VTA and VTF: How one affects the other

[PeterA]

I wrote this post a few months ago on a different sight in a discussion about VTA adjustments. I thought I would post it here to see if people have similar findings about the relationship between VTA and VTF.

I own the Audio Additives Stylus Force Gauge that Michael Fremer recommends in the Analog Planet link that Myles posted. I just calibrated it using the 5.0 gram weight and did some testing. As expected with my SME V-12 arm, if the VTF gauge is resting on the platter and not on varying thickness LPs, the VTF does change as I raise and lower my tonearm, changing the SRA.

I use a range of six arm height settings in 0.5mm increments from 16.0 mm to 18.5 mm covering the LPs in my collection. The Audio Additive scale is designed to test the VTF for an average thickness LP when placed on the platter. This is an approximation as we know that LPs vary in thickness by over 1mm (see table in this link: https://www.vinylengine.com/turntabl...p?f=41&t=93648) So, I set my arm at 17.25 mm, the average arm height for the LPs in my collection. I set the VTF, using the gauge, to 2.000g (see photo above) because this is centered within the range of 1.9 - 2.2g, according to the manual of my MySonicLabs Signature Gold cartridge. I then proceeded to measure the VTF at each of my arm height settings. Here are the results:

16.0mm: 2.019g
16.5mm: 2.011g
17.0mm: 2.005g
17.5mm: 1.993g
18.0mm: 1.988g
18.5mm: 1.970g

Interestingly, it is not precisely linear, but the scale is so sensitive/finnicky that each time I placed the stylus on it, the value changes by up to 0.003 or so. The range of VTF for my arm height settings is 0.049g (2.019-1.970g) or roughly 1/20th of a gram. If rounded to two places, it is 2.02g - 1.97g. This may or may not even be audible. The tracking force range of my cartridge (1.9 to 2.2g = 0.3g) is much greater at six times that 0.49g VTF range when I raise and lower my arm. And remember, this is with a fixed stylus height because the VTF gauge is sitting on the platter, not moving up and down with different record thicknesses. Arm height changes often correspond to different record thicknesses (if the original cutting angle is the same), but not always, and if the arm height increases by the same amount as the record thickness increases, VTF does not change at all. So, this change in VTF is within a 1/6 band in the center of my cartridge's recommended tracking force range, and even less when taking into account that the stylus is actually moving up or down as the LP thickness changes, causing even less change in VTF.

In real use, the VTF range with my varying arm heights may be within a much smaller band of the recommended tracking force range of my cartridge. Because the VTF gauge height is an approximation, the stylus on my thinnest LPs will be measured closer to the platter, and the arm will be much lower. Same with the thickest LPs, only in reverse. So, if one removes the two extreme cases of the 16.0mm and 18.5mm arm heights because the arm will be lower with thin LPs and higher with thick LPs, then the VTF range is only 2.011g - 1.988g or a 0.023g range. This is 13 times less than the tracking force range of my cartridge and within a tiny band of 23/1000 of a gram.

The LP thickness chart indicates that a 110g LP is 1.0mm thick and a 200g LP is 2.0mm thick, roughly. That is a range of 1.0 mm in typical LP thicknesses. However, my arm height changes cover a greater range of 2.5mm. So, I am raising and lowering my arm more than the differences in the record thicknesses in my collection. Either, the cutting head angles are all roughly the same and I am over adjusting my SRA settings by ear, or this increased arm height range reflects the varying cutting head angles in my LP collection. It could also be a combination of the two.

Fremer wrote that a 1mm change in arm height with a 9" arm roughly equals 0.25 degrees of SRA. My 12" is even less, say 0.2 degrees of SRA. So, my 2.5mm range in arm height corresponds to roughly a 0.5 degree of SRA change. (0.2 X 2.5 = 0.5). It is easy for me to imagine the cutting head angles vary in my records by 1/2 a degree or more. If Fremer recommends an average SRA setting of 92 degrees, a 1/2 degree variation means an SRA range of 91.75 to 92.25 degrees. This seems certainly possible. These numbers are small.

When VTF is measured at a fixed point like from the stationary scale resting on the platter, it does change very slightly with changes in arm height. However, if one considers that the stylus tip is also moving slightly up or down with changes in record thickness as one adjusts arm height, VTF values change even less, or not at all, as when the arm tube angle does not change with adjustments in height.

It is astonishing to me that with numbers this small, minor adjustments in SRA are audible.

 

[PeterA]

It does not seem that there is much interest in this subject. Perhaps the thread was missed, so here is a bump hoping that it starts a discussion.

 

[jazdoc]

Your experience is similar to mine. Unfortunately, all set up parameters are not independent and require rechecking after each adjustment.

