My Third “Techie” – well the last of them!

[Qwin]

.
This is my 3rd Technics project and it will encompass all I've learnt to date, so will be my ultimate Technics Deck.
I was looking at what options are available for an upgrade platter. I didn't want to spend the large amounts (up to £1,000) for a commercially available Platter/Bearing combination.
What I do have is one of these Pro-Ject RPM9 decks I purchased cheap off fleabay.



It has a 38mm thick Acrylic platter and a sturdy 10mm ceramic tipped spindle running on an inverted bearing. This bearing set up seems to be rated quite highly. I wonder ............

I looked at the compatibility of the two designs, the overlaid parts can be seen here:

http://www.jkwynn.co.uk/Project_Imag...r-assembly.pdf






Having established that the Technics motor requires very accurate alignment of the parts I started with the spindle assembly. I took an old Technics bearing and cut off the bottom section. The bush bearing was knocked out of the top part with a drift. The bush measures O.D. 12mm and I.D. 8mm so the 10mm ProJect spindle wouldn't fit. I just happened to have a couple of meters of Aluminium extrusion lying around that was O.D. 12mm and I.D. 10mm, perfect. I cut a small piece from this and pressed it fully into the housing in a vice, it was a tight fit. The ProJect spindle was a close sliding fit on the inside diameter, I couldn't have asked for a better combination. The Technics boss could now be centred exactly on the new spindle/base.







The Technics boss was glued (epoxy) and screwed into position while centred on the spindle. Once set the spindle was removed from its base (grub screws) and the nose cut off the Technics part, leaving just the motor location features attached to the ProJect spindle base.







Three through holes dia 2.5mm were drilled in the base to take the Technics motor retaining screws. These thread cutting screws were tried on a scrap piece of Alloy and seem to work with this diameter hole. I de greased the assembly and gave it a coat of Black etch primer. I had to mask the location faces as the fit with the motor/PCB is so close that the paint thickness may have prevented it from going together.







This is my test bed for the project, there is little point in making a plinth till I have proven the parts all work together. The open access allows measurements to be made easily, when establishing clearances etc. and of course it can be modified or adjusted more easily if required.







The platter components laid out. I tapped the Acrylic to accept M4 machine screws which will secure the magnet. The Brass adaptor to the right was made for me by a local model maker, it slides over the existing brass bush and is secured by grub screws. This is machined very accurately, centres the magnet and provides a platform for the position detection hub at the correct height.







The parts went together well, a very close fit with no play at all. I had marked the orientation of the sensor hub in relation to the magnet prior to removing them from the Technics Platter. I glued the sensor to the adaptor in the correct alignment, if necessary this can be adjusted by loosening the grub screws in the adaptor and rotating it.







The test bed has the motor PCB and regulator installed, I used a strip of Aluminium as a heat sink.
Ran into a bit of a problem, I purchased the PCB off Fleabay and it turns out to be quite a late version off a Mk5G. At some point Technics have changed the multi pin socket that connects the Start/Stop & 33/45 buttons, because the socket on the board is incompatible with the plug on the switch harness off a Mk2. Doh!







I lowered the new Platter into position with everything crossed. There was no crunching or grinding of coils, it went on smoothly and the magnet spins freely between the coils and the metal shield.







Well it certainly looks the part, the semi transparent nature of the textured Acrylic allows you to faintly make out the shape of the magnet and PCB which I think looks kind of cool, especially when the platter is spinning.
All I have to do now is rig up a power supply, solve the control harness socket issue and it should power up.







I removed the receptacles from the connector on the control harness and clipped them direct to the pins on the board. I heat shrinked every alternate connection to prevent them shorting. For the PSU, I couldn't wait for the correct leads and connectors to come through the post so I hard wired it for a trial. It powered up and runs perfect. The only tweak necessary was to give the brake about a quarter of a turn on the adjuster, this platter is 38mm thick Acrylic and weighs 3.5Kg which is approximately twice that of the stock Technics Platter.

Well that's the drive principle proven, I’d better design a deck to put it in.







