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Adding mass to a tonearm. Best principles?

Mike Reed said:
Should help with those torture tracks though.

Someone here is going to say "change cart's round" or simply "take the Proteus off for a rest and put the K on the gimballed arm" but setting up cart's (even with my Dr. Feickert) is very tricky for me, esp on my rear (unipivot) arm because of eyesight, along with dotage. Answers on a postcard? :)

I like the heavy screw idea, but they'd need to be around 3 g each ! Is that possible?
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Mike, I totally sympathise with that dilemma, having sight in only one eye and advancing years.

A couple of weeks ago I wiped out a brand new Ortofon Cadenza Bronze with less than 20 hours on it while trying to fit a Cadenza Mono in my second arm. I was having Hum problems fitting the Mono and getting frustrated so was doing comparisons with the Bronze. Trying to be careful I was refitting the stylus guards, but managed to bend the cantilever that then dropped off when I touched it with a stylus brush. I don't think it was entirely my fault as the stylus guards seem a very tight fit on the Cadenzas now. My previous Blue was no problem through 8 years of use and this is the first cartridge I have damaged in over 45 years. I contacted Henley and although they didn't believe there was a problem with the guards they did give me a bigger discount on a replacement after the usual trade ins. Still a very expensive accident leaving me about £750 down as not covered by my house insurance. I have very nervously fitted the replacement yesterday OK, but I'm now leaving the stylus guards off.

Not sure about using these heavy thumbscrews that stick up above the Headshell as they could possibly cause resonance problems? You only have to look at some resonance plots of headshells with and without finger lifts to see the difference.
 
You can get smaller fasteners in selection boxes from DIY shops, CPC etc. They often favour the smaller sizes because it increases the piece count within a smaller box. As a result I have M3, M2.5, screws to cobble dogs. These selection bozes are extremely useful for all manner of DIY purposes and a vast improvement on having to go to the DIY shop and hand over £1 for 4 items in a plastic bag. The more common sizes (M6, M5) get used up fairly quickly, usually in time for the German discounters to have another DIY special so you can buy another box.

If you know the sizes you want and head pattern drop me a line and I will have a rummage through the things.
 
A nice small metal plate, inline with the COG of the arm...

Recently lost the screw in arm lift on my 12" kuzma unipivot. Tiny thing 15mm of threaded 1.8mm brass with dipped rubber cover on the end. 30 quid for a new one. Marker penned sawn off cocktail stick does the job, had to adjust tracking and azimuth.
 
poco a poco said:
Still a very expensive accident leaving me about £750 down as not covered by my house insurance.
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Surprised by this, as most decent contents insurers give accidental damage to audio and video. There's the excess, of course, but that's usually <£100 and for under a £1K claim or so the premium isn't usually adversely affected.

Tricky thing, changing/fettling expensive coils and whereas some guards are good/easy to fit and remove (Lyra, Koetsu), some are awful (Transfig.). Benz don't even have them ! I leave mine off unless actually connecting to pins when installing, then off, of course for the geometry etc. and left off.
 
I built a 4 sided carbon box to protect my Benz LP, it flexes to squeeze the sides if the cartridge to stay in place and is deep enough so the bottom can never touch the canti, as the top edge placement is defined by the underside of the head shell.
 
Rockmeister said:
My SME M2 9 is quite light at 9.5g mass. It makes it edgy for some cartridges, esp those that are both light and low compliance (I'm thinking of a Lyra Delos which is not a perfect match as is). Ideally I'd like to add 7-10 grammes mass to the arm.

Reading around, the wisdom seems to swing from 'bung on a heavy headshell', to counterweight additions.
I think I can see that anything that causes the counterweight to be placed further back (like a heavy headshell would do) is not an ideal solution, so the added mass needs to be near the bearings...as near as possible. So? Behind the bearing assembly, (but is this in the right place, behind the balance point, to do any good)? Or maybe just in front of the bearing wrapped around the arm tube itself?

I have in mind cutting to size and weight some simple lead sheet (plumbers roofing repair type stuff) which has the obvious advantage of weight with little bulk, and the ability to stay in a shape (and hopefully, in place) once formed...I'll simply bend it around the arm tube.

All thoughts welcome. The present cartridge is also 'just' in the green OK resonance zone, so I'll try the final theory out on it and report back. Currently at 11Hz resonance, I can move it into the magic 'perfect 9Hz' zone by adding 8g.
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Rockmiester I fear you are going down the wrong path.

If I understand correctly, your arm - cartridge combo is having trouble tracking certain records; they sound edgy. If this is so it is a case of cartridge mistracking and has nothing to do with the LF arm-cartridge resonance. It is possible be that the arm tube is skewed, but that is highly unlikely. Many MCs are prone to mistracking, perhaps that is what you are hearing. I haven't used an MC for many years for this very reason. Bear in mind that when a cartridge mistracks, it damages the grooves. It would be helpful if you would give us the exact make and model of the cartridge(s) that is (are) giving you this problem. In the meantime, we can take a sample cartridge and do some sums to show you that added mass is not needed; indeed it is likely to be detrimental to the overall performance of the rig.

Let's pick the Ortofon Cadenza MC as an example. According to Ortofon's data sheet: C = 12 micro-m/mN and m = 10.7g = 11g (approx). Unfortunately ortofon do not specify whether this is lateral or vertical compliance, or an average, nor do they specify the frequency. Let's pretend it is vertical compliance, near the LF resonance for that is what matters. So we have effective m' = 21 g & C = 12 micro-m/mN. A bit of arithmetic gives a us an LF resonance frequency of approx. 10 Hz which is almost perfect! Your 11 Hz is even better, why would you wish to add mass to the arm to lower the LF resonance to the sub-10 Hz range where record-warps are worse?

A suggestion: Use a test record to check tracking and LF resonance. Only then will you be able to diagnose the actual problem.

Please play a badly warped record with your current rig. When going over sharp bumps, does the arm move up and down as it rides the bumps while the cartridge cantilever remains steady, or does the arm remain steady while the cantilever flexes to accommodate the bumps? Please report back and we can analyse further.


Edits:

P.S:- IIRC, an article published in the AES Journal back in the 1970s concluded that the optimum frequency for the LF resonance was around 12 Hz. It may have been by James Kogan of Shure.

P.P.S:- Poul Ladegaard of Bruel and Kjaer recommended even higher resonance frequencies. See: http://www.laudioexperience.fr/wp-c...-Resonances-in-Turntables-AN17-233-1977-1.pdf
 
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Just thought I would add something here with an "ultimate performance" viewpoint: Adding so-called mass to a tonearm is always going to be a compromise, as has been stated above. No one really talks about stored energy and its effect on analogue playback. Certainly what you don't want to be doing if you can help it is to be adding mass, especially where it is not desirable. As I said earlier, it is best to select a cartridge that will match the tonearm you have, without adding any mass. We are really spoilt for choice these days with so many good cartridges available, so finding one that perfectly matches should not be difficult.
 
A few quid for a weight vs a new arm, or suitable arm per cartridge/s.

Blimey you exist in rarefied air G. ;-)
 
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