Repairing an SA-74 suspension unit, from a Neumann VMS-70 disk mastering lathe, which arrived with the head lift/drop lever jammed in the down position, preventing the top lid from being removed! The Neumann SX-74 stereophonic motional feedback cutter head was still attached, as it had been glued to the mount adapter, which can only be removed from the suspension unit by opening the top lid! Several mechanical and electrical repairs, adjustment/calibration procedures and even a bit of machining on the 1961 Moore Special Tools Jig Borer later, it was fully brought back to original specifications!
Some time ago we were asked to repair a vintage Westrex 2B feedback cutter head. As with all Western Electric and Westrex products, their cutter heads were beautifully made and represented the state of the art in their time. Not only did they sound great, they also looked aesthetically pleasing, with curved lines that were not a trivial task to manufacture, in the days before CNC machine tools, CAD software and pocket calculators!
The Westrex 2B is a motional feedback cutter head, introduced in 1952 by the Western Electric Export Company. It followed hot on the heels of the Westrex 2A, dating from 1947, which was itself a lateral implementation of the principles first described by Wiebusch, Vieth and Yenzer in 1938, with a couple of relevant patents issued by 1939, for a vertical cutter head employing motional feedback.
Our popular Agnew Analog Reference Instrument Type 1501 Stylus shank adapter was intended to make it possible to use the Neumann-style taper shank stylus (Transco 320, Adamant NSH-2, etc) with vintage mono heads such as the Presto 1-C and 1-D, which need a long shank stylus.
Up to now, customers would just install the adapter and leave it there, only occasionally replacing the stylus. One customer, however, wanted to be able to leave the stylii aligned in the adapter, and change them out without needing to realign.
Presto 1-D and 1-C cutter heads are frequently encountered on our lab bench for repair and restoration. Some are just regular repairs to original spec, others are rewound to a different impedance, but some undergo more comprehensive and exciting modifications!
We have previously examined modifications where a feedback system was added to a Neumann MS-52H and an Audax R-56 cutter head. This time, we shall discuss adding feedback to a Presto 1-D, which arrived with damaged coils.
This Audax cutter head arrived with a fried coil and a completely crusted armature. The damping material had not aged well.
A complete disassembly, cleanup and reassembly would be required, with the renewal of the damping material and drive coil. This was yet another perfect candidate for our feedback modification.
Neumann cutter heads have a rib along the back, for mounting. Presto lathes, on the other hand, together with the vast majority of non-Neumann vintage lathes (Rek-O-Kut, Fairchild, etc.), have a mount with two slots, for cutter heads with two threaded holes on the back (Audax, Presto, Fairchild, RCA, etc).
Have you ever noticed the total absence of audio equipment from the luxury houses presented in glossy architecture and interior design magazines? It makes the inhabitants of such property come across as rather uncultured.
In fact, not only is an audiophile grade sound system a minimum requirement for the home of anyone affluent enough to hire an interior designer, but it is important to choose a designer who can appreciate the aura of sophistication and intellect projected by a beautifully restored vintage disk recording lathe, set in a handcrafted custom cabinet, in a conspicuous corner of the living room!
We recently had the pleasure of having Symatic over, from Bristol, UK, for a week of training on how to cut (and how not to cut) records.
Symatic runs Cut & Paste Records, a record label attracting some serious attention among skratchers, with high quality releases of skipless skratch samples, lock-groove tones, beats, and relevant music.
Tasos of Epos Laboratory (a Grado retipping specialist) from the beautiful south of Greece is the lucky owner of this 1950's Rek-O-Kut disk recording system.
It consists of a Rek-O-Kut Model V 16" turntable, which he found in the USA (where else?) as a non-runner. The motor was in bad shape and refused to run at all. Even if it would run, it was expecting to be fed on a regular diet of 110 VAC/60 Hz!
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.
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.
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.
But, in fact, almost any cutter head can be fitted to any lathe, as long as there is enough space for it to physically fit, by means of a suitable adapter. The eagle-eyed reader will probably have noticed that the cutter head mount on our prototype AM44 suspension is similar to, but not the same as, the mount used in Neumann suspension boxes. So, the adapter shown here was made specifically for our AM44 suspension unit.
