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PARAGON

DIY Turntable?

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Moderator
14 hours ago, sq225917 said:

Any manufacturer who claims perfect speed stability with a DC motor without optical, magnetic or electric feedback and control is just plain wrong. It's an inescapable engineering truth. DC motors drift with load and temp variance.

Bit of a sweeping generalisation there...for example, brushless DC motors can be driven with very good speed stability without the need for feedback, because they are essentially synchronous and their rotational speed depends on the stability of the oscillator used to generate the electronic commutation. That would be the obvious route to take these days, rather than using conventional DC motors and feedback loops.

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The following is taken from one of Edmund's ebay ads for the Mober unit. I am not endorsing the statements but I am interested in the topic so am aware of them. Reading Hi-Fi Choice from the 80's it appears there was a problem with DC turntables such as the early PT and the Ariston RD40 slowing under load. This may well be why adoption of DC was relatively slow. It appears to me that tacho or similar feedback mechanisms would resolve other issues with the use of a belt for turntables whether DC or AC.

"Beginning of 2015. I saw a review saying that the turntable upgrade from AC Motor to  DC motor sounds like an upgrade from CD to vinyl. So I determined to test it myself.

Why DC motor?

Normally, AC motor is operating at AC voltage 85 -100V AC. AC motor vibrating significantly whenever power is applied because of the higher power, you can feel the vibration with your finger touching the motor or its vicinity. That vibration transfer through the belt to the platter, it ended up to be picked up by your ultra-high sensitivity cartridge. And therefore, a DC motor operating at only a few DC V, especially a high-quality precision motor from Maxon Switzerland. When it runs, you do not feel anything by holding it in your hand or you don't know it is running or not.

Why Tachometer Speed Control?

It has been known that DC motor performs superior to 100 V AC motor. The question is how to control the speed, low voltage DC motor is very sensitive to voltage, only a few mV could affect the speed. So some claimed DC motor PSU excel AC motor, but the speed varies every second with influence by stylus force and records weight....etc, i.e records 120 g, 180g, 200g...etc. There is only a handful of DC motor turntable with computerized tachometer control. but they are the very expensive turntable. Mober used a photoelectronic tachometer, it reads 16 markers every rpm to calculate and correct speed, it is 500 times every minute and measurement down to microsecond and adjustment in mV level."

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Super Wammer
6 minutes ago, cre009 said:

Beginning of 2015. I saw a review saying that the turntable upgrade from AC Motor to  DC motor sounds like an upgrade from CD to vinyl

That depends on whether you think vinyl is an upgrade over CD. Technical specs will tell you it is not  :D

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Super Wammer
15 minutes ago, greybeard said:

That depends on whether you think vinyl is an upgrade over CD. Technical specs will tell you it is not  :D

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On 24/11/2018 at 09:59, Tony_J said:

Bit of a sweeping generalisation there...for example, brushless DC motors can be driven with very good speed stability without the need for feedback, because they are essentially synchronous and their rotational speed depends on the stability of the oscillator used to generate the electronic commutation. That would be the obvious route to take these days, rather than using conventional DC motors and feedback loops.

Isn't oscillator derived electronic commutation just electrical feedback?

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11 minutes ago, sq225917 said:

Isn't oscillator derived electronic commutation just electrical feedback?

Depends on how the oscillator is designed, but my point is that it doesn't involve measuring/feeding back the speed of the motor (or the platter).

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I didn't state that it did, hence the electrical feedback part. it could even be simply current compensated, it's still feedback. The point was that DC motors need a control loop.

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7 hours ago, sq225917 said:

I didn't state that it did, hence the electrical feedback part. it could even be simply current compensated, it's still feedback. The point was that DC motors need a control loop.

:zzzz:

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On 07/10/2018 at 18:17, PARAGON said:

Hi was wondering if anyone has built a simple, good quality turntable perhaps using another to donate parts etc? I have no problem building a plinth (out of solid oak preferably). Anyway, any advice, opinions or helpful links appreciated!
Steve
Sent from my SM-G960F using Tapatalk

If i wanted to build a turntable I would look for an original heavyweight Systemdek - they sell for about £100 to £150.  The turntable platter is heavier than a Linn and balanced as well.  The subplatter and bearing are fairly bullet proof.  It uses the same motor as a Linn.

The bad news is the turntable base was covered in Nextel which after a few years goes soft and awful.  Buy one and use all the parts to build your own beautiful creation either with the existing suspended subchassis or a completely rigid design in a massive plinth - the choice is yours.  The original Systemdek was better than the Linn sound wise and so your new creation will be at least a nose ahead of a Linn if you do it right .... happy building.

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On 24/11/2018 at 10:25, cre009 said:

Normally, AC motor is operating at AC voltage 85 -100V AC. AC motor vibrating significantly whenever power is applied because of the higher power, you can feel the vibration with your finger touching the motor or its vicinity. That vibration transfer through the belt to the platter, it ended up to be picked up by your ultra-high sensitivity cartridge.

