A unipivot made from scrap

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Ali Tait
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Re: A unipivot made from scrap

Post by Ali Tait » Sat Aug 05, 2017 9:25 pm

I bought a 30a one from Airlink for mine Ant.
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Ant
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Re: A unipivot made from scrap

Post by Ant » Mon Aug 07, 2017 6:15 pm

Cheers Ali and Phil.
Ive taken it back out and gone to normal mains to check im not hearing what i want to hear, and I think the is an improvement with it in.
So i'll make a nice box for it to go in. I can switch it off at the wall as there is a separate socket inside the cupboard it will be sat in, nothing else plugged into it, so no need for a switch on the unit.

What is the opinion on incorporating a dc blocking circuit? Given the transformer is so big id be surprised if much dc got to the secondary anyway

Cheers ant

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Dr Bunsen Honeydew
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Re: A unipivot made from scrap

Post by Dr Bunsen Honeydew » Mon Aug 07, 2017 6:57 pm

None does. The only advantage of a DC blocker will be to stop the primary winding on the BMU transformer rattling. If it is quiet at all times don't bother. One of the functions of a transformer (not auto wound) is to block DC.

I think, but many other disagree, that DC blockers have a side effect of increasing line impedance.

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Ali Tait
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Re: A unipivot made from scrap

Post by Ali Tait » Mon Aug 07, 2017 7:11 pm

I put one of Nick's blockers in mine Ant, was a wee bit noisy without.
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Re: A unipivot made from scrap

Post by Ant » Mon Aug 07, 2017 7:17 pm

There is a tiny bit of mechanical hum from it, I could probably pretty much shut it up with some thicker rubber washers anyway. As it will be in a cupboard its unlikely I would hear it anyway.
Didnt hear anything from it in use until I stuck my head in the cupboard to turn it off.
So just a thermistor to be added.

Odd thing is that it was noisier at mi dads, maybe the shelf it was on was singing along

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Dr Bunsen Honeydew
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Re: A unipivot made from scrap

Post by Dr Bunsen Honeydew » Mon Aug 07, 2017 9:55 pm

Different mains, the noise is all on the mains. Listen at 2am I will bet it is as quiet as a grave.

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Re: A unipivot made from scrap

Post by Ant » Tue Aug 08, 2017 4:15 pm

Ok, the at150 is on. Ooooh. We like

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Re: A unipivot made from scrap

Post by Ant » Tue Aug 08, 2017 4:40 pm

Listening to a new copy of led zep 4 atm, it hasn't half got some life to it. Seems to dig right in and bring more detail out, and and and ect.
Seems sensitive to azimuth, needs to be tweaked spot on or the soundstage gets small

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Re: A unipivot made from scrap

Post by Ant » Wed Aug 09, 2017 1:19 pm


Ant
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Re: A unipivot made from scrap

Post by Ant » Wed Aug 09, 2017 4:45 pm

Ok, a few thoughts on it after a couple of hours.
Bear in mind this is in comparison with my at-f7, and is on my own design unipivot arm on one of my lenco gl75 conversions.

Firstly, it is very clean. By that I mean that it is imo pretty neutral. Its not warm per se, but it isnt abit thin either. It seems its voiced to be just a tiny bit into the warm side of neutral.

Absolutely no end of side distortion. At all. Setup is a piece of piss due to the mostly square body, a novice could do it, however its a pig to see the stylus to get it on the null point on the protractor due to the long nose it has. So abit if care is needed there.

The azimuth needs to be spot on, otherwise the soundstage closes in, but get it right and it suddenly snaps into widescreen. My unipivot design can be set very accurately for azimuth which helped no end. Most arms other than unipivots dont have the facility to do this so bear this in mind.

Build quality seems excellent.

It seems sensitive to vta aswell as azimuth, so i'd want to put it in an arm that can accurately set these perameters.

If the arse end of the arm is a little too high, it starts to get bright, not strident though so this could be system dependent. I wouldnt want to use it in a 1987 linn naim system. But then again, I wouldnt want to use anything in a 1987 linn naim system....

So. My take on its Sq.

It is neutral, erring very slightly to the warm side, top end is very clean indeed. Cymbal decay goes on as long as its there for and doesnt get lost.

Instruments are separated properly and imaging providing azimuth is spot on is very good indeed. You can pick an instrument and follow it, then pick another and follow it at leisure.

Mid is where it should be, and vocals are absolutely spot on. And I mean spot on.

Bass is tight and fast, maybe a little tiny bit of Bloom around 100hz, but nothing that most would pick up on.

