User's Manual

To calibrate the system’s gain structure and PA2 limiters:

WARNING! Although it is highly unlikely that you are using tube amplifiers, since they are not practical for live

sound reinforcement use, please note that some tube amplifiers can be damaged if operated without a load (the speaker)

connected. Therefore, do not perform the following procedure if using tube amplifiers unless you have verified they can be

operated without a load connected. This is not an issue with modern solid state amplifier designs.

1� You will need to send a pink noise signal through the entire system to perform this calibration procedure. Some mixers

have a built-in pink noise generator, which will work. You can also check your smartphone’s app store, as there are many

audio apps now available which have a built-in pink noise generator, or search online for a pink noise sample and burn it

to a CD or load it into your portable music player or smartphone.

2� Once you have your pink noise signal, power down the sound system, disconnect all the loudspeakers from the amplifiers,

and turn all your amplifier attenuators all the way down.

3� Set the +4dBu/-10dBV switch on the back panel of the PA2 to match the nominal operating level of your mixer. See

‘Rear Panel’ on page 6 for more information on this switch.

4� Now, turn the mixer, DriveRack PA2, and amplifiers back on. Go into the PA2’s output limiters and ensure they are

all turned OFF, OVEREASY is set to OFF, and their THRESHOLD’s are set all the way up to 0.0 dB. Also, turn off all

non-essential PA2 processing if it is enabled (i.e., Compressor, GEQ, Subharmonic Synth, and AFS).

5� Set your mixer’s main output faders to unity gain (0). Play or enable the pink noise. If the pink noise signal is being fed to

a mixer channel, set the mixer channel’s fader to unity gain (0). Adjust the gain/trim control of the channel (or pink noise

level if using the mixer’s built-in noise generator) until the mixer’s main meters read 0 VU.

6� Raise the mixer’s main output faders until the INPUT CLIP LEDs on the PA2 just begin lighting.

7� Now, go to each amp channel and slowly raise its attenuator until the amp channel’s clip LED just begins to light.

TIP: Once all amp attenuators have been set, you may want to take note of their position using gaffers tape or

some other non-permanent means. This way you can retain the reference amp attenuator settings above which the

amplifiers will clip.

8� Go into one of the PA2’s limiter modules. Turn the limiter on and slowly lower the THRESHOLD parameter until the

corresponding amp channel’s clip LEDs stop lighting. Don’t lower the limiter THRESHOLD parameter too far, just far

enough to hold the signal level just below the clip point of the connected amplifier. Do this for each active pair of PA2

outputs (i.e., High, Mid, and Low).

9� Turn down the pink noise and main output faders on the mixer then power down the system.

10� Reconnect your speakers to your amps.

11� Power up the system, ensuring to power up your amps last.

The system is now optimized to provide the loudest levels possible, with adequate headroom between devices, and with the

least amount of noise. Now, sit back, play your favorite music through the system, and slowly raise your mixer’s main output

faders. When the mixer’s main faders are set to unity gain (0), the system will now provide the highest sound pressure level it

is capable of without clipping. If the system is not loud enough when the mixer is set just below the output clip point, this is an

indication that the system is inadequate for the application. If this happens, you can try adding PA2 compression with make-up

gain as it may provide a slightly higher system output level. If the system level is still inadequate for the venue, you may want

to consider amplifiers with greater output power, but still within the power rating of your loudspeakers, or additional speakers

and amplifiers. Most loudspeaker manufacturers recommend an amplifier which provides 1.5 to 2 times the rated RMS power