A unipivot made from scrap

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simon
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#286 Re: A unipivot made from scrap

Post by simon »

Haven't forgotten Ant, just crazy busy at the moment. Probably be a couple of weeks before I can get over.
Ant
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#287 Re: A unipivot made from scrap

Post by Ant »

No worries simon, i thought you would be rather busy
Might have both of the versions built by then, ive just ordered some more brass bar for a new pillar for this one, stuff i had in was 16mm not 20 as i thought it was
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shane
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#288 Re: A unipivot made from scrap

Post by shane »

Can’t help wondering how it would sound with an alloy arm tube instead of CF. I’ve always felt that the more complex resonances in CF are more difficult to control.
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#289 Re: A unipivot made from scrap

Post by Ant »

Funny you should mention that shane, ive been mulling over changing the wand for a titanium tube instead of a carbon fibre one for the last few days.

Im in two minds as to wether to do it as it would mean changing 2 things at once.

Ive settled on the design and material for the arm pillar, settled on the design but not the material for the bearing housing, and settled on the design but not material for the stub, cartridge carrier and cart mounting plate.

I could change the wand on this one (revision 7a) and view it as a parallel development, but it wont tell me what bit makes the difference.

I dont want to end up going in circles with it
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#290 Re: A unipivot made from scrap

Post by Ant »

Lathe threw a wobbler yesterday..
I was making a mounting boss for the arm when one of the change gears seized solid on its shaft while threading it for the mounting nut.
Luckily i was not using it powered and was hand cranking it otherwise it would have at least stripped teeth off the nylon gears, or worse shattered at least one of them..

Ruined the part i was making, but at least that was just about all the damage done.

Had to get the change gear stud out of the apron then attempt to get the metal inner of the gear off it.

Had to punch the stud out of the gear with a drift.
All the inside of the metal inner was galled up along with the stud, the gear inner had to be re bored to clean it all up and make it sevicable, then the stud cleaned up so that the gear at least spins on it.
Ordered a replacement stud for it, which was available through a guy ive used for other replacement parts.

No idea why it seized up, i couldnt find any obvious debris in it when i finally got it apart.

So at least the bloody thing works again with the scarred up stud which will get binned when the replacement arrives

Only got four parts to make, its taking forever to finish with problem after problem, mechanical issues, materials taking forever to arrive, and replacement tools and parts.

Im losing the will to live with this version....

Onwards!
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#291 Re: A unipivot made from scrap

Post by Ant »

Finally got all the parts made for the arm.
I've called it version 8 as there are a couple of subtle improvements to various ancillary bits as well as the material changes.
Its dry built at the moment, to make sure everything fits together correctly

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

material changes made are as follows.
bearing housing is aluminium on this version with a brass ring weight in the base of the housing instead of steel
the cart carrier is the aluminium one from version 6 instead of the brass one from version 7
The cart mounting plate is now aluminium instead of brass
the outrigger assembly has an aluminium ring instead of an acetal one
the mounting boss is also aluminium instead of acetal, and has a stainless retaining nut instead of the acetal one

The idea behind removing the acetal from the areas I'd used it before was to allow resonance to travel and get out of the arm assembly, as it occurred to me that the damping properties of the acetal parts may be blocking resonances and trapping them in parts like the wand instead of letting them out and into the TT plinth. Wether this is the case remains to be seen.....

I've altered the arm rest again so that it is more low profile looking and less bulky looking

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

I've also moved the fingerlift to the cart mounting plate to make the handling less brown trouser inducing when cuing, and altered the relative angles of the bias guide outrigger and the bias arm to give the string a smoother path.

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

Getting the finger lift onto the cart mounting plate wasn't as simple as it looked, it had to go in at an angle so it didn't interfere with the bolt holes, meaning the lift itself is quite a strange shape to bend, so it ends up with the lift at 90 degrees to the cart. Also used a bit of heatshrink over it to give it some grip.

