Koetsu Urushi + MC step up transformer

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?
.

The maths works out as 47000/(13*13) = 278 ohms and I'll give that a try tonight.

Trying to replicate a 47K load through the transformer works out as 8M (47K*13*13) ohms as Lew points out. That will require modifying the pre-amp and seems quite a big change that is surely going to have an effect on the phono stage as a whole.

My thinking is that I probably don't need 47K load to get the sound I am used to and that I should take the SUT out of the equation and change the loading of the MM stage down until I find the lower bound. If that turned out to be only 3K for instance then that means I would only have to change the pre-amp to be 500K which seems more reasonable. Does that sound right?

I actually got the Lundahls from diyparadiso but Benny has been on holiday so I haven't been able to go through this with him. I'll also checkout the Jensen website and lookup Zobel networks.

Thanks for all the help so far.

It is a transistor pre-amp, I don't have a schematic of the PF1, the instruction manual only states that it is the industry standard 47,000 ohms shunted by 100 pF. It describes how to lower the impedance with a parallel resistance but not how to increase it.

I cannot find a Zobel network diagram on the Jensen website but their MC transformer diagram adds a capacitor in series with the modifying resistor - that may be worth trying.

At the moment I'd rather not dig inside the pre-amp without some guidance, perhaps I should try contacting CJ for a schematic. Otherwise I'll wait and see if it burns with more use.

Yes, I've tried pretty much every combination of set up including directly connected with no other loading - which would be a 278 ohm load on the cartridge - it all sucks. And pretty much to the same effect, there doesn't seem to be much variation whatever I try.

Have I set up the rest of my system to over compensate for connecting the Urushi into a MM load, such that doing the "correct" thing into a MC load is now throwing the setup so far out of whack?

The "sucky sound" is a lot of harshness in the upper treble - quite unpleasant. Also, the sound stage has gone completely flat, all the air and space around the instruments has disappeared. Bass seems OK. There is no problem with the gain, the 13:1 ratio is just right.

I'm in the UK and didn't get the Lundahls from Kevin, although he did send me his spreadsheet for calculating the load resistance.

Both Sowter and Jensen recommend a Zobel network to reduce ringing in the transformer. It is just a resistor in series with a capacitor across the secondary windings. I have added such a network to the Lundahls and, on initial listening, this sounds very promising.

Of course, I don't actually have a CD player but I guess a tuner would do. I did try a few days with it connected to the output of the transformer (cartridge disconnected) but you think connected to the input would be better?