Aha!! It's the Jico wobble...

[dlaloum]

LD and I have been having a debate about "rules of thumb" for 10Hz to 100Hz conversion.

I have used the rule of thumb of a 1.5 to 2 times multiplier for the last couple of years - mostly for Japanese cartridges where the quoted compliance is measured at 100Hz.

LD being a physicist has been bagging me about this for most of the last couple of years. - As LD already knows I am very very stubborn (some would say "thick as a brick") - and have been looking for some way of getting a rough indication of compliance so that one need not have purchase the cartridge to estimate what it will match with.

LD's long time suggestion has been to use the VTF as an estimate rather than trying to convert the 100Hz to 10Hz compliance figures.... and much as I hate to admit it, I am gradually coming around (kicking and screaming) to his perspective.

At some stage I may do the required measurements to correlate the VTF spec of the cartridges I have, with the measured compliance.... and see whether I end up with a consistent table/chart that could be used for cross indexing. (actually it might be more usefull to have a chart correlating arm mass to VTF... not sure yet)

bye for now
David

(yes LD, you may consider this a "conditional" surrender.... )

[dlaloum]

OK I just re-ran the Denon LF sweep record, with my currently mounted V15V-SAS on the JVC Ql-Y5F - running at 1.25g VTF with no damping and the brush clipped up and not in use.

Calculated and Measured arm mass is 14.1g (including the currently mounted headshell), with cartridge mass at 6.6g, and 0.1g of nylon screws/nuts added...

Resonant frequency was measured at 4.8Hz - resulting in a calculated compliance @10Hz of circa 53CU

I couldn't quite believe it with my former measurements so I remeasured ...

The SAS is clearly not just high compliance, but VERY high compliance.

Keeping in mind that his measure is the VN5MR-SAS stylus, and that the compliance may vary for other SAS styli (I need to confirm CU for my other SAS styli)...

But based on my measurements it would be wise not to run the SAS styli without some form of damping, on anything but the very lightest arms - the brush itself does quite a good job, or an arm with fluid/servo damping.

So there you go, there is a very good reason for the Jico wobble!

If I remember correctly, the Hadcock arm is both low mass, and fluid damped - so the perfect match for the SAS.

bye for now

David

[Ldg]

....The Jico is obviously much higher compliance than I read,,I have now found this out..Yet it tracks up to 1.5 gms..Not 1.25 like my original V15 he stylus,,so I thought it would be quite a bit lower compliance.

At some stage I may do the required measurements to correlate the VTF spec of the cartridges I have, with the measured compliance.... and see whether I end up with a consistent table/chart that could be used for cross indexing. (actually it might be more usefull to have a chart correlating arm mass to VTF... not sure yet)

What you should find is that recommended VTF correlates with cartridge suspension internal damping, not spring. So VTF would mostly correlate with compliance@100Hz, which is mostly defined by damping. Whereas compliance@10Hz is mostly defined by spring, and wouldn't correlate so well.

In this case of Goaty's Jico, it seems the spring constant is quite small (compliance@10Hz is big), but the damping constant is relatively normal, perhaps on the small side (compliance@100Hz is up a bit). Hence the spec compliance@100Hz. But, there's still not enough internal damping to cope with all arm matches, hence the better match on lighter arms and general benefit of arm damping.

So yes, for stability it's best on a light arm, and even then with some external damping if poss, be it brush or fluid damper etc.

Stability is well worth striving for, it underpins so much of vinyl sound, IMO.

[Eoin]

Just for info, I also find a Jico SAS on a V15 3 tracks at more like 1.5 than 1.25. I was surprised.

That's on a fluid damped SME III which is an ultra low mass arm (effective mass 3-5g). But not a trace of any wobbles.

However I'm now using a Roksan MM cartridge loaned by satanfriendly and I find it much nicer.

[markcass]

OK I just re-ran the Denon LF sweep record, with my currently mounted V15V-SAS on the JVC Ql-Y5F - running at 1.25g VTF with no damping and the brush clipped up and not in use.

Calculated and Measured arm mass is 14.1g (including the currently mounted headshell), with cartridge mass at 6.6g, and 0.1g of nylon screws/nuts added...

Resonant frequency was measured at 4.8Hz - resulting in a calculated compliance @10Hz of circa 53CU

Yes, IIRC that was the compliance when Hi Fi Choice tested the V15-III - which, of course, lacks the handy damper brush of the IV and V. So it looks as though JICO have replicated this compliance.

The HFC review came out in the days of their A5 "consumer report" format dedicated to particular types of equipment, e.g. Cartridges and Headphones. There were still a few very low mass arms about in those days, but even in one of those the resonant frequency might be a little marginal!

HTH

Mark

[dlaloum]

In my testing I found that when the cantilever was "pre-stressed" by a higher tracking force, the high midrange distortion (THD) dropped noticeably...

This may explain the preference for 1.5g VTF over 1.25g VTF

I still have not gotten around to posting those charts on my website - I need to do that at some stage!

bye for now

David

[Ldg]

In my testing I found that when the cantilever was "pre-stressed" by a higher tracking force, the high midrange distortion (THD) dropped noticeably...

This may explain the preference for 1.5g VTF over 1.25g VTF

In layman's terms, you got less sibilence at higher VTF, DL.........hardly worth writing home about

More likely by far 'early onset mistracking'. Stylus riding the wall. That at least makes some sense. There's no evidence or mechanism that cantilever stress is involved, it's just speculation. Why would it be ? It's simply mistracking, or something else, if it's repeatable at all.

