Koetsu Urushi + MC step up transformer

I don't like SUT with fine MC cartridges because they defeat the great transient response for which MC cartridges are known. The reason they even exist is that back in the day, most if not all MC cartridges were really low output (around 0.25mV) and hi-gain lo-noise phono preamps not available yet. (BTW, the Urushi has a fairly healthy output for a MC cartridge at 0.6mV)

I would suggest that if your CJ is almost enough to amplify the Urushi all by itself, then before you do anything else, get it loaded properly for the Urushi. The Urushi has an output impedance of 5 ohms. So using the 'ballpark' 25x rule, the correct loading for it should be 125ohms (probably a bit lower as Sam indicated) but not 47K! Correct loading will not only increase the perceived volume, but you will get detail and bass you haven't heard yet. If the 40dB gain of the built-in CJ phonostage really isn't enough, then I would recommend one of the many fine headamps (Creek makes a nice one) which these days are a better alternative to a SUT IMO.

I agree with Nsgarch, but meantime you do have those Lundahls and maybe fooling around with the load resistors will help make them sound better. You say you "tried some different" values, but you don't say what values exactly. As others have said, the Urushi likes to see ~100 ohms load optimally but will probably work as well into slightly higher load Rs. Do you know the turns ratio of your Lundahl trafos? A trafo reflects an impedance that is related to the square of its turns ratio. If the turns ratio is 10:1, the square of that is 100 and therefore you want to place a 10K ohm resistor (100 X 100R, the preferred load for the Urushi) on the secondary side of the trafo that is driven by the Urushi on its primary. You don't say what values you've tried or whether you had professional help in selecting the values, but maybe this bit of info will help. If the CJ has fixed 47k ohm Rs in its phono input, you will need to calculate the value of R that will give you a net of 10K ohms, when placed in parallel with 47K ohms. Then solder those resistors in parallel with the 47K ones and you are done (or just remove the 47K resistors and substitute 10K ones). In addition to this simplistic approach, performance of the trafo can also be improved by a Zobel network, the design of which is much more complex. See the Jensen transformer company website for ideas on that or ask K&K.

spider, the values one uses to match a MC cart to a SUT have nothing to do with the load resistance you would use if connecting the cartridge to a phono preamp or headamp. You need to do a search on vinyl asylum or here on Agon to get pointed in the right direction. BTW, the SUT's themselves can come in two or three ranges which work best with certain cartridges. Wish I could be more help ;-)

OK here's the specifics of the set up so far:

Lundahl LL1681 MC transformers using the 13:1 tap.
With a primary resistance of 9.6 ohms and a secondary resistance of 1640 ohms, courtesy of K & K I get:

Req Load......Resistance
50..................15600
75..................24114
100................35310
125................50689
150................73135
175................108974

I've only got a couple of resistors to hand so I've only played around with parallel resistances of 18K, 47K (and 13K and 65K if you do the maths). None of them sound good.

Given the relationship of input:output load being the square of the step up ratio I can't see how I can get my Urushi to "see" the sweet 47K it used to?
.

Nsgarch, You wrote, "spider, the values one uses to match a MC cart to a SUT have nothing to do with the load resistance you would use if connecting the cartridge to a phono preamp or headamp." Are you suggesting that my advice in my previous post was completely incorrect? If so, I'd like to know, because I hate to think I've misinformed spider (or anyone else). When he bought the Lundahls (presumably from K&K), I presume that they knew how he was going to use them and that therefore the ones he's got are already a reasonable match gain-wise for the Urushi playing into the CJ.