Rewiring a Rega RB250

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Sounds like an old story, but...

I am intending to rewire a RB250 with the Incognito kit. Lurking around, I found this paper which seems of some interest :
http://www.tnt-audio.com/sorgenti/analogue_bits_e.html

But I also found this one and got a bit puzzled by the warnings :

http://www.william-reed.net/audio/rega1.html

I've noticed that according to the first author, rewiring a RB300 and a RB250 seems to be slightly different ; I quote :

"Having the main tube apart allows easy access to the tiny hole the wires are supposed to go through. Believe me, this sure beats messing around with a pull cable (as still is required for the RB-250, by the way!)"

So... Can I apply the first procedure to the RB250 and remove the arm tube ? I wouldn't want to destroy the bearings in the process, even though I don't really see where is the problem...

Thanks


Pascal
 
Hi, that second link is mine, and I really do recommend not taking an RB250 apart!

The very easiest way is to prepare for the re-wiring *before* you remove the old wire. Tie some fine thread to the old wire and pull it through, then you have the thread ready to pull your wire through with.

If you have to start with a bare arm, then the best method I've found is to strip a single core of Cat5 wire which is about the right stiffness to thread through. With the stub out, you can start at either end, but the base is easiest.

Once the Cat5 is through, you can either solder the wires to it and pull them through from the base, or use the Cat5 to pull some thread through and use that to pull the wires. I find the second method can work best.

If you're using the Incognito loom, you'll only have to do the cartridge tags as all the rest of the work is already done, so it's a fairly easy job.

regards, Jeff
PS, Although the RB300 just unscrews, the bearings were originally set up using a jig and there's no really accurate location for the two bits of Yoke (like dowell pins) so the chances are that you may not be able to replace them as accurately as originally. Bearing alignment and loading are really critical to performance.
 
Hi Jeff,

Thanks for your comments. Actually I had a slightly different method in mind : I was intending first to remove the existing counterweight and stubshaft (as I have to do it in order to install the Michell TecnoWeight...), then to introduce the Incognito wire from the base, to get the wires from the rear of the arm and to pull them (gently) along the tube with a very thin stick of bamboo (as suggested by someone ).

What do you think ?

Regards

Pascal
 
Hi, It might be hard to get the wires up the vertical tube from the base by pushing rather than pulling as they'll tend to bunch. Also, there should be a tiny rubber grommet at the top of the tube making it much more difficult (but that often gets displaced when de-wiring the arm. Pulling through on thread or wire is very easy once you have the thread in place and there's very little chance of damaging the very delicate wires.
regards, Jeff
 
"What is so difficult about taking them apart?"

Nothing hard about taking them apart, just putting them back together as you will definitely ruin the bearings and damage the brass stubs.
I've done six RB250s and never been able to get those stubs out without damaging them. They are in very tight and the brass is very soft, so you damage the screw slot badly. Unless you can devise and make a rather precise little puller to act only on the outer race, you have to drift the bearings out, which seriously trashes them.

The yaw bearings in the brass body can usually be left in place whilst their shaft is taken out, but replacement is so easy you might as well change them. Alignment and loading of the bearings is *very* critical, as I've found to my cost and there's not really a chance to adjust them afterwards. I really wouldn't want to tackle setting up new bearings using the standard Rega location method. I now make every component from scratch keeping only the arm tube, 'cos proper bearing location is easier that way!

Replacement bearings are about £4 each from RS components and all 4 are the same. do resist the temptation to try high-precision bearings in standard Rega mounts as the location isn't accurate enough for them and the results will be far worse than ABEC3 bearings. The RS ones are ABEC5 which is a bit tighet for this application, so running them in well before installing them is well worth the effort.
 
Hi Jeff,

I had a look on your site. Quite impressive. I like very much your counterweights, especially the low-cg one.
Is it just a one-shot project for your own personal agreement or do you intend to offer some of these modifications on a (even informal) commercial basis ?

Pascal
 
thanks jeff, as a man with way more experience than me ill take your word for it.
I only wanted to take mine apart to remove the paint.

I have been mesing with adding clips to the arm tube to reduce resonace with good results, so ive been thinking about drilling the arm tube to make the mod more permenant.
Any tips?
What would work best, your spiral way, or OL's slots?
Would a row of different size holes in the underneath of the arm work?
 
Hi, since putting those pages together, I've been working on a design where the bearijng housings would be adjustable, allowing really high quality, close tolerance ceramic bearings to be used. This is only a prototype, but it's working out really nicely.

sorry, kinda getting off topic here........

This wasn't really ready to show yet, but here's some rather crummy preview pics:

http://www.william-reed.net/audio/newpics/

The new ceramic yaw bearings feature a much longer brass/aluminium/carbon-fibre-damped shaft set in a split, adjustable carrier
and the pitch bearings are carried on a split, adjustable aluminium yoke. Both can be dismantled and re-assembled by anyone.

The nice thing about this is that because assembly doesn't require any machine tools, I could offer it as a kit(s), which could be:
1 - yaw bearings: the solid aluminium centre for the arm, the bearing shaft, the arm yoke, bearings
2 - pitch bearings: a modified Rega brass body, new bearing carrier, new spindle, bearings
3 - end stub and weight

Low pivot weights.
When measuring this arm, I decided that my previous ideas about low-pivot weights were seriously wrong - I was building in far too much stability which was OK when the record was completely flat but led to very low-frequency (<10Hz) resonance with warps. The new arm reverts to a centreline weight with a slight low bias, giving a just-stable result. I've tried to match the stability to the Music Maker III compliance, about .002gm/mm offset, but only listening will tell.

