Rega Arm on Technics SL-1200 mkII onward.

This deck has had a fair amount of use and the bearings in the old arm are about done.
I've wanted to fit a better arm for a while, as I never liked the plastic yoke at the centre of the Technics arm, that the bearings are mounted in. Yes it is electro plated Plastic, I've drilled one.

I don't want to spend a fortune, so the Rega Arms are a natural choice.

The Rega Arms sit much lower than the Technics Arm.
If you are using a variable VTA adjuster like the Michell on your Rega arm, then even lower.
If you put a 6mm thick mat on your Techie Platter and a 180g record on top of that - To get the Rega arm horizontal, with an Ortofon 2m Red Cartridge fitted (Average height) the surface the VTA adjuster sits on, needs to be 6mm below the top face of the mounting flange on the Technics deck (16mm below the TT top surface). If you use a thinner mat then the mounting surface needs to be that much lower still.

Rega use their own alignment geometry, which is almost the same as Stephenson's. This focuses on min distortion at the inner groves of an LP or for most of an 8" single. Many of us only play 33 RPM Albums or 45 RPM 12" singles and are more concerned with the distortion level over the whole of the playing area, on this size record. For this, Baerwald alignment seems to offer the best solution and there are various protractors around that try to do this. The problem is, they work on the stock Rega 222mm Spindle to Pivot distance. Using Baerwald null points and IEC start and end groove radii, this just doesn't work well.
You end up with the cartridge, to far forward, in the headshell, which also increases the stock 237mm effective length by about 2.5mm and requires the cartridge to be twisted a fair bit in the headshell to increase the offset angle to suit.

There is a better way!
Mount the arm at spindle to Pivot of 219.52mm and use true Baerwald geometry, while maintaining the stock Rega effective length of 237mm, so the cartridge sits at the right location.
John Ellison kindly distributed a spreadsheet that allows you to generate the numbers required for Baerwald alignment. Below is a screen shot of the data we need for the Rega Arm, using the correct Null Points and IEC start and end groove radii.

This gives:
Spindle to Pivot of 219.52mm
Effective Length of 237mm
Offset angle of 23.221 deg.
Note: Lofgren A and Baerwald are the same thing.

A lot of discussion centers on having to twist the cartridge in the headshell to achive the correct offset angle for Baerwald. As you can see, with the arrangement above, the offset of 23.221deg, is only 1.221 deg greater than the stock Rega angle of 22deg, this amount of twist will barely be noticeable.
I have drawn up an alignment protractor using this Geometry, it can be found linked in the T2_015 thumbnail of this project.

Ok, so lets crack on with it.

I purchased a pre-owned, Moth badged, RB250 and used this for my project.

I got a very nice blank Ebony Armboard made to my specification by Steve at Magna Audio.
No fixing holes or arm hole, I wanted to do these myself. He marked the centre of the board for me, to aid in my relocating the arm hole.

I fitted M4 Csk threaded inserts to the stock Technics location points.
The fixing holes were drilled on the Armboard using a clear Acetate template that lined up perfectly with the inserts in the deck.

I now needed to make a marking rod.
I used 10 x 10mm Aluminium "U" channel and measured how far it was down to the armboard when it sat on the motor cover.

I ground a point on a 70mm long M4 Stainless steel Bolt.

The bolt was fitted to the rod and I printed a rectangle on some thin card.
The length was the Spindle to pivot distance of 219.5 x the depth was what I measured to the armboard. With the Point of the bolt lining up with the corner of the rectangle I marked the length.
The second line is half the spindle diameter so 3.6mm shorter.

The rod was drilled 7.5mm dia and then cut, I extended the half hole.
The important thing is the edge of the hole should line up with the inner line as this rests against the platter spindle.

My modified bearing doesn't have a circlip holding the spindle in place. I lifted the spindle slightly, rested the cut out in the rod against it and struck an arc on the armboard to indicate the mounting hole position, which can be anywhere along this arc. Marking the hole position with the board in place removes the tolerance stack created by the board fixing holes.

