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Planar3/RB300 Azimuth

M

Mr Pig

^'- -'^
A friend of mine has just bought a beautiful condition old Planar3/RB300. Really lovely but I've noticed the azimuth is out. Obviously no provision for adjusting it so I'm trying to decide what do do. Only two things you can do, tilt the arm or tilt the bearing.

Has anyone done this on a solid plinth Rega? If so, what did you do and how did it work out?

Thank you :0)
 
If there's enough play in the hole, shimming one side of the arm mount would be easiest. Alternatively, you could try putting a shim on one side of the cartridge.

Or if you're game for an irreversible mod, grind the bottom of the headshell to the correct angle.

Another possibility: could it be the cartridge that's out?
 
Durmbo said:
Another possibility: could it be the cartridge that's out?
Click to expand...

No, measured the platter and headshell with bubbles.

Shimming the arm would be the easiest thing to do but you'll see it. I was wondering if anyone had moved the bearing.
 
Not done anything to a Rega, but if you have bubble levels, can you not work out which of the arm and platter is skew wiff? If you’re really unlucky, I suppose it could be both. In opposite directions.

How does the bearing attach? Any chance of grinding or filing a suitably large diameter washer to shim the main bearing?

One last suggestion, which probably won’t appeal for sake of appearances, is to shim the cartridge. Linn’s top cartridges have had 3 little lands to provide defined contact points for years, Ortofon* likewise,and John Burns of Pear Audio apparently advises 3 nylon washers between cartridge and headshell for mild decoupling. 3 washers of slightly different thickness would at least make it look as though it was done intentionally. Might even improve sound!

* Ortofon actually intends this for azimuth adjustment on fixed headshell arms - the Jubilee started it, but the Cadenza and Quintet series have carried on with it.
 
It's not far out so it doesn't really matter whether it is the arm or platter which is out. you can move either and fix it.

You can't really shim the cart as the arm swings in an ark. Say you shimmed the cart to be correct with the arm o the rest, it would be wrong at the end of the record. Unless it's the headshell which is squint, in which case yeah, you need to fix it at that point.

The bearing just drops through a hole and is held on by a nut underneath, exactly the same way as the arm attaches. I don't know how much clearance there is in the hole to move it.
 
Rega's brass bearing bush is designed to fit tightly in the plinth, often necessitating the use of a rubber mallet to remove (post removal of the nut/washer and hub/bearing spindle, obviously).
 
I wonder if there is a very slight twist in the base?
I've a couple of Regas at the moment and had a few before and never experienced a problem with azimuth?
You should be able to establish if the platter is or not true to the base with a couple of steel rulers. Maybe undo the nut underneath and turn the bearing 90 degrees and see if it is better / worse.
As Craig says there is no latitude in the platter bearing fit to the base to shim it.
I would check the cartridge mounting is dead flat too. Either way if there is a problem its the arm / mounting you will need to 'trim'. If necessary I would shim the cartridge /cartridge mount pad, not the arm base.
 
snowman_al said:
Maybe undo the nut underneath and turn the bearing 90 degrees and see if it is better / worse.
Click to expand...

Interesting idea. I think it's more likely to be the hole not drilled right if the hole is tight.

I've not checked the plinth other than looking along it, looks ok. A lot of Planar2s were not laminated underneath and those plinths can bend like bananas but the Planar3 plinth is pretty stable.

As soon as I realized there was an issue I told my friend it would need sorted later and got the deck up and running for him. I didn't see the point in investigating too deeply when I couldn't fix it there and then anyway. Just wanted to think about it for a while and get a few opinions before I pull it to bits.
 
No way would I mess with the bearing angle. Again, I second or third shimming the cartridge. It will be hardly visible, and why care about appearances if it corrects the problem? I don't see how the azimuth could change as the arm moves across the record.

Is the platter level with the plinth?

My platter used to have a small amount of up and down as it rotated. It didn't affect the sound and I thought the hole hadn't been drilled perpendicularly, but it turned out it was caused by the subplatter of early 80s vintage. Replacing it with a late model one fixed it. It's made of a much more rigid material. It also improved the bass markedly. Analogue Seduction sells the complete bearing and sub assy for 22 GBP. I can also recommend replacing the feet with newer ones, also a very inexpensive upgrade.
 
Durmbo said:
I don't see how the azimuth could change as the arm moves across the record.
Click to expand...

Let's say that the headshell is not level, let's say it is 1mm high at the right. Everything else is fine. As the arm moves across the record the cart will be 1mm high at the right the whole time. The azimuth will not change.

Now let's assume instead that the base of the arm is 1mm high at the right, looking from the front of the deck. While the arm is sitting on the rest, the net result is similar. Not exactly but the right side of the headshell will be up about 1mm. If you shim the cart on the left you correct this and the cart is now flat.

If you swing the arm over to the center of the record, the high side of the arm base is no longer to right of the arm but is more behind it. It is no longer raising the right side of the headshell so the fact that you've shimmed the left side of the cart means that the cart is now high on the left!

Right now I don't know where it's out. I need to go back and check before I'll know where to adjust it. I don't know if he platter is level to the plinth, but it doesn't really matter. Visually, it looks fine but you're only talking a millimetre or so. All that matters is that the headshell is level with the platter.
 
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