A unipivot made from scrap

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Ant
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#136 Re: A unipivot made from scrap

Post by Ant »

Hmm. This perspex I have is far too flexible...
Lets have a rethink
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#137 Re: A unipivot made from scrap

Post by Ant »

Found a thin strip of walnut and planed it down to 6mm, i'll use that
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#138 Re: A unipivot made from scrap

Post by Ant »

got the wand pretty much done, the stubs need gluing in with some epoxy

ImageDSC_0615 by anthony cresswell, on Flickr

this is the original

ImageDSC00975 by anthony cresswell, on Flickr

the black perspex was far less stiff than necessary, perhaps the doc can tell me what sort of perpsex to look at
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#139 Re: A unipivot made from scrap

Post by IslandPink »

Cripes ! Shoddy at the speed of light :shock:
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#140 Re: A unipivot made from scrap

Post by Ant »

Got the mk3 wand finished and wired, need some tags and a connector so it can be plugged into the same box as the current wand.

ImageDSC_0622 by anthony cresswell, on Flickr

Also remembered to add a fingerlift this time.
The bearing housing is turned to the same dimensions as the mk2 wand with the stubs exactly the same lengths and in the same positions relative to the bottom edge. The groove in the side is in the same position relative to the bottom edge, with the inspection hole moved around to the side and a little bigger so that its easier to see the bearing pin, which again is in the same position as the mk2. The only other difference is that the housing is 3mm shorter in height. This is so the underside of the flat wand is in the same position as the underside of the perspex deck on the mk2 headshell so that the cart is in the same position as the mk2. It weighs almost exactly the same as the mk2 bearing housing, the loss in height offset by the lack of a hole for the arm tube to fit through. So as close as possible to the current spec, any difference will be purely in the wand

ImageDSC_0623 by anthony cresswell, on Flickr

I laced the wire through some small holes in the wand so that the main stretch is held taught underneath the wand but the ends are able to be moved around without loosening it off. Quite a neat job if i do say so myself. Wether it will pick up a load of hum is anyones guess, but the air bearing arm I had on loan was the same wire without shielding and that didn't hum, and the long loop hanging out the back of the current wand doesn't seem to pick anything up either so it might be ok.
There is a different counterweight on it which is not as large to avoid the issue with the mk2 counterweight clouting the base if being abit cack handed when cuing it. I can put the other one on it if I want, to maintain continuity between the mk 2 and mk3
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#141 Re: A unipivot made from scrap

Post by Ant »

Ok. Finished the mk 3 today and had a listen. Some good points, it is abit more stable over warps than the mk 2 as the azimuth weights are a fair bit lighter on this one due to the tapered shape. Its bass tone is marginally better than the mk 2.
The downside is that it doesnt sound as well balanced as the mk 2.
Its abit softer, leading edges aren't as well defined, its not as clean.
I have this idea of what I wanted from it in my head, the improvement I wanted over the mk 2, and it isnt it.

However, it does have more body to it, and it is nicely dynamic, quite punchy.

This is with the at 150 in it, with the atf7 in it it may be a better match. The mk 2 can be a little cold with the f7 in it at times.

Its a touch too warm as it is.

It did solve the clearance issues the mk 2 has.

So ive sorted out the fingerlift on the mk 2 with a wire hoop, but the lighter counterweight off the mk 3 is stuck abit further out than I would like on the mk2 so i think ill need to make a heavier one that isnt so wide to solve that issue properly.
Mk 4 will go back to either a tube or a flat wand of a different material
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#142 Re: A unipivot made from scrap

Post by IslandPink »

I think there was some background on the design of the Talea
http://www.durand-tonearms.com/About/about.html
tonearm, poss some stuff that has since been removed from the website ..
about how non-cylindrical wands had a poor ( ie. non-harmonic ) resonance signature which detracted from the musical tone. However, you had one before that was like the 'Cantus' that was also flat, did you ? - how was that ?
Other q. - did you use Danish oil to deaden the wood , like Schroeder does ?
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#143 Re: A unipivot made from scrap

Post by Ant »

Yep it was soaked in danish oil like the mk 1 and 2.
Musically its fine, actually a little better than the mk 2, its the fact that it seems to smooth over the subtleties that the mk 2 doesn't. Its a little 'slow' if that makes sense.

I think its a resonance in the wand thats bouncing front to back.

