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Decca London Super Gold Compatibility Question

Can someone tell me what happens when you use the Deccas with the wrong arm? Is it a tracking issue or will it just not sound good? I tried it with my SME M2-12R with a Yamamoto wood headshell and the results were not great. Hoping it's just compatibility and not something wrong with the Decca.
dhcod
bdp24's avatar
bdp24
9,788 posts
 

The Decca/London is tricky because its’ lateral and vertical compliances are very different, the lateral being about 50% higher than the vertical. Schizophrenic! Of course, the effective (moving) mass of all arms is partially determined by the distance of the rear counterweight from the arms’ bearings. To increase an arms’ em, move the counterweight further away from the bearings. To keep the tracking force the same, additional mass is then added to the headshell, thereby further increasing the arms’ em. Serendipity! An arm with medium lateral mass and high vertical would be optimum for the Decca/London. Is there such a beast?

A good way to add mass to the "classically"-styled Decca/Londons (the Maroon/Gold/Super Gold, etc.) is to order it with the optional Decapod top plate/mount. A second benefit to the welcome added mass of the pod is the far superior mounting of the cartridge to the arm it affords. The stock cartridge holder/mount is a flimsy joke, completely unacceptable. Owners of stock cartridges can have the Decapod installed at the factory at the same time retipping is done. Well worth its’ modest price.

noromance's avatar
noromance
9,769 posts
 
@bdp24 I always thought an arm worked best the closer the counterweight was to the bearing assembly. That’s why I suggested a heavier weight to balance the heavier headshell rather than moving the existing one further away.
bdp24's avatar
bdp24
9,788 posts
 

@noromance, you make a good point. A heavier counterweight closer to the bearings can produce the same effective mass as a lighter one further away, plus create less moment-of-inertia, a good thing say engineers (I take their word for it ;-). The Zeta arm has a counterweight that has it’s rear plate bolted on, with two internal steel washers which can be added or subtracted as needed or desired. Mine was missing one of the washers, so I substituted lead weights bought at a hobby store.

I needed the extra mass to compensate for 1- the missing Zeta counterweight washer, 2- the extra mass of the Decapod on my London Super Gold Mk.7 (it doesn’t weight much more than the standard mount), and 3- the outrigger that is integral to the Townshend Audio Rock Elite table I have the arm mounted on; it gets bolted on to the cartridge end of the arm. The Rock/Zeta/Decca-London combination, a true classic!

br3098
994 posts
 
The horizontal and vertical compliance differences presented by the London Decca cartridges necessitate the use of a "stiff" tonearm.  Adding weight to the headshell and increasing the counterbalance weight of a tonearm will not compensate for a resonance compliance mismatch and, in fact, can make it worse.  Not all stiff tonearms are heavy and not all heavy tonearms are stiff (although most are).

Think of it this way: a PVC pipe is lighter and "less stiff" than an aluminum pipe of equal size, and an aluminum pipe is less stiff than a steel pipe of equal size.  A carbon fibre pipe of equal size would likely to be stiffer and lighter than the PVC pipe; especially if the carbon fibres were aligned down the length of the pipe and not wrapped circumferentially.

Adding weight to each end of the PVC pipe won't make it  any more stiff.  But the added weight, outboard of the fulcrum (pivot point) will almost always increase the resonance amplitude as they swing around the axis.

noromance's avatar
noromance
9,769 posts
 
Interesting. Yet because the tube in question is not PVC, the added weight worked. Perhaps because the added mass is harder to excite allowing the stylus to move without wasting energy vibrating a lighter tube. Even if that tube was stiff.
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