Dear Nrenter:
>I would be curious to know about some of the ideas / technologies you discarded as you finalized the Delos design, as they did not provide the benefits you intended.
I knew from previous experiences that high-strength body materials other than aluminum could sound excellent. Phosphor bronze (as on the Skala) and titanium (as on the Titan) are particularly good-sounding. So in addition to solid machined aluminum (which would I would consider standard practice for a cartridge in the Delos' price range), I looked into making various structural components from more exotic materials such as titanium or stainless steel, but keeping manufacturing costs within reason by using cheaper forming processes like casting and forging. Unfortunately the results were unacceptable. Although for marketing impact I would have been quite pleased if the Delos could have been made from titanium, listening tests showed that machined-from-solid aluminum sounded clearly better than cast or forged titanium, or sintered stainless steels. The lesson appears to be that not only the material, but also the forming process is critical for good sound.
In other experiments, I wound bifilar coils from two different wire gauges, which didn't give enough improvements to the sound to be worth the effort. Then there were many dead-ends with various types of dampers and suspensions. All in all, developing the Delos from first prototype to finished product took over a year.
>or because they will be saved for other cartridges (due to the monitary costs to achieve the experienced benefits).
There were more than a few of these, and not only regarding body material choices. However, I would prefer to keep these cards hidden for the time being. All in good time (smile).
>how do you select your stylus profiles for your various cartridges?
On the basis of price vs. performance, while avoiding profiles that are too difficult for most users to set up properly.
I prefer line-contact styli that combine a vertically long contact patch with the LP groove with a horizontally short contact patch. A vertically long contact patch gives greater groove contact for better tracking and better immunity to localized groove damage, and a horizontally short contact patch give better high-frequency performance and less time-smear. This leads to line-contact styli with a fairly large major radius and a small minor radius, but in practice neither radius can be too extreme. Too large of a major radius makes azimuth adjustment more critical than most users (and many tonearms) want to deal with, and too small of a minor radius tends to create edges on the stylus that are sharp enough to chew up the groove. Based on my own experiences and observations, I like the maximum major radius to be in the 70~80um range, and the minor radius to be in the 2.5~3um range.
For all Lyra cartridges other than the Dorian and Delos, I use a Lyra-designed variable-radius custom stylus which measures 3um (minor) x 70um (maximum major). This is an excellent stylus, but has one major flaw. As a custom Lyra shape, no other manufacturer uses it, therefore it is made in small quantities and becomes relatively expensive. A more affordable cartridge like the Dorian or Delos doesn't permit the manufacturing budget that would allow a custom stylus assembly to be specified, unless I were to reduce the manufacturing quality in other ways (which I refused to do). To keep what I deemed to be sufficient build quality (of body structure as well as stylus and craftsmanship) at this price level, I needed an off-the-shelf stylus. The closest stylus shape to the custom Lyra 3um x 70um profile was the Namiki Microridge, which I could get as 2.5um x 75um. And that's what the Delos uses.
>You are very crisp with your technical specifications, however, you openly offer a wide range for catrige loading (100 Ohms to 47 kOhms). Why such a range?
First, because the loading of a low-impedance MC is not really an issue for the cartridge itself. An MC cartridge is a mechanically-driven electrical generator, and a not-very-efficient one at that. Unlike loudspeaker drivers, the meager efficiency of a low-impedance MC cartridge implies that loading applied in the electrical domain will have relatively little effect in the mechanical domain (which is where you will see effects on aspects like tracking performance and distortion). Also, due to the very low inductance of the signal coils, electrical loading will have practically no effect on any signals in the audible range, and this has other benefits in keeping a relatively flat phase response in the audible domain (a general rule of thumb for good phase response out to 20kHz is that the electrical frequency range should extend to at least 200kHz). This is a completely different situation with high-inductance MMs and MIs, where changing the loading will affect the frequency response in the audible range, and the phase response even more so.
So, if electrical loading doesn't change the behavior of the phono cartridge in the audible frequency range by much, why does the sound change so dramatically? The answer is that the inductance of the cartridge coils will resonate with the capacitance of the tonearm cable (and distributed capacitance of the coil windings) and create a high-frequency spike. The magnitude of this spike can be extremely high, and may give many phono stages outright problems if it isn't damped with loading measures at the phono stage input. I don't have my lab notes at hand, but from memory loading a Delos with 47kohm can result in a 28dB spike at 6~7MHz. Some phono stages will have been designed so that they remain unflustered by this, but many phono stages will not be happy with such brutal treatment, and will not sound good because of this.
>What specific impedance would you suggest for the Delos?
It depends on the tonearm capacitance, and how much ultrasonic or RF energy your particular phono stage can tolerate.
As to what "sensible" loading values are recommended for most phono stages, I will quote verbatim the relevant section from the Delos instruction manual.
"Connect tonearm cables to RIAA-equalized phono input designed for direct use by low-output MC cartridges (0.6mV output voltage or less). If phono stage input impedance is adjustable, setting loading by ear should be sufficient, with 47kohm as highest and 91 ohms as lowest values."
"For listeners interested in mathematically correct input loading, the value depends on the total capacitance between Delos and phono stage (comprised mostly by the tonearm cable). Note that "input loading" of low-impedance cartridges has comparatively less to do with the cartridge and is more about taming RF energy which could otherwise trigger non-linearities in the phono stage and the generation of intermodulation distortion. Since different phono stages have different tolerances for RF energy, expect the best-sounding loading value to vary according to the tonearm cable and phono stage."
"Nonetheless, you may try setting your phono stage's loading according to these number pairs. In each pair, the first number is the total capacitance between Delos and phono stage (in picofarads), the second number is the corresponding optimal impedance range: 50pF - 510~270ohm, 100pF - 390~200ohm, 150pF - 330~160ohm, 200pF - 300~150ohm, 250pF - 270~130ohm, 300pF - 240~120ohm, 350pF - 220~110ohm, 400pF - 220~110ohm, 450pF - 200~100ohm, 500pF - 200~100ohm, 550pF - 180~91ohm, 600pF - 180~91ohm. In each pair the first number is selected to suppress any peaks at RF frequencies to approximately 3dB (which should be acceptable to nearly all phono stages), while the second number will give 0dB (at the cost of slightly poorer phase response and reduced dynamics)."
"If you do not know the precise capacitance of your tonearm cable, 100pF per meter is standard, while low-capacitance cable is likely to be around 50pF per meter (we do not recommend high-capacitance cable). As approximate loading figures we suggest 510ohms for 1m low-capacitance cable, 430ohms for 1.5m low-capacitance cable, 390ohms for 1m standard cable or 2m low-capacitance cable, 330ohms for 1.5m standard cable or 3m low-capacitance cable, 270ohms for 2m standard cable or 4m low-capacitance cable, 240ohms for 3m standard cable, and 200ohms for 4m standard cable."
I hope that this post was of some interest.
