The correct internal-inductance of Windfeld cart.?

Hi Lewm,
thanks for sharing the calculations.
1) Fidelity Research XF-1 type M, is 1:31.6 xfactor i.e. 30dB.
2) That Windfeld is a bit 'funny' since with no SUT it seems to like at least 500 to 1k ohm load and with some phono-pre's it's even better with 47k!
(I and also some reviewers came to this same finding)
3) I use PRIMARY loading, because if you get it right, it sounds more open --- using secondary loading is something else since as you pointed out the || of your sec. load with the 47k pre-input imp / by the square of (in this case) 31.6 is what the cart sees. Therefore with NO sec. loading the cart sees 47k / 31.6^2 = 47 ohm, didn't I go into that alread?
So any sec. loading now goes || with that 47ohm 'natural-impedance'(I'm neglecting the primary DCR (in the XF-1 case only 1.2 ohms which is also part of the deal)
PRIMARY loading with 100 ohm makes (in this case) the PW cart go beserk, higher like 250, 500, etc is also unworkable.
So you check the minimum spec. loading (usually 2.5 x DCR = 4ohm DCR x 2.5 = 10ohm, it happens to be min. spec by Ortofon, right)
What's left is to get a 1:1 impedance match to this! i.e. 47x13/(47+13)=10.18ohm ---- and as it turns out this sounds the best of the 1001 different versions I've tested.
So it seems to me, that you are working with loading that is non SUT relevant --- the big difference is that with an impedance matched SUT, that cart is working in 'current mode' (not 'voltage mode' as in a non-SUT set-up) and THAT changes EVERYTHING as I had to learn. You can not, I repeat NOT, compare 'current mode' to the 'normal'-voltage mode- loading i.e. with out SUT. Even when using secondary loading -current mode rules?- apply, just that we are now looking at ~ 18k ohm on the seconary producing [47k*18k / (47k+18k)]/ 31.6^2 = 14.1 ohm what the cart sees. Going down to e.g. 13k to make the cart see ~ 10ohm makes it to bright and brittle --- so not all things are quite equal between primary and secondary SUT loading either.
Also using secondary 18k ALSO damps the secondary SUT side --- not necessarily what is best, depending on the circumstances.
I actually just wanted to figure out what bandwidth I can expect by asking an apparently simple question about INDUCTANCE of the PW cart (not impedance as you rightly pointed out, I can measure DCR, but NOT uH!) So... I am still guessing we are looking at ~ 10uH and that gives me ~ 23kHz bandwidth.
Thank you for careing,
Axel

Axel, After I made my post, I re-read yours, and I realized I had slightly missed the point of your question. You might want to read the "white paper" on the Jensen transformer website, where they cover the complex issue of loading very well and describe the use of a Zobel network to attain flat fequency response. I've never used a SUT, so thankfully I have not needed to think it thru in as much detail as you have done. I would not have thought that the Ortofon or any other similar MC would be "happy" with only a 10-ohm load, but you have done the listening, whereas I have not. If you have a 47K resistance on the secondary side of you SUT, that will always reflect a 47-ohm impedance to the cartridge (if the tranny has a 10:1 ratio). So if you put 100 ohms on the primary side, the cartridge would "see" 100R in parallel with 47R (i.e., very low). For 10R, the net Z gets even lower. All of this interests me because I have a newly acquired Orto MC7500 direct-driving my phono section. By all accounts these Ortos like about 500 ohms. As regards bandwidth, does not the inductance of the SUT itself have much more effect than the inductance of the cartridge windings? Dunno.

Hi Lewen,
some "small" correction.
A SUT with 10 dB gain, 1:10 xfaxtor i.e. winding ratio, gives you 470 ohms on the cart side and NOT 47 ohm, since 47k / 10^2 = 470ohm -- agreed?

