Cartridge incompatibility, Soundsmith and Luxman

I looked at the specs for both the Zephyr Star and the Luxman 590. There is no obvious reason why this pairing cannot be made to work well. First, I don’t understand quite why SoundSmith recommends a 470 ohm load for this cartridge. It’s internal DC resistance is only 10 ohms, so in theory it should be able to drive the 100-ohm load of the Luxman MC input stage. The problem might be that this is not actually an MC cartridge; therefore it has an inductance much higher than that of a typical MC. (About 100X higher, if a typical LOMC cartridge has an inductance of about 25uH. Inductance of Zephyr is 2.75mH.) Maybe Atma can comment on how that would be an impediment, but perhaps that is also why SS recommends a 470 ohm load. We also know from specs that the output of the Zephyr (0.4mV) is not too low for the MC inputs to handle, because Luxman tells us that the MC gain (NOT stated on the Luxman website but can be calculated) is adequate for a cartridge with an 0.3mV output. Before doing the research, I had assumed that the MC gain of the Luxman is derived from using a SUT placed ahead of the MM stage, but the website, while very lacking in phono-related info, suggests that MC gain is done by an active stage. For one thing, in their many photos, I see nothing on the PCBs that looks like a SUT. OK, so if there is no SUT, then there is no problem to replace the 100 ohm load resistor with a 470 ohm load resistor. Any skilled technician can do that. I would do that way before throwing either baby out with the bathwater. I am a big fan of MI or "fixed coil" cartridges.

Oh, by the way, this problem cannot be fixed by paralleling an external resistor with the 100-ohm input resistor, net parallel resistance is always lower than the value of any one resistor in the bundle.  So paralleling an external resistor can only lower the net input resistance, not increase it.

@lewm Greatly appreciate your knowledge and input!!! In theory, it should work, but it's clearly rolled off (quite a bit...). The only logical answer I can see is the mismatch in loading. Gain should indeed be no issue. And I do really love the Zephyr Star, so I want to make it work if at all possible.

It seems like the options are either modify the Luxman or get an SUT... since I can only imagine is going to be pretty close to a wash cost-wise, I might just as well accept that I will need to go down the route of an SUT..

So with that said, any recommendations for a SUT? Don't want to break the bank (let's try to keep it less than $1k used), but sound is much more important than cost, so if that's the path...

Also, no experience with SUT's, I assume I should use phono cables out of it into the MM, but not just "regular" interconnects. Is this assuming correct?

When you use a SUT you should use short, low capacitance cables. Under 1m for sure, ideally 0.5m or as short as you can go. It has to be low capacitance - for example, the Audioquest LP / phono cables, and their Bridges / Falls IC cables are good, but their higher end Elements interconnects are BAD for this. Cardas interconnects typically have extremely low capacitance and are good for this.

I’ve done the 10x SUT thing for a Benz LPS with 0.34mV and 470 ohms MINIMUM recommended load (it seems like it wants a higher number), not too unlike your SS but MC based. Tried a few SUTs, 8x - 10x. It was an OK result, not stellar. I feel like this kind of cart is a tough match to a SUT (all my other carts love a SUT). With the LPS, I got a slightly better result from a Hagerman Piccolo2 which is a JFET headamp that has amazing gain & loading options and only costs $289. But the best result I’ve gotten from the LPS so far is on a Hagerman Trumpet MC, which only costs $1100 new and has an improved balanced Piccolo built in. The MM stage is tube based and (mostly) balanced circuitry. It’s not as quiet and refined as my VAC phono stage (which is SUT based), and the chassis & wall wart are clearly built to its low price point, but for that tough-match LPS it gave a better result than the ~$16K of phono stage & SUT.

The resistor mod to you Luxman sounds like it might be a great idea though.

Dear @audiojan : " need to go down the route of an SUT. "

Well, due to what you have in the Luxman that’s the bad move ( is up to you. ) that degrades the higher the cartridge signal against a " simple " internal modification below Luxman advise. Maybe I have to say SUT is the wrong way to go for the quality level of the cartridge you own, can’t benefit you in anyway but the other way around but as I said: is up to you.

" there is no problem to replace the 100 ohm load resistor with a 470 ohm load resistor. Any skilled technician can do that. I would do that way before throwing either baby out with the bathwater.  "

R.

Purchasing I rather inexpensive dedicated capacitance meter 

with zeroing lead capability can be quite handy for confirming

cable suitability.