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5 Band Speech Equaliser with Bass Cut and Gain Adjust

Overview.....Layout

The 5EQ Equaliser is a high performance custom designed circuit specifically intended for speech frequencies. As such, unlike conventional 1/3 octave equalisers, all the sections are useful and make a worthwhile contribution. The 5EQ is intended to match the microphone, speakers, amplifier and room acoustics together to achieve the best possible results, yet without destroying speech quality. Boost and cut is restricted to 9dB. It can be used to improve any sound system.

A seperate bass roll off facility is provided to reduce microphone handling noise or mains interference (hum). Provision is also made to adjust the overall gain from a small loss, to a fourfold gain. However care should be taken not to overload subsequent circuits since the 5EQ is capable of large outputs without distortion. Great care has been taken to provide a noise and distortion free output under all normal operating conditions and extensive use of surface mount technology ensures a stable and reliable product.

Installation

Remove the protective paper under the four mounting feet and position the card where it will be easy to see and adjust the controls. Assuming the card is to be used in an Electronic Services (Wolverhampton) amplifier, decide whether you want the 5EQ to affect just the microphones, or both microphones and music. For microphone use only, use the left hand facilities connector (where the frequency shifter would normally plug in). For microphones plus music, use the middle connector.
Set the preset Bass and Treble controls for speech to the centre positions prior to adjusting the 5EQ. Set the system to a normal operating position with all microphones in normal locations. Adjust each 5EQ filter in turn to flatten out the frequency response and reduce feedback frequencies. Aim for the best compromise between speech quality and minimum feedback. Note that ALL sound systems will feed back (ring) if you try to set the gain too high. Remove the Bass cut link if microphone handling noise or "popping" is a problem.
Note..Check the voltage supplies match the input connector BEFORE you switch on. If it is fitted the wrong way around, the two Integrated Circuits will get VERY hot. If this happens you can either reverse the Black and Red wires in the connector shell OR simply unplug and reverse BOTH Integrated Circuits.

Wiring Detail

  • Blue............Output
  • Yellow........Input
  • Green.........Earth
  • Black.........-15V dc
  • Red...........+15V dc

Specification

  • Gain Adjustment Range.............................-3dB to +12dB (Red dot=0dB gain)
  • Passband Ripple (all filters flat)................. 1.5dB max
  • Basic Frequency Response....................... 62Hz - 120KHz within 1dB -3dB @ 28Hz
  • Bass Roll Off Frequency...........................-3dB @ 160Hz Link Selectable In/Out
  • Hf Roll Off Frequency..............................-3dB @ 18KHz Link Selectable In/Out
  • Typical section boost/cut...........................+/-9dB
  • Filter Center Frequencies......................... 380, 810, 1K5, 3K2, 6K4
  • Maximum Undistorted Output (600R)...... +20dB (Vs= +/-15V dc)
  • Input Z.................................................... 10K
  • Output Z.................................................. 600R or higher
  • Noise...................................................... -90dB or better
  • Supply Voltage......................................... +/- 18V dc Max.
  • Size.......................................................... 95x65mm

Note: It is normal for the two integrated circuits to feel aired/warm.

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