Mavare: Apologies for the delay in responding - I need to fulfill my daily production and design responsibilities, and this particular period is even crazier than normal (since we are still scrambling to prepare for the commencing of Kleos shipments).
May I ask if you have already talked to Needle Doctor? If you did, you should have received the answer that if your Helikon SL wears out or gets broken, we can replace it with a new one (using 100% new parts), or if you want, we can rebuild the one that you have (using new replacements for all wearable or damaged parts). If your dealer, national distributor is out of inventory at the time that you require a replacement cartridge and a new one needs to built up from scratch, the complete production process could take about 35-40 days (we normally don't keep surplus inventory).
We also support our distributors in their trade-in and/or trade-up programs, so that would be another option for you when the time comes.
I must caution you that I don't have the authority to dictate the policies of our distributors or their dealers, so the person who you should be talking to the dealer that you purchased the Helikon SL from. If you can't get satisfaction, I can attempt to facilitate things on your behalf, but the general procedure should be that you talk to your dealer first, and as a next resort, to your national distributor. Our gross margin per cartridge sale is several times less than what the dealer earns, and taking good care of customers is a major part of how delears are supposed to earn that margin.
FWIW, although I agree that it would be nice to have more contemporary phono stages that were comfortable with low input voltages, and that it would open up more options for me (as a cartridge designer), your post suggests that you are overly fixated on low output voltage, but not considering how that is achieved. When you look at output voltages, you should also study the source impedance, because that will be a better guide to how much wire was used to wind the coils. Low output voltage can be the result of reduced coil windings, but it can also imply the use of generator systems which aren't particularly efficient. To make things more complex, generator efficiency and generator linearity are two separate things, and my experience so far has been that it's better to compromise a bit on generator efficiency if this enables generator linearity to be improved (IOW, reduced distortion).
Let's look at your cartridge list. The SPU and Benz Ebony TR do have low-impedance coils, and that tells us that the coils are made with fairly short wire lengths, and perhaps fat wire. But in the case of Denon cartridges, the lowest output is 0.25mV achieved from a 13-ohm coil, which suggests rather longer wire. The lowest coil impedances that Dynavector uses are 5 ohms. Same for Koetsu. This certainly isn't high, but neither is it extremely low (the non-SL Helikon is 5.4 ohms). And if the coil former (core) is made from non-permeable materials, chances are that longer coil windings will be required to achieve output levels that don't cause fits for even higher-quality phono stages. As a case in point, the Benz Ruby cartridges employ at least 38-ohm coils to achieve their output levels of around 0.35mV.
In my experience with designing phono amplifiers and cartridges, the outcome is usually best when designs don't excessively focus on one or two parameters at the cost of a half-dozen others. I normally keep coil impedance below 10 ohms, but I wouldn't hesitate to exceed this for a particular design if I thought that the net benefits could outweigh the demerits (although extensive listening tests would be performed to make sure that the net sonic effect was positive).
OK, I better get back to those Kleos'.
hth, jonathan carr
