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Old 19th May 2002, 10:50 PM   #1
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Join Date: Jan 2002
Location: Canberra, Australia
Default What to do for a tonearm?

Being a medium impoverished audiophile just starting out in vinyl, what am I to do?

I've been fortunate enough to snag a Technics SL120 and will likely get an Ortofon MC20 Supreme to use with it.
My problem is the tonearm. (SL120 has a blank armboard recess so it will fit prety much anything.)
At present the deck has an ARC ALT-1 arm. Not bad, decent bearings but a trifle lightweight. (Doubt it will balance the MC20)

The deck itself is pitch stable, hum free, bearings are in top condition and it's as silent as the grave. No rumble, no grind, no ringing. I'm very happy with it.

What are my arm options?

I'm more than happy to consider second hand arms and given the finances at present, don't have much choice. $250 US will be the limit of my budget. The other problem is that I'm in Australia. Don't get me wrong, lovely place and all but less population means less second hand gems.

Every second post in Netland seems to rave about OL modded RB250's. Ought I just hold off for a year till I can get one of them instead?

TIA

Drew

NL: Oscar Peterson plays Rogers songbook, Queen Innuendo, DSOTM
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Old 21st May 2002, 01:34 AM   #2
dice45 is offline dice45  Germany
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Join Date: Jan 2002
Location: Munich, Bavaria
Drew,

The MC20 supreme is neutral, musical, detailed. Slender, fast low end.

The Ortofon MC20 supreme is a very stiff / low compliant cartridge. Not as the Denon103, but stiff enough to bring any lightweight arm into trouble. Including the OL Rega250. Concerning the raves, well, in its price category the Rega has no real competitor. Not yet.

Suggestions:
build yourself a DIY unipivot arm, scan this forum of my other unipivot posts, there are a few and then come back pester me with QQ.

Or
build yourself a Ladegaard linear tracker.
There is a lot of info about it on the web.

Or
wait a bit and and build the DIY version of my mechanical linear tracker.

I hope to have a demo unit ready by August this year, maybe earlier, i want to show it at the Aarhus Triode audition festival (provided professional duties leave me enough time for that).
I plan to make it available as a kit with the two dimension-critical assemblies already mounted/glued together.
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Bernhard
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Old 21st May 2002, 04:32 AM   #3
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Location: Canberra, Australia
You serious that a homebuilt wood unipivot will outperform an RB250??

Don't be offended by the above but I have to say I find this hard to believe.

Either Rega and the rest of the arm producing world have no idea or something's seriously wrong in the world of hifi.

I've been contemplating the hardened steel spike of an engineers scriber as a nice pivot point. Didn't realise that you could just walk into your local watch repairers and buy jewel bearing cups off the shelf.

what's the current advice on types of wood to use? I'm thinking dense and non-resonant would be preferable. Jarrah, mahogany, ebony?

I think I'm right in thinking that the armwand central axis should be exactly in line with the bearing point and the counterweight should be underhung of course.

Guess I'll copy the distances and angles from my current arm. looks like the only issue where I currently have no idea is wrt anti-skate. You see the string and weight Heath Robinson affair pretty regularly but I'm still not exactly clear on the mechanics and the geometries.

I'll bug you folks again once things are more advanced.

thanks for the help

Drew
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Old 21st May 2002, 03:11 PM   #4
dice45 is offline dice45  Germany
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Join Date: Jan 2002
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Drew,

the advice was given lightheartedly but i meant it dead-serious

J.Epstein had a pivoted arm on his Teres before he built his Ladegaard airborne linear tracker (which costed him less than US$100). Dunno if he owned a Rega, but several other Teres owners do own it and i must presume he knows the Rega well from listening comparisons. Well, AFAIK, he sticks with his Ladegaard. And Thomas Mayer (vinylsavor) reported he was very happy with the sound of Jeremy's setup and the arm would work well. Pleasant, involving, transparent, terrific PRaT, not annoying at all.

Another story, on my TT there is an Ortofon Rohmann running which i bought from my friend Hartmut (hifidaddy) who is a tonearm expert with huge practical experience. At the time he sold me the cartridge, he thought it would not be that stunning and i wanted it badly, i just knew it is a stunning cartridge. At this time he was toying around with a Rega 250 and Rega 300 (Hartmut, please correct me if my memory fools me) and he tried out any modification kit on the market inculding self-designed parts and loving/caressing bearing re-adjustments. It more and more turned out to be impossible to tune the Rega to (almost) SME V level which was the initial goal. It turned out that the Rega does not have what it takes to guide a low compliant MC cartridge and to make it bloom. the arm wand is way from being stiff enuff. UNable to handle the inserted energy. Low end is a gooey mess. And treble end also has room for wishes left. Nice midrange.

Hartmut blamed the Rohmann for what the arm was guilty for. And sold it to me . And told me later he could kick himself when he heared it at my place.

Well, not a bad goof, Rohmanns can be bought both used and new and have proven to be awfully consistent. I am confident any replacement Rohmann will run just as fine. This will be the 1st cartridge in my life i buy a 2nd time.

Quote:
You serious that a homebuilt wood unipivot will outperform an RB250??
I am dead serious that a well-built DIY unipivot beats the Rega concerning $$$ (as a Ladegaard will do).
Provided you follow the advice given in the other unipivot posts of this forum, I am optimistic that your 2nd or 3rd try produces an arm wand usable for MC and sporting an impressive and detailed low end.

