A unipivot made from scrap

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

Post by Ant »

Ok, a breakthrough of sorts with the arm.
Ive had bloody flu for a week which still hasnt quite buggered off yet, hence slow progress, but this morning i felt relatively human, so have done some faffing, after thinking things over for a while.

Dressing the arm wiring inside the arm by twisting the bit inside the pillar into a spiral around a drill bit to form it into a spring shape has minimised the azimuth change, allowing me to actually hear what its doing.

Its not perfect, the azimuth is still changing marginally, but its good enough for my purposes today. I can lift the arm up when the azimuth is observed to be wrong and it will go back to where it should be when you put it back down, suggesting the wiring is hanging it up as it moves by getting stuck, probably on the edges of the cutout in the pillar. The silk insulation is probably dragging.

I can now tell what is azimuth change and what is arm.

That wierd 'cant put your finger on' characteristic seems to have been removed, it seems to have opened out.

It basically now sounds like it should do.

The next step is to find some internal wiring that isnt so grabby in terms of the insulation, and is more flexible, the transfi type wiring is a little stiffer than i would like for this application, used internally at least. As an external loop, the slight stiffness works to its advantage as it stays put and doesnt flop around.

So brute forcing it with heavier lateral balance weights cant override the grabbly insulation, but as a side effect its gained some more stability, and the weights are not far from being the same distance from the bearing housing.

Mark kings bass seems more solid on persuit of accidents than it did before, more fast and detailed, no overhang, more precise.
So do all the instruments for that matter, but for some reason i usually get fixated on his bass playing because it seems to be abit further back in the mix.

Pursuit of accidents is a brilliant 'torture album' because it can get so dense, its easy for it to get muddled and smeared because there is so much going on. Then it goes all orrible and confusing if the deck cant tease it all apart.

This version of the arm seems to be doing more teasing apart, although it could have been the over damped earlier arm tube masking something before

Im rather more happy with it. Its getting there, its almost where i want it to be now.

Its about 80% there, some more suitable wiring and some tweaks to the arm pillar design should get it where i want it.

Ive dismantled the earlier arm wand with the loop so that i dont have to buy another carbon fibre tube, the aluminium headshell can come off this one, just need another bit of aluminium for the stub.
Im debating on some brass for a tweaked arm pillar rather than steel, and putting a steel insert in the top for the bearing to sit in.
Either that or get a jewel.
We shall see
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Ant
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#227 Re: A unipivot made from scrap

Post by Ant »

Onto some heifetz, specifiacally, scottish fantasy, london symphony orchestra conducted by malcolm sergeant, to see if orchestral violins set it off in any way.....
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Ant
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#228 Re: A unipivot made from scrap

Post by Ant »

It passed the heifetz test. on the wiring, im surprised there is so much available that is imo too stiff to use. Cardas is too stiff, i know from using the bloody stuff in the past. Dont like cardas internal wire. The solid core :shock: silver thats available will be far too stiff for most arms i would have thought.
And the prices are pretty crazy too. Audionote stuff at 25 quid plus for less than 2 foot, van den hul nearly 40 quid a metre. Crackers.

Ive got a pro-ject internal wiring loom for 11 quid. Because i know its more flexible than the stuff im using. Hopefully its long enough.

The van den hul stuff is quite interesting though despite its hefty price, it 'looks' to be pretty flexible, i wonder if i can get a sample.

So does the kam stuff, but getting some from the us might throw up some taxes and charges. And take some time.
I was a little disappointed that i couldnt see a uk source from a cursory web search. Perhaps i missed it..
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Ant
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#229 Re: A unipivot made from scrap

Post by Ant »

Ordered a couple of sapphire v jewels from true point this morning for the pivot on the next iteration.

Reason being, is i want to use brass for the arm pillar instead of steel. I'll get a little more mass in the pillar with brass, and i will get a much better surface finish when i turn it which is the main reason for the change.
The brass wont be hard enough for the bearing cup to be machined directly into though, thats why i used steel for it in the first place.
The jewel however, can simply be glued into a rebate in the top of the pillar, and the problem is solved.

Onwards!

(i'll get there eventually)
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#230 Re: A unipivot made from scrap

Post by Ant »

Got some brass bar ordered for revision 27 or whatever number im onto now. Ordered a couple of sizes so i can make a brass headshell to try on it too. Ill have to work out the effective mass once ive made it.

Also found and ordered a smaller boring bar, an indexable one that comes with a couple of inserts that will fit up an 8mm hole. Solves the problem of not being able to drill out the correct sized hole for the mdin plug in the arm pillar. Drill out to 10mm, then bore it to 11.5
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#231 Re: A unipivot made from scrap

Post by Ant »

Rewired the arm with the pro-ject wiring loom and it is now behaving itself.
No azimuth changes now, so i can concentrate on getting it set up. Its missing something right now. Maybe i can tune it out, im not convinced ive got the vta right yet.

