ZapPulse 2.2 SE based power amplifier.

Exciting things are happening on the amplifier arena. PMW (Pulse Width Modulation) has been known for years, but only lately has the technique become good enough for use in HiFi. These amplifiers are also also called Class D amplifiers.

Currently there is only a handful companies making class D amplifier modules. Most notable are Tripath Technology, Inc, and two Danish companies - Bang & Olufsen ICEpower and LC Audio Technology Inc. Bang & Olufsen will not sell their ICEpower modules to end users, only to companies producing and marketing finished amplifiers. LC Audio, on the other hand, will sell their modules to anybody, and these are what I have used in my power amplifier. LC Audio's modules (2.2 SE) are probably as good as anything else on the market today, so they are an excellent choice.

The goal of this project was to build a very high quality amplifier at low cost. The amplifier modules are not very expensive - the ZAPpulse 2.2 Special Edition w/Black Gate VK is US$ 225 for one channel, and is capable of providing 200 W in 8 Ω, and 400 W in 4 Ω.

The savings start with the heat sinks - none are needed. The modules get enough cooling by simply being bolted on to a sheet of metal, the bottom of the cabinet is sufficient. The capacitors in the power supply only need to be 2 x 10.000 µF, but for best possible sound, I used T-power capacitors. The transformer should have been 2 x 42 V 500 VA, but the one I was able to get, was 2 x 38 V 500 VA. This slightly lower voltage will reduce maximum power, but with my speakers having an impedance of 5 Ω, the power it can deliver is probably 250 - 290 W per channel. During tests, I have measured sound pressures of up to 104 dB - in fact, once I heard the cones actually hitting maximum travel (not something you want to repeat). The sound was distortion free at all times, showing that the power supply is more than adequate. This lower voltage will also prolong the working life of the capacitors.

The next area to save in is - you guessed it - the speaker cable. I used a 15 pair variety for this project, 3 m long, biwired with 6 pairs for treble and 9 pairs for bass. The best possible connection of the speaker cable is to solder it directly to the amplifier, and at the same time I saved quite a lot of money by not having to buy expensive binding posts for the amplifier and spade lugs or banana plugs for the speaker cable. The speaker cables cannot be removed, so if I ever need to move the amplifier, the cables will have to ride coiled onto the top of it. But this is a small price to pay for the improved sound and lowered cost.

I finished the amplifier on the evening of February 13, 2004. I should have seen it coming. It was a friday. Gingerly I connected the mains power, ready to disconnect at the slightest sign of anything wrong. But my reactions were not fast enough - there was a brief flash of blue light, and then the whole appartment went dark. Apparently there had been a short circuit, and my first reaction was to sniff the air to see if I could detect anything burnt. There was nothing, so I reset the circuit breakers that had tripped. Visual inspection of the amplifier did not reveal anything wrong, so I moved it to a circuit with higher capacity and no load, and tried it again. This time it worked, and the blue light I had seen turned out to be a blue LED on each amplifier module. Whew! This taught me that a power supply with a 500 VA transformer needs a soft start circuit - it was the initial inrush of current that had tripped the circuit breakers.

What is the sound like? Like WOW - that Tandberg is never going back into my system. Immensly powerful and controlled bass, deligthful treble, and overall highly detailed sound with no coloring at any listening level. It is very relaxing to listen to with good source material, but it is unforgiving with poor recordings - it simply shows it as it is. My friend that was the catalyst to this hobby, listened to it for a while, and finally said that he now had to unlearn a lifetime worth of knowledge and experience with HiFi.

This amplifier has also shown that the 15 pair Cat 5 speaker cable is sufficient for just about anything, the 21 pair Cat 5 speaker cable is probably overkill in most cases.

Total cost of the amplifier was about US$ 750.

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