Strange Phenomenon

[Victor]

I wonder if anyone can explain this as I'm baffled.....
As a result of this experience I'm starting to believe in UFOs and that Elvis is alive

I had been enjoying my recently optimised new cartridge on my favourite vinyl and everything appeared to be going smoothly, good tracking and good sonic balance was manifest when I decided to try some "different music" : a collection of compositions by Lutoslawski, Berkeley, and Dave Bedford.....
(Dave Bedford's composition was called "Tentacles of the Dark Nebula" - kind of appropriate in a way )
Several times during the programme the sound went AWOL i.e. disappeared completely for couple of seconds, which was accompanied by the kind of trundle & thump one associates with the run out groove of the LP (similar to a breach in the record wall but without the infinite loop....) followed by resumption of the music as if nothing happened.

Having inspected the LP I could find no reason for this behaviour - especially given that I had undoubtedly played it once or twice in the past with a Linn MC and didn't remember any difficulties - so I invited a fellow vinylhead to borrow it and try to replicate the phenomenon. He used a Contrapunkt B mounted on a Clearaudio unipivot and reported nothing untoward ("the odd crackle perhaps but no severe pops".)

This bamboozled me given that everything else was running so perfectly. Dirty stylus I thought ? If it was a series of blockages on the disc, perhaps the Contra had cleared them and it was worth re-running the disc?

One of the "obstructions" had occurred within 60 seconds of the start of side 2 so that seemed like a quick way of checking it again. If I got past the 1 minute mark then maybe I was only imagining things......
Side 2 commenced and 4 minutes later I was beginning to believe that I was in the clear...when....the phenomenon happened again....silence...thump...music again....

Clearly it was something to do with the disc in general, not specific locations. Frustrated, I grabbed the magnifying glass and started to monitor the progress of the stylus in the groove. My eyesight was in good shape for a change and I was able to clearly discern the stylus outline as it progressed.
What happened next was startling, did I imagine it or did I just see the whole cart VIBRATE from side to side vigorously
A Close Encounters of the 3rd Kind experience ?????

Did the groove have some kind of periodic lateral deviation/oscillation in it that the arm was struggling to emulate? Then the horrible thought dawned on me....is it possible there is a 10Hz signal embedded on this album ?

I've inspected every other album since using the magnifier and the stylus is centred, stable, azimuthed and rock solid in every case. What is going on????

Welcome to the Twilight Zone guys....

 

[kach22i]

What happened next was startling, did I imagine it or did I just see the whole cart VIBRATE from side to side vigorously

Well, at least you saw it, with a "when" and "where".

All you need now is the "how" and "why".

 

[Tosh]

If you play the same section again, does it keep happening? Because if so it's probably not just your imagination....

I expect you'll also see some accompanying scary woofer cone movement (before your preamp cuts out)?

 

[RichTeer]

Sounds to me there might be compliance/effective mass mismatch that this particular record is exacerbating (perhaps by sub-sonic sound). What does the music do at this time? Is a loud bang, or a quiet passage? If the former (and perhaps even the latter), it could be that this record is testing the limits of your cartridge's tracking ability.

 

[Victor]

If you play the same section again, does it keep happening? Because if so it's probably not just your imagination....?

That opening section on side 2 was played twice and it happened in 2 different places....

 

[Victor]

Sounds to me there might be compliance/effective mass mismatch that this particular record is exacerbating (perhaps by sub-sonic sound). What does the music do at this time? Is a loud bang, or a quiet passage? If the former (and perhaps even the latter), it could be that this record is testing the limits of your cartridge's tracking ability.

My thoughts as well, Rich. I've played some pretty heavy material on it without incident. This afternoon I was playing Little Axe's "Slow Fuse" album which has some pretty heavy bass rhythms and the cart sailed through the material. Also some Lenny Kravitz which combined deep bass with ultrasonics on one track - again impeccable behaviour. Only a week ago I did the HFN/RR resonance test and the combination produced a resonance of about 9.5Hz-10Hz which is par for the course, so you can understand my puzzlement....

 

[Victor]

...Sorry...I didn't fully answer the questions. It doesn't seem to matter what intensity the music is at the time of the "event". It has happened during both moderate and quiet passages....
Freaky or what.....

 

[Victor]

More info : The cart shows obvious signs of slight mistracking (both L & R) approaching and during these strange episodes - most noticeable on voice....

 

[Speedskater]

Try listening only with headphones, to eliminate acoustic feedback as a possible cause.

 

[Victor]

Try listening only with headphones, to eliminate acoustic feedback as a possible cause.

Thanks for that Speedskater. A similar thought did occur at the time although not in the form of wearing headphones but just muting the whole system then studying the reaction. I haven't tried it yet but here's the other thought you've triggered : You just reminded me the effect that warps used to have on the pair of Linn Saras I used to own (you could easily see the bass drivers vacillate with the grills removed) and in so doing had me wondering what effect a warp of 9-10Hz would have on a cartridge and why I hadn't seen anything like this in decades of listening to vinyl....?????

BTW....I had completely forgotten the influence of "virtual DC" and infrasonic sounds in overheating the amplifier and voice coils of the bass drivers!
An inspirational suggestion - well played.

 

[Victor]

...and now for the results Speedskater.....

I dug the offending album out of the Archive (which had been labelled "off limits" for the time being) and ran the T/T with everything else powered down.
Then I studied the stylus behaviour with the magnifier for a several minutes - long enough to "let the dog see the rabbit...."

