Power Amplifier - General
The AP812/818 has a built-in800 watt stereo power amplifier. Each channel has an input sensitivity of +4 dBv (1.4 volts RMS) for full-power output and each can deliver over 400 watts into a 4 ohm speaker load. These amplifiers incorporate computer designed internal heatsinks and a variable-speedfan which automatically provides quiet operation consistent with cooling requirements. Cool air is drawn into the front of the mixer, and heated air is expelled along the bottom of the back. Even at maxi- mum power, this arrangement results in quiet, dependable performance.
PLEASE NOTE: THE AIR VENTS AT THE FRONT AND BOTTOM REAR OF THE MIXER ARE ESSENTIAL FOR PROPER
OPERATION. BLOCKING THE
FREE FLOW OF AIR THROUGH THE MIXER WILL RESULT IN SYSTEM SHUT-DOWN DUE TO OVERHEATING. REPEATED OVERHEATING MAY EVENTUALLY CAUSE DAMAGE. PLEASE KEEP THE VENTS FREE OF OBSTRUCTIONS.
Speaker Connections
Two 1/4-inch jacks and one Speakon®
connector are in parallel with each amp-channel output stage. This allows the use of speaker cables equipped with either type of connector. For full-power applications we recommend 14-gaugecables equipped with the Speakon® connectors. This will reduce risk of resistance buildup. The Speakon® system, developed in recent years by Neutrik in Switzerland, features block-style contacts capable of handling large amounts of power and the connectors lock down to prevent accidental kick-outs.
Connect one or two 8 ohm speakers or one (only) 4 ohm speaker to each chan- nel. When connecting the Speakon’s®, push them in firmly and twist in a clockwise motion. Push the tab and twist counter-clockwise to disconnect.
User tip: To connect two (8 ohm) speakers to one or both of the AP812’s powered output channels via the Speakon® connectors, run a single Speakon® -equipped cable, e.g. Yorkville model SP2-25SSor SP2-50SSwith Speakons® at both ends (most higher-powered speaker enclosures now feature Speakons® as well) from the AP812/818 to one of the enclosures. Now run a second cable from one cabinet to the next via their dual, parallel inputs.
Power Amplifier Protection
The AP812/818’s power amplifier is protected from damage due to open, shorted or excessively low speaker loads. It will continue to run into a low (less than 4 ohms) overall speaker impedance or even a total short-circuit for a brief time, however the amplifier’s defense system will be activated. First, the built-in limiter will reduce output power levels and the fan speed may increase. Then, if the condition worsens, a thermal protection circuit will shut the power amplifier down. When this happens, check your system for restricted air intake/exhaust at the AP812/818. Also check for shorted cables or connectors and/or reduce the number of speakers being driven. In a few minutes when it has had a chance to cool down, power amp function will resume.
User tip:
a)If the power amplifier shuts down as above, the mixer section will continue to function. This means that, if the AP812/818’s power amp fails to come back on (unlikely) and you have a spare power amplifier available, you can connect it to the AP812/818 via the LINE OUTPUT jacks. See under PRE and POST EQ LINE OUTPUTS for further information regarding connections.
b)Because the amplifier is also protected against open-circuit conditions, you may use the AP812/818 without any speakers connected, for example if you wanted to do some recording.