I have yet to detect vibration transfer through a belt on a belt drive turntable.  The motor is isolated on good decks and the rubber belt further isolates the vibrations from the platter.   Goddammit there are arguments galore in here about rim drives being better than belt drives and the propensity for vibration transfer with a rim drive are massively higher than with a belt. 

Every motor has its advantages and disadvantages and provided it is speed stable and working to spec it is probably the least item in a turntable chain to affect the sound quality.   

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Not convinced that the Systemdek is that good a candidate for DIY because they don't come up for sale sufficiently often as repair or spares that they can provide a good source of parts though they are often to be had quite cheap when they do show up. On mine the Nextel paint is a bit shabby but still ok. Don't see much point in splitting up a good deck which would be better being refurbished. As you say they are nice enough decks which were a Linn competitor in the early 80's. Mine gives a wide soundstage with quite pronounced bass with the arms I have tried. I currently have a Manticore Musician on mine which as a combo I rate about the same as my second LP12 when I had a Basik Plus on it. I now have a Ittok on that LP12 which gave a much bigger improvement than when I tried my Zeta on the Systemdek. Not tried the Ittok on the Systemdek yet.

With regards to the merits of different drives there are all sorts of options which is why the topic is so interesting. Any kind of DIY alternative will probably require compromises and tweaking.The wording I quoted is from an ebay ad which I put up for discussion because it was relevant to the arguments being made. The issue for me appears to be around how the belt interacts with pulley and whether motor vibrations could result in any extra minute lateral movements with belt pulling on platters. A quieter motor should be better regardless if all else were equal.

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22 hours ago, cre009 said:

Mine gives a wide soundstage with quite pronounced bass with the arms I have tried. I currently have a Manticore Musician on mine which as a combo I rate about the same as my second LP12 when I had a Basik Plus on it. I now have a Ittok on that LP12 which gave a much bigger improvement than when I tried my Zeta on the Systemdek. Not tried the Ittok on the Systemdek yet.

Interesting observations .. the one thing that sticks in my mind is many years ago at a show a guy called Peter Marshall demonstrating his Profile 11 loudspeakers had two sources - a Systemdek (I cannot recall what arm and cartridge) and a big pioneer tape machine with master tapes.  It was hard to determine which source was playing when he switched.   Which makes one wonder at the end of the day when we hear different views on turntables (e.g. "pronounced bass") is based in the end on a personal preference and not necessarily which is most accurate".

All I can say is when I was selling the stuff we ended up selling more Systemdeks in the shop which were chosen by customers usually with a blind comparison.

As to the arm of choice, much depends on the cartridge in my view.  The Alphason arm and the Mission 774 arms in my view were the nearest to "universal" in that they seem to be able to perform brilliantly with a massively wide range of cartridges (the same can be said of unipivots like the Mayware Formula 4 and the Hadcock).  

As to motor vibration and pull of belt - Audio Note bought the rights to the Systemdek II and it is basically exactly the same turntable but with two motors mounted opposite each other to counteract any such pull (although I guess it could be argued that could end up with a kind of oscillation). 

As to the suggestion of using an old one for a DIY project by that I meant you could either refurb, redesign a more substantial plinth or even try it with no suspension on a massive slab of your choice.  The bearing is fairly bullet proof, belts are readily available but of course with a diy you could add a second airpax or similar motor if you wanted to try it (they are readily available) or newer offerings from Origin Live and others. 

It has been interesting on ebay to see some of the creations made from old Jap turntables and those from Rega parts (the most interesting being a cradle to hold the rega plinth and provide a suspended type of suspension which I have not seen for ages .. the inventor perhaps did not sell many or just made a few and sold those). 

Last but not least the interaction of belt and the "pull"  I have to say in my experience with the heavyweight turntable models there may be an initial wobble on start up as it gets up to speed but after a few revolutions the flywheel affect of the turntable is such that there is no wobble .. 

 

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Maxon Dc motors are superior . They also use less voltage therefore youvcan mess with them without danger.

Dont take my word for it. Linn go to maxon for their dc motor and charge a fortune for it. You go direct and save yourself a fortune.

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4 hours ago, Danielquinn said:

Maxon Dc motors are superior . They also use less voltage therefore youvcan mess with them without danger.

Dont take my word for it. Linn go to maxon for their dc motor and charge a fortune for it. You go direct and save yourself a fortune.

First I'd heard of them, sounded interesting so I went on the Farnell website for a look.  The Maxon model 251061 is rated at 24V, 50W.  It's specs. state the resistance at 1.03 Ohms, with an inductance of 0.532mH.  The maximum power in reality is just below 24W and when spinning its inductive reactance will limit the power even further.  It's nominal speed is 5250 rpm, really fast and the speed load curve is exponential.  With Hall Effect speed control a constant speed is obtainable.  This motor cannot just be connected to a 24V DC power supply.  Very few turntable manufacturers would go to the expense and trouble to fit one.  They much prefer using AC synchronous motors.  Cheap and cheerful locked into the AC mains frequency.  With the price of  turntables being so high.  You are right they could do better.

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