Hey guys,
I have seen in several threads here people mentioning auto groove depth. To me, it is clear how auto groove width works but what about auto groove depth? Since probably all stereo heads are 45 degrees angle design, more volume produces deeper grooves (in my understanding). If the volume of some part is too high, the head will cut deeper groove which eventually will make the needle jump off the groove. So, using the preview mechanism on the high volume parts this auto depth functions will move the head a little bit up in order not to cut too deep groove. Is this how it works or I got it all wrong?
Second question:
What type of mechanism is used to move the up and down for auto groove depth?
Thanks,
Bob
Auto groove depth - please explain
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
Re: Auto groove depth - please explain
I saw in a scully suspension box that had a speaker that was connected to the system and did this depth adjustment function, if you put a tension the coil comes out and pushes the cutter head mechanism down
Re: Auto groove depth - please explain
That's not quite the reason for this.
The limit is more the need to maintain sufficient depth of cut at the shallow end then to avoid crashing into the substrate when going deep (which can also be done, but is usually indicative of a screwup).
It is possible to cut a perfectly cromulent record with fixed basic depth and even fixed lead, it just wont be a very LONG record!
Depth of cut matters to length because due to the 45 degree geometry of the groove walls, the instantaneous width of the cut is always twice the instantaneous depth, this is true at every point on the spiral.
The deeper you cut the wider the top opening of the groove is, and this space must be accounted for in the groove spacing calculation (Or you can just assume a worst case, but that does not do your record length any favours).
If rather then setting a fixed depth that has to be deep enough to maintain a groove even with pathological signals, you set two numbers, one being the basic depth to cut when everything is at idle, and another that is the minimum depth to cut, then the lathe can cut at your minimum until the preview indicates a need to be deeper to accommodate a large excursion in the shallower direction, at which point it lowers the cutting head slowly increase the depth to accommodate the modulation.
The fact that much of the time it is running at minimum depth allows a longer record because most of the grooves are narrower.
You probably need a feedback head to work with this as otherwise the change in cutting depth will modulate the groove amplitude (Open loop would need you for feed the depth control signal to a VCA to increase the cutter power when increasing the depth).
Usually a voice coil motor is used to vary the downforce on the cutter and hence the depth (Force required is generally square law with depth).
Control must be slow because it effectively introduces deliberate low frequency rumble.
The limit is more the need to maintain sufficient depth of cut at the shallow end then to avoid crashing into the substrate when going deep (which can also be done, but is usually indicative of a screwup).
It is possible to cut a perfectly cromulent record with fixed basic depth and even fixed lead, it just wont be a very LONG record!
Depth of cut matters to length because due to the 45 degree geometry of the groove walls, the instantaneous width of the cut is always twice the instantaneous depth, this is true at every point on the spiral.
The deeper you cut the wider the top opening of the groove is, and this space must be accounted for in the groove spacing calculation (Or you can just assume a worst case, but that does not do your record length any favours).
If rather then setting a fixed depth that has to be deep enough to maintain a groove even with pathological signals, you set two numbers, one being the basic depth to cut when everything is at idle, and another that is the minimum depth to cut, then the lathe can cut at your minimum until the preview indicates a need to be deeper to accommodate a large excursion in the shallower direction, at which point it lowers the cutting head slowly increase the depth to accommodate the modulation.
The fact that much of the time it is running at minimum depth allows a longer record because most of the grooves are narrower.
You probably need a feedback head to work with this as otherwise the change in cutting depth will modulate the groove amplitude (Open loop would need you for feed the depth control signal to a VCA to increase the cutter power when increasing the depth).
Usually a voice coil motor is used to vary the downforce on the cutter and hence the depth (Force required is generally square law with depth).
Control must be slow because it effectively introduces deliberate low frequency rumble.