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Heatsinks. Yes, this website demonstrates how to build a class A audio chassis with high performance heatsinks. For those who enjoy the sound of a bass horn, I've also added prints and layout parameters for the famous Jensen Imperial folded bass horn. If you wish to build a larger bass horn, visit my "DIY bass horn" page. The link is at the bottom of this page. There is also a link to my page describing how to construct circular, paper mache tractrix horns. My system uses both these high quality horns and sounds absolutely amazing!
Hi, I'm John Inlow. I'm interested in well engineered music, huge speakers/horns, and class "A" amplifiers. As a Do it yourselfer, my goal is to build most of my gear. I've had the pleasure of building my first single-ended single-stage class "A" power amplifier. "Zen" is its name and the designer is a decent fellow who's name is Nelson Pass. (A link to his website is located at the bottom of this page.) As promised, the amp sounds terrific! But, at only 20% efficiency the wasted heat is enormous! Out of 100 watts of power roughly 20 are generated into useful sound. The other 80 watts must be removed. I discovered it takes huge heat sinks to remove the waste heat from the transistors. I also discovered how unbelievably difficult it is to locate affordable, large heatsink stock! So, this is a web page that describes my solution to the problem. I hope this saves other diy'ers the time, trouble and frustration that I experienced.
This particular chassis will easily remove 160 watts of wasted power (heat). I don't know the heatsink's upper C/W limits, but I'll bet the specs are excellent. I can place my hand on the warmed up chassis with no discomfort. If this meets your requirements, get ready to roll up your shirt sleeves. Fortunately, this class "A" amp chassis, although time consuming to build, is easily reproduced by anyone with basic construction skills. I personally use a "chop saw" with a carbide tipped blade designed to cut soft metals. It's located at your local "Home Depot" and of course other hardware stores as well. Be sure to use plenty of cutting fluid designed for machining aluminum.
Because this design has been so effective, I've decided to use a larger version to house my Nelson Pass Aleph 2 project. A true gentleman, Mr. Pass has graciously shared his knowledge with many DIYers in the passlabs forum at diyaudio.com. His own website, passdiy.com, is loaded with many class A projects. I'll keep everyone posted on my progress. The fins on the newer model are nearly three times the size of the chassis displayed on this page.
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Construction tips: This chassis uses 0.25" x1.0"x 6.0" (6.35mm x 25mm x 150mm) bars for the spacers and 0.06" x 3.0" x 6.0" (1.5mm x 75mm x 150mm) bar stock for the heat dissipation fins. The spacers and fins are stacked in repeated, alternating fashion. To achieve the desired depth of your chassis, the plates are bolted together onto four 1/2" (13mm) threaded rods (two per side). Boring the holes is a tricky and time consuming job - they must be aligned perfectly. The difficulty of the process is lessened if you create a jig to support the stock as you drill the holes. It's very important to clean up the holes after the drilling is completed. Chamfer the holes to remove the lip that forms when drilling. If you avoid this step, the plates will not touch one another evenly and heat transfer will suffer. When everything is machined and ready to assemble, begin by placing a nut onto one end of the four threaded rods. Then slip onto the rods the rear plate, followed by the ribs in alternating fashion. When completed, the remaining end of the rods receive the front faceplate and then 1.5" (38mm) long nuts which serve to clamp the unit together. Lay a piece of 0.25" x 1.00" x 6.0" (6.35mm x 25mm x 150mm) stock (bored with 1/2" or 13mm holes) against the long nuts. Thread a short bolt into the remaining portion of the long nut and there you have it: handles. You will require an 1/8" (3mm) aluminum top and bottom plate and, as depicted, I've discovered it necessary to bolt 1" x 1" (25mm x 25mm) aluminum bar stock to the upper and lower sections of the front and back plates. Otherwise, they warp when you tighten the nuts on the threaded rod bolts. This reinforcement might be avoided if you choose to use thicker front and back plates. To limit heatsink warping, you should insert one or more full width partition/heatsink ribs across the chassis' span. At this point you would drill and thread the chassis to receive the 1/8" (3mm) top and bottom plates. Drill plenty of holes in the top and bottom cover plates to allow convection drafts through the chassis to remove extra heat.
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Take note, in the first drawing the transistor mounting theme is to extend some of the spacers into the chassis 1" (25mm). This creates a perfect location to mount a transistor. Extend as many spacers into the chassis as there are power transistors.
Another idea, I've yet to impliment, consist of replacing the spacer bars with standard nuts. They can be locked onto the threaded rods in between the heatsink strips. You would then attach a full length bus bar to the insides of the heatsink fins (which may need to be wider to allow mounting screws for the bus bar). Mount your transistors/ resistors to the bus bar as you see fit. This way a fan can blow cool air through the slots created by the spacer nuts. With some creative thinking, I'm sure you can develop your own methods of assembling a chassis. One final note: This unit is HEAVY, sand/file the edges of the fins or risk getting cut. Also, it WILL be easier to install electrical hook up accessories if you precut the rear plate for RCA jacks, power cord, fuse holder, etc. If you wish to view other class A drawings then follow my DIY links at the bottom of the page. Finally, I would like to thank the folks at Hi Fi Heaven for linking to my site. I would also like to thank another fine fellow: Rod Elliott. You'll find his link down below. He has designed a Bipolar transistor amplifier (he's named it DoZ) to create options and perhaps some playful tension besides the MOSFET Zen created by Nelson Pass. I admire both these men for passing their wisdom to the rest of us DIYers!
Feel free to email me, at the address at the bottom of the page, with any comments or suggestion, etc. You may link my site to yours if you wish.
Good luck!
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I have deep appreciation for Earthlink (their icon links are at the bottom of the page). Without their generosity, these pages would not be available to the public. If you require a great ISP then check these guys out. An easy to build, free website is offered to anyone who joins Earthlink.net; I highly recommend them.
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