A hi-fi visit to Minnesota. (Straits of the Art).

My wife and I recently made a trip through parts of the Midwest to visit relatives and fill in genealogy blanks. Our itinerary included an extended stay in the Minneapolis area, enabling us to visit AtmaSphere, Audio by Van Alstine, Magnepan, and the Pavek Museum of Broadcasting.

AtmaSphere: Our first foray was to meet Ralph Karsten at AtmaSphere. Although he gave me precise directions, we ended up on a tree-shaded residential street. I thought I had made an error in writing the instructions until we went up the steps to the front porch where the AtmaSphere and vacuum tube packing cartons told us we were in the right place. Ralph runs this business out of the house where he grew up in St. Paul.

Ralph has been involved in electronics from an early age. He started repairing and rebuilding electronic equipment as a hobby while in grade school. As his interest and knowledge grew, he saw ways to improve on designs, and eventually began creating his own circuits. His first love was the sound of good tube equipment, a passion that continues. AtmaSphere has been in business for 25 years and they offer several OTL (output transformerless) tube amplifiers of different power ratings. Among their offerings are pairs of mono and single-chassis stereo class A triode amps, all of which are without feedback circuits, as well as preamps.

I think Ralph's listening room would appeal to many. The walls were lined with sturdy bookcases filled with LPs and a sizable collection of CDs. An AtmaSphere 208 record player (based on an Empire 208 that Ralph has heavily modified into an .AtmaSphere design with new plinth, arm and resonance damping), AtmaSphere MP-3 tube preamp and Teac PDH-500 CD player were located near chairs facing two large Classic Audio Reproduction speakers. Several AtmaSphere tube amps of varying sizes were on the floor around the speakers. Ralph played a number of LPs and a few CDs (Bill Evans, Cannonball Adderly, Illinois Jacquet Birthday Party, as well as classical selections), all of which were reproduced with detail, liveliness, realistic timbre, and depth. The sound floated free of the speakers--the kind of reproduction that makes music enjoyable and captivating.

Ralph demonstrated the stability of his amps by removing tubes from the amps while in use. There were no clicks, pops or other signs of electronic distress--just (eventually) a decrease in volume as more and more tubes were removed. He also shorted the amp outputs with no ill effects--a demonstrably stable design. Ralph's circuits operate the tubes well below the stress point. He expects tube life to be about 10,000 hours. Ralph recommends periodic cleaning of the tube glass (when not installed or hot) with isopropyl alcohol or dish soap and water, using a soft, clean cloth. AtmaSphere uses mostly Russian power tubes and Chinese, Russian, and American driver tubes--the availability of American-made tubes is very limited.

We met two of the people who build amps and had a tour of the basement assembly line where product construction was in progress. Each amp is made by an individual who takes ownership for the quality and adds his own signature to the chassis. Workmanship was excellent and the point-to-point wiring was tied and neatly routed. If you've ever built electronics, you'll appreciate these visual and sonic works of art. www.atma-sphere.com

Audio by Van Alstine (AVA): We had the pleasure of visiting Frank Van Alstine in Burnsville, Minnesota, where we heard the fine-sounding Biro Technology L/1 loudspeakers at his combination home and business headquarters. The L/1s are visually unusual, in that a 1-inch metal-dome tweeter is mounted on the top of the enclosure, rather than on the front baffle. This location is designed to limit high frequency diffraction effects that could degrade the sound. The tweeter is set back a little from the front to align it with the 6.7-inch mid/bass unit on the front baffle. Both drivers are on the vertical centerline of the speaker, as is the vent tube near the baffle bottom. The L/1s were driven by AVA's FET Valve Hybrid (transistor/ tube) power amplifier controlled by a Van Alstine Transcendence hybrid tube preamp.

Frank demonstrated the Biro L/1s with and without the Biro Kensington subwoofer. The subwoofer driver is a 12.2-inch unit powered by a built-in 200- watt amplifier with electronic crossover. When Frank turned the subwoofer on, he also plugged the L/1 ports with foam rubber. He explained this raises the low-end cutoff of the satellite speakers to permit a better blend with the subwoofer. I had mixed feelings about the satellite/ sub combination. I thought the sound of the L/1s had a touch more spaciousness with the ports open, but I also enjoyed the added bass depth with the sub added. The overall sound, both with and without the subwoofer was very enjoyable. The combination of equipment and a rectangular listening room with all hard surfaces covered either by carpeting or acoustic-absorbent fabric was effective. It allowed the music (Dave Brubeck, Vince Guaraldi, and other jazz plus some classical pieces) to be heard with less reflected sound than many rooms. The result was perhaps a more accurate rendering of the actual recorded music and ambiance--a very involving result. Frank also demonstrated the stability of his components by turning off the preamp, then the power amp with none of the speaker noise one would usually experience with this shutdown sequence. We also had the treat of listening to their latest prototype digital-analog converter (DAC) which increased depth and spaciousness of the sound compared to other DAC (make/model unknown) in the system.

