VTF measurments with a unipivot

On the VPI JWM unipivot arms, from your baseline setting, the VTF increases as the stylus height increases. The VTF decreases as the stylus height is lowered. This is presuming the VTA is the same.
Another way to look at it, from your baseline setting, if you have VTA tower, as you increase the height of your VTA tower you lower the VTF. If you decrease the height of the VTA tower then you increase the VTF.

Another way to look at it, if you want precisely the same VTF on 120 gram, 180 gram, and 200 gram records, then you would need to set the baseline for 120 gram, then increase the height of your VTA tower to compensate for the additional record thickness.

From memory, the differences are slight, something around 0.03 grams or so, from 120 to 180 gram.

Since the difference in vtf between a 120g ad 180g record is less than 2% do we really care? Since VPI arms lack fine and repeatable vtf adjustment the issue becomes a moot point.

Hdm and Captain Winters,
Thank you for your responses; this is exactly what I was looking for! My digital scale has the same design as the one in your link, Hdm, only is a cheaper version. It does seem to do a decent job with the exception of a negative reading as the cartridge approaches the dot. However, I get consistent readings both ways (I place the stylus on the scale and then turn it on; once I get a zero reading, I lift the tonearm).

Brf,
Yes, I agree with you that the final adjustments should be done by ear, but Lyra cartridges have a very specific VTF recommendation for optimal performance. So before I start adjusting, I'd like to know what 1.75 g sounds like and take it from there. To get the best sound out of my Delos might be as simple as making sure the VTF is set up correctly.

Actusreus, you can always measure the distance from the plinth to the record surface, take the platter off the table and build a platform out of playing cards to hold your digital scale to equal the playing surface height desired.

Not sure if there is a difference at starting at 1.75g or 1.78g when you will make the final adjustment by ear.

I any event, good luck. Time spent dialing in a cartridge yields great results, although sometimes, it can be very frustrating.

Dear Actusreus : Cartridge set up always is important and critical to have a good quality performance level from the cartridge.

Now, IMHO it's almost useless to ask for the penultimate VTF set up in a cartridge/tonearm set up due that that " perfect " VTF set up never works ( not only because there are different thickness in the LPs. ) because each single LP is not perfectly flat so almost at each " groove " VTF changes " like it or not ".

Good that you are interested in " perfect " VTF but this does not works during playback and that's why cartridge manufacturers give us a VTF cartridge range. Normally I made my cartridge VTF set up at the middle of that range or a little over it.

regards and enjoy the music,
R.