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interesting phenomena in the cutting room

We've (my friend Bob and myself) been working on an LP cutting lathe for some years. Its been a while refurbishing the lathe itself, finding parts and solving problems/puzzles, rebuilding the electronics, etc.

The lathe itself is a Scully, the cutterhead a Westerex 3D and the electronics the 1700 series built for the cutterhead by Westerex.

About 6 weeks ago we finally hit upon the magic combination of stylus temperature, vacuum, depth of cut, etc. It works beautifully! So we have been playing with parameters, including different amplifiers. The stock amplifiers were built about 1972 and are solid state.

Now those of you that know me know that I am all about tubes. But the stock amps worked quite well! As we gained familiarity with the system, we found out why: the Westerex cutting system is a high efficiency cutterhead- it does not take a lot of power to make the head work. It can easily cut grooves that no cartridge could ever keep up with, and do so without breaking a sweat. So the amps, which can make 125 watts, are loafing through the most difficult passages.

I had a Dyna ST-70 that I had rebuilt so for fun we swapped that amplifier in and it did quite well. Our next step is to use a set of our M-60s, as the cutterhead is an easy load relative to most loudspeakers.

What is interesting about this is that we can make cuts that literally demonstrate the audible differences between amplifiers, something that can be demonstrated on any playback system.

Its also apparent that the cutting process is relatively unlimited as a media compared to any other recording system. The dynamic range is well beyond that of analog tape or any digital system- like I said, it can cut grooves with such range that no cartridge could possibly keep up, yet is dead silent (if the lacquer is OK, that is). The real limitation in LP recording is the playback apparatus, not the cutters.

There is a fun little forum website for more information called 'Secrets of the Lathe Trolls'. Here's a post on that side made by my friend Bob (Bob has run a recording studio for some 20 years and was a roommate of mine in college):

http://lathetrolls.phpbbweb.com/viewtopic.php?p=19435&mforum=lathetrolls#19435
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mapman's avatar
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mapman
15,679 posts
 
Very cool. All makes a lot of sense.

Of course what value is there in arecord that can't be tracked?

Reminds me of the challenges i recall getting most vinyl players of the day to track the original telarc digital recordings without clearly audible mistracking and distortion. Those seemed to push the limits of what was practical back then but clearly it would be possible to do more at the expense of playback time.
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pbnaudio
1,534 posts
 
Ralph - what cutting angle are you setting the machine to ? So we can get that pesky "RTA" set correctly :-)

All in good fun

Peter

PS For explanation of "RTA" see previous post about the USB Microscope
atmasphere's avatar
atmasphere OP
7,068 posts
 
Hi Peter, what we have found about that pesky RTA is its not really a standard. The problem is variance in the cutting stylus. Under the scope they all look a little different, and to get them to behave you have to adjust the head up and down a little. But for the most part the stylus temperature seems to play a bigger role. We did shoot for about 2 degrees negative but you can't count on that to work with every single lacquer. Plus the stylus is only good for about 10 hours and during that time you have to compensate for its wear. So RTA is more of a thing to try for as long as everything *else* is working :)

Mofi, the intent is for sure to release projects. I expect that most of them will be local initially, in fact we already have several lined up. But the plan has been all along to have the first transformerless vacuum tube LP mastering setup. Its nice to say we are finally there...

To that end we modified a set of M-60s to operate entirely without feedback. The system itself provides 30 db, which is needed to kill resonance in the head, and without it you can't get channel separation! This has to do with how the mechanism is suspended. Anyway, the stock amps employ feedback but in any servo design, nested feedback loops are usually a recipe for stability issues. But so far we've not run into any of that, once we started dialing in the trackball height, stylus depth, temperature and the like, its actually been pretty well behaved.
ptss
1,649 posts
 
Very interesting thread!
griffithds
851 posts
 
I also think this is a very interesting thread.
Ralph, I hope you will continue with this discussion and your findings. It would also be nice if and when you actually have a product to sell, that you provide us with a web address or phone number to order!
Regards,
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