A unipivot made from scrap

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

Post by cressy » Sat May 13, 2017 1:33 pm

Having listened further to the arm there seems to be an effect on pitch stability. Listening to persuit of accidents the slightly wobbly pitch on the fender Rhodes seems less wobbly than before. It seems to be a part of the recording as it has been wobbly on every deck ive played it on.

Presumably this is a result of the pivot point being on the same plane as the stylus as this has pretty much eliminated warp wow. That particular record is pretty flat as it is.

Strange, didnt notice it until it was gone, so a subtle change, but a nice change that was well worth the effort

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Re: A unipivot made from scrap

Post by cressy » Tue Jun 13, 2017 11:22 am

Had a conversation with Morgan re the arm on Saturday. Discussing a slight issue it had with skipping on certain tracks he suggested a tiny tweak to the physical weight of the bias weight rather than adjusting the pull. Reducing it by about 0.5g has cured the intermittent problem.

So thanks to Morgan for that little nugget of info, the finishing touch.

As an aside, I looked at ali's decoupling cradle that he had his deck on and decided to try some rubber feet on Mt deck instead of the spikes which is has.

A reduction in feedback from what it is stood on has lowered the noise floor abit, there is a very slight loosening of the bass that I think can be counteracted by installing a bearing grounding block as is on ali's.

And I decided on a whim to paint the platter matt black just because I can

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Re: A unipivot made from scrap

Post by cressy » Tue Jun 13, 2017 1:52 pm

Did an a/b between the decoupling feet and the spikes.

The spikes are long enough so that if I put them back on it lifts the feet well clear of the support allowing me to a/b easily and quickly.

I prefer the spikes. It is noisier, but it tightens up quite abit and on balance I prefer it. It should be noted that its stood on a slate slab that weighs in at about 15kg so that will have something to do with it.

It would be interesting to see what the psu Ali uses is doing to the motor vibration

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cressy
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Re: A unipivot made from scrap

Post by cressy » Tue Jun 13, 2017 2:46 pm

One black platter lenco

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Still looks like a pan lid

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Dr Bunsen Honeydew
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Re: A unipivot made from scrap

Post by Dr Bunsen Honeydew » Tue Jun 13, 2017 3:20 pm

Try dads BMU on it.

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cressy
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Re: A unipivot made from scrap

Post by cressy » Tue Jun 13, 2017 5:07 pm

Ive been musing more about what a dc offset on the mains would do to the coils. presumably the coils will start to saturate if there is a dc offset.

My train of thought is that if the coils do start to suffer from saturation that one coil will produce a stronger/weaker magnetic field than another, meaning the 'drive' is not balanced up between the coils, and lead to a physical 50hz vibration as the rotor gets pulled around in an alternating weak/strong field.

Presumably too, the motor would run hotter if there is a dc component on the mains, generating some ma in the motor. I did hear an improvement on the old mans system wirh his bmu installed, so maybe a small bmu specifically for the deck with a dc blocking circuit in the primary might result in a smoother running and quieter motor.

Opinions?

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Re: A unipivot made from scrap

Post by cressy » Tue Jun 13, 2017 5:27 pm

Further reading on it here

https://www.researchgate.net/publicatio ... r_Windings

It looks like small amounts of dc injected can cause instability in the motor so that line of thought might be worth persuing

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Re: A unipivot made from scrap

Post by Dr Bunsen Honeydew » Tue Jun 13, 2017 5:28 pm

I would get a 1000va one and power your whole system, it really works.

IMO both a regenerator and a BMU will do the job, they just do it differently. My personal choice is BMU having tried both (Power Inspired AG1500 regenerator), and now building a NVA BMU.

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cressy
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Re: A unipivot made from scrap

Post by cressy » Tue Jun 13, 2017 5:57 pm

Cant afford to do that.
A little transformer just to power the deck and a few components to throw together a rudimentary dc blocker circuit is much more achievable

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Re: A unipivot made from scrap

Post by shane » Tue Jun 13, 2017 6:16 pm

IIRC Phil had a load of 1kw transformers a while ago. Might be worth asking.
You know nothing, Jon Snow.

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Re: A unipivot made from scrap

Post by Ali Tait » Tue Jun 13, 2017 7:13 pm

cressy wrote:
Tue Jun 13, 2017 1:52 pm
Did an a/b between the decoupling feet and the spikes.

The spikes are long enough so that if I put them back on it lifts the feet well clear of the support allowing me to a/b easily and quickly.

I prefer the spikes. It is noisier, but it tightens up quite abit and on balance I prefer it. It should be noted that its stood on a slate slab that weighs in at about 15kg so that will have something to do with it.

It would be interesting to see what the psu Ali uses is doing to the motor vibration
I think it is having a significant effect on it. We swapped it in and out during the phono stage comparison on Sunday. The difference was not subtle.
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