Welcome to Höfi's Audio page 

The story, I tell you, started as my wife and I visited a friend of her, who was (and is) building professional speaker systems. He showed me, how a speaker system may sound. Due to the fact I used to work for Revox 13 years ago, I think, I know a bit how, music may sound. But believe me, I've never heard a sound so clear and real as on that evening. (Actually, he also used the equipment to drive the speakers Krell, Mark Levinson, Marantz and ......) I built the first speakers in 1975 with Jordan Watts Celestion and Kef. That evening I decided to overhaul my audio system.


This picture shows you my growing 50 watt class A power amplifier. As you can see in the picture the second part of the big capacitors in the power supply and the power transistors aren't installed. The transistors are missing due to the fact I hadn't paired them at the time I took the picture. The big heat sinks, my wife and I found them on a weekend trip in Barcelona. Click the picture and you get the big edition where you can see the nice parallel monoural construction you also get the technical datas about. By the way the speakers you see in the back are just the ones used for the soundcard of my PC.

Go to semiconductor amp page.


That's a picture taken from the prototype of the box, used to verify the performance of the bass drivers, at the start of the first listening tests and the general crossover tuning for the mid and high frequency drivers. You see only the finest quality parts are used for the crossover and belive it or not, it's possible for everybody to distinguish between different caps (MKT, MKP, MKS) in a crossover as in all audio applications. Of course are also differences between different types of coils. The material I built the prototype housing was just normal low cost filter board. The final housing i built with medium density filter board, assembled with screws and glue. Finally I applied a nice mahagoni veneer, and finally painted the enclousures with a silky shining varnish. On the next picture you see also my speakers mentioned earlier, built in 1975.

Go to speaker page.


My current project the shunted regulated push pull tube preamp. Because I didn't get my pots yet, I installed temporary and for test purpouses the cheap grey cable which actually has to go, as soon I get the pots and the cabling will be made finnaly. By the way the main artists in the line stage (12AU7A) we bought on our last America trip, in Lancaster by Frank Morris (Gold Aero) This tubes are selected and belongs to the gold series (matched pairs). This tubes have a verry good microphonic characteristic, I've tested it myself and the systems really have the same characteristics. As soon the design ot the phono stage is completed and finally approved, I think I've to order another 2 pairs from Frank because also the noise ratio of this tubes is much better than the ratio of regular tubes.

Go to tube preamp page.


At the moment i'm experimenting with some 300B tubes for 65 US$ each. I figured out already why they aren't so expensive as the WE's or equivalent products lifetime is approx. 3 months. More infos will follow soon.

In the meantime my last pair of cheap 300B's died also, all except one of the six tubes died due to a brocken fillament on the same side, by an exact filament voltage of 5V. Bought me a pair of the Audion R.O.D tubes, the ones with the dark plate, a local tube audio dealer gave me these tubes for a good price, till now they ran many many hours and i've not discovered any problem.

Go to 300B tube amp page.


My newest project started 2 months ago with some SV811-3 tubes for about 30 US$ each. I like the sound of this tube very much because I think the low frequencies are reproduced even more powerfull than with the 300B. I've finished the prototype and need  some time to compare the differencies of several brands of the R's and C's. Within this project I decided also to verify different wirings (cooper, oxid free cooper and silver wires), to see if all this stories I read about are true or just VooDoo.  For this tests I'm shure I've to spent a lot of time. In the meantime i ordered 2 SV572-3. Verification between 811 and 572 still ongoing. As soon the 6BQ5 amp sounds i'll try a new driver stage E88CC and EL84/6BQ5. The drawing and the calculations are completed ;-)

Go to 811/572 tube amp page.


That's a picture of the new ~15 watt class A/B tube power amplifier. I built this amp to verify once more the difference between a triode and a pentode tube amp and to learn more about pentodes connected as triodes. This amp sounds not bad for the first shot, even the power tubes aren't matched nor they are special brand or quality. 2 of them are in tube heaven already, but not because of wrong working conditions, i think it's the quality of the tubes. While shaking i heared the grids in some of them before the first usage. I've assembled and soldered this amp in 1 day schematics you get on the internet as much as you want. The parts aren't as expensive as for a triode amp.

Go to 6BQ5amp page.


Some time ago maybe 1 year i was searching for a Sovtek dealer in Switzerland. On the internet i found an address of a very friendly guy in the capital of Switzerland in Berne. We found out soon about our common hobby the music and the good old vacuum tubes. I got some tubes from him to do some experiments. You see them on some pictures on my pages. In the meantime i've modified some amps for him. 3 months ago i visited him once more, during lunch he told me about some tubes he would like to give me. Later in the afternoon he came around with a big box full of tubes. After 5 hours of work i had divided the tubes into a big box filled with used old Telefunkens, Siemens and Valvos and nice small box full of ..... see next page.            Thanx's a lot Mirko

Go to Treasure page.

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Last modified 29.10.99 by Erich Hofer

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