Miscellaneous Projects

It is with a dubious honor to present to you my AX Monoblocks. In no way, shape, or form would any of this be possible without Nelson Pass, Grey Rollins, HiFiZen and everyone else in the DIYAudio community. I am indebted to your contributions to the community. These babies are based on HiFiZen's PCboard which were built using Grey Rollins design based on Nelson Pass's patent. As any DIY'er can't leave well enough alone, I stepped-up and tweeked the original a little of course. The case, including the heatsinks are built from .25 and .125 inch aluminum plate. I cut all of the aluminum using my table saw and router. I calculated the stacked plate heat exchanger to be able to dissipate 750 watts with 30 degreeC rise. Not quite an accurate calculation but it turns out to be sufficient as it gets up to 55 to 60 degreeC and stays there. The power to heat the heatsinks comes from Victoria Magnetics 1.2KVA 20V torroidals into a dual hexfred rectifier. From there into a CRCRC filter. Total capacitance is 496,000 uF. The power supply delivers 21.5 Volts at 11 amps. Power is delivered into each half via 4 awg silver coated wire. The power rails are made from 4awg solid OFC and the gate rails from 10awg OFC. All signal wires are Teflon coated silver. All solder is "audiophile proper" silver. Each channel has 16 matched IRFP244 FETS. Actually they are matched to sets of 8. The input diff pair are in-situ matched irf9610. Absolute DC offset is 5mV for each channel. All source resistors and current sense resistors are precision matched. I drive these units in balanced mode using a X-SOBOZ which I will describe later. The Sound---- INCREDIBLE!!!. Detailed, with tremendous soundstage. I was a little nervous initially as they seemed to be bright, it turned out to be the current feedback caps breaking in, after about 2 weeks of intensive listening I noticed the amp really starting to settle in and develop a very balanced presentation. One thing that I am still amazed at is the seeming endless and smooth power these amps deliver. When I step back and look at these things I can't believe that this hobby started out as a low cost method to replace my broken CJ preamp. I wonder what is next? Thanks again to everyone for their support and insight. Scott Gregory

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