Any Old Arm

[Thermionic]

How’s this for a bit of (old) sound art?

http://i161.photobucket.com/albums/t229/VPR5/OldArm1.jpg


It’s a unipivot pickup arm that I made at home and in my school’s engineering workshops in 1969. I must have been pretty keen on Hi-Fi as a schoolboy to make this alloy, brass and string concoction. It was though a fairly state-of-the-art device back then, in fact the most complicated arm I had ever seen, and was based on a design by Jack Bickerstaff published in the February 1966 edition of Wireless World.

http://i161.photobucket.com/albums/t229/VPR5/OldArm3.jpg


The outrigger weights give the arm good torsional stability, and the bias compensator (which I understand is unusual in any unipivot) is virtually frictionless. Unfortunately while cleverly designed to provide a varying amount of compensation as was the thinking in those days, this concept I understand proved to be incorrect. The plug-in lead out wires are single stranded enamelled silver and they exit the arm directly above the pivot for minimum torsional effects (screened leads exit from the base of the arm when in use).

http://i161.photobucket.com/albums/t229/VPR5/OldArm4.jpg


Of very low mass construction I used it with a Shure M75E for about 10 years, and once set up properly it proved to be a very stable and un-fussy pickup arm. In the late 1970’s I bought an Ultimo 20A moving coil and an SME 3009 II (improved), and since then it has mostly gathered dust as a quaint ornament and reminder of past times. (I did though modify it to sit on an SME base plate.)


http://i161.photobucket.com/albums/t229/VPR5/OldArm5.jpg

Today as I did a bit of restoration work on it I though it might be worth a post. I even contemplated slapping it on my 401 as a stand alone arm, mounted perhaps on something like a massive alloy block, but I assume it would not be worth the effort for the few MC cartridges I have at hand.

I wonder though how many other people made these beasts, and what happened to the ingenious Mr Bickerstaff…

[The Vinyl Adventure]

Not worth it!?
I find it fasinating how people with technical skills capable of producing such things look upon their creations as something that might be "not worth it" or the like...
Get the thing wired up and be proud of it is my thoughts on the matter

[Reid Malenfant]

:wow: You made that at school? :eek:

& they say exams aren't getting easier :lol: That just says it all ;)

Amazing looking bit of kit you have there, i'd be pretty proud of work like that :)

[Barry]

:eek: Wonderful - well done!

Just some questions:

(1) How is the cartridge attached to the arm?

(2) Why did you choose a three-wire arrangement?

(3) Any idea of the effective mass of your arm?

Regards

[Alex_UK]

I made a toffee hammer in CD&T - I feel ashamed - that is seriously impressive Gino.

[Barry]

I made a toffee hammer in CD&T - I feel ashamed - that is seriously impressive Gino.

You made a toffee hammer? All I ever made was a brass toasting fork, a boot scraper and a letter knife. Oh, and some bits for the school stage lighting rig.

But then I wasn't really 'into' hi-fi in those days.

How does your arm compare with a Jelco Gino?

Regards

[Techno Commander]

WOW!!!

Stunning work.

[Thermionic]

Thanks for the appreciative comments gentlemen, I am indeed rather proud of the aged beast and am wondering why I didn’t go on to pursue an engineering career. I was in the upper sixth and had free run of the machine shops and it’s only recently that I realised how impressive the facilities were in my big London comp (now long gone). I was going to do an A level in engineering but in the end didn’t bother, perhaps though not a bad thing considering what’s become of manufacturing in the UK.

In answer to your questions Barry;
1) I used a cut down SME finger lift as a top strap with the arm tube sandwiched between that and the cartridge.
2) I couldn’t fit more than 3 of the single-pole miniature connectors I had in the space available, and it didn’t hum noticeably with the couple of MMs that I was using. Actually it was an improvement on Mr Bickersatff’s more Heath Robinson lead-out wires arrangement.
3) Sorry, but currently I have lost track of the original article though I think it was much lower than anything else at the time; possibly 5 gm.

I am at the moment not very aware of the Jelco, having only seen images of it on this site and therefore can’t really comment. I suppose the biggest problem with the the Bickerstaff arm by modern standards would be lack of rigidity and it’s likely resonant behaviour. It has a thin arm tube (with 4 bends) which is just clamped to the pivot block with a bolt, and the counterweight carrier is held in by one screw. It was of course designed for minimum mass and pivot friction, and to achieve stability without the need for fluid damping. High compliance cartridges such as the V15 were becoming the fashion back then, and these sorts of arms were intended for them. It was also designed to be easily built without the need for precision engineering - everything being adjustable on installation.

