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Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ.

RE: Null points for 7" discs?

Um, I think you might want to check your assumptions! ;)

For instance why are you assuming a fixed effective length tonearm?? It isn't applicable in the scenario suggested by the OP:

The OP is using an arm with a replaceable headshell so the fixed parameter will be the pivot/spindle distance. For want of a suitable spec, I chose 215mm assuming a typical 9" arm such as a Technics arm. For convenience, I just used the VE calculator which will give slight errors to your calculator due to rounding. However, the figures are correct using these constraints.

Secondly, you have simply chosen to compare the two over the reduced modulation envelope, whereas my frame of reference was with respect to the slightly wider envelope so naturally you will see a bias in favour of the theoretical RIAA/IEC optimisation. If you compare the two geometries using these two constraints, you find that my suggested nulls are superior for radii < ~55.5mm and will continue to be superior for any 7"s that are cut further in than the standard.

As I pointed out, the distortion figures are based on a simplified model which even for an LP suggest that Lofgren A over the IEC/RIAA envelope doesn't necessarily give the best result on the inner grooves. I have a 12" 33rpm cut at an insane amplitude up to ~52/53mm and several more cut well beyond 57.5mm with some around the 54mm region.
When you are talking about a 7" which may run at 33rpm, then I believe the effect of the groove velocity becomes ever more important particularly when the radius of curvature of the tip is becoming a signficant parameter with respect to the wavelength of the cut signal at HF. Consequently, as the rate of angular error with respect to radius increases, the distortion will increase at a higher rate than suggested by the standard model. I don't know what stylus design the OP is using, but certainly improvements are audible in the imaging with a MicroLine or similar type of Line Contact that retains full bandwidth to the innermost grooves.

I therefore assert that a more optimal solution is to be had by accepting a marginally higher tracking error at the outer edge and setting Rmin at a radius somewhat less than the minimum groove on the record which will give a gradually reducing peak weighted distortion envelope. In fact Stevenson was alluding to this with his solutions. You will notice that not only had he chosen to apply Lofgren A to smaller Rmin values, but he also chose reduced Rmax values. When you analyse his solutions over the wider envelope specified in the standards, you do indeed achieve a gradually decreasing peak weighted distortion envelope with respect to radius.

BTW I am extremely impressed if you can hear an absolute increase of 0.036% distortion between the nulls, although I'm sure you would point out that this translates to an increase of 22.6%..... :)
Regards Anthony

"Beauty is Truth, Truth Beauty.." Keats

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