Originally I was going to drill out the wand in various places to break up resonances in it, but i decided to start with it solid, so I could tell if there were resonances that needed kerbing in the first place.

The wand will not have uniform density, but it will have boundaries within it i.e the grain, the lighter coloured heartwood and the older darker parts will have different densities and will 'channel' certain resonances.

Plan is to drill it out in several places and see what happens
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#144 Re: A unipivot made from scrap

Post by Ant »

As its thrown it down on and off all day today making work outside impossible, I decided to go back to the modded rega arm.
Ive done this as a control, i.e the modded rega was the yardstick in the first place, so I think that in order to move forward with the design I need to listen to it again and see what progress ive made.
I have rewired the rega again, ive put the same wiring in it that the mk 1, mk 2 and mk 3 have so that im comparing apples with apples. Same internal wiring and the same output cable connects all 3 arms.
I'll make a new base up for the rega thats the same material as the unipivot base when i get around to it too to get as many things as equal as possible.
Ive also ordered some 8mm stainless steel tube for a mk4

To be continued......
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#145 Re: A unipivot made from scrap

Post by Ant »

Had a couple of hours with the modded rega back in place and Its kind of a blunt instument compared with the cx mk 2 wand. The modded rega is kinda... Well bland for want of a better word. Its well balanced, but hifi. Not really very dynamic. In a word, its still abit rega.
The mk 3 wooden wand is close to it, abit more euphonic. The bass on the mk 3 is abit bloated compared to it.
The mk 2 is much more solid sounding, its surprising how big a difference there is in terms of pitch stability from having the pivot point in line with the stylus.
There is abit of bloom in the bass with the mk 2 compared with the rega which id like to reduce abit.

So, conclusion is that the mk 2 form is the way to go for me. The modded rega is too hifi, the mk 3 too uncouth and nor well balanced enough, without the deft touch the mk2 seems to have.
The rega is abit dead, the mk 2 is alive.
So mk4 will stay on the mk 2 path in terms of design as I think I was on the right track with it.

Things im going to look at are the base and arm pillar, maybe a threaded pillar so that it can be locked in place with a threaded insert in the base and a locknut on the pillar ( note to self, see if i can get it chromed after drilling the cup in the end)
And the headshell. And make a threaded counterweight.

Ill leave the rega on the deck for now, its much more user friendly than the mk 2 and might reduce the chance of breaking the at 150, much less brown trouser using the regas arm lift/lower than hand cuing the wibbly wobbly mk2.....
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#146 Re: A unipivot made from scrap

Post by Ant »

Having had something of a lean period in terms of work, I decided to revisit the unipivot. I had some other ideas for it over the last couple of months, and having had the md65 lathe for a good while I decided to use it for this project. Or series of ideas rather than project.

So having got hold of some 25mm round steel bar, and an electric sharpener that I got for drill bits and wood chisels and modified to allow me to sharpen the metal lathe tools, I thought I'd build the ideas I had into something. To see if it would work.

It's taken about a week on and off to make all the parts, probably about 8 hours work in total. I didn't want to buy any bits in, I wanted to make them myself because I'm stubborn. Only thing left to make is the bias weight. All turned from steel apart from the headshell which is made from 3mm aluminium to keep weight down.

A collection of parts
ImageCx unipivot mk iv by anthony cresswell, on Flickr

Built up into the arm
ImageCx unipivot mk iv by anthony cresswell, on Flickr

The part not fitted is a heavier counterweight. The fitted on is 75g, the other is 100g

a top view
ImageCx unipivot mk iv by anthony cresswell, on Flickr

The cylinder stuck out at an angle is the setscrew for locking the arm height. I borrowed this idea from the audiomods arm as it is alot easier to get hold of rather than fiddling with an allen key or screwdriver to lock the arm in place.

and a side view
ImageCx unipivot mk iv by anthony cresswell, on Flickr

This is an inverted bearing, the spike is fitted into the arm wand pointing down, an sits in a cup in the top of the arm pillar. this can be filled with silicone fluid to damp the pivot, same as the original. I also kept the wire arm rest and bias weight 'thing' of the original as it was nice and simple

original
ImageLenco with u/p mods by anthony cresswell, on Flickr

This one however does not have the bearing pivot point at the same height as the stylus, as this led to unpredictable azimuth on stuff that was quite warped, so the pivot is set just a little higher than the top of the arm tube to get all the weight lower than the pivot. There were ways around this characteristic, by moving the weight around and reducing weight above the pivot, thats for the next prototype.