So my assumption of lack of rigidity and resonances are what prevent me from taking the trouble to put it back into commission. Though it occurs to me that a more modern version with perhaps a stronger (straight-carbon fibre?) arm tube with beefed up pivot block, counterweight arrangement, and revised bias compensation might be a worthwhile project for a modern moving coil cartridge. The outrigger geometry did seem to work very nicely and I do still have a small lathe/milling machine. Perhaps a ‘Bickerstaff for the 21st Century’ would give me something to do this winter.

[Barry]

Hello Gino

Would agree your arm has low effective mass: no more than 5g, probably less.

The obvious arm with which to compare it is the Transcriptors arm, ostensibly they are similar. Unfortunately I cannot find out what the effect mass of the Transcriptors arm is/was.

Arms which have a similar low-mass 'look' about them are:

Hadcock GH228; 6.5g
Infinity 'Black Widow'; 3g (uses a graphite fibre arm)
Breuer Dynamic 5A; 4g (uses a large diameter, thin wall arm tube)
Mayware Formula 4 arm; 4.5g

If you can supply the dimensions and materials used in your arm, I could calculate the effective mass for you.

Incidently, bending the arm will not reduce rigidity: it will move the flexural and torsional modes to a higher frequency.

Regards

[DSJR]

Just try hard to find an Empire 1000ZE/X or an ADC 25/26 tracking at .7g. You'll be well able to use these with suck a low friction and low mass device.

[bigmoog]

what a lovely piece of (school) engineering.....beautiful.

reminds me of my metalwork and engineering classes,we had some great teachers and equipment. Although we would often just make weaponry for the after school fights:rolleyes:

I wonder if this kind of educational stuff goes on in our schools today (not the fights, the real quality hands on engineering etc)

[Alex_UK]

lthough we would often just make weaponry for the after school fights:rolleyes:

No one argued with me when I was packing my toffee hammer...

[DSJR]

I think there's basic craft teaching going on, but it's as much to do with "Design Technology" these days. My Yr7 son is designing the pattern to stich on a cushion he'll be making and is actually enjoying the process (mine was the last year - 1968 - where boys did only woodwork/metalwork and Technical Drawing and girls only did domestic science and needlework). His school has a good kitchen and woodworking shops and I suspect that all of these skills will be taught to some degree or other as he progresses through high school. I covered a Tech Drawing lesson last year for Yr8's so think that's what happens ;)

[The Grand Wazoo]

A little while ago, those that apparently know better decided that it was not necessary to have the requisite skills to make something but it was vital to know how to design it. So they got rid of most of the practical subjects in schools - woodwork, metalwork, home economics all that stuff was replaced by 'Design Technology'. This is why my daughter was once required to 'design' a sandwich.
I think I'd have preferred for her to make me a tonearm!

The crimes that have been committed upon our children by Governments in the name of improvement are unbelievable.

[Alex_UK]

I'm seriously thinking about home education for my Avatar when the time comes after reading this thread... :( There's only room for one geek in this house!

[bigmoog]

I think there's basic craft teaching going on, but it's as much to do with "Design Technology" these days. My Yr7 son is designing the pattern to stich on a cushion he'll be making and is actually enjoying the process (mine was the last year - 1968 - where boys did only woodwork/metalwork and Technical Drawing and girls only did domestic science and needlework). His school has a good kitchen and woodworking shops and I suspect that all of these skills will be taught to some degree or other as he progresses through high school. I covered a Tech Drawing lesson last year for Yr8's so think that's what happens ;)


gawd, I loved woodwork/metalwork and TD (Technical Drawing) :eyebrows:....happy daze with a knackered pencil and third angle projection and the teacher (a mr bettis...top geezer) yelling at me to 'use a 3H pencil, stanley, its not charcoal!!!!)......:)......

[The Grand Wazoo]

4H in my school!
I still have my Stabilo 0.3mm propelling pencil and a stock of leads for it.

[bigmoog]

4H in my school!
I still have my Stabilo 0.3mm propelling pencil and a stock of leads for it.


4H! you must have gorn to a posh grammar, us comprehensive boys had to make do......:eyebrows:

[Thermionic]

Anyway,

Barry, I think this design predates the various arms you mentioned, I dumped all my Hi-Fi News(s) of the period a long time ago so could well be wrong. Were not all of those arms of the 1970’s period? A name that does stick in my mind is Audio and Design, and I think they made a fluid damped unipivot in the 1960’s. There probably were others of course, including the Decca possibly.