The stylus appeared to track stable and true for the duration with no signs of resonance.
Ok, now you've given me a new problem - given that it was maximum standard volume I was using
I can only conclude the Turntable may be too close to the speaker for that volume level...

Many thanks for your help in identifying this.

 

[Victor]

The aftermath :
While I was studying the stylus, I also observed that the warped surface could well be bordering on those destructive 9-11Hz frequencies for the odd moment or two per cycle.
The stylus did seem to survive the rough treatment though.

Neither the T/T or the speaker are going anywhere for the moment so I guess that particular LP will have to be labelled with a health warning and played at minimal volume as a precaution. The grotesque irony was that many modern (and visibly warped from 26 ft away) records were replayed at much higher apparent volume level and seem quite happy!

Hope this serves as a warning to the unwary....the Truth is out there...

 

[risabet]

Don't jump to conclusions. It is possible that the phono pre is overloading and muting due to some infrasonic signals that only happen at certain points on the LP.

 

[Victor]

Don't jump to conclusions. It is possible that the phono pre is overloading and muting due to some infrasonic signals that only happen at certain points on the LP.

Hi Risabet,
What you are suggesting is quite possible.
It's hard not to jump to conclusions though when the cart is visibly jumping around like a Tasmanian Devil!

I ran another 3 albums this morning, with varying degrees of warp (deliberately at "realistic" volume levels), to see if I could encourage any mistracking but it all sounded good.
Strange occurrences like this are depressing enough to make you want to sling the whole analogue source into the bucket. If only it didn't sound so good...

 

[Speedskater]

Victor, you really should solve the problem, because it's affecting many of your other recordings to a smaller degree.
Something in your vibration dampener system is causing a resonance in a frequency range that is making your tone-arm/cartridge unhappy.

 

[Victor]

Victor, you really should solve the problem, because it's affecting many of your other recordings to a smaller degree.
Something in your vibration dampener system is causing a resonance in a frequency range that is making your tone-arm/cartridge unhappy.

Hi Speedskater....you'll be pleased to hear that I didn't give up on this one. I did my research this morning and discovered that Grado carts (from which the Music Maker is derived) tend to be the worst suffering carts on the market for cantilever resonance problems. I know that Len adds extra damping - which may or may not apply to to this problem.

I've decided to let LG know about the problem and ask if it needs attention.
Best regards.............................Victor.

 

[Victor]

...Of course we seem to have forgotten that, thanks to your shrewd observation about feedback, Speedskater, this seems to be a contributory factor too (i.e. Turntable-Loudspeaker proximity)

The only things I can say in my defence in this respect are that I've seen the occasional setups with even closer spacing (and on wooden floorboards as opposed to concrete), and that I tend to balance the ML active subs to produce minimal bass (about -3db) to get the best imaging, so I don't think extreme LF excursions are particularly pronounced on these speakers - even at realistic volumes?

Sometime during the forthcoming week, I planned to find out what sound level actually triggers the effect on the offending disc.

 

[risabet]

I don't see how a resonance would cause no sound output, distortion yes, no output? I don't see how. I really doubt that is the issue here. If the stylus is in the groove, then there should be sound if the signal is getting through. Seriously strange problem though.

What is the rest of your system?

 

[Victor]

I don't see how a resonance would cause no sound output, distortion yes, no output? I don't see how. I really doubt that is the issue here. If the stylus is in the groove, then there should be sound if the signal is getting through. Seriously strange problem though.

What is the rest of your system?

It is puzzling Risabet. I'm inclined to agree as even if the stylus skidded across the groove I would would still have expected an accompanying sound rather than a brief silence (unless of course, extreme resonance physically precludes normal operation of the cart...?)

Analogue system from the bottom up is : Solid composition floor (concrete foundation), Podium (heavy wooden) Tripod in 3 stages for (please don't laugh ) isolation! Raven T/T with Stillpoints (LP12's successor - because I wanted to find out what life was like on the unsuspended side of the fence - again please don't laugh ), Linn Ittok LVII, Cartridgeman MMIII, Whest PS0.3R phono stage, Simaudio Moon i-7 amp, ML Vantage. System seems impervious to footfall which is an encouraging sign. Also seemed impervious to high volume bass heavy material on a few dozen other records.

As far as the cartridge enquiry goes, Len G is not in the best of health right now so I've elected not to impose on him other than to wish him a speedy recovery. His convalescence is coming along very well though.
My gut feeling is that there is nothing fundamentally wrong with the cart but the 2 salient factors identified thus far are 1. Disc Warp 2. Feedback exacerbated by close speaker proximity (and possibly a 3rd - disc content).

(2) is difficult to address (1ft gap from Podium to bass cabinet) because even if I centred the T/t between the speakers I'd end up with 2ft gaps to both speakers - which would only represent a marginal improvement
For the moment I'm deliberately trying to trigger mistracking with extreme feedback (i.e. excessive loudness) on other discs but with no success...
Also comparing loud/quiet listening on the same disc...
Best regards.....................................Victor

 

[Victor]

Ok....time for some feedback from the man himself (I gave Mr Gregory the option of replying or relaxing....but since he is in the process of working himself back into his routine, he kindly responded.... )

He said, "You are suffering from induced resonance....these things happen from time to time"....
"Yes", I replied, "but what about my vinyl problem !?!?"

Just kidding.....He felt that if other samples were ok, this sample of vinyl was exclusively at fault and suggested that the problem could be the result of a poorly calibrated lathe.
His recommendation was to find myself another copy of that LP.

Easier said than done but the solution for now is to put a Government Health Warning on it and consign it to Area 57....
Does this close the book on the problem? I hope so....