rotating the control clockwise will result in higher sensitivity (louder for a given input voltage). Rotating the control counter-clockwise will result in lower sensitivity (quieter for a given input voltage). To properly set each pair of amplifier channels for maximum clean output, please refer to Appendix C (pages 18, 19) in this manual.
After using this procedure, you can then adjust the relative level of each channel pair by adjusting the input sensitivity downward on either or both channel pairs, if they require attenuation to achieve the desired system balance.
Do not increase the “Input Sens.” setting for any amplifier in the system beyond the maximum level established during the procedure outlined in Appendix C (pages 18, 19). Doing so will result in audible distortion and possible speaker damage. Be aware that both “Input Sens.” adjustments
will have to be made, regardless of how many input cables are feeding the amplifier. These controls will allow you to set the appropriate relative levels for the “Front” channels relative to the “Rear” channels and any other amplifier channels in the system.
CROSSOVER CONTROLS
Crossovers are groups of electronic filters designed to control the frequency ranges that each speaker in a system will be tasked with reproducing. Proper crossover setup is critical to sound quality and reliability.
The HD600/4 has two individual filters, one for the “Front” channels and the other for the “Rear” channels. Each can be configured as a high-pass filter (attenuates low frequencies) or as a low-pass filter (attenuates high frequencies). Additionally, the user can select from a shallow (12dB/octave) filter slope or a more aggressive (24dB/octave) slope.
Each Channel Control section contains identical crossover filter controls.
1)“Filter Mode” Control: this switch allows you to configure the filter for that Channel Pair into one of two filter types.
“Off”: Defeats the filter completely, allowing the full range of frequencies present at the inputs to feed that pair of channels. This
is useful for systems utilizing outboard crossovers or requiring full-range reproduction from that pair of channels.
“HP” (High-Pass): Configures the CH 1&2 filter to attenuate frequencies below the selected filter frequency. Useful for connection of component speakers in a bi-amplified system.
“LP” (Low-Pass): Attenuates frequencies above the selected filter frequency. Useful for connection of subwoofer(s) in a bi-amplified system.
2)“Filter Slope” Control: This switch allows you to select from two filter slopes.
“12dB”: Configures the filter to attenuate frequencies above or below the selected filter frequency at a rate of 12 dB per octave (Butterworth alignment).
“24dB”: Configures the filter to attenuate frequencies above or below the selected filter frequency at a rate of 24 dB per octave (Linkwitz-Riley alignment).
Depending on the speaker system and the vehicle, different filter slopes may be required to produce a smooth transition between the sound of different speakers in the system.
In high-pass mode, the sharper “24dB” setting will do a better job of protecting small speakers with limited power handling. In low-pass mode, the “24dB” setting can also help by more aggressively removing lower midrange output from a subwoofer system.
The shallower “12dB” octave setting allows for more output overlap between the speakers being crossed over. In many cases, this will result in a smoother “blend” or transition between speaker systems.
Experiment to find the slope or combination of slopes which best matches the acoustic requirements of your system.
3)“Filter Freq. (Hz)” Control:
This control selects the frequency at which the filter begins to attenuate the signal and refers specifically to the frequency at which output has been attenuated by -3dB.
The filter frequency markings surrounding this rotary control are for reference purposes and are generally accurate to within 1/3 octave or better. If you would like to select the filter cutoff frequency with a higher level of precision, consult the charts in Appendix B (page 18) of this manual.
