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A weighty conundrum

I have recently encountered a problem with setting my tonearm pressure. I have 2 digital scales to confirm proper function with. The first is a Saga mini digital scale that has a weight spread of 0.1g to 350g. It's a flat scale with a metallic plate surface. The second is an arm load meter (no brand name). It too has a metallic plate with a white circular area center and a black dot in the middle. This model has a range of 0.1g, but only up to 5.0g. Both are calibrated with a 5g weight. Both check dead on with the 5g weight. I'm weighing the tone arm pressure on a Denon DP-47F direct drive table with a 2M Black Ortofon cartridge. The down and dirty Saga scale reads 1.6-1.7g. However the arm load meter (with newly replaced batteries) now reads 3+g. When I set it to the recommended stylus pressure I have to move the counterbalance weight almost out to the end of the arm. When I do this, the smarter than me automatic turntable won't even start. I'm flummoxed. Any ideas out there would be much appreciated. Thanks in advance, AB

128x128arizonabob

Showing 2 responses by lewm

lewm
12,503 posts
 

One other important issue with your two scales: be sure their weigh pans (the platform whereon you place the stylus tip) is totally nonmagnetic. Most steel has at least some iron in it, and that can really screw up measurement of VTF, because the cartridge contains powerful magnets as you know I’m sure. One sign of this problem is the scale indicates negative weights when the cartridge is hovering over but not touching the weigh pan. Because the magnets in the cartridge are pulling the weigh pan upward. I bet your 350g scale has a ferrous weigh pan.

lewm
12,503 posts
 

It’s impossible to say much about differences between your two digital scales, except that the one with the range from 0.1 to 5.0 g is the one to use. For best accuracy, you want the VTF you seek (or any measurement of weight) to be within a narrow range afforded by the gauge. A gauge that reads up to 350g (!) is unlikely to be so accurate in the range where you typically would measure VTF for any phono cartridge. The other issue is the position of the weigh pan (the area wherein you set down the cartridge in order to measure VTF). Make sure it is in the same plane or nearly in the same plane as that of the surface of a typical LP. If the two scales differ in that regard, use the one that places the stylus tip in the plane of a typical LP when measurements are made. This means, of course, that you want to set the scale down on the bare platter or platter mat, NOT on the surface of an LP which will inevitably raise the whole scale a bit too high.

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