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Old 14th February 2011, 04:30 PM   #11
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I'm going to take a look at vinyl engine, thanks for the link.

I think I'd probably better explain the project better, and why I probably won't buy a turntable.
You know how some people make steam trains as a hobby ? or working model internal combustion engines ?
Think of it like that, except with a turntable.

If I can make something which sounds as good as the Systemdek I used to own then I'll be happy.

Thanks for the information so far, it's very helpful.

( BTW I live not far from Sherwood Forest Jonathan, it makes more sense to tell you that way rather than naming a little village you won't have heard of )
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Old 14th February 2011, 07:53 PM   #12
dtut is offline dtut  United States
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Jonathon,

I've been working on some linear trackers and I'd like to see what you've come up with.
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Old 14th February 2011, 09:57 PM   #13
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Best of luck with it 7.62, a coherent design strategy is important.

Pick one flavour and go for it- high mass, low mass, suspended, none suspended, maybe a list of pro's and con's of various designs would help you choose a path? Here's some simple choices and their pro's and con's.

High mass deck, still requires isolation at low frequencies.
Low mass decks tend to require some damping at some point.
High mass platters aid speed stability, but increase bearing noise and require a clever motor start up.
Low mass platters have less flywheel stability but they do produce less bearing noise.
A suspended deck typically has instability across the belt and can feedback through suspension affecting pitch stability.
Idler drives require very high machining tolerance at drive points and are more difficult to make quiet.
Belt drives aren't typically great for speed stability.
Direct drives place magnets under platter but have good stability though require more complex motor controls.

And that's just the most basic choices before you get anywhere with materials and manufacture decisions based on available techniques of construction.

The choices should keep you occupied for a long time...
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Old 14th February 2011, 10:24 PM   #14
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Hi dtut,
I'd like to claim I am creative but it is not my design that I am referring to. I am though, very good at cutting articles out of audio magazines!!! No, the one I have mentioned is from the UK mag' "Wireless World" (now called something else) about 30 odd yrs ago. I haven't got it in front of me at the moment but the arm is pivoted so as to be free to swing in the horizontal plane and the pivot is carried on a carriage with appropriate threaded pieces that key into a long (8-9"?) threaded rod. The rod is free to revolve one way or the other and hence the carriage moves back and forth. I am not good on the various characteristics of small electric motors but the one driving the threaded rod goes either cw or anti-cw depending on the polarity of a signal generated from two sensors which I think are LDR. I haven't looked at it for ages but their are probably a couple of LEDs and an off-set circuit to set up neutral conditions.
As the arm/cartridge combination moves relative to a datum the signal to the motor varies in polarity(?) and the motor moves the rod in the corresponding direction to keep the arm at 90 degree to the rod and hence tangential to the grove.

Again I haven't checked it for ages but I think it is v.similar to the Bang& Olufsen model of the same period. I also recall a purely mechanical version at that time from a US maker whose name escapes me now. I think that one had a rubber wheel riding in a rotating rod (plain this time) to gain lateral movement but I'm not sure.

Someone gave me the Tandy/Realistic version a few yrs ago and to my shame I haven't even opened that one yet. May be another, different principle altogether.........I'll have a look when I get the other material out of the basement........

I simply thought the "WW" diy project would appeal to 7.62 as it involved some fine fitting and turning work and was UK based.....you know parts availabilty etc

( SevenPointSixTwo. I was at Donnington Park race track in Nov' last year soaking up the Grand Prix cars at the old Tom Wheatcroft museum so can't have been that far from you. Both near Nottingham aren't they?)

Btw I apologies in advance but I do have trouble spelling.....feel free to translate where appropriate if it makes more sense !!!
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Old 14th February 2011, 10:27 PM   #15
benb is offline benb  United States
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Quote:
Originally Posted by sq225917 View Post
Best of luck with it 7.62, a coherent design strategy is important.

Pick one flavour and go for it- high mass, low mass, suspended, none suspended, maybe a list of pro's and con's of various designs would help you choose a path? Here's some simple choices and their pro's and con's.

High mass deck, still requires isolation at low frequencies.
Low mass decks tend to require some damping at some point.
High mass platters aid speed stability, but increase bearing noise and require a clever motor start up.
The OP said he read everything on turntables here, but in case he didn't, there's this thread on using a magnetic bearing:
Magnetic turntable bearing
The thread discusses using magnets to completely lift the platter off its existing thrust bearing (but still using the vertical shaft to hold the platter in place horizontally), but I've also read about (not sure if it was in that thread or elsewhere) using magnets to only reduce the force on the bearing, thus making for lower noise with a heavier platter. Someone wrote there's a difference in the platter being totally held up magnetically versus sitting firmly on a hard bearing, and the latter was claimed to be preferable, "completing the mechanical circuit" from the stylus/tonearm/chassis/platter/record, which I've read long ago (Audio Amateur?) should always be a solid mechanical path.
Quote:
Originally Posted by sq225917 View Post
Low mass platters have less flywheel stability but they do produce less bearing noise.
A suspended deck typically has instability across the belt and can feedback through suspension affecting pitch stability.
Idler drives require very high machining tolerance at drive points and are more difficult to make quiet.
Belt drives aren't typically great for speed stability.
Direct drives place magnets under platter but have good stability though require more complex motor controls.

