Listening #117 Page 2
The Line Magnetic driver appears perfect: like a time-machine Western Electric 755a in virtually every respect. From its beautifully formed 7.25" pulp-and-fabric cone to the coating that gives the integral surround its characteristically low compliance to the lustrous hammertone finish of its metalwork, every detail looks and feels right. One can't help being impressed with the knowledge, effort, and sheer love that have apparently gone into this product.
The 755 I's aperiodic enclosure is constructed entirely of plywood, the heaviest panel being a central baffle that's rigidly fastened to the inside front. Within the cabinet is an extra pair of sidewalls, positioned to leave narrow gaps between them and the outer panels; on each side, those gaps are open to the larger volume of air inside the cabinet through only a single small vent, and to the outside of the cabinet through a trio of narrow vents. The inner surfaces of all panels except the front are lightly damped with thin, woolly pads.
Stranded copper wire is used for both the interior signal leads and the two field-coil leads, the latter soldered to a separate electrical connector on the 755 I's removable back panel. Dedicated 10' cables are used to carry DC from the outboard PR-3 supplies, each of which uses a 300B direct-heated triode tube as a voltage regulator. To some, this may seem the audio equivalent of hiring a fine artist to paint signs (or a Wall Street CEO to prepare income-tax returnsan even more appealing incongruity), but I'm told that the quality of the field-coil supply current can make a distinctly audible difference.
Aesthetically, the removable and decidedly retro grillework borders on being a bit too much; that said, this may be the most memorable recent instance of a bit too much being just enough. That said, I preferred the performance of the Line Magnetics without those grilles in place.
That performance has, from day one, been extraordinary: full of touch, impact, nuance, detail, and humanness. With "Search for Peace," from McCoy Tyner's The Real McCoy (LP, Blue Note BST-84264), the 755 I found some dynamic nuances that had eluded my Audio Note AN-E, adding to the ultimate sense that a human being was attached to each instrumentand especially to the tenor sax. Joe Henderson's breath was far more audible through the Line Magnetic than the Audio Note, despite the former's comparatively limited treble extension. Subtle dynamic nuances, including Elvin Jones's great one-hand rolls, came across much more forcefully through the 755 I. (The Audio Note, for its part, had more bass extension and bass impact.)
The 755 I's tonal characteristics have continued to evolve throughout the weeks they've been here, and show no sign of ceasing. As one might expect from brand-new samples of a limited-excursion driver, the bass extension has improved, from an initial performance level best described as sufficient, but barely, to one better characterized as modestly surprising But I'd prefer not to focus overmuch on that one characteristic: As with certain other very good loudspeakers, this is a case where the levels of overall musical involvement and excitement were so high that my attention tended not to wander to individual aspects of sound.
I believe I'll be allowed to keep the Line Magnetics for at least another month, and I promise to write more about my experiencesin speaker positioning and power-supply settings, as well as the maturation of the driversin time for the November Stereophile, at the latest. Even so, it's already apparent that the 755 I is very reasonably priced for what it has to offer, and seems poised to become a popular choice among the vintage-curious.
Charlie McCarthy was here
For months I've kicked around the idea of writing a column titled "Six Equipment Measurements You Can Perform at Home." ("Just the thing for the litigious!") But such projects require a bit of groundwork, especially for the person who wishes to measure amplifier power: Before one can test an amp, one must have a dummy load for it to drive. And dummy loads, like s'mores, are things that one must make for oneself.
And as any serious electronics hobbyist can happily tell you, heatsinks and high-power resistors, the two main ingredients of a dummy load, are rather pricey these days.
So here's a tip for the frugal hobbyist: The best source I've found for these parts is the colorfully named Surplus Sales of Nebraska. There I found a 5.75" by 4.75" predrilled aluminum heatsink (model 20788-8) for just $25, and a quantity of Dale 30W, 7.87-ohm, aluminum-body resistors (ERH50-7.87) for the insane low price of $5.95 each. The person who's interested only in measuring low-power amplifiers, one channel at a time, can get by with just two of those resistors, wired to provide loads of approximately 4, 8, or 16 ohms. Various connectors, a rotary switch, a few bits of wire, and a chunk of wood will also come in handy, but you can worry about those later; for now, jump on these parts before they're gone!