Interesting difference between 12" and 9" tonearms


So I just got my 1987 Decca Super Gold cartridge back from John Wright with a Decapod fitted and new Paratrace stylus. Modified Garrard 401 with 2 arms. (see my Virtual System). I installed it in my 9" Jelco TK-850 and it didn’t sound good. Lots of surface noise and missing inner detail. I adjusted VTA and VTF and improved it some but it hadn’t a patch on the other Decca (Garrott Bros Gold with new LC stylus and Decapod) on the 12". A little irked, I tried it in the 12" version of the same arm on the same table. Same cables and armboards. Ridiculous. Transformed. Minimal surface noise. Tons of detail. Crystal clear. Musical as all hell. In fact, I can’t stop playing album after album. Ridiculous! (Cross posted from a comment on @halcro post)
noromance

Showing 4 responses by noromance

@millercarbon There's no cantilever on the Decca. 
@rauliruegas The 12" Jelco 850, knife bearings or not, sounds fantastic with the Decca. 
@chakster The 12" Jelco 850 sounds fantastic with all three of my Deccas. 
Gentlemen, thanks for your comments. It seems that the 9" is not a great match whereas the 12" is completely fine. I'll try it again with some mass added.
@stringreen Set up exactly as the 12" except for overhang. They're on the same table. However, you got me thinking. The 9" has the standard Jelco base while the 12" has the Ammonite base. Could there be an azimuth issue? Would that cause surface noise? I run other Deccas without issue on the 9" but they all sound better on the 12". I wish the plinth supported 2 x 12". 
Dan,
My guess is the additional mass of the larger arm and possibly the better tracking ability of a long arm made all the difference.