1: FRONT PANEL EXHAUST VENT: The SPA-400 employs a variable-speed internal cooling fan to draw air through the unit to keep it running cool even under extreme operating conditions. The air is drawn in through the unit’s rear and side intake vents and is forced out through the front panel exhaust vent. This method of cooling draws air out from the interior of the rack and provides more efficient cooling than methods which bring air in from the front and exhaust it through the back. Keep these vents clear and free from obstruction at all times to insure proper cooling.

2: SIGNAL INDICATOR LED: This LED will illuminate when signal is detected at the amplifier’s output terminals, providing accurate visual confirmation of signal presence, often helpful in hookup and troubleshooting. The level of the signal must be at least 1% of the amplifier’s full rated output to make the LED illuminate.

3: LIMIT INDICATOR LED: The SPA-400 employs an internal "Automatic" limit circuit to prevent the amplifier from clipping. The Limit LED will illuminate whenever the input signal attempts to overdrive the amplifier’s output section, indicating that the Limiter has been called upon to prevent clipping. (Not only does clipping produce harsh sounding distortion, it is also capable of damaging speaker components – particularly high frequency drivers.) Periodic flashing of the Limit LED indicates operation at or near full output and is no cause for alarm. Steady illumination of the LED indicates constant operation of the Limiter, with the possibility that the input signal should be reduced by means of the Sensitivity control (#6). The Limiter within the SPA-400 is fully automatic, with no defeat switch, insuring you complete protection against clipping at all times.

4: FAULT INDICATOR LED: This LED will illuminate whenever the internal protection relay for the channel is activated. The protection relay is activated for a short period upon initial turn-on and at turn-off to prevent transient "spikes" from being reproduced through your speakers. A fault condition is also indicated in the event of an over-temperature status, or if DC voltages are present at the output. During thermal protection, both channels are shut down until the temperature returns to a safe operating level. In the event of DC voltage on the output, only the affected channel will be disconnected. The circuitry associated with the LED indicator provides valuable protection for both the amplifier and your speakers.

5: POWER INDICATOR LED: This LED will illuminate when AC power is applied by means of the Power switch (#7). If the LED fails to illuminate, check the AC outlet or the fuse on the rear panel (#9).

6: SENSITIVITY CONTROLS: These rotary potentiometers control the level or gain of each channel, with the fully-clockwise position of each providing a sensitivity of +2dBv. Normal calibration of the SPA-400 to a mixer would cause the Limit LED to flash at the same time that the mixer’s VU meters indicate full output.

7: POWER SWITCH: This switch applies the power to the amplifier. The amp is on when the top of the switch is depressed, off when the bottom of the switch is depressed. The Power LED indicator (#5) will illuminate when the amplifier is on.

8: FAN INTAKE AREA: Air for cooling the SPA-400 is drawn in by the fan at the rear and side, directed through the amplifier, and exhausted through the front panel vent. Do not block or impede the airflow through these vents and keep the area free of foreign materials.

9: FUSE HOLDER: The SPA-400 employs an AC line fuse to help protect it from damages due to excessive current demands. If the amplifier does not function, check this fuse. If it is blown, replace it ONLY with the same size and type as indicated below the holder. If the fuse blows repeatedly, have the amplifier checked by a qualified service person.

10: POWER CORD: This heavy duty power cord must be connected to a grounded AC outlet of the proper voltage for the amplifier to operate. IN ORDER TO AVOID THE POSSIBILITY OF ELECTRIC SHOCK, DO NOT REMOVE OR BYPASS THE GROUND PRONG OF THE POWER CORD.

11: 1/4" PHONE JACK INPUTS: These jacks accept line level signal sources by means of cables fitted with standard 1/4" phone plugs. Low impedance balanced or unbalanced, as well as high impedance sources are acceptable for these inputs. Low impedance balanced inputs are to be wired as follows: Tip = Signal +, Ring = Signal –, Sleeve = Ground. Both 1/4" jacks are wired in parallel; when one jack is used as an input, the remaining jack may be used to obtain a line out signal. In the Mono Mode, Channel 1’s input jacks are used; Channel 2's input jacks are disconnected.