Slight con for some people, may be a tiny bit more surface noise if youre used to an elliptical stylus cart, but its certainly no Deal breaker.

I wouldnt describe it as smooth, as some have described the 2m black which I suppose is the closest equivalent, id describe it as alive. Musical.

The f7 will go back in its box. I honestly think that you would need to spend at least 750 to a grand to get appreciably better performance.

One caveat, watch the capacitance of leads ect. I first used it with the denon ha500 step up still in line with it and the benedict audio hothead, so it had an extra 2 foot of cables to go through and whatever the step up added. When i took it out the treble and microdynamics were noticably better.

Whatever pf the cable I made up for the arm, and the phono stage presented to it was about right.

My conclusion.....
Love it. It does what i wanted.

Of course, the biggest caveat of all is that the prose above is my opinion, and as mentioned, system dependent.

So a rundown of the system itsself is appropriate so you have an idea where im coming from.

Tt - lenco gl75 conversion
Arm - unipivot of my own design
Phono stage - benedict audio hothead (mm)
Pre - passive
Power - dual mono pass f5
Speakers - prototype metronome speakers (2 way with sb acoustics tweeter and faital 6fe100 mid/bass)
Mains - straight out of the wall, although I am buggering about with a balanced mains unit at the moment, this was not in at the time ( needs a thermistor in there so it doesnt pop the breaker due to inrush current)

Ive copied and pasted this from my post on tas, hence the system description, you lot probably knew that bit anyway

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Re: A unipivot made from scrap

Post by Ant » Sat Aug 19, 2017 9:32 pm

Update on the CX arm, I finally dealt with the clearance issues and took the connector out of the arm base.
I got a little plastic enclosure box from Maplins and put the connector on there and a din socket for the arm cable to plug into.

ImageLenco with u/p mods by anthony cresswell, on Flickr

Not the most elegant of solutions, but hey ho. Stuck a spirit level in the hole it left in the base, just cos it fit. The arm adjustment now works too as I can freely rotate the base to line up the cart properly.

So Iv'e solved one of the last issues with it. The other idiosyncrasy is a lack of clearance between the counterweight and the base, if you're not careful and lift the cart off the record a little to high, it will clout the base. I'll need to make a new base to solve that problem.

And the finger lift is still crap. i might just buy an SME one that fits onto the cart bolts. Maybe.

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Re: A unipivot made from scrap

Post by Ant » Fri Aug 25, 2017 6:19 pm

Have now got an offcut of 5mm black perspex about 35mm wide by 18" long.

I feel a mk3 project with a flat wand coming on

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Re: A unipivot made from scrap

Post by IslandPink » Fri Aug 25, 2017 6:27 pm

This is a question I'd like to see answered :D , I haven't got time atm to try & build the ebony unipivot, but I was torn between making a simple cylindrical wand, a slightly conical one, or a flat 'Cantus' style wand with holes, last time I thought about it. They all have slightly different resonance 'harmonics' .
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Ant
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Re: A unipivot made from scrap

Post by Ant » Fri Aug 25, 2017 7:21 pm

The last time I did a flat perspex arm wand was about 7 years or so ago, that was a 12" arm and was really nice. Even though it was rather crudely made. That was the one Mr I alluded to earlier
A solid wand is easy enough to turn either straight or conical, the difficult bit is the headshell which needs to be left as a block and machined with a different tool.
I tried several times to do this in order to make a one piece wand, failed every time.
Id have to look at it differently and work out how to do it properly.
Or just make a separate headshell and glue it on.
The constantly expanding dimensions of a conical one make it rather irksome to join to a bearing housing, again, something id have to look at.
The flat one is a doddle to make compared to the other 2.
The plan is to have it taper from front to back as I did with the original one and have holes drilled in it to reduce weight and break up resonances.

I have another pin the same as the one in the cx for the bearing, and some more walnut for the bearing housing so i can make a complete want without butchering the existing arm. The loom pulls out of the current wand so that can be transferred over, just stick it on underneath with a bit of tape.
Or I might just buy another set of wiring off vic and another plug for a couple of quid

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Re: A unipivot made from scrap

Post by Ant » Fri Aug 25, 2017 7:53 pm

found the thread where i built the perspex unipivot.

viewtopic.php?f=3&t=948&hilit=upcoming+ ... t&start=60

I find it odd and a little amusing that 9 years later I seem to have come full circle with a lenco 75 and unipivot :D

i have to say that its rather a good job that I'm slightly better at building things than I was then

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