Stereo-Cw: The Filters behind the Filtering

In the original 1976 73-Magazine article and my original Blog about Stereo Cw, the original
audio circuit utilizes fixed frequency filters to accomplish the stereo separation effect.  Using fixed filtering simplifies the circuit, making it less expensive.  The main disadvantages to this method are SPECIFICALLY the fixed frequency filter and the requirement to build the circuit, putting it in some sort of enclosure or burying the circuit board somewhere inside the receiver or external speaker enclosure.

Being a "Knob Twiddler", I already own a bevy of external audio filters that can be additionally-purposed into creating Stereo-Cw/Ssb audio.  Filters I have played around with (most of them
still in active use @ my WQ6X installation) include:

• JPS NIR-10 & NIR-12 Outboard DSP Units
  
• Autek QF-1A and MFJ-752x Analog audio filters.
• An MFJ-784 DSP unit and even an MFJ-CW2 passive filter.

 

 

 

 

 

 

As it turns out, a pair of Autek QF-1A's (one for each ear) best creates variable frequency
filters for each ear.  Adjustable cutoff frequencies allow changing the spatial-location of signals
in my listening experience, while also offering the opportunity to PEAK a specific signal and work
that station quickly, making "room" for other stations in the passband.  Because these filter units ALSO have analog notch capabilities, annoying signals can be "de-emphasized" in the receive passband.  

Additionally, the current installation includes an MFJ-784 DSP for processing the left ear and the
JPS NIR-12 DSP to process right side audio during an intense frequency run.  Twiddling the filter knobs bring stations into the passband to log them quickly and then immediately moves them out, allowing me to "locate" the next station in my Left/Right listening experience.

 

 

 

Recently, an NIR-10 has made its way into the shack.  While I really like the DYN Peaking in the NIR-12, the auto-notch filter in the NIR-10 is FAR superior to that in the NIR-12.  While the NR feature in both units are similar, the NIR-10 seems to do a better job, altho BOTH units have a noticeable 130ms delay in processing the audio.  If you have the same signal in both ears, running the JPS
units introduce a near-echo on the right side, which can be annoying.

Use of the above filters create another excuse to repurpose vintage filter boxes that might either end of on the scrap heap or end up being parted out for other purposes - NoT!  Also, as you can see in the above picture, those different filter units give me plenty of knobs to twiddle, which is a good solution to boredom, when a run frequency all of a sudden becomes quiet.

Have YOU ever used any of the above external audio filters?

What unique ideas have YOU created with them?