[dlaloum]

Totally repeatable - cartridge was meticulously set up, and tracking tested using the HFN torture tracks and an oscilloscope - the cartridge tracked all the way up to the +18db track 9 torture test cleanly (!!)

In this case, I strongly disagree, the test signal is at a relatively low level (-20db with 0db being the usual 5.6cm/s...)

There really should be no mistracking with that type of signal at that level, on a cartridge the easily passes the torture test.

There is a high midrange "hump" in THD which appears to correlate with the high midrange "trough" in frequency response - this effect is not eliminated by increased VTF - but it is reduced...

An unexpected effect, and one that appears to indicate that at least part of the midrange trough common to all cartridges (btwn 2k and 10k roughly) is generated by something that is sensitive to VTF.

THD at frequencies above 10k was completely unaffected by the varying VTF - another reason for doubting mistracking as a cause.

My assumption is that it points to some sort of cantilever behaviour, and that the additional VTF is pre-stressing the cantilever, and therefore making it behave as a more rigid device... of course that is just a guess... but it is based on some interesting measurements!

bye for now

David

[Ldg]

Totally repeatable - cartridge was meticulously set up, and tracking tested using the HFN torture tracks and an oscilloscope - the cartridge tracked all the way up to the +18db track 9 torture test cleanly (!!)

So you didn't actually repeat it then.....eg across cartridges, setups etc. That's not actually 'totally repeatable' then..... C'mon, this is misleading stuff !

In this case, I strongly disagree, the test signal is at a relatively low level (-20db with 0db being the usual 5.6cm/s...)

Well no, because of RIAA, at 8kHz -20dB is about 2.2 cm/s physical velocity, for example. That's not exactly a low level.

There really should be no mistracking with that type of signal at that level, on a cartridge the easily passes the torture test.

'Torture test' stresses completely different aspects of trackability, at radically different frequencies, with different limiting mechanisms. And, in any event, 2.2cm/s@8kHz is not a low level physical level.

There is a high midrange "hump" in THD which appears to correlate with the high midrange "trough" in frequency response - this effect is not eliminated by increased VTF - but it is reduced...

IF it's real and repeatable, it could have many candidate mechanisms, including mistracking distortion.

An unexpected effect, and one that appears to indicate that at least part of the midrange trough common to all cartridges (btwn 2k and 10k roughly) is generated by something that is sensitive to VTF.

Like.....mistracking ? Friction and flicker noise ?

THD at frequencies above 10k was completely unaffected by the varying VTF - another reason for doubting mistracking as a cause.

No, trackability at hf is relatively insensitive to VTF. No matter how much vtf is applied it can't be usefully applied to the stylus. At massive risk of confusion, it's because of cantilever impedance. That's an entirely seperate mechanism from what you're suggesting here, DL.

My assumption is that it points to some sort of cantilever behaviour, and that the additional VTF is pre-stressing the cantilever, and therefore making it behave as a more rigid device... of course that is just a guess... but it is based on some interesting measurements!

Indeed, it's entirely a guess. Without a mechanism, and without evidence. C'mon it's unsupported speculation, without a basis, and where preferable explanations aren't contradicted. If it's real and repeatable at all.

[dlaloum]

Mechanism is a guess...

Measurements are empirical:


If the issue were mistracking, I would have expected that the increased THD would continue and get worse as frequency rose, instead it peaks then drops again at 10k, before rising to another peak that coincides with what appears to be a resonance.

the two measurements that show a 30% reduction in THD at 8kHz are both tracking at 1.5g... one with brush down (total VTF 1.7g) one with brush up.

I previously posted the results in viewtopic.php?f=19&t=41128&start=45#p322832

at which time your comments LD were:

A few guesses at why harmonic distortion and channel seperation might vary with VTF :

1. The obvious one : VTA varies as suspension sits at different heights. Not only mechanical tracing distortion, but generator neutral position might shift. Need to reset VTA after varying VTF, to remove this unwanted variable.

2. Stylus sits in the groove at a slightly different 'rotation', if the stylus is not perfectly vertically mounted and/or geometrically perfect. Perhaps !

3. Pre-stress, or pre-flex, in the cantilever varies. Perhaps !

bye for now

David

[Ldg]

But that's hardly either demonstration of VTF having an effect, or repeatabilty, DL. If you look at dozens of cartridge measurements on Paul Miller's site, you'll see only a minority demonstrate a mid 'hump' in distortion. And in any event, this does not correlate with PM's measurements of 'mid-dip' in frequency response.

IIRC, PM's distortion measurements don't typically show a hf droop either, which is exactly what one might expect. However, I'd be suspicious of hf distortion measurements anyways, not least because of bandwidth requirement.

Idle guesses at candidate mechanisms is no basis for an assumption any are true, or that there is anything to explain. IF you can go on and demonstrate a repeatable effect across cartridges that is definitely not due to mistracking, then there's a place for discussion about mechanisms, and it becomes interesting. But such things have to stand on rigorous proof of effect beyond the obvious first. Otherwise it gets silly v quick.

[dlaloum]

In due course others will get the full VTF varying THD measurement treatment - but given the amount of time it takes, I'm not rushing to test every cartridge I have!

Still the phenomena was unexpected...

[phivates]

ld: are you female?

[Ldg]

ld: are you female?

Why you wanna know, phivates ? Thinking of requesting a VE dating agency section for physicists with an interest in how vinyl works ? Ballroom dancing ? Tennis doubles ?

Still the phenomena was unexpected...

Well, if it's not mistracking, yes. Seems worth repeating across a few carts, to get some confidence and feel for if it's real, and if so what extent. And find a way to eliminate the obvious, then go fishing for mechanisms. The grouping of the initial results could also just be random, of course.