Presto disk recording lathes are often still in active use nowadays, nearly 80 years after they originally left the factory in New York. Let us have a closer look at what keeps them spinning!
For some reason, the people involved with the manufacturing of vinyl records are rather stoic types. The rare occasion when they are in a talkative mood, they mostly talk about the manufacturing process and equipment. They are not often talking about what happens after the records have been manufactured, the actual reproduction of these records, for pleasure or for the most critical step of manufacturing: Quality control.
What follows is the story of the restoration, modification, assembly, calibration and testing, of some components, which, if used properly, can result in a highly accurate phonograph disk reproduction system.
In 2015, J. I. Agnew started developing a high-end cutting amplifier for disk mastering systems, to be used with motional feedback stereophonic cutter heads. During this process, he investigated the design and implementation problems of such transducers in great detail. As usual, he documented his progress, which evolved into an engineering report, titled “An Investigation of Motional Feedback Disk Recording System Design”, which was accepted for publication in the November 2018 issue of the Journal of the Audio Engineering Society, following the customary peer review process.
Happy new year! Time to reveal what has been secretly developing in the lab throughout the past year: A stereophonic cutter head of an entirely unique design, invented by J. I. Agnew during his work with experimental transducers for measurement and testing purposes.
Working together with Eric on upgrading his Scully Disk mastering system, Sabine grabbed the chance to give our readers a little peek into the head of an experienced mastering engineer. Eric Conn works together with Don Cobb and a small Dog called Chaco at Independent Mastering in Nashville, Tennessee.
It started life in the 1940’s as a completely manual machine. A sturdy design, capable of very decent results, these lathes were extensively used across the USA and other parts of the world for several decades. Many are still in operation today. In the original condition, they were quite limited in what they could do. But, as with most good lathes, they can take a lot of modification and improvement.
There is a long history of use of precious stones as industrial materials, from precision bearings to cutting tools, lapping compounds to grinding tools and several other specialised applications.
The recording of phonograph records is essentially a machining operation, performed by means of a machine tool called a disk recording lathe. A special cutting tool is used to cut a continuous spiral groove on the surface of a blank disk. This tool is called a disk recording stylus, or simply cutting stylus.
The big difference to other forms of machining is that there is sonic information stored as modulation of the cut groove, which can be reproduced on another special machine, often called turntable or record player, or disk reproduction system.
Many different stylus materials and geometries have been used through the years, along with different blank recording disk materials. The superiority of precious stones as cutting stylii was already evident from the early days of disk recording, so they are now the only type of stylus used for cutting masters for vinyl record manufacturing.
We are excited to announce that we have just finished assembling and testing the first prototype of the Agnew Analog Reference Instruments Type 710 Disk Recording Pre-Emphasis and Cutter Head Protection Module!
In the previous episode, we had a look at taper shank stylus adapters and saw a vintage magnetic monophonic cutter head fitted to the AM44 lathe. The two are not normally compatible. Neumann lathe suspensions do not have the same mount as the suspensions of Presto, Fairchild, RCA and other lathes of the monophonic era, which were originally designed to accept such cutter heads.
Stereophonic cutter heads developed by Neumann are designed to accept a cutting stylus with a conical shank, resembling a micro-miniature version of a Morse Taper, a type of fitting frequently encountered in machine tools, especially metalworking lathes. Vinylium and FloKaSon cutter heads also adopted the same fitting for the sake of compatibility. But most other cutter heads, especially all those predating the stereophonic era, used long, thin cylindrical shanks, often with a flat machined on one side, to allow a set-screw to align the stylus and secure it in place.
Meet George Vardis, a retired biologist with a Master’s Degree in Food Technology, residing in Athens, Greece. George is a sophisticated man with many interests, including sailing, photography, motorbikes, and music. He plays the piano and the guitar, but his career always steered well clear of the music industry. He was never a recording artist, nor was he a recording engineer. In fact, he has probably never seen a recording studio in real life.
Read the full report here: Schaublin 102 Swiss Precision Lathe Restoration
Back in 2015, we started a big lathe project, taking a beat-up Fairchild lathe from the 1930’s, fitting it with an RCA cutter head, and eventually going full-on with a stereophonic feedback cutter head, vacuum clamp-down platter and automatically variable pitch.
The project was founded by Flo Kaufmann, in Switzerland, when he managed to find a pile of these rare beds in the unexplored depth of a warehouse. The plan is to build them up into fully functional disk mastering systems, using newly designed and manufactured parts.
In 2016, Sabine and J. I. Agnew acquired one of these beds, built up and further developed it, into an exceptional quality disk mastering system, which was put to professional service at Magnetic Fidelity.
John Delias, the guitar wizard of the popular rock group “Naxatras”, filmed J. I. Agnew while cutting the master lacquer disks, from which the vinyl records of their debut LP were manufactured, at Magnetic Fidelity, and edited the footage to produce this short informative video, offering an insight into this seldom seen, mysterious process.
One might think that the whole issue of absolute polarity for a medium essentially invented around 130 years ago, would have been adequately discussed and standardised by now, leaving no room for further debates. Indeed, it has been, so why bother writing anything further on this topic?