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Old 21st Mar 2017, 12:10 am   #1
dinker11
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Default Is Blu-Tack the magic cheapo option for non audiophiles?

I've been having a few resonance feed back problems with a Citronic Pd100 mk2 deck fitted with an AT95E cart for a while now.

Tracks beautifully at 2 gms without any syllibance and groove pinch at the inner groove.

After various experimentation, I have packed the inside of the head shell with Blu Tak, re balanced the arm and reset the tracking weight.

The feedback resonance is now totally gone, although I know that the arm mass has now increased.

Will this produce any problem that i'm not aware of, as everything sounds far better at high listening levels now.

I've considered spiked T/T feet and various other after market fixes but this seems to have done the trick.

I've also used Blu Tak to stop wall hanging pictures rattling and even stuffed a little in rattling windows.
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Old 21st Mar 2017, 4:29 am   #2
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

Besides damping vibrations in the headshell/cartridge, the Blu-Tak also increases mass at the playing end of your tonearm. Increased mass is not bad. With a low or medium-compliance cartridge, too low a tonearm mass can cause the mass-compliance resonance to be too high, into the audible range. It could be that the increased mass has put your resonance down farther toward the desired 12Hz range.
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Old 21st Mar 2017, 4:56 am   #3
stevehertz
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

If you've "packed the inside of the headshell with blu tak" it sounds very likely that the combined mass of the headshell + cartridge has been changed greatly - we're talking about things that weigh a few grams here. It's all very well re-balancing the arm and cartridge for the correct tracking weight but the mass of everything affects its resonant frequency. Cartridges and arms/headshells have to be matched in order that the low frequency resonance falls within of a certain band. Not too high as to affect normal listening and not so low that it will become excited by external vibrations.

It's quite complex, but it's explained in this web page from which I extract the following quote. The problem or issue being, does the resonance of your cartridge/arm/headshell combination now fall outside that critical band?:

"Resonant Frequency (of the cantilever) The acoustic frequency at which the cantilever will become excited and vibrate out of control. )) This frequency is measured in cycles per second. Also referred to as 'hz'. Resonant frequency of a cantilever is regarded as inescapable and the effect is controlled by manipulating this frequency to exist in a range below human hearing but not so low that it will become excited by external vibrations such as foot fall disturbance or that of a warped record. This ideal frequency range is 8 to 12 hz. The lowest of low organ notes rarely go below 20 hz. Footfall and record warps happen below 6 hz.

"The effective mass of a tonearm in combination with the compliance of the cartridge cantilever serves to determine where the resonant frequency of a given tonearm/cartridge match up will be. In general terms, arms with high effective mass fitted with cartridges of high compliance result in resonant frequencies that fall below the ideal range. At the opposite end, arms with low effective mass mated to cartridges of low compliance result in resonant frequencies above the desired range. Both extremes are to be avoided."


http://www.theanalogdept.com/cartrid...m_matching.htm

In practical terms you need to know the total mass of your blu tak, headshell, cartridge and arm (summed) and using the attached graph, mate it to a cartridge with a stated compliance that used together falls within the shaded area of the graph. Outside that and you're asking for trouble. So for example if you had an effective mass of 15g and a cartridge with a stated compliance of 17CUs, then if you look at where these two points intersect on the graph, it's 10Hz, within the shaded area, so you're fine, it's within the desired band of 8 to 13Hz.

Saying all of that, being as you say that your set up is now free from resonances (you may not hear them though!!) it could well be that your set up is ok. You need to check things out according to the graph. I suggest you weigh your blu tak separately and add it to the published mass figures for the arm, cartridge and headshell. FYI, the AT95E has a moderately high compliance of 20 x 10-6 cm/dyne, so apart from anything else (resonance wise) it needs a low/more medium mass arm/headshell combination in order to track nicely.
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Old 21st Mar 2017, 8:04 am   #4
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

If it sounds better to you then just do it. 2g is a bit high for an AT95E though.
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Old 21st Mar 2017, 8:37 am   #5
dinker11
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

Thanks for all of your replies and suggestions.

I can see that there is a lot of science and mathematics behind matching carts/headshells and arms together which is somewhat beyond my scale of understanding but as paul has suggested, It does sound better so I'll leave it in place and give it a few weeks of test play.

I'm tracking it slightly higher than normal as it's been suggested that too high a tracking force is less wearing on vinyl than running too light and it seems to be sounding great when playing mostly 12 inch 45's which have a high level of groove modulation.

