A unipivot made from scrap

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Ant
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Re: A unipivot made from scrap

Post by Ant » Sat Aug 26, 2017 5:04 pm

Hmm. This perspex I have is far too flexible...
Lets have a rethink

Ant
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Re: A unipivot made from scrap

Post by Ant » Sat Aug 26, 2017 6:14 pm

Found a thin strip of walnut and planed it down to 6mm, i'll use that

Ant
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Re: A unipivot made from scrap

Post by Ant » Sun Aug 27, 2017 2:39 pm

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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IslandPink
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Re: A unipivot made from scrap

Post by IslandPink » Sun Aug 27, 2017 10:02 pm

Cripes ! Shoddy at the speed of light :shock:
White flags of winter chimneys waving truce against the moon ( Mitchell )

Ant
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Re: A unipivot made from scrap

Post by Ant » Thu Aug 31, 2017 1:41 pm

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

Ant
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Re: A unipivot made from scrap

Post by Ant » Wed Sep 06, 2017 7:29 pm

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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IslandPink
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Re: A unipivot made from scrap

Post by IslandPink » Wed Sep 06, 2017 8:06 pm

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 ?
White flags of winter chimneys waving truce against the moon ( Mitchell )

Ant
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Re: A unipivot made from scrap

Post by Ant » Wed Sep 06, 2017 9:06 pm

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

Ant
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Re: A unipivot made from scrap

Post by Ant » Fri Sep 08, 2017 7:05 pm

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......

Ant
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Re: A unipivot made from scrap

Post by Ant » Fri Sep 08, 2017 11:50 pm

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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