I recieved the tiny little jewel bearings yesterday but not the brass bar so the new pillar will have to wait yet. Im not convinced the damping is right yet either, but i can get at at least one piece of it to get it out.

The changes have not been entirely successful yet
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#232 Re: A unipivot made from scrap

Post by Ant »

More small changes

I re made the bias guide from some 2mm brass bar as i noticed there were some gouges in the loop in the stainless one where the wire went through. Must have been made by the pliers i bent it with. The weight was swinging as it was pulled up, and the cotton was fraying, so it was dragging and catching over a sharp edge Its pulling much more smoothly now.
Setup has been tweaked so the vta is very slightly nose down.

Getting there, although my hearing is going all screwy this morning. Popping when i swallow and abit dull.
Bloody flu still has a bit of a grip....
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IslandPink
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#233 Re: A unipivot made from scrap

Post by IslandPink »

I can see you're in the grip of an obsession !
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#234 Re: A unipivot made from scrap

Post by jack »

Ant wrote: Sun May 16, 2021 11:51 am More small changes

I re made the bias guide from some 2mm brass bar as i noticed there were some gouges in the loop in the stainless one where the wire went through. Must have been made by the pliers i bent it with. The weight was swinging as it was pulled up, and the cotton was fraying, so it was dragging and catching over a sharp edge Its pulling much more smoothly now.
Setup has been tweaked so the vta is very slightly nose down.

Getting there, although my hearing is going all screwy this morning. Popping when i swallow and abit dull.
Bloody flu still has a bit of a grip....
This is a really interesting thread! Thanks!

BTW. Have you tried the usual, i.e. pseudoephedrine? Always found it worked for me...
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Ant
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#235 Re: A unipivot made from scrap

Post by Ant »

Havent tried anything to be honest, i usually just put up with it until it goes away

Hopefully minor changes to the construction of the arm will get it where i want it.

We shall see what the brass does in place of the steel
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Ant
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#236 Re: A unipivot made from scrap

Post by Ant »

Swapping between the air arm with the at33 on it and the unipivot with the dv on it, the air arm is much much more open.
Theres something fundamentally wrong with how the unipivot sounds. Its like its shut in a box, strangled and lifeless and i dont know why.

It just sounds dead and i dont like it one bit.

Theres bugger all damping in the arm tube now but its still sounds dead as a doornail..

Theres only the bearing housing made of acetal now, i dont think its the acetal because the wand on the air arm is 3d printed nylon plastic.
Perhaps the carbon fibre is the problem, i just dont know and its maddening
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#237 Re: A unipivot made from scrap

Post by Cressy Snr »

You can’t evaluate when your ears are blocked. I would just stop for now. You have a good product so put it away for a week or so, either that or I’ll collect the TT and listen to it myself.
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Ant
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#238 Re: A unipivot made from scrap

Post by Ant »

Its not my ears at the moment, the difference is clear even with slightly wonky hearing.....
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#239 Re: A unipivot made from scrap

Post by Ant »

I made some setup changes this morning, changed the mat to an orrible felt mat and altered the vta so the arm is more nose down than it was. Id estimate that it is about 2 degrees off horizontal sloping down to the cart end.

Im marginally happer with it.

Although i am somewhat baffled by the fact that a felt mat seems to make a difference for the better, this is completely at odds with what i have usually found.

Perhaps i have become somewhat narrow minded in my views on what works and what doesn't

And perhaps i am comparing it a little unfairly with the linear tracker, but thats the reference, and i dont have any other arm to compare it with as gregs mayware has issues that need fixing. The counterweight bush needs something doing so the counterweight cant rotate and cock up my nemesis..... the azimuth...... perhaps a setscrew can be put in the counterweight that can be tightened against the bush.
Something to think about. And the outrigger for the rest, bias arm and lifter needs re making as the plastic has cracked with age around the setscrews.

Really, if i want to properly assess it, i need a comparable arm to a/b it with, a pair of the same cartridges, and practically the same deck for each arm and cart.

The deck, i can do, theres this lenco and the other big one which should be close enough, the carts i cant, and the comparable arm needs alot if work.

I refuse to be beaten :D
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Greg
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#240 Re: A unipivot made from scrap

Post by Greg »

Ant wrote: Mon May 17, 2021 12:52 pm ………………..as gregs mayware has issues that need fixing. The counterweight bush needs something doing so the counterweight cant rotate and cock up my nemesis..... the azimuth...... perhaps a setscrew can be put in the counterweight that can be tightened against the bush.
I replaced the original dried out and shrunk soft bush with a small section of leather. Maybe a drop of linseed oil or other conditioner would restore its gripping qualities?
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