Joe,
Good job as usual and thanks for the pix. No need for me to say more, this is simply a mandatory, no-brainer upgrade for anyone with a Rega/OL arm and a low-mid compliance cartridge. In all our time living with both mods (we discovered the VTF mod while demoing the HIFI mod) there have been no downsides.
*****
Note to all: the VTF mod should properly be called Paul's Mod. I stuck the HIFI mod weights on with a bent paper clip for testing, but my partner is the one who immediately recognized that swivelling the clip fore or aft would affect VTF in a controllable fashion.
*****
Here's a link to the original thread for those who need more help than Joe's picture! ;-)
http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1074206586&read&keyw&zzvtfBTW Joe, nice round curve on the paper clip. Ours is sort of an upside-down "V" shape. Yours is better looking.
Dan_Ed,
VTF change would be affected both by the weight of the paper clip and the distance forward or aft of the pivot.
There are two issues that one might want to address: the overall range of VTF's that can be achieved without moving the C/W and the fineness of adjustment within that range.
Adjustment range
On our rig the one clip gives a range of slightly more than .3g. Moving the clip away from vertical adds or subtracts up to .15g. That's enough range so that I only have to move the counterweight twice a year. In the Autumn I set the C/W so that VTF is 1.85G with the paper clip vertical. This gives me a useable range of 1.70-2.00g, ideal for a Shelter 901 during colder weather. In the Spring I back the C/W off so the center point is 1.70g, with a range of 1.55-1.85g. This is good for all Summer.
Adjustment fineness
With only .15g difference between straight vertical and nearly flat horizontal, it's easy to hit a spot withing .01g. If I really cared, I could drag out my digital scale and set it for exactly 1.77g, or whatever. This would be silly of course. I use the scale to set the counterweight to the appropriate point (as mentioned above) then fine tune the paper clip by listening to music. Who cares whether you're at exactly 1.77 or 1.81?
As Twl mentioned, the Shelter cartridges (501 and 901 anyway) are amazingly VTF sensitive, and the right setting is heavily dependent on the weather. We find ourselves fiddling the paper clip nearly every day, no doubt due to the very changeable weather here in New England. Nevertheless, for our purposes the range and the resolution afforded by a single paper clip are more than sufficient.
Folks, I just wrote nine paragraphs about a paper clip. Now there's an assignment any sadistic English teacher could hand out with pride.