This is the Michell type VTA adjuster (Left) I intend fitting and its fixing nut.
The collar diameter measured 28.2mm, so this was going to be a large non standard drill size.

I used a 27mm dia 8 point Tungstan cutter and then an adjustable hand reamer to gradually enlarge the hole, until the VTA adjuster went in as a tight fit, no play at all.

I used an Acetate template and the marking rod to check the hole centre position. I had left some wiggle room in the fixing screw holes, so when it lined up they were tightened.
The lower of the two cross hairs is the center of the armboard and Technics arm mount location. I moved the centre of the new hole position back in the deck till it intersected the arc I had struck from the spindle. This distance is just over 10.8mm but is irrelevant, it just means my new hole sits centrally behind the old Technics location and is symmetrically located Left/Right.

Thats it finished, the cut out and csk screw for the front fixing, allows the full range of the VTA adjuster to be available, without it the underside of the Rega arm rest will bottom out against the armboard.

Thats what it all looks like and I'm very pleased with the end result.
I treated the deck to a new lid and the arm has had a single run of Copper litz wire from the Cartridge tags to RCA sockets. An Ortofon 2M Blue has been fitted. For the platter mat, I glued a 3mm thick Cork/Rubber item on to the back of a 3mm thick Acrylic mat. The Cork/Rubber mat sits inside the raised rim of the platter, the acrylic mat is slightly larger and sits over the rim. This total 6mm thickness, reduced the depth required of the armboard.

The Rega Arms are not an easy fit on the SL-1200 MkII+ but all problems can be overcome if you persevere. Note, there is only 5mm clearance from the back of the counter weight to the lid when it is closed.

The stock Rega arm lift is short and when mounted like this is virtually unusable. I modified it, by bending it up (while removed) and adding an extension to the handle made of aluminium tube.
This brings it up to a much more suitable location and is now a joy to use.
A Michell Tecno Weight was also fitted while I was doing the rewire.

Further on the subject of Cartridge twist.
With the Baerwald Geometry I used and the 219.5mm Spindle to Pivot distance, it allows the correct Baerwald Null points to be used, while maintaining the Rega effective length of 237mm. This means the Cartridge sits well into the headshell and the twist of 1.22 deg is barely noticeable, as pictured.

Edit: I have removed the Acrylic platter mat. It had detail and plenty of bass/punch, but I questioned how neutral and natural it sounded. Some strange placements in the soundstage, with certain items way to far back in the mix and others too prominent.
I have lots of mats. After testing Rubber, Cork, Cork Rubber mix, Neoprene closed cell, Leather, Wool Felt, Acrylic Felt and combinations of each and various thicknesses. I have gone with a 2mm 100% wool felt against the platter with a 3mm 100% Acrylic felt on top of that. The Acrylic felt is denser and has a brighter crisper sound compared to Wool, this combination just does it for me on this deck. It gives the most natural tone across the full range of instruments and voices and everything seems placed correctly.
I tried to optimise each as I auditioned, fine tuning VTA, Anti Skate and Phono Settings, they made little difference to the overall flavour though.
This combo certainly doesn't work on my main deck, which has a 38mm thick Acrylic platter. What works works so I'm leaving it at that, time to move on to other projects.

2nd Edit: After doing more tweaking of settings, I began to realize that the anti skate on Rega arms is very sensitive, this is my first Rega so I'm not used to setting one up.
Small movements of the anti skate button and eventually I dialled in the L/R balance and placement of instruments even further.
I decided to give the acrylic platter another go and this time was able to fine tune the sound stage using the anti skate.
Much better results, the level of detail and punch in the bass is better with the Acrylic than the Felt, now the sound placement is sorted, it is a much more enjoyable listening experience.
I'll stick with the Acrylic now.