The SL-20Q was made for Quad! The MCA-76 was made to go with it. I purchased a used SL-20Q and was still getting a bit of "sandpaper" on the innermost grooves. I chalked that up to the stylus being a bit worn. I believe that the Q model differs from the others in more than just the Shibata tip.
Also I was getting good results with the post quad era Sony XL-MC3. I have two of those the one with the most miles on it produced the same sandpaper effects on the inner grooves. The newer one worked much better, better than anything that I had tried previously.
Now I use the Audio-Technica AT-ART9XA. It is expensive but worth it! Sound quality wise it is even better than the Sony. Coupled with the MCA-76 I don't hear the sandpaper anymore. That being said I find that CD-4 records are never quite as clean sounding as stereo or matrix.
Why play around with vintage cartridges when you don't have to. The AT-ART9XA is a much newer design "Neodymium magnet and permendur yoke significantly increase magnetic energy".
I think that the CD-4 button on the MCA-76 just filters out of band signals (like you might get from an old style TV set). I don't notice any audible difference switching it in and out.
Although conventional non-magnetic cores struggle with output voltage, the AT-ART9XA features a newly designed coil armature with an improved output voltage of 0.2 mV (1 kHz, 5 cm/sec). The dual m ...
Edit: Oops, I posted about the Denon not the Ortofon! will try to find it and post!