Thanks once again for all of your help but just wondering if anyone else keeps blu tak in their toolbox for other fixes?
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Old 21st Mar 2017, 9:34 am   #6
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

Quote:
Originally Posted by paulsherwin View Post
If it sounds better to you then just do it. 2g is a bit high for an AT95E though.
The point is, it may sound 'better', especially if things were so bad before, but if mistracking (not talking about resonance now) has been introduced as a result of mismatched cartridge compliance vs arm/headshell/blu tak mass, then the resultant mistracking can cause permanent damage to vinyl records, and that will be heard in due course, and permanently.

But in any case it transpires the OP is more concerned with uses of blu tak, and yes it has been legitimately used to bond cartridges to headshells while maintaining best operating parameters wrt tracking and resonance as I have described. The required scale of understanding to achieve that being the ability to add up three numbers and see where two points on a graph intersect. So in conclusion (my conclusion) my answer to the question "Is blu tak the magic cheapo option for non audiophiles?", my answer is, it is cheap, it does have its uses, but it's not magic.
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Old 21st Mar 2017, 10:22 am   #7
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

Quote:
Originally Posted by paulsherwin View Post
2g is a bit high for an AT95E though.
Actually, the manufacturers recommend 1.5 to 2.5g, so I'd say it's about right
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Old 21st Mar 2017, 10:32 am   #8
paulsherwin
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

That's true, but they tend to be used in better quality arms tracking at the lower end of the range. A budget arm needing a higher tracking weight would normally use an AT91, which also has a spherical stylus (and is cheaper of course).
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Old 21st Mar 2017, 10:37 am   #9
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

I use blu-tak from time to time to bodge in a cartridge to see if it will do the job in a particular set up. I haven't used it as damping but it makes sense to me.
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Old 21st Mar 2017, 11:20 am   #10
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

Now try playing a slightly warped record! (but use one you don't care about!)
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Old 21st Mar 2017, 12:04 pm   #11
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

At the end of the day it's a Bodge Job! If the original manufacture of the turntable had used Blue Tack to put the cartridge in the OP would be complaining of poor workmanship. If it came back from a repair workshop the same, you wouldn't go there again!

At the end of the day it's not like something has broke and there is no other way to solve the problem, but to use Blue Tack.

My advice to the OP is to remove the stuff and find a way to correct the problem in the right way.
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Old 21st Mar 2017, 1:07 pm   #12
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

Blu-tak is useful for matching the weight of cartridges in interchangeable head shells. If they don't match, changing the head shell will make nonsense of the tracking force scale. And I know for a fact that bright pink Plasticine was used inside the Garrott P77 cartridge for weight matching!
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Old 21st Mar 2017, 1:56 pm   #13
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Default Re: Is blu tak the magic cheapo option for non audiophiles?

In my experience headshells come in all sorts of shapes and designs, but speaking of damping headshells two companies come to mind, SME recommended using a small blob of there own damping compound (dum dum) between the cartridge and the beautiful but very resonant S2 headshell, Technics on the EPA-100 arm used rubber inserts to damp down the headshell rssonance.
The bottom end of headshells tend to be flimsy aluminium jobs that offer little damping of cartridge resonance, so by all mean use blue tack it will work, I used to use 1mm thick rubber sheet cut to shape and glued in the headshell this has the same damping properties.
Then of course you move right up the scale to beautifully cast (various metals and compounds are used) headshells that are very non resonant in themselves and well suited to moving coil cartridges etc.
So things can be tweaked I believe, a bodge? no not at all just recognising the short falls of a budget design and trying to improve it, I say well done, sit back and enjoy
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Old 21st Mar 2017, 2:45 pm   #14
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Default Re: Is Blu-Tack the magic cheapo option for non audiophiles?

I use Blu-Tack to hold turned pin IC sockets in place on a PCB until I've soldered a few of their pins.
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Old 21st Mar 2017, 3:06 pm   #15
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Default Re: Is Blu-Tack the magic cheapo option for non audiophiles?

I agree that pickup resonances are largely down to what's going on in the headshell and its interaction with the cartridge.

I found the headshell of my trusty Linn Sondek Basik arm produced slight metallic coloration in the otherwise excellent sound of the Ortofon MC25 moving coil cartridge. Some might say it's all part of the Linn Sondek 'pace & rhythm' character, but I find it sounds much better when properly damped by a penny coin stuck on with a thin layer of Blu Tack. Blu Tack damping is at its most effective when it's the filling in a sandwich between two layers of metal..

