Dear Nrenter:
My observations have been that you can get pretty far in engineering circles by simply being able to "see the obvious" (smile). Actually, once you understand the underlying rationale and logic, the majority of engineering decisions should appear obvious, as properly defining the problems and issues is what gets you the majority of the way to formulating a solution. The catch to all of this is that many things are obvious once you grasp the underlying logic, but are elusive until you grasp that underlying logic (grin).
For example, consider the spindle and bearing design on Bill Firebaugh's Well-Tempered turntables. Somewhat like the Delos' mechanical pre-biasing system, the WT bearing is designed deliberately to place the spindle in the wrong position and wrong configuration under static load, precisely so that the dynamic load of the rotating belt will force the spindle into the right place and configuration. Once you understand the Well-Tempered's logic it is a very obvious thing to do, and given the simplicity of Bill's implementation the feature could have been incorporated into a belt-driven turntable from the 1960s if the designer would have had the insight. But did anyone do this before Bill Firebaugh?
>the design goal of symmetrical magnitic flux in the gap with an optimal tracking force applied seems intuitivly obvious to the layman.
I will point out that the magnetic circuits in traditional-style MCs do not even have symmetrical magnetic flux across the gap, as the asymmetrical positioning and proximity of the magnet exerts a warping effect on the flux-lines. The first challenge is therefore to design a magnetic circuit that has as symmetrical magnetic flux across the gap as possible, but that requirement by itself eliminates the majority of MC cartridges.
Regarding the novelty of the Delos' mechanical pre-biasing system, because I fully agree that it appears to be an obvious design feature (in retrospect of course - grin), I have discussed it with various Japanese cartridge designers and audio reviewers (some of whom have a good overview of the entire cartridge industry, including historical perspectives). The closest that I got to hearing about anything similar was with Matsudaira (formerly with Supex, Entre, Audiocraft, and now with his own My Sonic Labs). Although Matsudaira didn't specify exactly what he did, he said that he had tried to achieve similar goals with a few prototypes that he made many years ago, but chose not to take it beyond the prototype stage. I surmise that his magnetic circuit wasn't capable of creating sufficiently symmetrical magnetic flux across the gap, which reduced the effectiveness of the mechanical pre-biasing system, and made the project appear (to him, and at that time) to be not worth the extra effort and cost.
Regarding the entire cartridge industry, it appears that the focus has been primarily on achieving the correct VTA and SRA, and the angle between coil former and magnetic circuit under VTF-loaded conditions hasn't received the attention that it deserves (I haven't been able to find any previous article on this subject, whether in German, Danish, English or Japanese). Also, my experience has been that the coil former angle is quite sensitive to VTF amount, so if the cartridge manufacturer allows the user a fairly broad VTF range, we can deduce that most likely the relationship between VTF and coil angle (and by extension, the desireability of keeping the coil former and magnetic circuit angles as tightly aligned as possible) isn't a priority for him. In contrast, I'm stipulating a 0.1g VTF range (1.7~1.8g) for the Delos.
>what were the engineering challenges you had to overcome to put this approach into practice?
First is that the mechanical angles of the body structure will be a few degrees different from any of your designs that don't incorporate the mechanical pre-biasing system, so you will create a fair amount of component incompatibility among your product lineup, which normally is something to be avoided in manufacturing (particularly if you maintain large component inventories).
Second is arriving at the right combination of shape and elastomer hardness for each damper type, which is essential when progressing from theory to practical implementation. A key part of the mechanical pre-biasing idea is to consider the damper deformation due to vertical tracking force as an asset rather than a liability, and aggressively take advantage of it. But since the rate of damper deformation per unit of tracking force is influenced by shape, thickness and elastomer hardness, if the elastomer compound or thickness changes, so will the damper shape. Since a cartridge builder relies on a variety of elastomer compounds and thicknesses for different cantilever materials, coil metals, suspension wires, body material and structural choices, frequency ranges and so on, and also since good-sounding elastomers are not known for being particularly precise or predictable in terms of mechanical behaviour, extensive trial-and-error testing will be required. I believe that we went through over 50 different combinations of shapes, thicknesses and elastomer compounds before settling on the damper choices used within the production Delos'.
Third is that the suspension and dampers in a normal cartridge are non-directional, which means that the builder doesn't need to think about which way the dampers face or point. But since the Delos' mechanical pre-biasing system requires directional dampers, the cartridge builder needs to make sure that each damper faces in the right direction, and he must also rotate each damper until he finds the precise orientation that gives the proper amount of cantilever deflection for the target tracking force. Cartridges of this type are more demanding on the builder's abilities and attention to detail, and will take longer to build and adjust than a normal cartridge.
BTW, yesterday all of the printed instructions arrived, so we got busy putting everything together and writing export documents for our very first Delos shipment. We shipped out 29 Delos' yesterday, and more followed today.
kind regards
