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Rega P3 and Ortofon om20... Should I shim?

post #1 of 9
Thread Starter 
My total satisfaction audio wise has kept me from the forums for while. However, lately the wiring on my Dual 505 started giving out. Since for some reason summer means vinyl, also the limitation of the om10 needle started to bug me. So it started, I bought an om20 needle last weekend, and I found a great deal on a P3 (250 euros, all set up). Listening to this kit right now with Getz & Gilberto on the platter has me right back in bliss :)

However, there is a question in here too. The beautiful rb300 arm sits a bit low for my cart... Practically this means the lever to drop the arm on the vinyl does nothing: I have to carefully drop the arm myself. Like I said, you should hear this setup, it is pure beauty. But I also hear that one should preferably add a shim. However, the interwebs fail in giving me clear directions on what kind of shims I should get from where and how to add them. Has the combined wisdom of headfiers some help for me?
post #2 of 9
Thread Starter 
Also, while we're at it... What is the purple cart that I just replaced? Didn't sound that great, but perhaps it has some resale value?



(plug: anyone interested in a purple rega cart? A dual 505-2 with shitty cables? An ortofon om10 cart with needle, but without the brass weight? ;) )
post #3 of 9
Thread Starter 
Wow, nosing around I see this place has turned into a 99% DAC centric area in the past year. Guess I need to look for a different audio forum then...
post #4 of 9

The OM10 isn't a great match for the RB-300 as it's a high compliance cart designed for Ultra Low Mass arms like on the Dual CS-505. You should probably get a more modern medium compliance Ortofon like the 2M series Blue or Red.

 

As far as shims for your RB-300 go, you basically need to remove the bolt under the arm and lift the whole thing off and then put washers in between the deck's plinth and the base of the arm to lift the height of the arm.

 

Rega themselves sell these and you can order directly from them or a Rega dealer. Or else just go to a plumbers supplier and buy large washers. It's a faff though as you really want to listen to the cart at each adjustment and of course going through the whole rigmarole of removing the arm means you've forgotten what subtle changes you might have heard by the time you do this.

 

A much better solution is a VTA adjuster  http://www.hi-fi-accessories-1.com/vta-adjuster.htm

post #5 of 9

My number crunching says that the OM-10 should work OK with the RB300.

 

Eff mass of the RB300 as 11g

mass of the cart as 2.5g OR 5g

mass of fasteners: 2g

 

I get a oscillation frequency of ~7.5 or 8hz which is not too shabby based on rules of thumb I have heard which usually say that the "optimal" arm/cart resonances are in the 8-12hz ranges. Its a rule of thumb and Id factor in some wiggle room.

 

The system that got me into Vinyl was a P1 with an OM-10 (it may have been an OM20).


Edited by nikongod - 7/6/10 at 12:49pm
post #6 of 9
Thread Starter 
Quote:
Originally Posted by nikongod View Post



My number crunching says that the OM-10 should work OK ...



Huh, what are you talking about here? I don't need numbers to know if something works or not, and I'm not asking for recommendations on other carts, i just told you guys it sounds fine. If I could calculate how something sounds I'd listen to a computer. So, no actual experience on the merits and difficulties of shimming an rb300? The fact that tightening the nut on the arm mount would also change the sound kinda demotivates me about modding anything that may only affect calculations...

Edited by Braver - 7/6/10 at 2:52pm
post #7 of 9

The VTA adjuster is the way to go. The OM-20S should work fairly well. I have the 20S myself (and like it a lot) used with an old Mission arm on a vintage Revolver table I bought back in 1982 (not as good as the RB300 but similar in concept/design). No VTA adjustment though.

 

You might want to explore some options locally if you can (a decent Audio shop should be able to set your table up for you for a fee). This way you get the arm/table/cart optimized without all the fuss of actually doing it yourself (but DIY is a good way to learn how to do it for future reference). Maybe a DVD setup guide would be a smart investment for the future.....I'm sure the local dealer could provide such a thing or at least info where to buy it.

 

Peete.


Edited by Pricklely Peete - 7/6/10 at 8:45pm
post #8 of 9

 

Originally Posted by Braver View Post
Huh, what are you talking about here? I don't need numbers to know if something works or not, and I'm not asking for recommendations on other carts, i just told you guys it sounds fine. If I could calculate how something sounds I'd listen to a computer. So, no actual experience on the merits and difficulties of shimming an rb300? The fact that tightening the nut on the arm mount would also change the sound kinda demotivates me about modding anything that may only affect calculations...

 
 
The numbers referred to here are to do with matching the mechanical resonances of the arm and cart so they don't colour the sound or cause mistracking.
 
 
Basically the further up the Ortofon OM range of stylii you go the higher the compliance which means that lower mass arms are more suited. This is a '70s  design paradigm long since abandoned by tonearm designers so what matches a ULM arm on vintage deck like the Dual CS-505 and what matches a Rega RB250/300 tonearm are different in this respect.
Remember a turntable is first and formost a mechanical device and every part of it has audible resonances which can be tuned but never dismissed.
The OM-10 and 20 are a borderline match for the RB300 so you may find you get more mistracking than you would with a more modern or lower compliance cart.
None of this has got much to do with your subjective appraisal of the way it sounds.


 


Edited by memepool - 7/7/10 at 4:19pm
post #9 of 9

The arm on the P3 is set for Rega Cartridges, an OM-20 is taller than a Rega so yes you should raise the arm. The purple cart, if it's kinda tapered looking is probably a Rega Elys. Compare the height on that cart to your OM-20 and you'll see the difference.

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