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Experimental method for setting VTF

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Experimental method for setting VTF

Postby luckydog » 15 Aug 2009 17:09

Apols if this is not new, but it is to me.

Is it appropriate to use a dynamic measurement of VTA to set VTF ? That is to say, when playing a 'typical' height record with typical dynamics, can one use the VTA as a guide for how to set the VTF ?

For example, assume optimal arm and cartridge alignment (azimuth, zenith, overhang, top of cartridge parallel to playing surface, nominal VTF say mid point of range.) By using a digital camera, one could capture and measure VTA when playing. If measured VTA does not meet cartridge manufacturer's spec, then VTF could be adjusted (and height reset afterward) until VTA was exactly on spec.

Why bother ? VTA sets the stylus rake angle, which has a fairly narrow band of optimal setting for best tracability, trackability frequency response and distortion. VTA sets the bias point for the cartridge engine. There can be only one setting of VTF that gives a correct VTA/SRA and a parallel cartridge. VTF can be dynamically decreased by both the moment of frictional drag force if the stylus and tonearm pivot aren't on the same horizontal plane, and dynamic skate force since the groove wall is 45 deg vertical where the force is applied.

Looking at the 'pics of your cartridge' thread, I noticed that, amongst the hundreds of pics when playing records, many have a visibly non-vertical rake angle, SRA. I know that not all cartridges are designed to have vertical rake angles, but most eliptical stylii are set that way with vertical contact faces as I understand. Almost all pics showed 'correct' parallel cartridge top with record surface, at least to the eye.

I tried this out on a 2M red (eliptical) in a Pro-ject 9c arm. At spot on 20 deg VTA, zero anti-skate, parallel cartridge top with playing surface, Decca 180g vinyl, I required 2.4g of static VTF. I have to say the sound is superb, tracking and tracing excellent, image is superb. Best sound I've ever produced from this rig.

I'm more than a bit concerned that 2.4g of static VTF is 'out-of-spec' for the 2m red (2.0g max)........but if that's what it takes to meet VTA spec dynamically, i.e. whilst playing, is it really out of spec, or are dynamic upforces helping out ? Interesting, what ?
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Postby luckydog » 15 Aug 2009 19:50

Thanks, . My result was an experiment, of course, just that it had a surprisingly good sonic result, and a surprising VTF. That said, looking at the pics in the 'pics of my cartridge' thread, it would seem common enough for the rake angle to be visually off, which also surprises me. Perhaps you're right and there's something wrong with my cartridge suspension, but it's in the prime of life and I've no reason to suspect any problem - I guess there's too many other pics to be coincidence......?.

What I did was prioritise the manufacturer's spec for VTA (SRA), and measure it in situ whilst playing, rather than prioritise the spec for VTF. Keeping the cartridge level. So in fact the VTA is spot on. Tonearm bearings seem fine, no reason to suspect that.

Does it seems reasonable to assume some decrease in effective VTF, as in the OP ? Perhaps a manufacturer can't assume any upforce when specifying max VTF, can't cover every case ? That might be why there's a tendancy to sound best at higher VTF in any event.
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Postby Brian75 » 16 Aug 2009 02:10

Hello,
This is really interesting thread as I have been doing exactly this on my project arm these past few days. I've been aligning the stylus perpendicular to the LP at the recommended VTF rather than arm to platter. I'm noticing that in my case, to get that result, the VTA has to be set quite high compared to it being set level to the platter.

Still experimenting and learning as always. Keep this thread going, I'm just starting to get into fiddling with VTA and I'm loving every second of it!! :)
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Postby luckydog » 16 Aug 2009 09:44

Your problem is that you don't understand how the record is cut. It's not cut perpendicular to the vinyl surface. While they do vary, a normal angle would be 22 degrees. Thus you are in error by that amount if you set the stylus perpendicular to the vinyl.
The shank or major axis of an eliptical stylus should usually be vertical for playback. This can be seen from the 'pics of my cartridge thread', the rake angle generally vertical. Point is to get the VTA (i.e cantilever angle) on spec, then the stylus rake angle is automatically on spec. Groove is made to be traced by an on-axis contact surface, give or take a fraction, i.e a vertical stylus in the case of eliptical, but that's academic because the VTA spec sorts out the detail for each cartridge/stylus.

