Miscellaneous Projects

Reason for building this amps was that I reached the point on building my system, where the evaluation was not possible anymore without high further costs. Since I`m not from the electronics field by education and I was aware of my lack of knowledge, I couldn`t afford playing around a lot, by trying changing, searching, building and rebuilding etc. I had to be quite sure, that my limited budget will be spent with a good possibility for success. After a lot of thinking what to do, I decided to make a try. Equipped by information, support and good will of the people making this site, and with the help of the guys on http://www.diyaudio.com forum, I made a decision to build A2 clones. And… thank god I did so. I`d certainly regret very much, if I decided not to do so, knowing now how much fun and pleasure gave that project to me, not to mention that the final product came out as a pure audible and visible satisfaction for my ears and eyes. Thanks to Nelson Pass and his team, not just for releasing all those documents and schematics, allowing DIYers to use them, but a specially for taking an active part in DIY community. I`d like to say thanks to Mark Finnis specially. I found him very patient guy, with the wide field of knowledge. He helped me a lot, and I`m not sure that I`d be able to accomplished my project without his help. Thanks Wayne S., Grollins and the others on forum. General notes Chassis: Since I`m machine technician I constructed chassis by myself. I left the functionality to determine the design, and the clean lines of the monoblock`s are result of that approach. Fronts and tops are made of 10mm Al, brushed and black anodize. Heatsinks 300x200x40mm on 10mm base plate where used for sides of the amps. Cover and bearer of the toroid`s, bottoms and back are perforated 2mm copper sheets. Everything is bolted on the Al cage made of 10x10mm bars (see pictures) Parts on short: Toroids 1,5kW 33+33V per channel, SAMXON Chinese filter caps 6x22 000uF per channel, 800V-35Amp bridge, 10Amp NTC`s, IRFP240 ST Moroco - 12 pieces per channel, SMD 1/4W m.film resistors, ISKRA wirewound ceramic resistors 3W and 5W (source resistors), Elna cerafin`s 220uF/25V electrolytes, Silvered micas-small caps. XLR- Neutrick`s, RCA – standard goldplated, speaker terminals WBT. Main plugs without the filter. Cables Tara labs speaker cable. PCB is a combination of Mark F. and Wayne S. design, one side printed cooper with tin layer protection. Sound Excellent partner for my SMG-C Magneplanars. With Electrocompaniet EC 4.6 preamp, delivering a great, real live dimension images of instruments, which are placed in the space behind the speakers on the stage, full of ambient and soft transient details. Bass response (little slight before amps did 50 hours or so) is limited only by capability of the speakers, tight, very fast and dynamic, with excellent slew rate. Middles are liquid and hypnotic like on the my tube amp, but without any improper softness or darkness covering the scene. Highs – like a said , you should hear the brass section on this baby. Generally – original A2 monos probably sound better (did not compare), but if I say that I`m surprised and enthusiastic by result, that does not describe my impressions properly. It is great. Considering the costs of building them they are for free. Basic Measuring I`m running at little higher bias on IRF9160 (27 instead of 25mA). Bias on the output 2,8-2,9A totally. Hefty 100W pure A class, clip. on 115W. Offset on output term. 15mV. All the other values fit to schematic of A2. Tuning Amps where made on budget, using some parts which could be better quality. But I wanted to know first, did I implement the design correctly. Now I know I did. In the terms of reliability the filter caps will be replaced. I`ll replace the source and the input resistors also some day with Caddocks, Vishy or similar. That`s all. No need for anything else if anything at all. Good luck I won`t be helpful on the lot of questions on electronics to much, but if someone feel that he can use some information from me, he is welcome. regards Marijan

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