As you can see, most of the work's done but I'll write it up properly when it's finished.

Regards, Jeff
 
Hi Graham.
A couple of things I've found:
- Only taking the paint off a rega casting makes the thing *much* worse. That thick black stuff really helps damp it.

- Polishing the arm is pure vanity and I confess to being guilty. I suspect it actually does harm, because castings have a surface "skin" that will probably help damp the tube as will ting surface imperfections and cracks. The Michelle technique of bead blasting would restore this effect. It's a shame, but laquering the arm after polishing helps.

- I don't really think that the kind of holes are critical, but opening up the tube really does help. In theory, cutting a slot is surely mechanically bad as it seriously weakens the tube. In practice, that might not matter. The spiral holes work well for me and are really easy to do with a regular small bench drill if you mark out a strip of tape then wind it round.

- the very best thing I've ever done to a Rega arm tube is to put in three little disks across it at intervals down the length. This is the most effective way to damp the thing that I know.

regards, Jeff
 
thanks jeff, i would be very interested if you offered your latest bearing mods in kit form.
I like the arm, but its got weaknesses, serious ones too if putting plastic clips on it makes it loads better in the treble!!

I assume the discs cant be added without taking apart the bearings? (sorry, ive forgotten your diagrams, ill have another look in a bit.)

It will be good to know how the new bearings work out sound wise, ill keep an eye on your site.
 
"I assume the discs cant be added without taking apart the bearings?"

Hi, I'd never really thought about it, but I thing they can, but not whilst the arm is wired. Once the stub of an RB250 is off, you look straight down the tube with nothing in the way.

There's no reason you couldn't drill the arm with the bearings in place, too, although I think you want to keep the bearings clean by maybe stuffing the stub end of the arm with cotton wool before you start.

I'll try to look out my last lot of measurements for the disks, but each arm varies a little.
Whereabouts in Essex are you, if you're near to the M25, I'm just off junction 5 and you'd be welcome to use my (rather crappy) home workshop.

Regards, Jeff
 
Thanks for that, the dimensions of the discs would be great.
At the moment everything i do will be with the bearings in place as i dont want to get into that yet.

I was down your way last week (went to sevenoaks) but unfortunately im now in sheffield, but thanks for the very genorous offer.
I still get down that way quite often as my parents live in romford so may one day swing by for a chat if thats ok.

For now ill fit an aftermarket sub and weight (probably michells) and drill the tube.
If i can get some made, or manage it with my limited tools, ill add the discs too and rewire while im at it.

That should keep me busy for a bit:D

Actually, on the subject of end stubs and weights, sou say you didnt like the low slung weight.
Michells weight is low slung, do you think the Origin Live set up is better?
 
The whole point of low-slung weights is that they add stability to the arm in the vertical and horizontal planes (which is why they appear on every unipivot). It will tend to return to it's original position when deflected because of the geometry change and therefore "weight" change as the arm rotates. the Michell weight cleverly keeps this effect to a minimum by making the cross section small - it's a cylinder. The one i made had a very large stability effect because it put a lot of mass way below the centreline - I know now that it was a bad move because although the sound was greatly improved on flat discs, it excited almost-subsonic noise from the very compliant cartridge on warped discs. Less compliant cartridges (like MCs) can take a more stable arm and I think the Michell would be ideal.

regards, jeff
 
Jeff

it looks very interesting. I found your site last year and was very interested in what you have done to the RB250... especially the VTA adjustment!
I would be very interested in the your bearing mod kit if you ever offer it.
Would you still use the Rega anti-skate, or move over to the thread and weight system?
I did rewire my Rega with Satcure, nearly drilled it... but didn't.
I think I might try this as well as your disc idea. I think it is possible to do this without removing the bearings as you've pointed out.
The discs might be harder to machine...I don't have a lathe, which I think would be a great help in machining them.
Any way very much appreciate you sharing with us.
Regards
Gerry
 
Hi Gerry,
Those disks are something that you could make with just a drill - it's just an awful lot easier with a lathe.
Assuming no lathe, no way to cut threads and no micrometer, start with a length of M3 threaded rod and some nuts.

Cut out and drill some 1/2 - 1mm thick aluminium to roughly the right shape - cut 6 or 8 of them.
Mount one on a bit of the rod in the drill and use files to round it to a little oversize. You can now use that as a guage to see where it fits down the tube. Get it to size for the smallest fit - at the cartridge end. This will need lots of test fits! You'll want to be able to push it to within about 5mm of the finished place. Now mount the rest of your disks on the rod with your trial disk and use that as a guage to size the others - give the whole lot a slight taper. If you make lots of disks and want two or three, you'll find the ones that fit where you want them.The size difference is very subtle A slight burr left on the edge will help when fitting.
You then use your rod with just one nut on to insert the disks onto the arm. Once they are pushed home, give the end a tap with a hammer - this is where the extra 5mm movement comes in. Job done!
The very best way is to heat the arm tube as well, but you can only do that with a bare, stripped tube.
 
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