Vertical Modulation Angle is 15-30 deg depends on label, and is a pre-emphasis at the cutting stage to minimise harmonic distortion on cartridges with cantilevers, because a cantilever can only move on its radius, e.g 20 deg. Without a cantilever, the engine would have to be vertically over the stylus, and it's tough to get enough clearance to clear warps. This means the cutter head moves at an angle of 15-30 deg off vertical, not that the cutting edge/playback edge isn't vertical. To complicate things, there's also springback in lacquer after cutting, hence variation in VMA between labels. I read the cutting edge remains more or less vertical, but the cutter moves off vertical, if that makes sense.

brian75 wrote:............
This is really interesting thread as I have been doing exactly this on my project arm these past few days. I've been aligning the stylus perpendicular to the LP at the recommended VTF rather than arm to platter. I'm noticing that in my case, to get that result, the VTA has to be set quite high compared to it being set level to the platter.

Still experimenting and learning as always. Keep this thread going, I'm just starting to get into fiddling with VTA and I'm loving every second of it!!

I think its interesting too, might lead somewhere. Post your results, especially sonic. Seems you've been experimenting the other way, i.e to get VTA/SRA on spec by height adjustment. What VTF did you use? I went for level cartridge and varied VTF until VTA/SRA on spec.
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Postby Thomas_A » 16 Aug 2009 13:20

You will decrease distortion with higher VTF, but also increase wear.

Correct VTF is when the stylus magnet is perfectly aligned with the coils, given an already perfect mounted stylus. IMD (60 Hz & 4 kHz) with OM40 varying the VTF within its limits:

1.3: 2.98%/2.08%
1.4: 2.02%/2.00%
1.5: 1.74%/1.84%
1.6: 1.57%/1.65%
1.7: 1.46%/1.56%

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Postby luckydog » 16 Aug 2009 22:28

Rather strange approach. No VTA adjustment on the arm?

When you increase the VTF, you also change other aspects of the sound. The stylus/cantilever is under more weight, causing a difference in its movement. It's the cantilevers' movement that generates the signal.

The idea started when thinking about what is optimum VTF. Is it the minimum force needed to keep the stylus tracking & tracing the groove, or the force needed to keep the cantilever central so the cartridge engine is optimally biased i.e on spec VTA? What VTF setting does both? Fixing VTA by adjusting arm height or headshell angle doesn't achieve central cantilever bias, this can only happen if both the cartridge is level and VTA is on spec.



Thomas_A wrote:Correct VTF is when the stylus magnet is perfectly aligned with the coils, given an already perfect mounted stylus. IMD (60 Hz & 4 kHz) with OM40 varying the VTF within its limits:

1.3: 2.98%/2.08%
1.4: 2.02%/2.00%
1.5: 1.74%/1.84%
1.6: 1.57%/1.65%
1.7: 1.46%/1.56%

That's interesting, Thomas_A. Agree with that definition of optimal VTF. Those figures show IMD decreasing as VTF increases, suggesting it may decrease further were VTF to be increased further still beyond spec limits. Definitely not suggesting an OM40 is for such experimenting though ! But I wondered if the dynamic weight on the cantilever is really less than the static VTF, and that's why VTA was off spec with a level cartridge. Reasons set out in OP. Is that why those IMD figures have not peaked within spec VTF limits ?

Lastly, thanks for the Jon Risch article, . I was already aware and that's part of what got me thinking of measuring VTA/SRA.
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Postby Rice » 16 Aug 2009 23:36

Point is to get the VTA (i.e cantilever angle) on spec, then the stylus rake angle is automatically on spec



Hi ld ,


I`m not sure whether you mean that the VTA is the same thing as the cantilever angle.And it is certainly not ideal ,to have the stylus positioned vertically on the record surface.

