Side loading of cantilever/stylus

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Straight Tracker

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#1
Hello All,

As everyone knows, the skating force will cause the stylus to bear against the left channel side of the groove. As everyone also knows, a sticky horizontal tone arm bearing will cause the stylus to bear against the right channel side of the groove.

My question is: is there an electronic method to look at the stereo signal coming from the cartridge and isolate and extract that part of the signal that is caused by the pressure of the stylus against the groove walls due to the conditions mentioned in the first paragraph?

This is the simplest way I could think of to pose my question.

Sincerely,

Ralf
 
#2
Hi, zou got rite and left mixed up. Are you thinking about error/feed/forward? This is usually only done with linear errors, because these ones are simple multiplications, where absolute levels are unimportant, while non/linear errors are equaliyed bz non/linear calculations, which depend on absolute level. Else, people would do it all the time in order to equaliye their loudspeakers and get a few dB more undistorted bass and unmodulated treble, before it finally clips. Uli
 
#4
Possibly FFT would show something on distortion measurements? Independent amplitude measurements on both channels I suspect would show something. Not entirely sure this is so. Bill generally is right IME..

Strain gauges, yes it is possible, but you have to know all about the static errors first and correct for them. (Both in the cartridge and the electronics driving the cartridge.) I haven't bothered so far, but I might.
 
#6
how about this....
there are test records with Left and Right channels having same frequency tones (but separate bands on vinyl). one can record them, take it to sound editing programme like Adobe Audition. Example And view audio spectrum.
Bottom region is low frequency top region high frequency. The more amplitude will be shown in yellow color. So if stylus is pressing more against one wall it will give more yellow color. Or one can record tones of both channel and subtract one channel from other to see the difference. If noise gets mixed in the tones and is difficult to decipher, one can remove it by recording blank groove, take noise data from it and subtract it from tone recordings then compare two channels.
Will that work ?
 
#7
Straight Tracker said:
Hello All,

As everyone knows, the skating force will cause the stylus to bear against the left channel side of the groove. As everyone also knows, a sticky horizontal tone arm bearing will cause the stylus to bear against the right channel side of the groove.

My question is: is there an electronic method to look at the stereo signal coming from the cartridge and isolate and extract that part of the signal that is caused by the pressure of the stylus against the groove walls due to the conditions mentioned in the first paragraph?

This is the simplest way I could think of to pose my question.

Sincerely,

Ralf
Click to expand...

Ralf,

This has already been done. In 1975, researchers at 3M Company used the signal from a strain gauge cartridge to detect and control absolute stylus force with the intent of using stylus displacement feedback to keep the stylus centered. They did this by applying a corrective signal to the vertical motion of a tonearm that was fitted with a voice coil actuator near the pivot. The goal was to optimize damping and resonance control, primarily for warp effect mitigation. A 9 page paper was published in the July/August issue of the Journal of the Audio Engineering Society.

AES E-Library >> Overcoming Record Warps and Low-Frequency Turntable Rumble in Phonographs

Here are some key points and issues from the paper:

Ø The corrective signal was applied in the vertical direction, primarily for warp control.

Ø Their first attempt used a conventional offset tonearm and did not work. They noted that the left and right channels exhibited a different natural resonance frequency, and the phase angle between the left and right channels was so great that they were not able to extract a useful feedback signal.

Ø The amplitude and phase anomalies were traced to the influential effects of the offset angle on arm dynamics. They eliminated the left/right amplitude and phase anomalies by substituting a servo-driven linear arm. The vertical components of the left and right channels were summed electronically and the stylus feedback control system was functionally effective for vertical warp control in the 5-15Hz region.

Ø They were not able accurately measure below 4Hz because the signal was swamped by background noise.

Ø Unfortunately, the paper does not cite the cartridge or tonearms that were used in the study.

While the 3M group extracted a feedback signal for vertical tonearm control, presumably the same could be done for horizontal control as well. It would seem that the same issues and pitfalls would be encountered as were seen by the 3M crew in dealing with vertical feedback control. In particular for your case, it seems that the forces/errors that you are trying to compensate for would be down close to DC in the frequency spectrum, and they noted that feedback control below 4Hz was not achievable. I know that Sony made several turntables with their ‘Biotracer’ electronically damped tonearms, but I’m pretty sure that they did not rely on a signal obtained from the cartridge.

The AES paper is $33 for non-members. Sorry I can’t post any of it as the AES is very strict about maintaining their copyright protection, but it could save you from a lot of head knocking on the wall.

Ray K
 
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