Feature Details & User Tips
Channel Strips
Inputs
Each channel has both a MIC and LINE input (except for channels 9/10 & 11/12 (15/16 & 17/18) which have RCA type inputs as well as 1/4-inch TRS inputs). The LINE input will accept either balanced or unbalanced signals from all types of sources and the MIC input is optimized for low-impedancemicrophones. The LINE input
is Tip-Ring-Sleeve balanced, with the Tip in phase, the Ring reverse phase and the sleeve, Ground. The XLR is wired Pin 1= Ground, Pin 2 = in phase & Pin 3 = reverse phase. This configuration is the standard throughout the world.
User tip: Problem; Hum and Buzz When Source is Unbalanced...
Unbalanced connections may be made to the LINE input with an unbalanced shield- ed cable. However, field or leakage-induced ground currents between separate pieces of equipment can sometimes produce hum and buzz. Most electronic instruments, for example, still use unbalanced connections. If the equipment has more than one out- put feeding the mixer, even floating the circuit ground may not help.
CAUTION: We urge you to NEVER remove the ground-pin on the AC cord or other- wise disable the earth safety Ground connection as doing so can expose you to a seri- ous shock hazard. Additionally, your radio interference problems will likely increase and in some cases your hum problems will get even worse.
What to do: Hum and buzz can be safely reduced or eliminated with the AP812/818’s input balancing, even when the signal source is unbalanced, Simply use standard Tip- Ring-Sleeve balanced patch cables. However, in some worst-case instances it may be necessary to create a special patch cable. In this case, use a 1/4-inch TRS (stereo) cable.
Attach a 1/4-inch TRS (stereo) plug to the end which will plug into the mixer’s balanced-input as follows; 1) solder shield to Sleeve, 2) solder wire #1 to Tip, 3) solder wire #2 to Ring. Now attach the mono plug to the other end of the cable as follows: 4) solder the shield and wire #2 to the Sleeve, 5) solder wire #1 to the tip. Now connect this mono end to the output of the unbalanced piece of equipment and the stereo end to the AP812/818’s LINE input.
This technique will always reduce hum, and it can be used to connect any equipment having a Balanced INPUT to any other equipment having an Unbalanced OUTPUT.
Phantom Power Button & LED
Located on the back panel near the SPEAKER outputs, this push-button activates the
24Volt PHANTOM POWER feature built into the AP812/818. When the PHANTOM POWER is activated, the +24V LED on the front panel (just below the PHONES jack) will illuminate. Now you may connect condenser microphones to any channels without the need for external power supplies. You may also connect dynamic mics to any channels with the PHANTOM POWER activated without any problems or loss of sound quality.
Gain Control
With signal applied to the input, adjust this control so that occasional flashes of the CLIP LED are observed. This will ensure that the signal level fits comfortably within the channel strip’s headroom ~ low enough to prevent distortion, and yet high enough to preserve the signal to noise ratio. This control covers a wide range, so it may seem rather sensitive until you’re used to it.
Monitor Send
The MON send control is post-EQ& pre-fader. This means that the bit of channel sig- nal it sends to the MASTER MONitor bus is tapped off at a point after the channel EQ circuitry, and before the level fader. As a result it is not affected by the channel fader.
