A unipivot made from scrap

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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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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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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.

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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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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.
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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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Re: A unipivot made from scrap

Post by Ant » Sat Aug 05, 2017 3:40 pm

Bought a new cart today, I decided to go (after much deliberation, carts seem to be a bloody minefield these days) with an audio technica at150 sa moving magnet.

I like the new audio technicas, i couldnt stand the old ones such as the original oc 7, 9 ect and the low end stuff like the at95 ect. Bloody orrible.

The new at-f range and the high number at range are a completely different kettle of fish. The f7 is a complete bargain. I find ortofons abit hazy although I do like the kontrapunkt b. Cant go spending that kind of money though.

The 150 has a shibata stylus on it though. And tracking is, according to the specs, very very good indeed which is what I look at these days. Try getting an mc with a shibata stylus and you're looking at spending at least 600 quid ish on a hana, and the sky is the limit on other options with stylus profile other than elliptical.. Cant justify that.

Also borrowed the balanced power supply off mi dad to give it a try. Plan is to plug the f5, the deck, the beresford dac and the phono stage into it.

Im abit wary of plugging the computer into it, i'll just plug the stuff that shouldnt blow up into it.

If it makes an appreciable difference i'll build one into a nice box so its safe

To be continued

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Re: A unipivot made from scrap

Post by Ant » Sat Aug 05, 2017 5:48 pm

Ok, so plugged the amp, phono stage, step up and deck into the bmu and I can hear a difference. in the hf mostly, on decay on cymbals ect. The micro detail. It seems smoother over the range, a subtle tightening up in the bass.
Wether this is the motor in the deck behaving better I'm not sure, there seems to be less noise overall.
Tbh it seems to have done the same thing as it did to mi dads system when he was using it, so I think there actually is a change rather than it being just me expecting one

It did pop both the breaker for the sockets on the consumer unit and its own double pole breaker when i switched it on, once both were reset, it switched on fine.

Quite why im not sure, presumably there was a surge on switch on, the consumer unit breaker popped first so the breaker on the unit saw an imbalance and popped as it should.

Not sure I want to leave it on all the time, p'raps a thermistor in there would do the trick to limit inrush current if it is that that popped the breaker.

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Re: A unipivot made from scrap

Post by pre65 » Sat Aug 05, 2017 5:54 pm

Ant wrote:
Sat Aug 05, 2017 5:48 pm


Not sure I want to leave it on all the time, p'raps a thermistor in there would do the trick to limit inrush current if it is that that popped the breaker.

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Re: A unipivot made from scrap

Post by Dr Bunsen Honeydew » Sat Aug 05, 2017 7:55 pm

Leave it on, it is inrush current as the transformer charges up. People think only capacitors do it but a big coil does it as well. If you leave it off long enough to discharge then it will kick the CU trip out again. The current flow is so instantaneous there is absolutely no problem or danger.

https://en.wikipedia.org/wiki/Inrush_current

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