A unipivot made from scrap

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Ant
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#241 Re: A unipivot made from scrap

Post by Ant »

The leather part you replaced is inside the cursor weight that slides along the arm tube, that bit is still spot on, it slides and grips lovely.

Its the rubber bush that the fits between the couterweight itself and the metal bush that slides along the counterweight stub that is the problem. You set the azimuth by rotating the counterweight, but it creeps downward because the rubber bush isnt quite gripping it and keeping it in place
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Greg
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#242 Re: A unipivot made from scrap

Post by Greg »

Yes of course. Sorry to bullshit. A grub screw sounds a good solution although is the original isolation important? What about another bit of leather? Go and cut up a pair of the good lady’s shoes :D
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#243 Re: A unipivot made from scrap

Post by Ant »

I think i would end up missing fingers if i decided i needed leather from that particular source :shock:

A small setscrew should do it as it would compress the rubber bush into the metal internal bush so it grabs that, and anchor the counterweight into the bush by sticking out into it.

I found a sheet of 8mm thick acetal that i forgot i had so i could mill out a new outrigger to sort that problem.
Getting the bias arm pivot out of the original one might be a problem though
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#244 Re: A unipivot made from scrap

Post by Ant »

I could do with a test record with a frequency sweep on it to see what the arm is doing. Ive got the shure ttr110 test record but it doesnt have a sweep or pink noise. Any recommendations for a suitable test record?

I realised that the creative external soundcard i got a while back has a phono stage in it so i could plug that into the laptop and run a sweep or pink noise via a test disc to see if i can spot anything anomalous, and compare it with the linear arm to try and figure out what it is that is bothering me about the unipivot.

This is assuming that the internal phono stage measures flat. The cart has a bruel and kajer plot so i can take the itself cart into account if this idea isnt a daft one

It also occurs that i havent run the arm with any silicone fluid in the bearing cup, because like a fool i didnt drill an access hole in the top of the bearing housing so i could get to it....
I could get to it by taking the bearing pin out, but being able to see how much im putting in there will be tricky. Some silicone might reduce any high frequency osscilations, im grasping at imaginary straws.... can you tell....

Thoughts?
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IslandPink
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#245 Re: A unipivot made from scrap

Post by IslandPink »

It's most likely to affect the bass and timing I would say. If you have tonal problems, colouration etc then the wand is probably the issue.
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#246 Re: A unipivot made from scrap

Post by izzy wizzy »

Ant wrote: Thu May 20, 2021 12:54 pm I could do with a test record with a frequency sweep on it to see what the arm is doing. Ive got the shure ttr110 test record but it doesnt have a sweep or pink noise. Any recommendations for a suitable test record?

I realised that the creative external soundcard i got a while back has a phono stage in it so i could plug that into the laptop and run a sweep or pink noise via a test disc to see if i can spot anything anomalous, and compare it with the linear arm to try and figure out what it is that is bothering me about the unipivot.

This is assuming that the internal phono stage measures flat. The cart has a bruel and kajer plot so i can take the itself cart into account if this idea isnt a daft one

It also occurs that i havent run the arm with any silicone fluid in the bearing cup, because like a fool i didnt drill an access hole in the top of the bearing housing so i could get to it....
I could get to it by taking the bearing pin out, but being able to see how much im putting in there will be tricky. Some silicone might reduce any high frequency osscilations, im grasping at imaginary straws.... can you tell....

Thoughts?
I think the Analogue Productions Test LP has two sweeps 10Hz to 1k and 1k to 20k. I have it and can check later if you want?
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#247 Re: A unipivot made from scrap

Post by Ant »

Ooof, 50 quid is abit much for a test disc, no worries on that one but thankyou anyway
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#248 Re: A unipivot made from scrap

Post by Greg »

Ant wrote: Thu May 20, 2021 8:14 pm Ooof, 50 quid is abit much for a test disc, no worries on that one but thankyou anyway
Classic👏 Oh, you’re from Yorkshire as well🤣
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#249 Re: A unipivot made from scrap

Post by Ant »

I am a tight sod at the best of times, 50 quid for a record without music on it would go against all my yorkshire instincts :mrgreen:

Got some more out of it by making another cart mounting plate out of brass instead of the delrin one.
2 gains infact, the effective mass is now higher at 10g which is around where i wanted it in the first place, and the mounting itself is more rigid. The plate is 7.5g instead of 1.5g and there is less damping because of the material change. Its opened the top end up quite abit, both ends infact, probably because the extra mass is pulling the resonance down abit

As a consequence, the counterweight is further out, but a change of material for the stub to brass instead of aluminium should counteract that. I could also change the counterweight to brass instead of steel, should be abit heavier for the same dimensions.

Marginally happier again
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#250 Re: A unipivot made from scrap

Post by Ant »

Fixed the wonky mayware counterweight, a little m3 setscrew did the trick
It doesnt need much tension on it to get the rubber bush to grab properly

On inspecting the outrigger there are cracks around all the setscrews so making a new one is probably the best bet.

Another problem is that the arm clip is broken, id forgotten about that. Acetal doesnt bend like whatever plastic the clip is made from so that will require some thought and abit of research into what plastic it is to either make or source another one
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Ray P
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#251 Re: A unipivot made from scrap

Post by Ray P »

Ant wrote: Sat May 29, 2021 6:31 pm Another problem is that the arm clip is broken, id forgotten about that. Acetal doesnt bend like whatever plastic the clip is made from so that will require some thought and abit of research into what plastic it is to either make or source another one
Maybe something to get 3D printed?
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#252 Re: A unipivot made from scrap

Post by IslandPink »

Ditto !
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#253 Re: A unipivot made from scrap

Post by Ant »

2 more problems dealt with with the mayware

In order to put it on the big lenco i made some arm board inserts to fit in the rebate in the main board. You may remember that because the acos arm that was on it was so tall i had to mill out a big section of the board.

The inserts are made of bamboo. couldnt find anything in my stash that was suitable so i went in a local b&m to see if they had any chopping boards or placemats or something made of something i could use. They had some bamboo serving platters for 3 quid. That will do.

Made three inserts out if it, cocked one up, and was left with 2.

Problem solved.

Second problem was related to the outrigger. I thought that the fact that it wouldnt stay put was solely related to the fact that all the setscrew holes have cracks.
Not exactly, there is a locating pin cast into the top of the outrigger which locates into the underside of the top flange of the arm pillar.
It wasnt in there because the corresponding locating hole wasnt in the right place. I didnt know that the bearing cup is actually a separate part that can be rotated in the pillar. Sorted that out by rotating the pillar so that the locating hole was in the right place, so now the outrigger doesnt move. Didnt bother to make a new outrigger because i am lazy..

So the arm is now fully functional. It still needs an outrigger making and a new clip, but it now works properly
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#254 Re: A unipivot made from scrap

Post by Ant »

A diversion, found some glass drinking straws while i was looking for the arm board insert materials. 300mm long.
I bought them because they were cheap, anyone know of an arm with a glass arm tube? Ever been done? Or just a silly idea.... :mrgreen:

I shouldnt be allowed out....
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shane
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#255 Re: A unipivot made from scrap

Post by shane »

Interesting. What diameter are they?
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