The Secret Society of Lathe Trolls

Ask me for anything but time... I am increasingly convinced that I will wind up doing my own motor driver for the thing as the servo loop is overly difficult to stabilise when swinging a heavy platter at near zero torque, it is just not where that drive electronics really lives, which is a little an...

If you are running an open loop head then more or less anything big enough will do fine, there is significantly more HF energy in this application then would be expected in normal audio, so straight AB is likely to be better behaved then some class G/H stuff where the boosted rail might not quite ma...

There is a decent explanation of the stylus geometry in "Physical Processes Of Cutting Gramaphone Records" collected by Fritz Nygaard (Note that he mostly comes from an Ortofon perspective). The questions of the shank geometry and mounting the jewel are IIRC discussed in one of the two JAES 'Disk Re...

Fit a snubber across the motor or switch, this is an RFI issue due to the general shitness that is the USB electrical interface, easiest to clean it up at source.

No such thing as a square wave in digital audio, you have to band limit, and in fact the best you can really do at 1kHz is not all that square... You only get a 1kHz fundamental plus odd harmonics out to the 19th, and what is fun is that above 6.66kHz a square wave will look exactly like a sine wave...

Damn, that sucks, and as I get older it seems to be getting disturbingly common!

cd4cutter, Completely off topic, but you just might be a man who was in a position to know. Were you by any chance involved with the JVC Cutting Centre Colorado in 1977? There was a very unusual disk cutting job that came thru, namely the master for the Voyager space probe golden disk, and I am tryi...

There are inertia dampers available explicitly to quiet down steppers, but steppers are still a bit nasty even if you try to do everything right.

See for example https://www.phytron.eu/products/mechanics-equipment/dmp-20-29-37-inertial-damper-for-stepper-motors/

There are certain hard limits that particularly come to a head in the the 7 inch single format. Firstly, the radial velocity of the cutter can never be allowed to exceed the tangential velocity at the cutting diameter, this is because the back angle of the cutter is 45 degrees so if you do blow that...

Steppers are simple but are usually the wrong choice in a system designed for low mechanical noise and wide speed range, a coreless BLDC with FOC is a far superior approach, but the software is massively more complex. I highly commend strain wave gears for this sort of thing as well BTW, near zero b...

Not sure I would do it with an Arduino, bit lacking in ram for the various delay lines and grunt for the filtering, but it is not too hard in a PC or something like a snickerdoodle. Trick is to have well calibrated controls and servo motors, having precisely known DAC value per um and well understoo...

https://portal.aes.org/commerce/store then Anthologies on the left hand menu.

Regards, Dan.

The old speaking clock mechanisms that the phone companies used to run were the same basic idea, optical variable area tracks much like cinema film of the period on glass disks run by a synchronous motor so everything kept time. "At the third beep, the time will be 9 52 and 25 seconds...... beep, be...

Odd they are on the AES web site, $30 each for members, $40 for non members, I just checked.
What have they done to that website, it is now awful!

Not really because a LPF will itself introduce phase shift (actually well before it has much impact on amplitude). You do the frequency and phase response shaping as part of the error amplifier but you usually want to avoid any extra phase shift thru the electronics inside the loop (It is much easie...

You need the amp to be flat at least in terms of phase (And that tends to imply flat amplitude as well) out to well above where the feedback compensator board runs out of loop gain because excess phase shift thru the cutting amp will hurt the phase margin available to the compensator and thus reduce...

You can do a bit better then that given some form of encoder that can produce speed feedback to close the loop, but 100:1 would be a big ask even there.

The right answer here is a coreless BLDC with an encoder, those have a speed range mostly determined by how good your driver software is.

Anyone else been playing with DIYAudio Wolverine as a cutting amp, it is a fairly conventional class AB amp running at fairly high bias (0.5A or so per side), and manages a couple hundred watts in the 4 pair configuration, if you remove the input filter it is flattish out to 100k with little excess ...

I am playing with a Yaskawa coreless direct drive servo motor SGMCS-05B3C11 as a direct drive on a 14 inch platter, 5nm =~ 50kgcm of torque which should be fine. One thing I did find is that the servo driver seems to chop at 6kHz, which given the very low running torque can wind up audible in the ai...

Yea doing it from scratch is a serious LEARNING experience, especially if mech eng of the fairly serious sort is not really your thing. Lots of precision parallelism over annoying distances and fun with vibration management (I am on Rev 3 of my build, hint epoxy granite is your friend for stiff, wel...