It’s not “different”, it’s just another way of stating output, in this case with respect to stylus velocity. In those days the standard stylus velocity was 3.54 cm/sec. If you multiply that velocity by 0.9, you get around 3.2 mV, which is a bit less than the typical output of an MM and might account for the OP observation. Or it might not.
ADC moving-iron cartridge has "low" output
I have two identical ADC gold-body XLM-III carts from the late 70s. I purch'd them used, as part of two turntables that were each purchased from different parts of the US. Each cart has a different model of stylus (XLM-III and QLN-2) , and styluses can be interchanged.
The MI series from ADC should output 5.5mV, which I have not measured. However, BOTH these carts are challenged wrt output volume. Not only do I have to crank up the vol. more than 1/3 above other carts, but the sonics are a bit "small" and not "full bodied". It might be due to weakening permanent magnetism -- these are both getting close to 50 yrs old .
The perm. magnet in ADC moving iron series is mounted in the removable stylus, just above the stylus/cantilever assemble.
Not sure what else the low volume may be due to??? These are my my only MI carts in my collection. Anyone know more?
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Good call on the stiff suspension, as this can be an issue. One of XLM-III stylii had this issue, the other did not. The stiff sus. also leads to DISTORTED sonics. But I was able to mostly restore with a bit of WD40 (see the AK forum for this). About 5.5mV ... I have the orig. box.manual/spec sheet: https://i.postimg.cc/vZ17dbdr/IMG-9864.jpg
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lewm, it's different by a factor of 5, or 3.54, or .... I don't fully understand the velocity, but I think Yogi's source got the number from the sensitivity spec, not the output spec. OP's folded model sheet in the box says 5.5mv output strength and, that specimen's specific calibrated data says sensitivity 1.1mv the ADC chart spec I posted above defines various model's output at velocity 5 cm/sec, so using lewm's method (but using 5 rather than 3.54) if you multiply sensitivity/cm 1.1 x 5 you get 5,5mv output strength at 5cm/sec. for lewm's comparison, that unit's sensitivity 1.1 x 3.54 = 3.89, I just checked, found the Shure V15Vxmr output at 5cm/sec is only 3.0 (I would have thought higher) and the AT440ml is a high 5.0mv, also at 5cm/sec (I would have thought lower) the vintage AT160ml's with Beryllium cantilevers I just started using a few months ago are 5.0mv
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