Regardless of what connections are used, the typical parallel speaker load should always be limited to 2 ohms per channel or 4 ohms Bridge mode for any application. Operation at loads of 4 ohms per channel or 8 ohms Bridge mode is more desirable for sustained operation applications due to the fact that the amplifier will run much cooler at this load. Operation above 4 ohms per channel, and even open circuit conditions can always be considered safe; however, any sustained operation at loads below 2 ohms could result in temporary channel shut down due to the thermal limits and/or the amp fault circuits.
LOW-Z INPUT (9)
A conventional 3-pin, female XLR input jack is provided and may be used as the channel input. When the (PL-2) line balancing transformer is not used, this XLR input becomes Quasi-Balanced with pin #3 as the positive input (connecting to the tip of the i/4” input jacks above), pin #2 as the negative input (connecting to the floating sleeve of the l/4” input jacks above), and pin #l going to the internal power amplifier ground. When the (PL-2) line balancing transformer is used, this XLR input becomes fully Transformer-Balanced (Pin #3 positive, pin #2 negative, pin #l ground). (See the PL-2 SELECTOR SWITCH section (next) for details on related settings.)
PL-2 SELECTOR SWITCH (10)
This switch is used in conjunction with the PL-2 transformer to allow the LOW-Z INPUT to function with or without a PL-2 module being inserted in the receptacle. The “out” position of this switch selects the Quasi-Balanced mode of operation for the LOW-Z INPUT (XLR jack), and routes the input signal directly to the HI-Z INPUT jacks. In this position the HI-Z INPUT jacks may be used as outputs after the LOW-Z INPUT to allow patching this signal to another input on this amp. Normally, in this switch position, a (PL-2) transformer is not present (“out”) in the transformer receptacle; however, if one were “in” the receptacle, the LOW-Z INPUT would still be Quasi-Balanced. It becomes fully Transformer-Balanced only when the “in” sw,itch position is selected. Notice this is a very effective means to “test” for the necessity of a line-balancing transformer. The “in”position of the switch routes the signals from the XLR jack through the (PL-2) line-balancing transformer, thereby selecting the Transformer-Balanced mode of operation for the LOW-Z INPUT. In this position the HI-Z INPUT jacks may be used as outputs after the line balancing transformer to patch the signal to another input jack on this amplifier or other amps/ equipment. If the “in” position is selected without a (PL-2) line-balancing transformer “in” the receptacle, the LOW-Z INPUT will be rendered inoperable.
TRANSFORMER RECEPTACLE (11)
This receptacle only receives the optional (PL-2) line-balancing transformer. When conditions exist that demand the usage of a Transformer-Balanced XLR Input for either or both channels, then the (PL-2) transformer must be put here, and the selector switch must be in the “in” position.
MODE SWITCH (12)
This switch is used to select either Stereo or Bridge mode operation. When BRIDGE mode is selected, the channel B LED power indicator will go out indicating Bridge mode has been selected. Accidental selection of this mode could damage loudspeakers. Bridge mode will be covered in more detail later in this manual.
HIGH-Z INPUT JACKS (13)
Two parallel (bridged) input jacks are provided for each channel. This allows for one to be used as a conventional input, and at the same time the other to be used as a “line out” (Y-cord) to connect to another input jack on this amplifier or other amps/ equipment. These l/4” jacks are not “chassis grounded” and when used will provide a Quasi-Balanced input capability due to a unique “ground loop” elimination circuitry associated with the inputs. This feature will normally allow “hum free” operation when relatively short l/4” cable patches are made between the various jacks on this amp and other jacks on various other equipment that share the same rack with this amplifier, This Quasi-Balanced capability is automatic and cannot be removed from the system’s circuitry.
DDT COMPRESSION SWITCH (14)
This switch is used to either ENABLE or DEFEAT the DDT compressor. The DDT function will be covered in more detail later in this manual.
