Rega RB-300 tonearm on Technics SL-1200Mk2

[Khom]

Inspired by Qwinn. Origin see here: https://www.jkwynn.co.uk//Tech2_HTML/Tech2_14.html

Part 1 - Tonearm base and fitting

I posted early my DIY silicon fluid damper for SL-1200Mk2 tonearms https://theartofsound.net/forum/showthread.php?49767-Internal-damping-of-stock-arm-experiences&p=848704#post848704 . Despite it works perfect, I decided to replace the whole tonearm, RB-300 or -250 was the best performance/price choise for me. Bought RB-300 on e-bay in good condition (-250 could be cheaper choise but I didn't find suitable offer).

Loading spring was tuned to zero force and damped by small soft textil pieces (I leave backdoor).

The first issue is the tonearm base. All necessary calculations already made by Qwinn, see link abowe. I've make several top view photos/measurements and by simple geometry calculations got absolutely the same (no wonder).

Ok, all drawings are ready, tonearm base will be made from oak. Simple rotary attachment to mini-mill, some lathe finish, varnishing and base is done.

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The next issue is tonearm height adjustment. Classical Techie has perfectly designed (really perfectly) hight adjustment mechanics but it can't fit RB-300 tonearms. I turned out aluminium hub (upper part) and nut (both have metric thread with 1 mm pitch) according to tonearm 'leg' thread. Don't ask me why british tonearm has metric thread, I expected something like 15/16-20. BTW, there is one of prototype of tonearm base I've made by 3D printer on photo (3D print is very useful for prototyping).

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The next point is internal and external wiring. Of course, default ones should be replaced. Internal wirings replaced with litz, external - with Klotz shielded twisted pair, it requires new wires holder on the tonearm 'leg'. Lathe again, drill press... done. Sure, I fitted balanced XLR connectors instead of RCA.

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Again - many thanks to Quinn. Next is new couterweight.

[Khom]

Part 2 - new couterweight

Further upgrade of RB-300 is counterweight. The main requirements are correct weight and mass center which should be as low as possible relating tonearm longitudial axes, I decided to make something like this:

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Again - drawings, calculations, drawings, calculations and machining. Counterweight body is made from pure aluminium (aluminium, not Al alloy), two additional masses turned from copper and glued to main part. Both metals are acoustically inert enough.

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Total weihgt is about 102 g, I coated it with laquer to prevent of corrosion.

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Now new tonearm and it base are ready to install. Not so complicated work, special protractor for RB-300 was printed earlier.

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Sound. It's definitely much better than stock SL-1200Mk2 tonearm (even with silicon fluid damper). Sound is solid and clean, so this upgrade definitely worth it.

https://www.youtube.com/watch?v=u1cIle6QHnw

PS My Techie works with self-made step-up transformer 1:10 made on Fe-based toroidal nanocrystal core (1.1 H, 100 Ohm), folloved by self-made fonostage described here https://theartofsound.net/forum/showthread.php?41854-Phonostage-with-balanced-input

[diviy]

Love your counter weight do you have the cnc file for it by any chance ?

[Khom]

Thanks. No, I haven't CNC machines, all parts are made using desktop mini-lathe and mini-mill (you can see it at the end of my video). This is not so hard work even on these diy-class machines. If you want I can leave here dravings of countermass details.

[diviy]

Thanks. No, I haven't CNC machines, all parts are made using desktop mini-lathe and mini-mill (you can see it at the end of my video). This is not so hard work even on these diy-class machines. If you want I can leave here dravings of countermass details.

If you would please

[Khom]

See the attached drawings. There is no hard tolerancies, all parts can be mashined easy with small ('desktop') DIY-mashines, like mine.
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[Barry]

Part 2 - new couterweight

Further upgrade of RB-300 is counterweight. The main requirements are correct weight and mass center which should be as low as possible relating tonearm longitudial axes, I decided to make something like this:

31019

Again - drawings, calculations, drawings, calculations and machining. Counterweight body is made from pure aluminium (aluminium, not Al alloy), two additional masses turned from copper and glued to main part. Both metals are acoustically inert enough.

31020

Total weihgt is about 102 g, I coated it with laquer to prevent of corrosion.

31021

Now new tonearm and it base are ready to install. Not so complicated work, special protractor for RB-300 was printed earlier.

31022 31023

Sound. It's definitely much better than stock SL-1200Mk2 tonearm (even with silicon fluid damper). Sound is solid and clean, so this upgrade definitely worth it.

https://www.youtube.com/watch?v=u1cIle6QHnw



Excellent work Valera - well done! :)

[Gazjam]

Great Job!

[diviy]

See the attached drawings. There is no hard tolerancies, all parts can be mashined easy with small ('desktop') DIY-mashines, like mine.

Do you have a better image of the sizes cant make them out ?

Cheers Gerry

[Khom]

Sorry, something was wrong with my attachment - forum engine compressed pictures to small volume. See here on google: https://drive.google.com/drive/folders/1pMpK0vbhZy93AumzEDkmK0LfS8NpAwJL

[Jimbo]

Some great engineering, particularly like the idea of keeping low centre of gravity on the tonearm weight. Well designed. My VPI tonearm counterweight has employed the same design principles but your machined weight looks far more substantial. Very nice.

[eldarvanyar]

Really impressed with what you have done. Great ingenuity with the counterweight.

Has the new power supply made much of a difference?

Thanks


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