A unipivot made from scrap

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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?
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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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#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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#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?
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Ant
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#321 Re: A unipivot made from scrap

Post by Ant »

Ordered one of those 40 quid arm cables off the vinyl adventure, rebel, i think its called. we will see if its any different to the oem one ive been using that was included with all sorts of japanese arms in the 70s.
I just really cant be arsed to make a cable. Hate making cables
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#322 Re: A unipivot made from scrap

Post by Ant »

Built another one

ImageCx unipivot tonearm revision 9 by anthony cresswell, on Flickr

Revision 9, I think, I've changed the counterweight stub and weight. The stub on this one is carbon fibre with a 10g brass insert, and the weight is brass in order to make it lower profile for the same weight, although this one is a little underweight as I made it a little bit small. The cartridge carrier stub is also slightly different, just a detail change to the shape so it looks better

I also found a set of buffing wheels and compounds that I forgot I had so it's a bit shinier.

Still need to make another bias weight and guide
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Ant
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#323 Re: A unipivot made from scrap

Post by Ant »

All finished and wired

ImageCx unipivot revision 9 by anthony cresswell, on Flickr

A new bias guide and bias weight were also made as the weight from the older acetal bearing housing revision was too light, and the bias guide from that one was the wrong shape.

I couldn't be arsed to make another arm rest so the earlier one remains on it

I've put a Grado black in it as I still haven't gotten around to getting another stylus for the 760 and this is the only thing I've got that isn't set up in something. I don't want to faff with the dv in the other one at the moment.

Need to dig out another deck to put it on. The big Lenco needs some work doing on it as I noticed there seems to be a bend in the chassis plate, and I'm not sure if it will fit on Pauls 301. I shall have to check wether the retaining nut for the mounting collar will fit in the rebate under the arm board, if not I'll have to make a new one

hmmmm
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Ant
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#324 Re: A unipivot made from scrap

Post by Ant »

turns out it was easier and much faster to sort out the lenco chassis plate than to make a new arm board for the garrard, which didnt have one in it, and i cant find it either. A couple of taps with a rubber mallet on the chassis plate sorted out the misaligned lenco platter

The bearing shim must have shifted and pulled the bottom of the bearing slightly out if square because i heard the bearing shift and click into the very shallow rebate in the shim

While i was at it i made some height adjustable feet which it didnt have before. The new arm should just drop straight in.

Simples

Ill make a new arm board for the 301 when i get round to it, i could put the mayware f4 on it

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

Post by Ant »

Sorted

That was a pain in the rear to get done, had to pull the motor unit out to sort out the power as it wouldn't run. I'd not plugged the wiring back into the IEC socket and it was caught on something.
Got there eventually

ImageCx unipivot revision 9 on lenco by anthony cresswell, on Flickr

just ran my setup disc so i couldn't say wether it sounds any different

ImageCx unipivot revision 9 on lenco by anthony cresswell, on Flickr

Haven't heard the Grado on these arms either so it's a bit of an unknown

ImageCx unipivot revision 9 on lenco by anthony cresswell, on Flickr

Back up to 4 TT's in the living room.......
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Ant
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#326 Re: A unipivot made from scrap

Post by Ant »

Had to do some re jigging to get everything connected up.

Changed my switch box to another one that has more inputs, the jbe and the small lenco are running into the cole, the jvc is running into savvypauls borrowed old project phono stage, and the big lenco into the benedict audio phono stage.
Getting some grado hum but its not too bad
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#327 Re: A unipivot made from scrap

Post by Ant »

Just been listening to 3 of the decks with headphones. Playing the track eyes waterfalling off level 42 persuit if accidents.

Very interesting (to me at least) is that the 2 lencos sound so similar. Practically the same deck, practically the same arm, and the better one is the one with the dv on. As expected. The differences between the 2 are in the carts and it shows. The grado sounded musical but sort of soft and diffuse when i put it on the jvc, not particularly detailed, soft leading edges, but pretty pleasant to listen to nontheless.

In the new arm on the big lenco its rather less soft, theres more detail coming out of it, and its abit grippier. still a pleasant listen.