From what I know ,the VTA is the angle ,which is being formed by the (imaginary) line ,which goes from the stylus tip ,to the point where the cantilever is fastenend in the suspension.And the record surface.Setting the VTF and making sure that the top of the cart ,is in parallel with the record surface ,will be a good starting point.

It`s very difficult to measure the VTA (if not impossible).But with the cart`s manufacturers specs ,you can get a long way.Remember though ,that whenever you change the VTF ,you need to set the VTA again.

Furthermore ,the anti skating should also be adjusted correctly.The azimuth adjustment ,is also something to check.


greetings ,


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Postby Thomas_A » 17 Aug 2009 06:36

ld wrote:
Rather strange approach. No VTA adjustment on the arm?

When you increase the VTF, you also change other aspects of the sound. The stylus/cantilever is under more weight, causing a difference in its movement. It's the cantilevers' movement that generates the signal.

The idea started when thinking about what is optimum VTF. Is it the minimum force needed to keep the stylus tracking & tracing the groove, or the force needed to keep the cantilever central so the cartridge engine is optimally biased i.e on spec VTA? What VTF setting does both? Fixing VTA by adjusting arm height or headshell angle doesn't achieve central cantilever bias, this can only happen if both the cartridge is level and VTA is on spec.



Thomas_A wrote:Correct VTF is when the stylus magnet is perfectly aligned with the coils, given an already perfect mounted stylus. IMD (60 Hz & 4 kHz) with OM40 varying the VTF within its limits:

1.3: 2.98%/2.08%
1.4: 2.02%/2.00%
1.5: 1.74%/1.84%
1.6: 1.57%/1.65%
1.7: 1.46%/1.56%

That's interesting, Thomas_A. Agree with that definition of optimal VTF. Those figures show IMD decreasing as VTF increases, suggesting it may decrease further were VTF to be increased further still beyond spec limits. Definitely not suggesting an OM40 is for such experimenting though ! But I wondered if the dynamic weight on the cantilever is really less than the static VTF, and that's why VTA was off spec with a level cartridge. Reasons set out in OP. Is that why those IMD figures have not peaked within spec VTF limits ?

Lastly, thanks for the Jon Risch article, . I was already aware and that's part of what got me thinking of measuring VTA/SRA.


I do not know what factor that decreases the IMD yet, but higher VTF does decrease distortion in general, due to better contact (but higher wear). But IMD is a little different since it also should be affected by alignment (vertical tracking angle, lateral tracking angle). This is however, lateral IMD signal, and not vertical. So while lateral tracking angle may be affected (dependent on antiskate force?) I am unsure how increased VTF (and VTA) can affect the distortion here. see thread in cartridge forum.
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Postby Thomas_A » 17 Aug 2009 06:37

ld wrote:
Rather strange approach. No VTA adjustment on the arm?

When you increase the VTF, you also change other aspects of the sound. The stylus/cantilever is under more weight, causing a difference in its movement. It's the cantilevers' movement that generates the signal.

The idea started when thinking about what is optimum VTF. Is it the minimum force needed to keep the stylus tracking & tracing the groove, or the force needed to keep the cantilever central so the cartridge engine is optimally biased i.e on spec VTA? What VTF setting does both? Fixing VTA by adjusting arm height or headshell angle doesn't achieve central cantilever bias, this can only happen if both the cartridge is level and VTA is on spec.



Thomas_A wrote:Correct VTF is when the stylus magnet is perfectly aligned with the coils, given an already perfect mounted stylus. IMD (60 Hz & 4 kHz) with OM40 varying the VTF within its limits:

1.3: 2.98%/2.08%
1.4: 2.02%/2.00%
1.5: 1.74%/1.84%
1.6: 1.57%/1.65%
1.7: 1.46%/1.56%

That's interesting, Thomas_A. Agree with that definition of optimal VTF. Those figures show IMD decreasing as VTF increases, suggesting it may decrease further were VTF to be increased further still beyond spec limits. Definitely not suggesting an OM40 is for such experimenting though ! But I wondered if the dynamic weight on the cantilever is really less than the static VTF, and that's why VTA was off spec with a level cartridge. Reasons set out in OP. Is that why those IMD figures have not peaked within spec VTF limits ?