A 1:31.6 xfactor (30 dB gain) give you 47 ohm, since 47k / 31.6^2 = 47 000 / 998.56 = 47.067... ohm :-)
I hope we can agree on the maths, so I won't comment on your 100 ohms consideration etc.
As to the bandwidth:
The trannie(a good one) has about 200kHz bandwidth, so the cart is VERY well within that envelope AND thereby (to interested folks) truely to a degree of interest.
Since, if by some bad coincedence this bandwith goes well below 20kHz and you wonder about all the 'air' that's missing ---- you know where to look.
Greetings,
Axel

Sorry, you are correct about my math error. 470 not 47. Much better.

Your findings as to the sonic differences between loading the PW with NO trannie vs loading it either on the primary side or the secondary of a SUT are quite fascinating, and I don't know of anyone else who uses a SUT and loads the cartridge on the primary side. Tonight I have been listening to my MC7500, father of your PW, with no SUT and a 100R load. I don't hear any particular tonal imbalance, but the sound seems a tad closed in compared to my Koetsu Urushi (but tonearm and mat and tt are also different so not a good piece of data). Nevertheless, I am prepared to try 500R next, as this was advice I got from the previous owner of the MC7500. Can you once again describe the circuit you are happiest with? Reading two posts up from this one, I think you are using a 13R resistor on the primary side and a 47K resistor on the secondary side of your SUT, so that the PW sees 13 in parallel with 47 to give about 10R. Is that correct?

Hi Lewm,
That a trannie sounds better (ONLY MC!) is simply due to it using its "strength" - current delivery, rather then it's "weak point" - voltage (micro Volts).
It enables the cart to 'dig up' more detail / dynamics etc. More current through the cart's coil, not to forget, gives it superior damping, a mostly ignored fact these days.
However, there are A-PLENTY phono-pres that do it any way, since they use trannies as part of their design, EAR and Manley, come to mind immediately, it's just not too obvious.
EAR not only with their tube pres, but also with their SS-pre like the EAR 324. So it's not SO out of the ordinary after all.

Now to the 500ohm loading of your MC7500. Try it by all means, BUT if I estimate it right, the "mechanical damping" of the MCxxxx carts is NOT at all the same as Ortofon's newer cousins PW, Jubilee, Kontra-Punkt, Vienna, Venice, etc.

That simply means you will have to load higher (using a SMALLER R value!) simply to damp out the typical > 10-12kHz resonance frequency, please bear that in mind! 500ohm might get already too "loosy-goosy", 1k I can't imagine.
Now recall that a PW still works jolly fine with 47k (no loading at all, other than the phono-pre input impedance). The top Dynavectors do the same too, as their damping scheme(s) take care of this typical > 10-12kHz over-shoot / resonance.

So, the SUT secondary "sees" the 47k input-impedance of the phono-pre! If you put -another- 47k R (as you implied) and it will be || with the 47k pre input-impedance and so you'd have the SUT see: 47k*47k / (47k+47k) = 23.5k! on secondary.
This 23.5k, reflected back to primary, as we saw (taken a 1:31.6 xfactor (30 dB) SUT => 23.5k/31.6^2 = 23.5 ohm) is now in || with the primary load! AND is now WAY too low, (about 5ohm) if you'd have a 13ohm R for primary load!! So, NO secondary loading, the 47k input impedance of the phono-pre is your load.

Now, it MAY not end there... since (depending on the trannie's resonance behaviour) you might have to consider an RC (on the secondary) to damp any trannie resonance. It will be THEN when you want to know your cart's L! My original enquiry, to figure out the values for this RC.

My XF-1 does not have an issue (as it seems) but if you get some of the new fangled 'high-speed' core material trannies it could well be in need to damp out somewhere around 20kHz. It's a tricky lot of calculations and completely dependant on the trannie / cart combination, there are ball-park figures but I guess it would require some trial and error. This RC would act as a Notch-filter in case that makes it more clear.

The other SUT loading method: secondary loading, might take care of such resonance, I mentioned it earlier since e.g. 18k secondary load (for a 1:31.6 xfactor!) will dive you ~14 ohm the cart will see, AND it damps the trannie also. That is why primary loading (not damping the trannie) gives you more detail / clarity -- if you can make it work for your trannie / cart / phono-pre combination.
Cheers,
Axel