And that's just the most basic choices before you get anywhere with materials and manufacture decisions based on available techniques of construction.

The choices should keep you occupied for a long time...
Or if you have enough time to devote to it and expect to live long enough, make one of each type.
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Old 14th February 2011, 11:15 PM   #16
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Quote:
Originally Posted by Jonathan Bright View Post

I simply thought the "WW" diy project would appeal to 7.62 as it involved some fine fitting and turning work and was UK based.....you know parts availabilty etc

( SevenPointSixTwo. I was at Donnington Park race track in Nov' last year soaking up the Grand Prix cars at the old Tom Wheatcroft museum so can't have been that far from you. Both near Nottingham aren't they?)
Small world ! ages ago a mate gave me a pile of old Wireless Worlds and I do remember that article. Sadly they never survived the last house move
Another friend of mine however runs a business dealing in back issues of hobby magazines, I bet he'll have a copy of it if you can give me the date and number ?
Nottingham is my nearest city, and I visited the Donington museum last spring. I love race car engineering, especially from the 50's and 60's

Anyway I thought I had read every DIY turntable thread here, but I had missed one of the best - the Corian turntable. The most important idea I got from that is using the turntable bearing as a support to machine the platter on a mill. Pretty obvious when you think about it, but I hadn't

The magnetic bearing I had seen and it appeals to me, there is something quite cool about the concept. If it doesn't work out in practice then I can always use a more conventional thrust bearing arrangement.

I do have access to some vibration measuring equipment. A friend of mine who often helps me out in the workshop used to work in aerospace and he's still got all sorts of weird and wonderful tools ( which probably aren't much use unless you are servicing a turbofan engine - but in this case.... )

Maybe I should just dive in now and make the main bearing.
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Old 15th February 2011, 05:27 PM   #17
Nanook is offline Nanook  Canada
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Default TT design methodology

guys, this doesn't need to be as complicated as many are making it. Regardless, here's my 2:
[LIST][*]Determine what you are after. In my opinion the single largest thing to consider is maximizing the inertia in the platter as it is playing. There are competing views on this. A heavy platter with a small(ish) motor, or a light platter with a large motor or multiple motors. Many HQ turntables have platters in the range of 3.5-5 Kg. [*]Once the torque requirements are met to maintain inertia, then seek out the quietest motor possible within a specific budget.[*]Once the motor requirement has been met, develop some sort of control mechanism (if AC , then often a single cap can be used to create a phase shift), be it a 'sphisticated electronic AC or DC controller.[*]Look at various drive types. Belts, DD, idler, or rim drive.[*]Determine if a suspension is something you want to have. I personally view suspension systems as a means of energy dissipation rather than environmental isolation. For environmental isolation look at a good wall mount TT shelf, like Target, etc[*]Look at the mechanical properties of the plinth material(s) and platter material. Again often over-looked[*]Consider a reasonable bearing. You can easily over-engineer one. Or seek out good examples of each here on diyaudio. Examples: magnetic, magnetic "assist" "oil pump" types, inverted, non-inverted, grease type....[*] Take all the information you have gathered, and then toss out your original design and start all over.[*] As a first project you might start with an existing modest turntable and improve it. Practical experience supersedes much information.

Regarding a tonearm, either improve an existing one (such as the well built and very low priced Rega RB250), using well known modifications. Is a modified RB250 as good as an SME-V ? I don't know, but you might be surprised how good they can get. If you have machining capabilities, you could certainly make your own "mod" parts. (I am absolutely jealous of your capability to machine most anything small).

Recognize that there are some great designs out there that may prove better than what you can make. Most engineering and development has already been done for you.

Of course, YMMV.

My suggestions are culled from the last 10 years or so doing diy analog stuff.
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Old 15th February 2011, 06:20 PM   #18
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I recognise your avatar picture Nanook - that guy is something of a hero of mine....

I fitted an RB250 arm on my last turntable, a Systemdex IIX. In terms of mods I only got as far as making a new armboard for it with VTA adjustment. I was very happy with the package as a whole although my experience of good hifi is limited.

What I want to do is build, experiment and tweak ( Actually I don't even have any vinyl any longer and will need to restart my collection ) That's the real purpose of the exercise.
No way am I going to come along with just some machining abilities and make a high quality ( or possibly even acceptable ) turntable straight away.
But I will have fun trying, making and messing with mechanical devices is what I like to do
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Old 15th February 2011, 10:40 PM   #19
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I've modded bearings to work both with reduced vertical load and with no point load on the bearing, which sounds better is not hard and fast as someone has hinted at, but seems to depend on many variables, bearing type, maglev construction, all sorts of things.

It might be as simple as where the greatest bearing noise comes from, the point/ball or the sidewalls.

7.62 start with a decent design and replace parts, but do it with an eye to the end point.

best measuring device for a deck, stethoscope or your amplifier turned up to 11.
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Old 18th February 2011, 09:41 PM   #20
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Hi 7.62 and dtut.

Over the last few days I have tried to contact you both through the forum email channels without what we in the industry call "any real success".

Would it be possible for you to email me? bright@gil.com.au

I got into the basement archives and in the SECOND LAST BOX (inevitably!) found what I was looking for.

Cheers,
Jonathan
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