PBM8 500 Powered Mixer

The PBM8 500 is a MK2 powered mixer amplifier manufactured by the Alto Corporation in 2005. It is an 8-channel stereo powered mixer amplifier with built-in DSP. The amplifier delivers 2 × 500 W power output. The mixer section consists of six line / microphone input channels each with a three-band graphic equaliser. These input channels are balanced.

Power Output

The power amplifier produces 500-watts per channel with 4 Ω speakers, or 300-watts per channel with 8 Ω speakers. In bridge mode, the total power output is 1000-watts through an 8 Ω speaker.

Amplifier Design

The amplifier has a Class AB complementary Symmetrical Output Stage, which appears to be of robust design. Each channel uses six power transistors consisting of a pair of GCA1943T, a pair of GCA5200. Their drivers are a complementary pair consisting of MJE15032 and MJE15033.

Fault / Repair

A short or overload condition usually burns out the power resistors making them go open. It is also associated with one or more power transistors being short. In a symmetrical output stage, all the transistors in a channel require checking thoroughly, as a single shorted transistor may damage the rest.

Replacement Transistors

Replacement power transistors are expensive, especially the genuine Toshiba brands. Usually, eBay has some old stock however make sure the transistors are genuine.

The Church Amplifier

This was the church amplifier, which belonged to Father Clarke. He used it to amplify his sonorous voice even further during his sermons. The story of how it came to me is in the article, no good deed goes unpunished.

Review

This amplifier is actually great! It is very sturdy, and built to a very high quality standard. Having a built-in mixer and preamplifier, makes it a complete solution for anyone on the road. I love the fact that it also provides phantom power to the microphones through the XLR sockets. It saves a lot of money from having to buy separate boxes and wiring them all up. You can kick it out of the van, connect the speakers and microphones and it is ready to rock-n-roll. It is a very neat portable solution.

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