 

[Ron Resnick]

I think the thread was missed. Thank you for resuscitating.

 

[Calle_jr]

It is astonishing to me that with numbers this small, minor adjustments in SRA are audible.

Nice evaluation.

I think the conclusion by Fremer is of another sort.
I don't believe these small variations in tracking force is affecting the scanning at all, and certainly not from VTA change.
I think it's all due to changes in contact area, i.e. pressure rather than force. The contact area of a line contact shape will change with small VTA changes. Much more than a spherical shape.
Of course, if the VTF is changed, the bending of the cantilever will also change and hence the contact area. But, I would rather study this from the point of contact area change, because that will affect the scanning loss and HF pinch effect. To a high degree for some stylus shapes I guess. Especially towards the inner bands due to the lower speed.

It's a bit tricky to look at the contact mechanics for these complex stylus shapes. But if one would do it, I'm certain we would clearly see the reason why the changes are so audible.

 

[Calle_jr]

I think it is appropriate to look at this by looking at the error. Everything that deviates from the modulated groove is an error.
This error will mainly be dependant on; modulated frequencies, contact area (stylus shape in groove + VTF) and groove velocity.

For vertical modulations, the error will be small beyond the audio band for a modern hifi stylus. The contact area should be big, but only transverse to the groove. When stylus angle is changed, the area may get too big parallel to the groove, causing audible errors.
For lateral modulations, the error may be substantial for incorrectly assembled cartridges. The contact area becomes different for convex and concave groove wall and there's a pinch effect when the modulated wavelength gets close to the stylus radius.

Ps, there's also HF resonance effects, dependant on cantilever geometry, stiffness, mass, record compliance, assembly damping etc. But let's leave that in this discussion.

 

[Calle_jr]

Remember, vertical modulation is only containing the side signal, i.e. the out of phase signal, i.e. the discrepancy between the recorded left and right signal. This signal is usually minor.
Anyway, below is an illustration of what happens with different VTA:

A. Correct VTA. B. Too big VTA >24[SUP]o[/SUP]. C. Too low VTA <15[SUP]o[/SUP].

In my view, the biggest effect from error in VTA is between labels and periods (i.e. it's in your record collection). Over the years, RCA, Columbia, Decca etc have had VMAs (Vertical Modulation Angles) varying by 15 degrees! As well, it is signal-dependent and varies across the record. Even if you optimize the slant acc to above image with a test record, your test record is not equal to your record collection. So, measuring VTA with two decimal points is in my opinion totally wasted if you own more than 1 record.

So, my advice is to look to get a cartridge with correct VTA (~18-20[SUP]o[/SUP]). Install to get SRA~92[SUP]o[/SUP]. Use as low VTF as possible within recommended range. Then forget about VTA.

 

[Zeotrope]

Interesting thread. My intuition was that VTF will increase as you increase VTF. I guess this is not true?

With my Fritz Gyger stylus shape, a 0.5-1mm change in VTA is definitely audible.

How does VTA affect tracking ability? Will a slightly higher VTA improve tracking, as it’s providing the stylus a more aggressive ‘angle of attack’ to the grooves?

 

[mtemur]

How does VTA affect tracking ability? Will a slightly higher VTA improve tracking, as it’s providing the stylus a more aggressive ‘angle of attack’ to the grooves?

Yes, if you increase VTA but leave all other the same, tracking increases.

 

[Zeotrope]

Yes, if you increase VTA but leave all other the same, tracking increases.

Which means that increasing VTA will increase (slightly) VTF, correct?

 

[mtemur]

Which means that increasing VTA will increase (slightly) VTF, correct?

If tonearm is dynamically balanced then no, VTF won’t change but if it’s statically balanced then it depends on location of G point and pivot point. Most tonearms are statically balanced.

 

[Zeotrope]

Even small changes in VTA are audible with my FGS stylus shape. I think that when people say they are not audible because SRA changes < 0.1 degree, it’s with an elliptical or conical stylus shape. And this is where the various setup tools will never get you the optimal setup, they simply don’t have the accuracy or resolution to allow you to measure such small changes.
There’s no substitute for adjusting by ear!

 

[theophile]

I've always thought that raising and lowering the pivot point subtly changes the overhang as well.

 

[Zeotrope]

I've always thought that raising and lowering the pivot point subtly changes the overhang as well.

Yes, that’s what I have read as well. But it’s small a small change to HTA which is not really noticeable since a pivoted tone arm is only really tangental to the grove at two points.
The bigger change is getting VTA right - assuming you have a stylus profile that rides “deeper” into the grooves. I never noticed the need to adjust VTA with my elliptical Kondo IO-M, for example.