I am dead-serious the Rega will not come close to the midrange and treble resolution of a well-built unipivot. And same with pace, rhythm and timing.
What i can tell fromown experience with Hartmut's Rega is that it always was boring. I did not step closer, i was not interested.

Quote:
Either Rega and the rest of the arm producing world have no idea or something's seriously wrong in the world of hifi.
Rega has quite a clue what they are doing, consider it is a budget product and they still exist and prosper. It is a budget product not having competition due to a market not any longer considered to be worth worked on further by other companies. The other arm manufacturers, well, better ask Hartmut, he can give you details, there are not many arms he keeps for himself, most ofthem he buys, evaluates and sells them again. And then, look at other forums, there is is a huge crowd fervently seeking a religion to follow and to be its new priest 2 weeks later. But few trace of own experience reports, most people just believe what a friend of a friend told.

As soon as you dare to build your own tonearm, you are starting to gain own experience and to know what you like and what you are talking about. and you cease to be intimidated by common sense and public opinion.

Quote:
I've been contemplating the hardened steel spike of an engineers scriber as a nice pivot point. Didn't realise that you could just walk into your local watch repairers and buy jewel bearing cups off the shelf.
Yes, you can do that. You can even take a knitting needle and wood (or maybe a tiny piece of PTFE) as bearing. One guy did so and was surpised over the sonics of his $5 unipivot.
But you can do even better, go to www.smallparts.com and order their catalog. Lots of inspiration there. And AFAIR, they have a vee jewel bearing, consisting of a vee cup made from synthetic sapphire and a a pivot pin made from stainless steel and the tip radii of cup and pin are made so that they perfectly fit together. Just for the case you want a unipivot with high-Q and low damping and hence high decoupling of audio frequencies.

Quote:
what's the current advice on types of wood to use? I'm thinking dense and non-resonant would be preferable. Jarrah, mahogany, ebony?
Bamboo? Framework of matches? Virgin bone? Who knows. Have to try that out myself. But i do know that the arm wand has a big influence on sonics. Different wood densities have to be tried out and resonance behaviour is unpredictable.
Witchcraft something appearing terribly resonant could turn to have gorgeous sonics.

David Shreve modified his Rabco SL8 linear tracker. He tried a wide variety of materials and shapes and ended up with a combination of basswood and balsa.
Very lightweight, but David is a fan of the Shure V15 which needs vertical effective in the region of 4 grams. For a Koetsu or Ortofon, i am sure he would end up with other arm wand constructions.

Also a possible option is thin airplane grade plywood, over here it is available both in beech and in birch. Maybe a combination together with balsa makes it? i will try it out. Yes, and lacquer one sample with snake oil, oops, should read Ennemoser C37

Do not skip metal tubes. Alu, stainless steel, titanium, yes, even brass is worth tobe tried out. Bamboo (oops mentioned it already). Carbon fibre tubes like sold by kite shops, or maybe u have an old/broken golf bat you could salvage the tube.

Hunch: avoid pure carbon fibre tube, too resonant. Better combine it with other materials.

If you do a bit of brain sports, you can figure out how mount this bearing into the arm wand in a removable way so that you can try out different arm wands to meet your sonic expectations.

Quote:
I think I'm right in thinking that the armwand central axis should be exactly in line with the bearing point and the counterweight should be underhung of course.
The bearing point should be level with the record surface. Its height should be adjustable for VTA adjustment (VTA: vertical tracking angle).
Counterweight: should be located in a way that the tonearm's center of intertia is slightly below the bearing point.
And as you will find described in my other unipivot posts, the arm should have additional sideweights mounted as close as possible to the bearing point which increase the rotational moment of inertia (i mean the azimuth orientation) without affecting the vertical effective mass.
Without those sideweights, sorry, no real low end sonically.

Quote:
Guess I'll copy the distances and angles from my current arm.
Good idea.

Quote:
looks like the only issue where I currently have no idea is wrt anti-skate.
Not a big issue. Antiskating has to be adjusted by ear anyway. Do not hesitate to ask as soon as you need it. I can tell you what to listen for. If i haven't described it already on my website then.

String and weight is not a bad idea at all. AS varies between 91 and 100% of its maximum value. In a 1st approximation we can assume AS force as constant (always presumed that friction force is constant which i doubt to be the case, so let's talk of the average friction force). So if the string is pulling from a vertically oriented cylindrical surface, it will work better than most commercial tonearm's weird AS mechanisms. If one wants to do it really precise, one can use a rim with an outer groove milled to variable depth according to the angular AS function. But then the rim and the position of the string has to be properly oriented.
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Greets,
Bernhard
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Old 22nd May 2002, 05:51 AM   #5
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At this point (and for the sake of my wife) I don't think the parallel tracker option is for me.

Done a lot of reading of the other diy tonearm posts though.

I see what you mean about the sideweights. The physics is simple enough too I guess. The weights seat the arm more firmly on the pivot point and oppose horizontal vibration while at the same time havng almost no affect on the arm's effective mass. Neat. And so simple once someone else has figured it out for you.

I'll do some designing and see what I can produce in the garage.

thanks for the input.

drew
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