Yes, I would be very interested if you could calculate a rough effective mass of the beast, approximate dims as follows:

Arm Tube Length (pivot to end of tube): 228mm, Dia. - 8.3mm, Wall - 1mm, Aluminium
Front Outrigger Weight: 19x11mm, 6mm Hole, Brass
Pivot to Counterweight Centre (typically 30mm)
Counterweight Rod total length - 60mm, Dia. - 6.5mm, Brass
Counterweight: 25x34x13mm, Hole: 11mm Dia., Brass
Rear outrigger Rod: 3.5x46mm, Silver Steel
Rear Outrigger: 13x10mm, 6mm hole, Brass

I take your point about the bends in the arm and hope the above is enough to go on.:)

[Barry]

Anyway,

Barry, I think this design predates the various arms you mentioned, I dumped all my Hi-Fi News(s) of the period a long time ago so could well be wrong. Were not all of those arms of the 1970’s period? A name that does stick in my mind is Audio and Design, and I think they made a fluid damped unipivot in the 1960’s. There probably were others of course, including the Decca possibly.

Yes, I would be very interested if you could calculate a rough effective mass of the beast, approximate dims as follows:

Arm Tube Length (pivot to end of tube): 228mm, Dia. - 8.3mm, Wall - 1mm, Aluminium
Front Outrigger Weight: 19x11mm, 6mm Hole, Brass
Pivot to Counterweight Centre (typically 30mm)
Counterweight Rod total length - 60mm, Dia. - 6.5mm, Brass
Counterweight: 25x34x13mm, Hole: 11mm Dia., Brass
Rear outrigger Rod: 3.5x46mm, Silver Steel
Rear Outrigger: 13x10mm, 6mm hole, Brass

I take your point about the bends in the arm and hope the above is enough to go on.:)

Yes, the Audio and Design was a damped unipivot (I still have mine) as was the Decca International (however I don't know the effective mass for that, or for the later London International).

It'll take me a little time to calculate the effective mass for your arm. Essentially, it entails calculating the moment of inertia of the arm about the pivot. The information you have provided should be sufficient.

Regards

[spendorman]

Nice looking arm, strange thing in the same year, 1969 I had just started City and Guilds Engineering at technical college. In the workshop time I built a uni pivot arm to a Hi Fi News design. The headshell, was cast in resin. I still have it somewhere, it wont be as shiny as your one!

It worked quite well fitted with a Shure cartridge.

[Rare Bird]

The obvious arm with which to compare it is the Transcriptors arm, ostensibly they are similar.



I thought of the Fluid arm straight away Barry.The kite shape headshells were really cool, believe it or not, i actually wore a hole under the armtube of my old fluid arm with the lift/lower gadget..Well you know how it worked.

[Barry]

Hello Gino,

I’ve managed to get around to calculating the effective mass of your arm. Expect you thought I would forget or give up? Well I wasn’t easy, but I have done my best.

Essentially the effective mass is the moment of inertia of the arm, about the pivot point, divided by the square of the effective pivot-to-stylus length (228mm for your arm). The difficulty lies in calculating the total moment of inertia, since the arm is made up of several components. The moment of inertia for each component (arm tube, counterweight, out-riggers etc.) about its own centre of mass has to be calculated, and then this value is converted to the value about the pivot point using the ‘parallel axis theorem’.

http://en.wikipedia.org/wiki/List_of_moments_of_inertia
http://en.wikipedia.org/wiki/Parallel_axis_theorem

Despite the elegant simplicity of your arm, I have had to make some (reasonable) assumptions and approximations.

The Assumptions
For the materials, I have assumed the following:

Aluminium
That this is HE30 grade aluminium, having a density of 2.7g/cc.

Brass
That this is ‘free machining brass’, having a density of 8.47g/cc.

Silver Steel
That this is what is known as ‘tool steel’, having a density of 7.83g/cc.

The Approximations
I have totally ignored the presence of the bias/anti-skating mechanism. I don’t believe it is considered when arm manufacturers calculate and quote the effective mass, and anyway it is too complicated a mechanism for me to calculate its contribution to the effective mass.

In the absence of dimensional or material information of the portion of the arm having a square cross section near the pivot housing, I have ignored this and assumed the circular cross section arm tube and counterweight stub are contiguous.

The arm tube is cranked. I have, by scaling off your photographs, determined the total arm length to be 235mm, i.e. the length the arm would be if straightened out. However in bending the arm, the moment of inertia relative to the pivot point is slightly higher than it would be for a straight arm. Not knowing the bend angles, I cannot do any more, so this approximation slightly underestimates the inertia.

I have also ignored the cutaway section at the end of the arm. In doing so this will slightly overestimate the inertia. The arm wiring has also been ignored.


