Alesis Matica 500, Matica 900 manual System Setup and Testing

Installations

What we're doing here is compensation for the fact the Matica's B Channel is normally internally inverted and then re-inverted at its output. This improves the amplifier's ability to respond to high power low frequency signals better than conventional amplifiers. The input and output wiring changes above "invert the inversion" so the net effect is proper signal polarity and amplification with the ability to operate both channel's outputs tied to a common speaker lead.

System Setup and Testing

Before applying power for the first time, double check the wiring to insure that everything is firmly connected and that the proper signals are being fed to the proper places. If a low frequency signal in a multi-amplified system is applied to a high frequency transducer, the transducer can be damaged, and a loose connection can cause noise which can damage any transducer.

Be certain that the amplifier front panel gain controls are set to minimum when the system under test is first powered up. After the power is applied, slowly advance each gain control to confirm that there are no driver-destroying hums or buzzes presentÑif there are, turn the power off and locate the source of the difficulty. When first applying program material to the system, it is also advisable to keep the gain controls turned down to confirm, once again, that the wiring is correct. Once the system wiring is determined to be correct, the gain controls can then be set to an appropriate level for the system gain structure.

Setting the system gain is fairly straightforward, but if it is not properly adjusted, the systemÕs distortion and noise characteristics may be less than optimum. The input sensitivity of the Alesis amplifiers is 0.775Êvolts (0ÊdBu) for rated output with the amplifier gain controls at maximum. If the signal at the amplifier input is higher than this, the input gain controls must be turned down to avoid amplifier clipping.

It is generally best to try to keep the gain of the source device balanced for best signal-to-noise ratio consistent with distortion and to turn down the amplifier inputs to reduce the amplification of noise artifacts originating prior to the signalÕs reaching the amplifier.

The maximum level at the amplifierÕs input terminals is +22 dBu (10ÊVÊRMS). It is possible that the output signal from the source may be too high and, thus, distorted before it reaches the amplifier gain control, either because the source device is clipping or the amplifier input stage is overloaded. In either case, no amount of level control adjustment at the amplifier can remove this distortion, and the device feeding the amplifier should have its gain lowered until the level is within proper bounds.

It is also possible, particularly when using very efficient loudspeakers, that the sound level from the loudspeakers may be too high when the amplifier is driven to full output. In such cases, leaving the amplifier gain at maximum and turning down the signal sourceÕs output level can result in audible noise products in the signal coming from the source device or wiring. As above, keeping the source level as high as possible and lowering the amplifier input gain will keep the noise level at a minimum.

12 Matica 500/900 Reference Manual