FX75-B Stereo Flanger

All three cosmetic variants of the FX75-B, from late 1987 (left), 1992, and 1995

The DOD FX75-B Stereo Flanger was introduced in mid-1987, replacing the FX75 in DOD's FX-series lineup. With the addition of a Delay control, DOD at last had a flanger that could compete with the venerable (and great-sounding) Boss BF-2, and the FX75-B was produced for the next ten years. Like the FX70 and FX75, the FX75-B is an analog flanger, using a MN3007 BBD chip. Also like DOD's previous FX-series flangers, the FX75-B produces a rather musical-sounding tremolo effect with all knobs turned up all the way (as opposed to the obnoxious oscillation common in other contemporary flangers, including those by Arion, Yamaha, and the Boss BF-2). The FX75-B was manufactured until about mid-1997, when it was briefly replaced by the final-series FX747 Supersonic Stereo Flange (which in turn was replaced by the FX75C in late 1998-early 1999).

• Controls: Delay (0.5-6 milliseconds), Speed (0.8-8 Hz), Width, Regen
  
  
• From the manual (1987, shared with the FX72): "The FX75B and FX72 delay the input sound and then mix the delayed and original sounds together. The DELAY time control adjusts the amount of delay time in conjunction with: the WIDTH control which sets the range through which the delay time may vary, and the SPEED control which adjusts the rate at which delay time changes. The REGENeration control adjusts the height of the comb filter peaks by controlling feedback through the delay circuitry. The REGENeration control allows the adjustment of the effect from very subtle to very pronounced."
  
  
• Technical info:
  
  
  • Specifications (1987): Input impedance = 500 k Ohms, Output impedance = 1 k Ohms; Bandwidth = 40 Hz-16 kHz; Gain = 0 dB; plus the Delay Time Range and Sweep Speed listed above
    
    
  • Notable IC chips: MN3007 BBD chip driven by a MN3101 clock generator/driver CMOS chip; one TL022CP and two 1458-type op amps (early versions) or one 358-type and two 1458-type op amps (later versions)
    
    
  • Internal trim pots: three; however, we do not recommend messing with trim pots
    
    
  • Component-side circuitboard images: December 1987 April 1992 December 1995
    
    
  • Related circuit: FX72
  
  
• FX heritage: FX70 FX75 FX75-B FX747 FX75C
  
  
• External links:
  • @ ftp.dod.com - instruction manual (1987), .pdf format
  • @ discofreq's FX site
  • @ harmony-central.com
  • @ noiseguide.com
  
  

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