Lastly, thanks for the Jon Risch article, . I was already aware and that's part of what got me thinking of measuring VTA/SRA.


I do not know what factor that decreases the IMD yet, but higher VTF does decrease distortion in general, due to better contact (but higher wear). But IMD is a little different since it also should be affected by alignment (vertical tracking angle, lateral tracking angle). This is however, lateral IMD signal, and not vertical. So while lateral tracking angle may be affected (dependent on antiskate force?) I am unsure how increased VTF (and VTA) can affect the distortion here. see thread in cartridge forum.
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Postby Thomas_A » 17 Aug 2009 06:37

ld wrote:
Rather strange approach. No VTA adjustment on the arm?

When you increase the VTF, you also change other aspects of the sound. The stylus/cantilever is under more weight, causing a difference in its movement. It's the cantilevers' movement that generates the signal.

The idea started when thinking about what is optimum VTF. Is it the minimum force needed to keep the stylus tracking & tracing the groove, or the force needed to keep the cantilever central so the cartridge engine is optimally biased i.e on spec VTA? What VTF setting does both? Fixing VTA by adjusting arm height or headshell angle doesn't achieve central cantilever bias, this can only happen if both the cartridge is level and VTA is on spec.



Thomas_A wrote:Correct VTF is when the stylus magnet is perfectly aligned with the coils, given an already perfect mounted stylus. IMD (60 Hz & 4 kHz) with OM40 varying the VTF within its limits:

1.3: 2.98%/2.08%
1.4: 2.02%/2.00%
1.5: 1.74%/1.84%
1.6: 1.57%/1.65%
1.7: 1.46%/1.56%

That's interesting, Thomas_A. Agree with that definition of optimal VTF. Those figures show IMD decreasing as VTF increases, suggesting it may decrease further were VTF to be increased further still beyond spec limits. Definitely not suggesting an OM40 is for such experimenting though ! But I wondered if the dynamic weight on the cantilever is really less than the static VTF, and that's why VTA was off spec with a level cartridge. Reasons set out in OP. Is that why those IMD figures have not peaked within spec VTF limits ?

Lastly, thanks for the Jon Risch article, . I was already aware and that's part of what got me thinking of measuring VTA/SRA.


I do not know what factor that decreases the IMD yet, but higher VTF does decrease distortion in general, due to better contact (but higher wear). But IMD is a little different since it also should be affected by alignment (vertical tracking angle, lateral tracking angle). This is however, lateral IMD signal, and not vertical. So while lateral tracking angle may be affected (dependent on antiskate force?) I am unsure how increased VTF (and VTA) can affect the distortion here. see thread in cartridge forum.
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Postby luckydog » 17 Aug 2009 12:30

Thomas_A wrote:I do not know what factor that decreases the IMD yet, but higher VTF does decrease distortion in general, due to better contact (but higher wear). But IMD is a little different since it also should be affected by alignment (vertical tracking angle, lateral tracking angle). This is however, lateral IMD signal, and not vertical. So while lateral tracking angle may be affected (dependent on antiskate force?) I am unsure how increased VTF (and VTA) can affect the distortion here. see thread in cartridge forum.

Thanks Thomas_A, see also my post in your thread. Lateral modulation forces act laterally on groove walls, but groove walls are 45 deg vertical, so there's a vertical component to the reaction force. That component is distortion if it causes variations in cantilever position by moving the cartridge minutely, asuming the stylus can't move.

I'm of the view that when a stylus is in contact with groove walls, there's no such thing as 'better contact' Contact is contact irrespective of force, it does not become 'better contact' per se. There are 'better angles', finer lines, less pinching, but not affected by downforce other than via VTA. One caveat, vinyl is slightly springy though. There's 'better held down', of course.
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