AVA has been around since the early '80s, and all of the reviews I have read have been very positive. Our limited visit and listening session certainly corroborated compliments I had read. Frank said he has had an interest and involvement in electronics since he was in grade school, and upon his retirement from the Minnesota Highway Department was able to work full time on his products. AVA builds to order from their catalog, which is available in hard copy or as a download from their website, www.avahifi.com

Magnepan: Later, we were able to visit Magnepan, Inc., the 50,000+ square foot headquarters of the Magneplanar speakers at White Bear Lake, not far from the Twin Cities (Minneapolis and St. Paul). Our timing was such that Steve Winey, manager and son of the founder, was able to give us a guided tour of the factory. A combination of automated and manual work is used to fabricate the speakers. A CNC (computer numerical control) routing machine cuts the frames for the various sizes of Magneplanar. This process replaced the original piece-built frames with stiffer, stronger, one-piece units. Even with the availability of modern machines for some tasks, many steps in the fabrication process are still done by hand to preserve consistent high quality. For instance, the mylar film that is at the heart of each speaker is properly tensioned manually, and the conductor is applied to the film by hand. Each of the processes evolved and were perfected over time.

For those who are not be familiar with Magneplanar speakers, they come in various sizes and levels of performance, having in common a flat panel design with low mass dipolar diaphragm. Sound radiates from the front and back of the panel. A combination of lightweight electrical conductor on the mylar diaphragm and permanent magnets close to it cause the surface of the diaphragm to be driven. The dipole radiation and large surface area result in a very open sound. As with any dipole radiator, some distance is required between the speaker and the wall behind it. Even the largest of the Magneplanars can be easily moved out for serious listening and back for decor reasons--this could be a definite plus in actual use. The larger the panel, the deeper the bass and the greater the available output sound level, although I heard beautiful music from the smallest Magneplanars.

Near the end of the production run, before the grille cloth is added, the performance of each speaker is tested both audibly and electronically and compared to standard parameters. Adjustments are be made to correct minor variations outside the designated limits. Steve said that their experience shows such adjustments to rarely be required because of the close quality control during the manufacturing process.

During the time of our visit, the listening room had been set up with a surround-sound system, using MGMC1 speakers. We auditioned them as part of a home theater setup. These two-way planar speakers are designed to be attached to or placed next to a wall or cabinet and intended for stereo and home theater front, side and back speakers. When not in use, the speakers can be folded back against the wall or cabinet, a feature my wife particularly appreciated. Optional floor stands are available where other means of support are impractical.

The Magneplanar operation is impressive for its carefully thought out processes and careful attention to detail. The machines and jigs used for production have been precisely crafted to help ensure precision and repeatability of manufacturing and assembly operations, www.magnepan.com

The Pavek Museum of Broadcasting: Before we left the Twin Cities area, we had time to visit an important local museum in a suburb. The Pavek Museum of Broadcasting at 3515 Raleigh Avenue in St. Louis Park, Minnesota 55416 is well worth a visit. It houses three major collections of antique radio and hi-fi items, television, and broadcast equipment. It is a combination of three individual collections:

The Joseph R. Pavek Collection of radio receivers, transmitters, and televisions from the first half of the 20th Century. It includes a rotary spark-gap transmitter, a chronological collection of vacuum tubes (including deforest Audions), and extensive radio literature

The Charles Bradley Collection of products from 60 radio manufacturers from the Twin Cities area

The Jack Mullin Collection, documenting the history of audio recording technology.

The displays are well maintained. Everything was properly organized and appeared to be dust-free. Although the age of many items was evident, all the pieces were well preserved and obviously benefited from loving care. The venue is a spacious area where one can wander amongst the displays. There is a complete '50s broadcast studio that can operate at a low legal level for an unlicensed facility. School groups often visit, where they learn about broadcasting fundamentals and actually have the opportunity to use the studio. We were lucky to arrive early, when there were few others there, and received a great guided tour. There are, however, only so many staff people, and when there are lots of visitors, a self-guided tour might be a necessity. www.pavekmuseum.org

--JTF