This is the deck mocked up in a CAD package. The taller platter means the arm has to stand on a block to bring the cartridge up to the right height. The plinth is going to be plywood this time and I am chamfering the edges to make it look slimmer, it’s actually 76mm thick. The "Terminator" Arm will be installed and this now has the new mounting base fitted, which will allow me to experiment with different wand lengths. Construction can start when I get my hands on some decent Birch Ply.............

[Tarzan]

Once again excellent work Ken- a very interesting and well thought project Sir.

Do keep us posted on how it goes.

[CageyH]

Another totally inspiring modification.
I hope the end result sounds as good as it looks.

[DarrenHW]

Outstanding!

Why are you using ply for the plinth? I'm quite surprised, thought you'd have cast another concrete plinth after the success with your last. I take it you'll have to laminate your own 76mm sheet? If so how will you clamp it? Will you veneer the sides?

[NRG]

Great engineering, very ingenious! One thing looking at your test setup, I can't help thinking the COG of the platter is a somewhat high. Would it be possible to machine a relief into the platter base and accommodate the drop of the platter rim...

[John]

Looking forward to seeing this project develops

[Andrei]

Great engineering, very ingenious! One thing looking at your test setup, I can't help thinking the COG of the platter is a somewhat high. Would it be possible to machine a relief into the platter base and accommodate the drop of the platter rim...

Alternatively the platter does not have to be that thick. There could be some merit in keeping measurements (weight of platter and center of gravity) closer to the original spec. Either way it does look like we are watching The Ultimate Techie evolve.

[Qwin]

Hi Darren

I considered concrete - I love to work with it as its so stable when set. Trouble is this design has a lot more mass than the last one and I could barely lift that one precicely when decked out with delicate arm and cartridge in place. I have to set my deck up on the kitchen table then lift it into position on top of the rack which is situated in my chimney breast. Not much head room and very easy to bang into something and damage things. So I decided to go for plywood. It will probably be veneered as painting the end grain on plywood is a waste of time, you can get a piano gloss finish but after a few months the laminations and joint lines start to show through. If I do veneer I will be going for a very high quality finish, better than anything else to date.

I considered the lightweight concrete approach using Pumice stone as the aggregate and was prepping for that but the shape I am working on has some undercuts that makes casting pretty difficult with my basic facilities.

The lamination will be x4 layers of 18mm + x1 of 3.6mm = 75.6mm this is available at a local store and allows the right hights for bearing mounting and platter height without having to do a lot of routing. I will be clamping each profile in place while glue dries, not sure which type of clamps yet. I have a few and I can borrow a few off my brother.

I will have to work out all the fixings (t-Nuts) required and place them in the back of the sheet (counter bored) before glueing it in position, so a bit of thought required.

[mafrega]

Hello Qwin.

Your design is very original, I like much

Also I like much the solution that you have taken for the bearing.

Regards


In a few days it will start modifying the arm of series of 1200 following your modifications.

[Qwin]

Neal/Andrei
Not quite that simple, if the platter is lowered the magnet is lowered which means the PCB/motor and bearing has to be lowered which means the base has to be lowered to accomodate it, so you don't gain anything except lift a wall up around the platter, the physics remains the same.

Its only taller than the Techie by the difference in height above the magnet which is 23mm.

On the other hand it has an inverted bearing so the point if contact for the thrust bearing (centre of rotation) is well inside the platter/mass and above half way. The Techie thrust (centre of rotation) is considerably below the platter/mass.

Its a bit like trying to balance a stationary spinning top, compared to balancing a cymbol on a pencil, so as I see it the centre of gravity is considerably better than before. Its physical height above the plinth or table top does not matter to any great extent given the mass of the plinth, its the relationship with the bearing point that matters. Otherwise anyone building a taller plinth is raising the centre of gravity. Thats my take on it anyway.

It wasn't a problem on the project deck and I don't see it being one when transfered to here, its just a different approach and some would say better.

Edit: Apologies Neal I see you meant machine the platter away. I don't have the equipment for that, but in principle it could work as the spindle can be lowered by the same amount in it's housing to keep the magnet/motor heights correct.