The Equipment: Crosswinds Sound Systems stereo high pass filter, an outboard subsonic filter in metal case. Dimensions: 9 1/2 by 2 1/2 inches (front panel), 5 inches deep plus clearance for connections.
Price: $100. Warranty: "limited," five years parts and labor.
Manufacturer: Crosswinds Sound Systems, 5307 Harvest Lane Austin, Tex. 78745, USA.
Comment: Warped records, recorded rumble, and turn table rumble are perennial problems that plague the home music listener and, equally undesirably, subject his equipment to unnecessary stress. Subsonic noise wastes amplifier power and uses that power to drive woofer cones through long excursions at frequencies at which they are poorly loaded and thus easily overdriven and damaged.
And because of the low-frequency boost inherent in the RIAA playback curve, phono feedback at these frequencies can be particularly pesky. The solution to this problem is, of course, a rumble filter, an amenity that is not always incorporated in receivers and preamps. But even in components that do have such filters, often the slope and break point make the device much less than ideally effective.
The Crosswinds high-pass filter is a simple "black box" with a power cord and one pair each of input and output terminals. The box isn't really black, but since the final cosmetics had not been chosen when we tested it, we are not sure what it will look like. Practically, we would not expect the appearance to be critical, as the device is easily concealed and need not be touched once installed. It is meant to be connected in a tape-monitor or adapter loop or between a preamp and power amp. In the latter position, it cannot be switched out.
The circuit (which we did test in its final form) is an active filter whose response is -3 dB at 30 Hz with a rolloff of 18 dB per octave below that. We find the break point and slope very effective in suppressing rumble with virtually no effect on program material. But if you want a different break point, Crosswinds will make it up for you at extra cost. According to the manufacturer's claim, total harmonic distortion is less than 0.08%. While we did not verify this with test equipment, we can find no logical or audible reason for skepticism concerning it--nor concerning IM distortion, which is not specified. Hum and noise are rated at better than 65 dB below 1 volt. Capable of supplying 8 volts across a 10,000-ohm load, the filter will drive just about any power amp we know of.
So far as we can tell, this is a unique product, at least in the consumer audio marketplace. And, record warps being as common as they are, it fills a genuine need. Crosswinds has been using the circuit for some time in commercial installations and says it is satisfied with the track record. To our ears, the filter does its job well and does not degrade the signal audibly. If you have a preamp or receiver that you love dearly-except for its rumble filter (or the lack of one)-this could be just the thing to give it a new lease on life. The unit is currently available by mail only ( Texas residents are advised to include 5% sales tax) although Crosswinds is looking for dealers.
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(High Fidelity, Apr. 1977)
Also see:
Audio-Technica AT-605 Audio Insulators
Ortofon moving-coil phono-cartridge system (ad, Apr. 1977)
Technics SB-6000A floor-standing speaker system (Equip Profile, Oct. 1977)