The problematic bias location on the original has been moved so that it follows the Hadcock pattern of being on the left rather than out of the back of the housing as on the original. this caused issued with setting the cart tracking weight and was too fiddly.

the counterweight is not dropped and is on axis with the main arm tube instead, as I wanted to separate the azimuth and the tracking weight adjustment. The azimuth is adjusted by the two weights on the left and right of the bearing housing and is much less fiddly than skewing the main counterweight off to the left or right, and gives plenty of clearance at the back which was a problem with the original, plus, the majority of the weight of the assembly is lower than the pivot on this version so its not necessary from a stability point of view.

The arm tube is a composite of 8mm stainless tube at the back and Makore hardwood at the front. The idea was gotten from an origin live arm that uses aluminium and carbon fibre sections to alter the resonance of the arm, and I liked the wood and steel idea. the wooden section was turned on the wood lathe into a larger blank, which was turned down on the metal lathe so that a 30mm section could be glued into the steel, then it was all turned and trued on the metal lathe into a complete wand.

To get the headshell on, I bodged myself a rudimentary milling machine out of the pillar drill and an old lathe cross slide. Stuck a twin flute router bit in the drill chuck and used the cross slide to mill the 3mm deep section out of the end of the wand. Worked perfectly. No good whatsoever for metal, but fine for this particular job. It was spot on for drilling out the holes to make the bolt slots in the headshell though, it meant that the chain of holes were positioned perfectly.

One thing I did forget to do was to drill out the inside of the wooden section of the arm tube to take the wiring, so I'll have to tape the wiring on the outside to test it. There is always something.......

It took abit longer than strictly necessary to make the parts, but in my defence, I needed to get a feel for the lathe and how the steel turned having not really made anything in steel on it other than some really small things where dimension weren't important. Also used a shit-ton of wd40 as cutting fluid especially when boring and tapping as the proper stuff I ordered still hasn't turned up... Martin at the local engineering place suggested it in the interim as he didn't have any I could buy, he just had a huge great drum of the stuff that they use in the workshop. Worked nicely though.

I also got an aerosol air duster to blow the chips away at his suggestion, they use an air line, but also have some of these knocking about for if the air line is in use on something else. A quid from the local pound shop, it was really useful. Nothing worse than the chips building up on the tool and sticking to the cutting fluid so you cant really see the cutting edge of the tool, the steel cut fine dry on the exterior cuts but abit of fluid was needed to get a nice fine finishing cut. The interior boring needed loads of fluid though, you can feel it when it needs abit more.

Haven't got the hang of thread cutting with it yet though so I just used taps this time. Need more practice....
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#147 Re: A unipivot made from scrap

Post by Neal »

Nice one Ant, any listening impressions yet?
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#148 Re: A unipivot made from scrap

Post by Toppsy »

Nice one Ant,
I like what you have made a lot. Shows you have put a lot of thought into the design and your lathe machining skill sets are improving. Keep it up.
As you may be aware I am a fan of the uni-pivot arm, though they are a real pig to set up. Well my Hadcock arm is. Looking forward to your report on how the arm sounds and perhaps compares with commercial uni-pivot arms.
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#149 Re: A unipivot made from scrap

Post by IslandPink »

Wow ! :D - nice work.
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#150 Re: A unipivot made from scrap

Post by Ant »

made the last of the arm parts today and permanently assembled it. The stub and wand are epoxied into the bearing housing to make sure everything is rigid rather than just using setscrews

Made the mounting plate (wrong wood, I couldn't find the bit of Makore big enough for this bit...) which is glued to the steel height adjuster base, and the bias weight. I ended up with a 3.5g bias weight after checking the figures with the James Kogen bias research paper, this gives a bias range of about 0.75 to 2.4g bias which is plenty of range.

also made a new bias guide as I wasn't happy with the loop one. the new one presents a smoother travel for the string as it's a smooth curve rather than the tight bend in the first one, and it allows the string to run at the same height as the bias arm which is in line with the pivot point so the pull doesn't affect stability. Now it doesn't affect the azimuth by pulling it upward either.

ImageCx unipivot mk iv by anthony cresswell, on Flickr

I also sorted some wiring out, this needs a terminal box making for it so it can be connected

ImageCx unipivot mk iv by anthony cresswell, on Flickr

onward!
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