Orbit arm - improving an RB301 arm.

By dave | January 3, 2016

arm closeup

After many other upgrades, finally the time came for the arm to be upgraded. Reading on the forums, ISOKinetik and DIY site Audio Mods there’s no end of information and examples of how to modify Rega arms. Here I try and provide the path that I took, which led me to a successful arm that I’m pretty happy with. This guide deals specifically with the RB301 arm, it may be applicable to other arms as well.

In the spirit of DIY this is a pretty complex task and I’d say its more than possible you could end up with a broken arm. You’ll certainly not be able to reuse the original Rega wiring so a wiring kit is a must. Countering that, once the arm is apart, most of the parts can be replaced. Before starting take a look at the Audio Mods website. This site contains vast amouints of detail on Rega arms and also sells finished arms and kits. Also ISOKinetik sell arms and wiring looms. I do not get any remuneration from either - but think the products deserve consideration.

 

After much deliberation, I came up with the following steps:

  • Strip down arm and remove tracking weight spring
  • Remove the paint from the arm and sand to decent finish.
  • Drill holes into the arm to break up resonances.
  • Rewire with wiring loom of choice
  • Fill around the wire exit from the arm.

Stripping down the arm:

Before starting you'll need to totally strip down the arm. This is done by removing the bolts at either side of where the arm meets the rear section. You also need to remove the two smaller bolts that hold on the vertical tracking. To be able to remove paint fully, the tracking weight plastic dial also needs to be removed. This requires the removal of the holding bolt and also the removal of the spring - see diagram below. Note that after this you will not be able to use the tracking force adjustment any more, and any such adjustment will need to be done by moving the main weight. ONLY do this if you have an ISO weight or similar that is easier to fine adjust.

At this point it is useful but not essential to remove the tracking weight stub, to do this I had to put the arm in a vice and use a plumbers wrench (with a lot of care). You will probably find it is tightly fastened - maybe even locktight applied too.

At this point the bearings are visible at either side of the arm, cover them with tape to avoid dirt getting into them at this point.

Arm in vice  arm in vice grips

Left: arm in the vice to help with strip down. Right: Grips with may be needed to remove the stub. Wrap insulation tape around arm to protect first.

tracking force spring removal

Above: removal of tracking force spring. NOTE: Once removed tracking force adjustment only possible using counterweight.

Removing paint from the arm and getting a finish.

To do this I used Nitromoors paint remover. This had to be left on for a while and then I had to use wire wool with a bit more product to get the paint to shift. It takes a while but it will eventually shift. There are plenty of videos on youtube that show examples of doing this.

Once the paint is off, clean down the arm in white spirit, again carefully avoid the area where the bearing are, they should still be covered by tape.

At this point it's time to sand the arm down, to achieve a brushed look. I started with 300 grade sandpaper and worked up to 1000 grade. To be honest the results of this approach are generally pretty good. There will be some casting lines, sand these out first and personally I'd avoid any kind of machine sanding - the alloy is mild and easily sands by hand. This is complete once you're happy with the look of the arm. That for me was after 1000 grade sanding.

At this point ensure the point where the cartridge mounts is entirely flat, sand this until the cartridge mounts absolutely flat. I decided to spray two very thin coats of lacquer onto the arm to protect it from marks. 

arm during sanding down

Above: arm during sanding down.

Drilling holes to break up resonance

There are many drilling patterns advised for this, but I chose a simple two line approach I found on the internet, it seems to work. From what I can tell the holes don't need to take up any specific area. Different arm makers use different drilling patterns into Rega arms. The science goes that the holes break up resonance in the arm and slightly reduce the available mass, further reducing resonance. If you take off the paint, you really do need to do a bit of drilling. Be very careful using a centre punch to mark out, the alloy is very mild and bends easily. To drill the holes I used a pillar drill with a mini vice using soft material on the grips. Set the drill to high speed and use a good quality HSS bit, given this the drilling should be easy.

I also tapped a small M3 bolt into the arm that is connected to earth on my wiring loom. This can be seen in the image below.

arm drilling example

Above: one example often found on the internet for drilling a rega arm. There are other drilling patterns too (http://audiokarma.org/forums/index.php?threads/lf-audio-mods-drilling-template-for-rega-tonearm.561891/) for example.

Rewiring the arm

There are many, many rewire kits for rega arms. You pays yer money and takes yer choice. Personally, I went for an ISOKinetik Cardas wire to KLE plug rewire but there are many other choices. While rewiring the arm I would also change the counter-weight, again I got the ISOWeight, but there are many other choices, pretty much the same as the wiring. All arm rewires generally come with full instructions.

Assembling the arm

Reassembly is pretty much the reverse of the prior instructions. Basically just bolt the arm back on at both sides. Make sure that the wiring loom allows the arm to move freely and is not doubled up at the pivot point.

Filling the lower part of the arm

Originally I had filled the lower part of the arm with foam from in-ear hearing protectors. This did not work as I think it over-damped the response. I've now removed more than 90% of the foam and just left a little around the end of the arm where the cartridge wiring is. Just a very small amount, maybe equivalent to 1/2 to 1 ear protector. This seems much better to my ears, but I quite like my treble. At the end of the day it's easiest to start with a very small amount and build up. Since the most recent changes, I ran some measurements and the response is now nice and flat. Further, it passes pretty much every test on the HIFI news test record.

foam filling the arm tube

Above: foam filling the very end of the arm tube by putting small amounts of ear protection where the wiring leaves the arm.

Below: complete arm

complete arm fitted to deck

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