FX65 Stereo Chorus

From left, original series from 1985 (early issue) and 1988, and second series (1990)

The DOD FX65 Stereo Chorus was introduced in 1985. Because the two-knob FX60 Stereo Chorus was not discontinued at that time, the three-knob FX65 was likely intended as a "step-up" chorus for intermediate musicians, with the FX60 re-marketed as an "entry-level" chorus for beginners. Like the FX60, the FX65 is an analog chorus and uses a MN3007 BBD chip, but also offers a control for Delay Time and two separate output jacks for stereo output. The FX65 was manufactured until about 1997, when it was replaced by the final-series FX65B Stereo Chorus.

• Controls: Speed, Delay Time, Depth
  
  
• From the manual (1987, shared with the FX60 and FX62): "The ... FX65 chorus unit [is a] variable delay unit that gives the impression that more than one instrument is playing. It does this by delaying the sound of the instrument a small amount (4-6 milliseconds) and continuously varying the amount of delay ... [which] changes the pitch of the delayed signal. The delayed, slightly pitch shifted signal is mixed with the original signal and results in the chorus effect. ... The FX65 Stereo Chorus is a three-control chorus effect, offering adjustment of the sweep SPEED, the DELAY TIME, and the sweep DEPTH."
  
  
• Catalog description:1988
  
  
• Technical info:
  
  
  • Specifications (1986): Input impedance = 500 k Ohms, Output impedance = 5 k Ohms; Maximum Input Level = 4V P-P; Gain = Unity; Delay Time = 2-6 ms; Speed = 0.2-6 Hz; Bandwidth = 40 Hz-16 kHz (dry), 90 Hz-12 kHz (delay)
    
    
  • Specifications (1987): Input impedance = 500 k Ohms, Output impedance = 1 k Ohms; Delay Time = 5-8 ms; Sweep Speed = 0.8-8 Hz; Bandwidth = 40 Hz-16 kHz
    
    
  • Notable IC chips: the FX65's circuit was revised at least four times, but always featured a MN3007 BBD chip driven by a MN3101 clock generator/driver CMOS chip; plus three op amps (TL022, TL062, 1458-type, or 358-type)
    
    
  • Internal trim pots: one or two, depending on the year; however, we do not recommend messing with trim pots
    
    
  • Second LED variants: The two oldest FX65 pedals we have opened up (1985 and early 1987) both featured a second LED on the circuit board, possibly as a lower-noise substitute for a "regular" diode. Both circuits had completely different layouts, but by early 1988, the circuit had been revised again and the LED was gone, probably because the LED was always on when a battery was installed and a cord was plugged into the Input jack. We have also seen a FX60 Stereo Chorus with a second LED.
    
    
  • Component-side circuitboard images:September 1985 (two trim pots plus second LED, and only two transistors) February 1987 (revised circuit with 5 transistors, still two trim pots plus second LED)February 1988 (one trim pot, no second LED) August 1990
    
    
  • Related circuits: FX60 (later versions), FX62, FX68 (loosely based)
  
  
• FX heritage: FX65 FX65B
  
  
• External links:
  • @ ftp.dod.com - instruction manual (1987), .pdf format
  • @ discofreq's FX site
  • @ harmony-central.com
  • @ noiseguide.com
  
  

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