A unipivot made from scrap

Love it or hate it, it just won't stop
Ant
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#316 Re: A unipivot made from scrap

Post by Ant »

Well after a week of faffing about with it i think im happy enough with it.

Ive gone through 4 of the 5 carts i have on hand a few times and can easily tell the differences between them, and tried different setups. I.E nose down (92 ish degrees), nose up, different bias settings, and come to the conclusion that setup snaps in where you would expect it to with each cart, and that changes are audible.

So its doing what its told and behaving as expected

At the moment im running it with the 760 in it, and the jbe/air arm/at33 combo into the cole. The 760 is running into the 47k input and as the at33 is on the end of nicks ha1 head amp, which probably doesnt really care what impedance it runs into, is on the 33k input.

The setup has been a pain in the arse as the feickert relies on its pin being sat directly on the pivot axis to line up the overhang point.

Problem is that because the bearing is just over an inch below the top of the housing centrepoint, that the azimuth has to be set first and as well set up as possible.
And watched very closely.

any lean on the bearing housing means that the centrepoint that the feickert pin is sitting in at the top of the housing is not above the pivot, which cocks up the placement of the overhang point.

Once the overhang setup is done it doesnt matter, but getting the overhang setup right is the key bit of using the bloody thing.

Normal protractors arent a problem though, but the results after fighting with the feickert are better.

I think the design and materials are now finalised.

Anyone want to come for a listen?
Also starring Rex Hamilton as Abraham Lincoln

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izzy wizzy
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#317 Re: A unipivot made from scrap

Post by izzy wizzy »

I've seen some folk align those protractors over the pivot with arm off. Don't know if that's any help or just more faffing.
Ant
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Location: Yorkshire

#318 Re: A unipivot made from scrap

Post by Ant »

The wand doesnt come off because of the wiring so i cant just line it up using the bearing jewel.

I had to set the azimuth up first, then set the vta so the arm is parallel to the record surface, that sets the top of the bearing pin smack above the bearing jewel centre. Once that was done, i could then put the jig in place using the recess in the top of the bearing pin, making sure that it wasnt moving the housing from its correct position.

Then just taped the base of the jig down and used a cardboard wedge to stop the platter moving so the overhang point couldnt move relative to the arm. Then removed the jig pin so that the arm could move freely and i could set up the overhang with the jig locked in the correct position

With most other arms ive set up with it, the locating point on the tonearm that the pin in the arm of the jig sits on, doesnt move relative to the lateral rotation axis of the arm.
but with this one it can, and because ive set the pivot as low as i can, the distance between the bearing pivot point and the jig locating point is about 25mm. So any slight deviation from vertical is magnified quite abit by the distance between them.

So for example when i set the arm to 92 degrees, the bearing pin was angled forward by 2 degrees, meaning that the centre of the top of the pin was offset forward of the pivot point by 1.2mm (drew it up on paper and measured it, i was curious how far out it was once id realised what was going on)

Doesnt sound like much, but it moves the jig out of alignment with the bearing centre and moves the overhang point. If there was also 2 degrees of deflection in the azimuth as well, so another 1.2mm in another direction, say to the left and assuming 90 degrees to the first direction, you end up with an offset of 1.69mm from the bearing centre point, (pythagoras, should have used that in the first place instead of buggering about drawing it and measuring) which is a fair amount out, meaning that the overhang point on the jig is also out of position by a fair amount. Didnt work out how far out because my brain hurt, but its largely irrelevant how far out.

I suppose the same is true of lining up any unipivot using this type of jig, but not to the same extent. the distance between the pivot and the point the jig pin sits in is usually much less. The bearing pin in gregs mayware is less than half the length of the pin in my design, so the possible offset will be a lot less. probably not absolutely negligible, so care would still be needed, but it wouldnt be anywhere like as far out as its possible to end up with mine.

Ideally, i could lift off the wand and use the jewel to set the jig position by wedging the platter and taping the jig base down, that way it would be in the right place by default, but the wiring loom precludes that......

Onwards!
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Ant
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#319 Re: A unipivot made from scrap

Post by Ant »

Just broke my 760slc stylus.

FFS
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Ant
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Joined: Mon Jul 31, 2017 6:45 pm
Location: Yorkshire

#320 Re: A unipivot made from scrap

Post by Ant »

Well after 3 days of weeping ive put the dv back on it.

Broke it by hitting the arm with my elbow while reaching over it to unplug something from the pre which is up above it on a shelf. The plug came out suddenly, my elbow shot back and whacked the arm out of its rest, the stylus dug into the rubber mat as it shot across the platter. Result, one very bent stylus..

I am still rather unimpressed. Thats 2 fairly expensive carts ruined by ineptitude, i killed the eroica i had by trying to wipe the deck down with a microfibre cloth and got its stylus caught in the cloth...

At least it wasnt the dv, i can get a new stylus but probably not the correct vmn60slc one. Either a vmn40ml or a vmn50sh. 469 quid is a chunk to pay for the slc stylus, the shibata one is half the price....
I did put the worn ml stylus off mi dads 540ml in it which didnt sound much different, so we will see.

Ive taken the arm off the big lenco and put it on the smaller one, only difference is that the mounting boss is the acetal one off the brass version instead of tbe aluminium one from the newest one. Because i couldnt be arsed to swap them over. Perhaps i should. Later.

Surprisingly (or perhaps unsurprisingly) there is a subtle difference, it sounds ever so slightly warmer, but the arm board on the big lenco is made of 3 different types of wood (oak, bamboo for the insert and sapele for the base layer) where the small lenco has an oak and perspex arm board which is quite abit lighter. So it could be that.

I also took the nitrile o rings out of the bottom of the feet on the small lenco as the big one has solid spike feet rather than the rubber decoupling that the small one has.

This was to try and get as much parity between the 2 decks as possible. The motor units are practically identical, other than the fact that the big one has a slightly bigger rear curve to the chassis, and the plinths are as close as i can get without building another identical plinth.

Useful though as i can hear the difference between 2 almost identical setups so id call that a win.

Ive ordered some more aluminium to make another one in the same spec, what id like to do is send it around for people to try to get some feedback on it on different decks and compared to other arms.

It compares quite favourably with my air bearing arm and the jvc but thats all ive been able to compare it with

Is anyone interested in having a play with it?
Also starring Rex Hamilton as Abraham Lincoln

www.bte-designs.weebly.com
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