I can't readily measure the resulting mass, but the cartridge tracks well at 2.3g and measures within 0.5 dB 30Hz - 18kHz

The small ball of Blu Tack on the end of the finger lift is optional, but I feel it damps another potential resonance. Matt black paint finishes off the whole thing.

Photo attached.

As a general rule, Blu Tack customising looks much more professional when painted matt black.

Martin
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Old 21st Mar 2017, 5:52 pm   #16
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Default Re: Is Blu-Tack the magic cheapo option for non audiophiles?

That's got to be a classic picture! Talk about shades of Dansette. The real beauty of it is that any audiofule who doesn't understand the physics behind it would be horrified by the sight of it.

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Old 21st Mar 2017, 6:18 pm   #17
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Default Re: Is Blu-Tack the magic cheapo option for non audiophiles?

If you have a scope, you can measure the resonance. Sit the stylus on a play-out groove, motor turned off. Connect the scope to the headphone out on your amp, or directly to the phono out of the deck if you prefer. Tap the deck / thump the shelf / stamp on the floor.

(A physics interlude - the Dirac delta function, which has value at one point in time only and is zero everywhere else - contains all frequencies. This means it will (potentially) set off all resonances of a system, so long as you apply it in the right place. Since you only want low-freq info, a lo-pass filtered delta function - a woolly thump - will do you fine).

You'll see a (very) LF decaying sine wave on the scope - if it's very well damped, you might not see so many oscillations, and perhaps not even a complete one, but it's worth a go. Find the period T, and F_res is 1/T.

It's unlikely that there are any more-lightly damped electrical filters in the path, compared to the oscillation of the arm on the stylus compliance, but I guess it might be possible. If so, you'll measure them too...

cheers
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Old 21st Mar 2017, 7:15 pm   #18
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Default Re: Is Blu-Tack the magic cheapo option for non audiophiles?

Re Hartley and his Linn/ blu-tac/ coin combo and the countless aftermarket mods and enhancements marketed for the most expensive of decks, I find it really hard as a consumer to accept why very expensive (to me at least) and reputedly well engineered pieces of kit still benefit from this sort of thing.

I've seen the Linn arms being made, perfected and tested... no mention of blu-tac.

I suppose what I am saying is that is thinking of spending a decent amount of money on a good deck to last me many years, I can't believe that the 2/3/400 quid I may end up spending will still need to be topped up with 17p worth of blu-tac. This is exactly the sort of thing I want to avoid! I love my vintage gear, but I think vinyl is worth spending a bit on for the satisfaction of owning a precision item (I don't rate my chances of getting a vintage deck running as it should).

No criticism of this post by the way... I speak as someone who packed a load of the blu stuff into a Technics CD player in the 90s (it was free tac and I was advised by a proper audio engineer).
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Old 21st Mar 2017, 8:30 pm   #19
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Default Re: Is Blu-Tack the magic cheapo option for non audiophiles?

Couldn't agree more Martin. But this stuff is not rocket science, the turntable, arm, cartridge (and blu tak) need to be considered holistically. It's all very well saying that it sounds "ok", but basically, very basically, there's the tracking and resonance aspects to consider if one is looking for best sonic performance from the assembled components. The stated masses of all components is well documented (hey, we have the internet now, it's packed with data...) and all one needs to do is to take cognisance of the cartridge manufacturer's data/requirements and set up the arm etc accordingly. In my opinion there's too much reliance on subjective 'testing' (inexperienced, self believing audiophools) and not enough acceptance/uptake of the use of objective, measured results and the recommendations thereof. Honestly, you see more ridiculous arguments, statements and debates regarding how a certain amp may/may not 'match' a certain speaker (really, try adjusting the tone controls..) and yet the all important cartridge/headshell/arm matching/combinations are not given a second thought. Anyway, we're veering into serious audiophool territory here, and I'm not supposed to be here..
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Old 21st Mar 2017, 9:22 pm   #20
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Default Re: Is Blu-Tack the magic cheapo option for non audiophiles?

John Crabbe, then editor of Hi Fi News, published an excellent book called Hi Fi In The Home around 1968. It should be required reading for anybody interested in the subject. Some of the social references may seem quaint now, but it explains in a straightforward manner many of the wrinkles which some more recent recruits find hard to fathom, the present topic included. Available from all good charity shops...
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