BiAmp MixPak 7/300

BiAmp MixPak 7/300

The BiAmp MixPak series is what is known as Powered Mixers. They are essentially a mixer with a build-in power amplifier. The 7/300 means she has seven channels of low impedance microphone inputs. These are over-ridden when a line level instrument like a guitar or keyboard is plugged into her. The 300 stands for 300W of power into 4Ω. The MixPak 7/300 has only one power amplifier, hence a mono output. Let’s take a closer look at the design of the amplifier.

BiAmp MixPak 7/300Fig 1 – BiAmp MixPak 7/300 Amplifier Schematic

The signal enters the input differential Q3 (Red line). It then drives the VAS (Q7) with the inverting leg. The MJE15031 emitter follower drives the output transistors MJ15023. An op-amp (TL072) servo is used for DC Offset. A feature not normally seen is the use of a Vactrol at the input. When the MixPak is over-driven, this Vactrol is activated, thus shunting the input signal to ground.

Summary

The BiAmp MixPak has garnered a solid reputation for robustness and build quality. They are often seen in sound reinforcement like Live bands, in small clubs and even places of worship.