12: XLR BALANCED INPUT JACKS: These jacks will accept any balanced or unbalanced low impedance line level source by means of a three-pin XLR plug. The wiring for the plug is as follows: Pin 1 = Ground, Pin 2 = Signal +, Pin 3 =Signal –. Both XLR jacks are wired in parallel; when one jack is used as an input, the remaining jack may be used to obtain a line out signal. In the Mono Mode, Channel 1’s input jacks are used; Channel 2's input jacks are disconnected. The input channel circuitry is transformerless electronically balanced, and requires a line level signal of 1V RMS or greater to drive the amplifier to full output.

13: MONO/STEREO MODE SWITCH: This push/push switch selects the operating mode of the amplifier. With the switch "out" (switch button flush with chassis) the amplifier is in the Stereo Mode; with the switch depressed (switch but-ton indented below surface of chassis) the amplifier is in the Mono Mode. In the Mono Mode, Channel 1 functions as the input channel; Channel 2 inputs will be disconnected. NOTE: Caution should be exercised! Improper hookup or misuse of the Mode switch could cause damage to yours speakers. See the specific hookup configurations in the Installations sections of this manual.

14: 1/4" PHONE JACK OUTPUTS: These paralleled output jacks offer an additional method of connecting to your speakers, using cables terminated with 1/4" phone plugs. Since these jacks are not as well suited to high current applications as the binding posts, they are NOT recommended for extended use at high power levels, or when driving 4 ohm loads. (Methods of connecting are shown on pages 7 – 13 of this manual.)

15. 5 WAY BINDING POST OUTPUTS: These output connectors offer an excellent method of connecting the amplifier to your speakers using cables terminated with spade lugs, banana plugs, or bare wire. Use of these connectors is highly recommended for high power operation. When using the amplifier in the Mono Mode, you MUST use these binding posts. (Methods of connecting are shown on pages 7 – 13 of this manual.) On each channel, the binding posts (#14) are wired in parallel with the 1/4" jacks (#15): the tip of the 1/4" jack is connected to the red ("+") terminal of the binding posts and the sleeve is connected to the black ("–") binding posts. Use of both the 1/4" jack and the binding posts simultaneously to connect two cabinets in parallel is possible, provided that proper polarity and impedance are observed.

On each channel, the binding posts (#14) are wired in parallel with the 1/4" jacks (#15): the tip of the 1/4" jack is connected to the red ("+") terminal of the binding posts and the sleeve is connected to the black ("–") binding posts. Use of both the 1/4" jack and the binding posts simultaneously to connect two cabinets in parallel is possible, provided that proper polarity and impedance are observed.

Speaker Impedances And Power Ratings: When connecting speaker cabinets, you must observe proper load impedances. Whenever connecting multiple cabinets to an amplifier, the total load impedance must be calculated to insure proper performance from the amplifier. The impedance chart which follows shows the total load impedances of many common parallel speaker combinations. Power Output: The power output of an amplifier changes as the total load impedance increases or decreases. The total output power of the SPA-400 increases as the total load impedance decreases as follows: total load impedance (in ohms): 8 (stereo mode) 4 (stereo mode) 16 (mono mode) 8 (mono mode) total output power (watts RMS): 125/channel 200/channel 250 400 Output Power Per Speaker Cabinet: If each parallel connected speaker cabinet has the same rated impedance, divide the total power output by the number of cabinets used. For example: Four 16 ohm cabinets have a total load impedance of 4 ohms (see the impedance chart above), which allows a total output power of 200 watts RMS (Stereo Mode): 200/4 = 50 watts RMS for each cabinet. Speaker cabinets with different rated impedances will draw different amounts of power. To calculate the power output per cabinet, obtain the total load impedances from the impedance chart above and divide it by each speaker impedance. For example: Three speaker cabinets, one with a rated impedance of 8 ohms and two at 16 ohms are connected in parallel. According to the impedance chart, the total load impedance is 4 ohms, which means a total power output of 200 watts as above. Divide the total impedance by the impedance of each speaker and multiply the results by 200.