| ...fabled... Dahlquist DQ-LP1 Active/Passive Crossover  The Dahlquist DQ-LP1 is a unique line-level crossover which combines an electronic Low-Pass filter with a passive High-Pass filter. The LP1 is intended primarily for integrating a subwoofer into an otherwise full range loudspeaker system. It may also be used to bi-amplify a single loudspeaker system where the crossover point is tunable from 40 to 400 Hz. As with other electronic crossovers, the LP1 is connected between the preamplifier and the two power amplifiers; one amplifier feeds the main speaker, the other drives the subwoofer(s). The active Low-Pass section, which feeds the subwoofer amplifier, is continuously variable from 40 to 400 Hz and provides a cut-off rate of 18db per octave. This steep slope is achieved through a non-ringing, staggered arrangement of 6-12-18 db/octave slopes, preserving bass transients. Distortion is exceptionally low, measuring 0.005% THD. Of particular importance in a device of this type is the performance of the High-Pass section which feeds the main power amplifier. Any distortion introduced in this stage will noticeably degrade the important middle and upper frequencies. In order to avoid such degradation, the High-Pass section of the LP1 is purely passive. Distortion is unmeasureable by normal techniques. If it were possible to measure the THD of the LP1's high-pass section, we would expect a figure like 0.000001%. Since the High-Pass section is passive, it may be necessary, depending on the desired crossover frequency and the main amplifier's input impedance, to insert a capacitor or resistor into the terminals provided on the LP1's printed circuit board. We have designed this to be simple enough for the average consumer to do himself (instructions and a kit of resistors and capacitors are provided with each unit) but, of course, Audiophile Consulting ServicesTm at AllegroSound.com may be called on when needed. The High-Pass section (6db/octave) can be set for any desired crossover frequency. The front panel frequency control does not effect the High-Pass frequency. A chart showing typical values for Cx and Rx is contained in the LP1 owner's manual. Film capacitors (polyester, polyproplene, polycarbonate, etc.) and carbon film or metal film resistors are recommended for this application. Push button switch S1 allows complete passive defeat of the High-Pass section and muting of the low frequency section to instantly restore the system to single amplifier operation. This combination of active and passive circuitry insures the sharp cut-off and tuneability required to best integrate a subwoofer with a loudspeaker system while not degrading main speaker performance. The Owner's manual provides complete instructions for the hook-up and tuning of the LP1, including an easy to use chart showing the appropriate combination of resistors and/or capacitors to achieve a variety of crossover points.  AllegroSound (Est.1973) Los Angeles, California USA Rick@AllegroSound.com 
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