Flat vs square vs round belt

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ahlborn
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Flat vs square vs round belt

Post by ahlborn » 23 Oct 2017 17:36

Good morning.
Some turntables have a flat belt, others round, others square.
What are the benefits of each form?
I noticed that the round belts are assembled with a silicone wire glued to the two ends.
When the belt passes around the pulley goes a little off the axis.
Are there any round belt built without glue?

Thanks

Coffee Phil
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Re: Flat vs square vs round belt

Post by Coffee Phil » 23 Oct 2017 19:32

Hi Ahlborn,

Good question. I know there is more to belt design than most folks would believe. If you have a mains driven synchronous motor the belt is critical for speed accuracy. I'm thinking precision grinding a flat belt is easier than square or round belts. With motors which have adjustable speed I would guess if the pulley and belt are well designed it likely does not make much difference.

My mid '70s B&O Beogram 3000 has a round belt. It does not appear to have been glued. It appears to have been molded as a belt rather than formed by joining the ends of a length of rubber string. It does not appear to have been ground in any way. There is a molding line around the entire circumference of the belt. It does not appear to be anything special. That said however it still is perfectly good after ~ 40 years. The little 2 pole induction motor developed speed issues so I replaced it with a brushless DC motor using the same belt. It is quiet and works fine so there must be some secret sauce used in it which B&O knew about.

Phil
ahlborn wrote:Good morning.
Some turntables have a flat belt, others round, others square.
What are the benefits of each form?
I noticed that the round belts are assembled with a silicone wire glued to the two ends.
When the belt passes around the pulley goes a little off the axis.
Are there any round belt built without glue?

Thanks

Alec124c41
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Re: Flat vs square vs round belt

Post by Alec124c41 » 23 Oct 2017 23:27

Note that there is little to be gained from switching between belt types. The effective thickness of the belt is important to hold the correct speed.
Rega used w round belt, in a V-shaped pulley. I have used a thin square belt in there, successfully.
A flat belt will center itself on the crown of a pulley that is convex. This is the most common one.
BTW there are turntables that use a thread to drive the platter.

Cheers,
Alec

JohannesM
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Re: Flat vs square vs round belt

Post by JohannesM » 16 May 2019 02:44

It will depend on the turntable drive system. Some like the JH or Silcron models have a small concave grove on the outside of the platter, meaning it can only be used with silicon round belt. Most other turntable platter have a flat inner platter underneath the platter and these are suitable only for flat belts. So no, you cannot or should not use belts that are not made for that particular turntable. Belts should never be glued as it will effect the playing speed. New belts should not be sold if these are glued.

scrapjack+
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Re: Flat vs square vs round belt

Post by scrapjack+ » 16 May 2019 05:20

There also used to be round belts made of stretchy metal springs. I'm fairly certain they did not use glue, maybe solder though. I don't think I've seen one of those on anything made after the 1960's however, and there is probably a reason for that. I've worked on a few Croslys that had flat belts without glue. It seems weird that anything better than a Crosley would have such a cheap belt.

I've heard of people running machine shop tools with belts made of layered duct tape. I don't recommend it, but if there really are no other options, it is always an available last resort.

raphaelmabo
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Re: Flat vs square vs round belt

Post by raphaelmabo » 16 May 2019 08:26

In general it is like this:
Turntables with the belt on the outside of the platter: round belt.
Turntables with a smaller sub-platter under the main platter: flat belt.

Some 'tables with a smaller sub-platter under the main platter, like Rega/Edwards Audio, has a round belt. They also have fully manually operated speed change - you lift the belt with your fingers to move to another track on the pulley. Other turntables, like Thorens, Dual and many others, has electronic speed change (you change speed by turning a knob or press a button). A round belt is easier to operate when you change speed with your fingers.

So it's the choice of platter type and drive that determines the choice of belt.

Ottermel
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Re: Flat vs square vs round belt

Post by Ottermel » 16 May 2019 17:51

Raphael
Check out my avatar! Flat belt on the platter!

JoeE SP9
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Re: Flat vs square vs round belt

Post by JoeE SP9 » 16 May 2019 18:00

Teac TN-550: It has no sub platter and a flat belt. Electronic speed change is also included.

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Re: Flat vs square vs round belt

Post by raphaelmabo » 16 May 2019 18:14

When I say "In general", I mean generally speaking, that is "often" but not "always".
And I do know that there are turntables with belt on the platter that has speed control, like Thorens TD350 for example or Acoustic Signature, among others.

JoeE SP9
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Re: Flat vs square vs round belt

Post by JoeE SP9 » 16 May 2019 19:26

Lighten up! I know what you meant. I'm just messing with you. :mrgreen:

I bought a Teac TN-550 for my bedroom. This was despite an extremely negative review from a regular contributor to several forums. He heard a high pitched noise when ever the platter was powered and rotating.

When I received mine the first thing I did was connect it, start the platter rotating, increase the volume to max and place my ear at the grills of my speakers. I heard only a very slight hiss. IMO/E a slight hiss through the phono input with a maxed out volume control is to be expected.

The online pictures of the TN-550 do not do it justice. It's IMO gorgeous. It's also heavier than I anticipated and has adjustable feet.

I replaced the stylus on the included AT-100 cartridge with a VNM20EB. There are two other cartridges I'm going to audition with/for it. They are a Radio Shack RXT-47 w/Jico stylus (actually an OEM Shure M-95), and a Shure V-15IV w/Jico SAS stylus. An AT MC cartridge is in its near future.

ChrisfromRI
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Re: Flat vs square vs round belt

Post by ChrisfromRI » 16 May 2019 21:09

I like round belts only because I can make them myself any size I need by heat fusing Urethane drive drive belt stock, available in at least ten diameters at modest cost and with stippled or smooth finish. I make them for tape decks too. However, I do have many turntables that need flat belts, including where the flat belt goes on the outside of the platter.

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