Horn/dipole speakers and amplifiers

By Thomas Dunker
01 Jan 1996

More projects

Fig. 7. magnet.jpg is a picture I couldn't help but include along with the others. This is an alnico magnet from an old hard disk drive (back before step motors took over and the disks were 15" across) made by Norsk Data some time in the 1980's. I have two of these magnets, which I hope to use in some wild speaker project in the future. The gap is 3.5 cm deep (!!! underhung voice coils, anyone?) and has a diameter of 3.5". Each magnet assembly weighs something like 20 kgs. The tube on the corner is a 12AU7 for a sense of scale.

Fig. 8. oneside.jpg shows one channel of the completed speaker combo. The 12" record is there to give you a sense of scale, and because a pretty picture of Kate Bush always is a good idea. And the black and white photo and gold letters went well with the black chiffon cloth and brass piano hinges. This is how I have the speakers set up in my somewhat crowded living quarters. The room isn't very big, but the sound is.

Fig. 9. preamp.jpg shows my new preamp, which is not quite operational yet (April 18th). There are three detachable modules. At the left is my new Siren Song phono stage. from left to right, the tube lineup is 6SL7WGT, 6SN7GTB and 5694. I have managed to get hold of some 6SU7GTYs and 5692s which will take the place of the 6SL7s and 6SN7s. The black cans in the middle of the Siren chassi is a pair of Cornell Dubilier oil caps which make up part of the plate decoupling of the input stage. They were so cool looking and just the right size, so I had to place them there. The mid section holds a selector switch, input jacks and an attenuator built on a quadruple Elma O4 switch. The knobs come from the plumber and cost 3 bucks apiece plus a day of polishing. The section at the right side is the combined line stage and 3-way crossover, and the exact tube lineup is not totally decided upon yet.

Fig. 10. preamp02.jpg is another picture of the preamp, from a different angle. The sides are made from mahogany, and it actually looks better than it seems on the picture after I spent some more time on the looks. The chassies are made from 2 mm brass sheet, which is polished with a wad on a power drill and Solidox Total G toothpaste and then painted with transparent spray varnish. The power supply for this preamp is enormous and not very pretty, but it's filled with a lot of nice parts and weighs a ton.

Fig. 11. working.jpg shows me, Thomas Dunker, in the process of assembling one of the cell rows for one of the bass dipoles. This picture is taken at Omega Verksted. I always look dumb on pictures, and this one is no exception.

Fig. 12. zen.jpg shows my Zen amp. The PSU is about ten times as big as necessary, but I couldn't find any other uses for these monster low voltage PSU parts. The cooling is not really sufficient for 2A bias current per channel, it gets VERY hot. For my very efficient horn drivers, I found that the amp worked just as well with 1 amp of current, and about 4 watts max power, and then the Mosfets have a comfortable temperature. The Mosfets I used are the complementary pair 2SJ201/2SK1530, which do the job very well.

'That's all, folks!' - for this time, anyway. I expect to have some pictures of my SE 6B4G amps some time in the not too distant future.

I sure would like to see pictures of other people's DIY projects, and it's also fun to see the faces of the people you only know through e-mail. Here's my contribution so far!

Thomas Dunker

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