The dv is much more detailed, nice and crisp with much better grip and control, not soft, not diffuse. An unfair comparison.

But the inherent signature of the deck/arm combo is the same. Which rather suggests that the changes i made to the newest arm have made little difference, or are being masked by the difference between the dv and the grado, so cant be particularly big. I can live with that, the changed bits are easier and faster to make.

The arm traits are the same, the tight precision ive heard with all of the versions is evident with both carts and the timing is spot on. Simon commented that the earlier version bordered on the analytical, hes probably right.The headphones showed just how tight the bottom end is without room interaction from the speakers.

Its also interesting that the cart traits were so easy to spot, and follow.

Im quite chuffed with that

The jvc sounds different, same track, it acquits itsself well as an everyday deck. It has an empire 1000gt on it at the moment as a stand in for the broken 760, and has a nice well rounded sound

The 2 lencos are better, the jvc is nice all rounder that i wouldnt be without.

Didnt try the jbe because i ran out of sockets to plug the air pump into.......
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Thermionic Idler
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#328 Re: A unipivot made from scrap

Post by Thermionic Idler »

I was over at Ant's yesterday (popped in on the way from collecting my VdH cartridge from Peak HiFi) and listened to the one with the Grado in it. Very nice indeed, I recognised the Grado sound from the Music Maker cartridges I used to have years ago.

I'm probably going to be a customer for one of these arms when budget allows - we have a GL75 that needs fettling and re-plinthing, but it's in such nice condition visually that I'd like it to remain stock as much as possible, and I had the idea of leaving the lifter mechanism in place as well, to work with Ant's arm fitted in the hole vacated by the old Lenco arm.
Deck: Garrard 301 - Audio Origami PU7 - Van Den Hul Black Beauty
Phono: Whest PS30RDT
Linestage: AMB α24/LCDuino
Power amps: 'Newton' 300B PP based on a design by Lynn Olson
Speakers: FF225WK 'Big Met' Metronomes c/o Cressy Snr
Ant
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#329 Re: A unipivot made from scrap

Post by Ant »

Yep the cheap grado has something about it, nowhere near as good as the dv, the empire or the at33 at the frequency extremes, but its got such a nice fluidity to the midrange and a particular sweetness to it that it can be forgiven for having sizzly top end and being abit hazy. It actually tracks fairlt well, even going from the shibata and line contact stylii on the other carts on the other decks

That soundsmith i had had similar qualities, but unfortunately the nasty top end and rubbish tracking even in the linear arm outweighed the plus points. Which was a shame.

Re fitting one of these arms to a bog standard 75, i think it would work pretty well, the arm rest outrigger could be left off as the chassis has the lifter and arm rest on it already, and the bias arm outrigger would be left on.

It'd have to be something of a one off, shorter as it would need to be lenco geometry, but it wouldnt end up too different. Isolating it from the deck to curb rumble might be a little troublesome, but maybe the mounting boss could be rubber mounted

Perfectly doable though
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#330 Re: A unipivot made from scrap

Post by Thermionic Idler »

Ant wrote: Mon Oct 25, 2021 12:15 pm Isolating it from the deck to curb rumble might be a little troublesome, but maybe the mounting boss could be rubber mounted
Mmm, interesting point. Maybe attach it to the wood underneath, kind of 'through' the metal chassis hole but leaving a small gap around it - so that looks-wise, it still appears to be attached to the top plate but in reality it's fixed to the plinth? Could that work?

I remember trying to put flexible washers on an SME 3009 mounting at one point to try and cure a rumble issue I was having at the time with a Garrard, but the results really weren't good - I think arms like to be solidly mounted, certainly the SME's anyway.
Deck: Garrard 301 - Audio Origami PU7 - Van Den Hul Black Beauty
Phono: Whest PS30RDT
Linestage: AMB α24/LCDuino
Power amps: 'Newton' 300B PP based on a design by Lynn Olson
Speakers: FF225WK 'Big Met' Metronomes c/o Cressy Snr
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