lewm
03-15-2016 12:10pm
JP, can you amplify on your cryptic comment about the effect of a heavy platter mat? "Drive gain"?
Okay, but I’m more than rusty on root locus and complex conjugates. :)
My very hasty research this morning indicates rotational mass isn’t going to have an affect on the PLL if the drive is compensated. It may not have a meaningful effect regardless.
Increasing the rotational mass means a given correction to be performed in the same amount of time will require more energy. If not the reaction time will be slow. Note the sync position timing for the MK2A and MK3 are the same, yet the MK3 platter is just over 3x heavier. Most of that mass is inboard but it’s still a significant difference.
I think this is one of the reasons these DDs can be so polarizing - there’s no way to tell how different techs are calibrating them without measuring one first-hand, thusly no way to really know that they’re performing the same. A MK3 can be dialed back so far the motor will actually overshoot and bounce off phase lock 2-3 times before settling, or set over-critically such that the drive MOSFETs will self-destruct in seconds. I’ve mentioned I’ve seen these running in belt-drive emulation mode before - that’s wasn't a joke.
I haven’t measured a MK3 or MK2A with additional platter mass. On the MKII the W&F measurements were negligible, but I don’t think that’s a spectacular measurement for how a drive system reacts to real-world conditions anyway; more of a steady-state baseline.
The TT-101 at a block level is really no different than an SP-10 aside from what it takes to drive their coreless motor, so I wouldn’t expect a little extra mass is going to have a broad affect on what you hear. The motor will not be as critically controlled, though depending on the mass that may be negligible, or actually preferable.