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

Hopefully this version addresses the handling issues of the last version.

just needs gluing up, then it can be wired

Onwards!
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#292 Re: A unipivot made from scrap

Post by Ant »

Got it all assembled and fitted onto an arm board on the big lenco

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

I've not wired it yet as I've fount that the cart mounting plate needs the bolt rebates need to be a touch deeper, and the bearing pin needs to be reground to the correct angle

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

Also missed the threaded hole for the setscrew that holds the mdin socket into the pillar

I'll get there eventually
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ed
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#293 Re: A unipivot made from scrap

Post by ed »

hey Ant, top photo in last post, top left behind the photo, wassat?
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#294 Re: A unipivot made from scrap

Post by Ant »

An unfortunate arrangement of buddleia leaves
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#295 Re: A unipivot made from scrap

Post by Ant »

It lives!

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

I've had to use the cable off the other version as I forgot to get another one, just completely slipped my mind.
The cart on it is mi dads VM540ml as I know the cart well and I didn't want to take the dv off the other one straight away.
last cart I used on this deck was the same one, in the acos gst1, so I have an idea as to what is the arm and what is not.

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

Before I set the arm up I gave the lady (the nickname for the deck, Paul Tiernans is the 'Grand Lady' and mi dads is the 'Little Lady') a bit of a fettle as it has been stood for 12 months. simple stuff, a clean of the motor spindle with degreaser, a clean of the underside of the platter with degreaser and a going over of the idler wheel with some rubber renue.

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

The bias weight is another nut on a string because I couldn't be bothered to make another one, the only other thing I had to do was to move the pivot slightly higher than I wanted to get the stability back. The extra weight above the pivot because of the aluminium housing for the bearing wasn't quite countered by the heavier ring weight I put in, and it is only 1mm higher than the design spec.

ImageCx unipivot revision 8 by anthony cresswell, on Flickr

I only listened to one track so far just to check its working so I haven't formed any impressions.
we shall see
I also have the ortofon 2m blue to put in it that Pete loaned me, but familiarity first.
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steve s
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#296 Re: A unipivot made from scrap

Post by steve s »

Impressive work Ant...
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#297 Re: A unipivot made from scrap

Post by Ant »

Ok some initial impressions
Ive got persuit of accidents on and know it very well

There is an immediate jump in the sharpness of the start and stop of everything. The leading edges seem to start and stop like lightning. The version 7 one is no slouch in this respect, but its as if this version doesnt have the slight blur to transients. I put this down to the aluminium allowing resonances in the arm tube to get out down the bearing pin and pillar.

It seems to have retained the ease of presentation of the earlier ones, the way it presents everything in such a manner that you can pick and follow a part then pick something else and not have to zero in on it, it doesnt seem to lose track of anything in the mix

It does however have a more analytical feel to it which some people might not like. This may be in part the cartridge interaction as the 540 is particularly good at teasing apart things in the soundstage

This combo is a little into the cold side of neutral if that makes sense

Shove something else on the end of it and i suspect it would change

It doesnt seem to have that slight forwardness in the midrange that version 7 has, wether thats the cartridge remains to be seen.

Handily, it seems to be doing what i expected it to, rather than sounding completely different
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#298 Re: A unipivot made from scrap

Post by Ant »

Done some further faffing, tried the 540ml, then the 540 body with the 760slc stylus, and then petes ortofon 2m blue.

The interesting thing about this is that the differences between the carts is immediately apparent, but the intrinsic neutral characteristic of the arm teasing everything apart is still there.

It doesnt seem to be adding anything now

Im rather pleased with that
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#299 Re: A unipivot made from scrap

Post by Ant »

Back on with the dynavector, same pattern continues.

The dv is obviously the 'top of the class' so to speak, what is interesting is how obviously different it is to the 760slc
The slc is brighter, and more detailed, not so coloured. The Dv is not so matter of fact, and the bass is fuller, not so controlled. The at is probably the more accurate cart of the two, but the dv is 'nicer' for want of a better word

The difference between the AT and the DV is clear, and this version of the arm is showing the differences plainly

This has been an interesting few hours
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Paul Barker
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#300 Re: A unipivot made from scrap

Post by Paul Barker »

Nice
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