Active Filters

ACTIVE FILTERS

Active Filters originally found fame in professional sound systems i.e. cinema's and theatres where electronic filtering of sound sources at low signal level was developed to replace high power passive crossovers. The resulting signals were individually amplified and fed to each driver. This system whilst offering significant acoustic advantages was naturally expensive and did not find general acceptance in the domestic environment due principally to the location and cost of suitable amplifiers. With the advent of multi-channel audio systems now in abundance this problem has largely disappeared and QTA are pleased to offer active filters on their two premier models the Apex 100 and the TLA.

Shown is a typical stand-alone two way active filter which is supported by an independent power supply (not shown). Two inputs from the signal source, left & right or 1 & 2, are processed at low signal level to provide suitable crossover characteristics for the loudspeaker. This is done with chips and transistors whereas the normal crossover board contains large coils, caps and resistors operating at relatively high power.

As the signal is split before amplification and routing to the speaker, it follows that each driver requires an amplifier. Hence for a two way system their are four channels, and for a three way their would be six. Each filter is tailored or matched to the mechanical / electrical properties of the loudspeaker model and like existing passive designs the filter cannot be substituted into other systems. Amplifiers of similar performance / characteristics should be employed for best results. Volume / gain controls are required either at source level or at the pre-amp / main amp interface.

This item is only available in 'finished' format for 'use' with QTA's own designs and should not be viewed as an upgrade to other suppliers products as the filters would not be suitable. For the DIY enthusiast however, a set of circuits, filter component tables and a PCB are available for experimentation. Power supply, components and hardware are not included although advice is available on request.

        (1) Faster circuitry, resulting in improved transient response.
        (2)Increased / improvement in dynamic range.
        (3) Lower IM Distortion due to reduction in required cable bandwidth .
        (4) Improved crossover performance due to constant load.
        (5) Subjectively sounds better than high power crossovers.

LOW PASS FILTER FOR SUB WOOFERS.

    (1) Provides high quality line level LF output for sub woofer.
       (2) Sums L + R Signals from Line or Speaker Outputs.
          (3) Buffered inputs with option of 180 degree phase reverse on one input.
             (4) Single frequency operation, (adjustable by component selection), with
                     gain control.
                (5) Option by component selection of 1st to 4th Order filter.
                   (6) Timing delay circuit, seconds to minutes for system settling. No pops
                         and bangs at switch-on using a high quality signal relay.
                      (7) Buffered output.
                         (8) Options on signal chip set, Standard (TL072 ) upgrade1 (TL052).
                             (9) Supplied pre-built, or with all parts, documentation and
                                     hardware. Excludes power supply.

    NOTES    (a)   Supplied complete with pre drilled black ABS case, PCB mounting
                         hardware, phono sockets, internal wire and power supply connector.
                  (b)   Available with upper 3dB roll off points @ 80, 100 or 120 Hz
                         depending upon components.
                        Please specify when you order. If you don't specify you get 100Hz,
                         4th Order, 24dB/ Octave.
                  (c)   May be used to assist HF clutter removal from Band-pass sub bass
                         units or used with full frequency range enclosures to restrict upper
                         frequency activity.
                  (d)   This board does NOT drive a Sub on it's own. You still need a Power
                         Amplifier.
                  (e)   Requires dual rail power supply, unregulated (20 - 24)Volts per leg,
                         DC input @ 50mA.
                         NOT Supplied. If you have a dual +/- 15 volt supply available you can
                         bypass the front-end voltage regulators. Higher input voltages can be
                         accommodated with zener diode clamping.

Prices GBP inc VAT & Carriage UK Mainland.

Order Code	Description	Options	Price GBP
AFM1 *	Active Filter Complete	-------	349.00
AFM1DOC	PCB and documentation	-------	32.00
SWLP1	Low Pass Sub Woofer Filter. Pre-Built. Excludes Power Supply	Frequency, Filter Order,	72.00
SWLP2	PCB Board, Circuit, Components. Excludes Power Supply	Frequency, Filter Order,	59.00
SWLP3	PCB and Documentation only.	-------	22.00

Order Code	Description	Options	Price GBP
RSET1	Extra set of 80 Hz filter parts.	-------	2.50
RSET2	Extra set of 100 Hz filter parts.	-------	2.50
RSET3	Extra set of 120 Hz filter parts..	-------	2.50
CSET1	Chip-Set Upgrade for SWLP1 or SWLP2.	-------	5.00