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Pedersen armboard mod for Michell turntables

[Italian version]

Products: Armboard mod for Michell turntables
Manufacturer: Pedersen - Denmark
Cost: 70 €/$ approx
Reviewer: Geoff Husband - TNT France
Reviewed: December, 2003

[Pedersen bits]


Anyone reading my turntable tests will know that throughout the reference has been my Michell Orbe/SME4 combination. Though a fine pairing in many ways it has been shown up by several of the test turntables as having a bloom in the upper bass. Various fiddling made me increasingly sure that the problem lay in the way that the SME, being ultra rigid and very solidly clamped to the turntable, transmitted vibrations into the cast aluminium turntable chassis which 'rang' in sympathy. Placing the stylus on a stationary record and then tapping the chassis with a fingernail produced a 'bong' at exactly the problem frequency. Damping the springs with a finger didn't help so the chassis was the culprit.

There were two possible solutions. First to damp the chassis in some way. Michell were obviously on to the case because one of the 'upgrades' to the Orbe compared to the Gyro is a load of black damping gunk pressed into the cavities of the chassis. Trouble is it doesn't damp it enough.

The other possibility is to break the circle of cartridge/arm/armboard/chassis/mainbearing/platter/record/cartridge... The simple answer is to use a unipivot or other similarly 'lossy' arm design that won't dump so much energy into the armboard - interestingly Origin recommend that their arms are only done up 'finger tight' on the Orbe for this reason. But hell's teeth, the SME is such a wonderful match in every other respect it would be criminal to loose the chance of using one. Again Michell were obviously aware of the problem as they'd started using lossy plastic rather than metal spacers between armboard and chassis, but again it wasn't enough.

Then by chance I came across the 'blue-tac' solution, for the story go here, and at a stroke the problem was much reduced and at zero cost. You see the Michel solution of those plastic spacers is fundamentally flawed because the armboard is still bolted down and so any vibrations will simply travel down the bolts. With the blue-tac solution the armboard is clamped down, squishing the blue-tac, then the bolts backed off. Result? A big improvement in clarity, bass speed, imaging and mid-range detail. In fact so great was the difference that the mod had to be removed in order for the reference to remain valid - the modded Orbe being a much more difficult nut for other turntables to crack than the stock version.

But the mod isn't perfect. First, unless you are very careful you can see blue-tac and it's not really appropriate on a work of art like a Michell table. Then of course blue-tac isn't consistent. Its elasticity varies with temperature and it hardens over time.

Enter Gert Pedersen

Of course someone else was looking at the problem:-) Pederson have been modding Gyro's for years now and the latest tweek was an armboard isolation kit designed to address exactly the same problem I had encountered. The kit consists of a perspex spacer, and selections of rubber washers etc. The diagram is self-explanatory. It's a half-hour job to fit and of course it's totally reversible.

[Pedersen diagram]

Look carefully at the diagram. The armboard is isolated from the chassis by the acrylic, a layer of rubber and washers. But most important the bolts are isolated by rubber washers under their heads and rubber tubes down through the board itself. This means that the armboard is isolated top and bottom - floating between the two. Unlike many mods the result looks even better than the standard spacers and unlike the blue-tac mod the result is consistent and by altering the tightness of the bolts the level of isolation can be varied. BUT personally I'd leave a little blue-tac on the threads of the bolts otherwise there is a chance they may rattle against the chassis.

The Results

This kit should be offered by Michell as an upgrade to their turntables - it is THAT good. All the advantages of the blue-tac tweak are there. The cleaning up of the critical upper bass, lower mid is dramatic - it sounds literally like the 'window' is being opened further. At a stroke allows the Orbe to give much more expensive turntables some serious worries.

Now I'm sure there are some people out there for whom the drying up of the sound, the increase of precision, will be unwelcome. If you have a dry, pushy system then a bit of bloom doesn't go amiss. Perhaps one reason why the standard 'Orbe' (and incidentally the old LP12) have remained with such a glaring and easily remedied fault, for so long, is that in Britain the combination of small and well-damped rooms, and necessarily small speakers, prefer a flawed presentation that better rooms quickly flag up.

So here's my advice. Try the blue-tac mod and see if you like the result. If you do, then next time you have 70e burning a hole in your pocket go order the Pedersen board because it'll be even better and you won't have to keep renewing the blue-tac. If you don't like the result just unpeel the blue-tac and use it to stick up your England rugby-team poster...

systems used

© Copyright 2003 Geoff Husband - www.tnt-audio.com

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