No details were given of the front outrigger arm. I have derived some approximate dimensions for this, again by scaling off your photograph. I have thus assumed that the arm has a horizontal dimension of 21.25mm, a vertical dimension of 41.8mm and a diameter of 6mm (the latter based on the 6mm hole of the outrigger weight). Despite it appearing to be covered in a black plastic coating, I have assumed that it is made of silver-steel. This approximation may slightly overestimate the inertia.

I have taken into account the central hole in all of the counterweight and outrigger weights, but have ignored the presence of the (presumed) plastic insert allowing these weights to slide on their respective arms. These too, will slightly underestimate the inertia.

Dimensions quoted by you and those derived by me by scaling are shown in the marked-up photos below.

http://i780.photobucket.com/albums/yy88/barrydhunt/IMG-8.jpg?t=1286656020

http://i780.photobucket.com/albums/yy88/barrydhunt/IMG_0001-6.jpg?t=1286656686

Now there are two effective masses to be calculated, one for each arm motion:

(1) Pitch motion or the up and down motion, the arm will undergo when negotiating record warp,
(2) Yaw motion or motion in a horizontal plane, the arm will undergo when coping with record eccentricity.

These two masses will be similar, but not identical due to the arm’s deviation from axial symmetry.

Without going into the full details of the calculations (some nine pages worth!), I’ll simply state the results. Should you care to check them, the method is explained in the two references cited above.

For pitch motion the effective mass is 4.9g. For yawing motion the effective mass is 4.4g.

For a figure to use in order to calculate the cartridge/arm resonant frequency, take the root-mean-square, say 4.65g.

Since I have made some approximations, which will underestimate the effective mass, it might be a good idea to add roughly 10% and call it 5g. This is still a very low value; so your design is a very good one. Well done!

Effective mass = 5g

Remember that the arm/cartridge resonance frequency depends on the square root of the product of the total mass of the arm/cartridge combination and the (dynamic) compliance of the cartridge stylus suspension. Relative error in the resonance frequency will be half the sum of the relative error of either the mass or the compliance. It is quite likely that any quoted compliance is only accurate to 20%, so with a possible error in effective mass of 10%, the uncertainty in the calculated resonance frequency will be no more than 15%, that is, for a calculated figure of say 10Hz, the resonance frequency could actualy lie anywhere between 8.5 and 11.5Hz. Also, assuming the presence of viscious damping grease about the pivot, this will tend to lower the resonance frequency as well as, of course, reducing the amplitude and Q-value at resonance.

Trust all of this is of some help

Regards

[Alex_UK]

Respect, Barry - the knowledge and expertise on this forum is just amazing.

[DSJR]

Nice looking arm, strange thing in the same year, 1969 I had just started City and Guilds Engineering at technical college. In the workshop time I built a uni pivot arm to a Hi Fi News design. The headshell, was cast in resin. I still have it somewhere, it wont be as shiny as your one!

It worked quite well fitted with a Shure cartridge.

It's long lost in the mists of the mid eighties now, but the 401 I had given to me (and is now lost in an audio archive somewhere) came with another Hifi News designed unipivot, which looked suspiciously like a Hadcock (this latter may just have been developed from it for all I know), fitted with the then ubiquitous Ortofon VMS20. I just didn't have the room for the thing and the LP12 "programming" was still too strong then, so I asked my "museum owning" mate to store it for me. As of a couple of years ago, he had no recollection of it (and I do trust him).

[spendorman]

It's long lost in the mists of the mid eighties now, but the 401 I had given to me (and is now lost in an audio archive somewhere) came with another Hifi News designed unipivot, which looked suspiciously like a Hadcock (this latter may just have been developed from it for all I know), fitted with the then ubiquitous Ortofon VMS20. I just didn't have the room for the thing and the LP12 "programming" was still too strong then, so I asked my "museum owning" mate to store it for me. As of a couple of years ago, he had no recollection of it (and I do trust him).

I will look for the arm that I made to the Hi Fi News design. I know that the headshell got broken as I did not protect anything whilst not in use. If I find it, will take some photos.

[spendorman]

http://farm5.static.flickr.com/4126/5068062560_dff0ce8c70_b.jpg

http://farm5.static.flickr.com/4113/5067451353_6757c9890d_b.jpg

Dirty, broken headshell and missing lever for lift lowering device.

[DSJR]

You know, with a polish up, a re-wire and a rethink on the counterweights, you could have a really good tonearm there.

[spendorman]

You know, with a polish up, a re-wire and a rethink on the counterweights, you could have a really good tonearm there.

And a headshell!

In fact it was used with a 401 and gave good results, doing a good job of HFS 7?