Where to insert the step up transformer

If you have no out-put RCA cable comming out of the step-up (going to the phono-pre), make sure it is as low in capacitance as possible!!!!!!
The capacitance of this interconnect is 'reflected back' to the primary i.e. what the cart sees. It 'stepped-up' by the square of the winding ratio of your trannie. Example a 30dB trannie has a 1:31.6 ratio, therefore the capacitance of that cable makes your cart "see" 31.6x31.6=~1000 times the capacitance of that trannie-to-phono-pre cable!

Actually, it's the opposite, Axel. Since there are (many) more turns on the secondary side, the impedance seen looking into the primary of the transformer would be REDUCED from the secondary side load impedance by the square of the turns ratio.

As far as the op's question is concerned, in the absence of further information my instinct would be to have the longer set of cables on the secondary side (between xfmr and preamp), and to keep the cabling between cartridge and xfmr as short as possible. That way most of the noise which may be picked up in the cabling will not be boosted by the step-up transformer.

Regards,
-- Al

Hi Almarg
I think you read this too fast...
*** The +++capacitance+++ of this interconnect is 'reflected back' to the primary

You talk now of IMPEDANCE --- I spoke of CAPACITANCE!

And as it so happens THAT works the other way round, I hope we can agree on that, and I totally agree on the IMPEDANCE point you made.
>>> ... the ***impedance*** seen looking into the primary of the transformer would be REDUCED <<< Oh yes!

I hope this is not too confusing to our audience :-)

Next, and there I TOTALLY DISAGREE!
>>> my instinct would be to have the longer set of cables on the secondary side <<<
NO WAY, since every bit of cable length on the secondary adds to unwanted CAPACITANCE, therefore, the shorter the better.
The cable between the primary and the tone-arm must be considered *differently* when using an SUT, since CURRENT has no issue with CAPACITANCE and RF as voltage with a minute current would have.
The SUT is like a short circuit (almost) to the cart, and increases current by more than 20 - 25 times in lieu of cart output voltage (some say it's a generator maintaining voltage, but let's not confuse that issue any more than needed)
It may sound counter intuitive, but capacitance = roll-off you hear, is because the C is REFLECTED back from secondary to the primary by the ratio squared.
RF noise is no issue on primary in my experience and due to the higher current as would be the case without SUT. ALL (most) current is converted to Voltage on the secondary i.e. and not to be confused with 'shunted loading' as in normal MC loading across the phono-pre's input.

Normally you'd go into a 47 000 ohm input impedance and added parallel/shunted loading of the phono-pre, with an SUT the cart going into a e.g. 32dB trannie sees a MAXIMUM of 30 ohm (the "natural impedance" based on a 47k phono-pre input impedance)! That, if now further trannie loading is added and quite easily 10 ohms, when applying secondary or primary SUT loading.

Therefore, put the lesser IC in front and the best and shortest on secondary.
Greetings,
Axel
PS: I did have had plenty time to get my XF-1 going with my PW MC cart...

Yes, you are right Axel, I read it too fast. I was thinking impedance, but you had written capacitance. Capacitive impedance (reactance), of course, being inversely proportional to capacitance. Mea culpa!

Concerning the high load capacitance which the cartridge would see if the lengthier cables were on the secondary side, I'm uncertain without having specific data on the cartridge resistance and inductance. As you realize, but others may not, moving coil cartridges are essentially insensitive to capacitive loading, WITHIN REASONABLE LIMITS. What is "reasonable" after the capacitance on the secondary side is multiplied by a factor of 1000 or so would be dependent on those cartridge parameters.

I did find a reference indicating that the MC10 is rated for 0.2mv (not 0.1mv) output under the usual test conditions. I believe that cartridges with comparable outputs tend to have resistances in the vicinity of 5 to 10 ohms, and inductances in the area of 15 or 20 microhenries (0.015 to 0.020 mH). If your 0.1mv figure is correct, those numbers would probably be a bit lower, which would be in the direction of further reinforcing my next paragraph.

Plugging those inductance numbers into the resonant frequency calculator shown here, in combination with say 100,000 or 200,000 pf capacitance (100 or 200 pf from cables plus preamp, factored by the square of the turns ratio), gives resonant peaks in the vicinity of 100kHz or more, well outside of the audio band. Which in turn would probably be reasonably well damped by the 10 to 50 ohm or so resistive load that the cartridge would see, based on the 47K preamp impedance divided by the square of the turns ratio. The bandwidth resulting from the combination of inductance and resistive damping would also be in the 100kHz+ area, as shown by the calculator further down the page in the linked reference, under the heading "mc cartridges."

I am not particularly experienced in this area, while you are, and so your instincts are more likely to be correct in the absence of more specific information. But fwiw those are the thoughts that occur to me in the absence of quantitative data on the cartridge and xfmr.

Regards,
-- Al

Hi Cucurello,
are we still value added, not loosing you?
I hope it'd still of some use to other folks.

Almarg asked:
>> What is "reasonable" after the capacitance on the secondary side is multiplied by a factor of 1000 or so would be dependent on those cartridge parameters. <<

I give an example: 10nF is a pretty reasonable C to be used with a 'lively' MC as most Lyras, and even an Orpheus --- but NOT with a Ortofon Windfeld.
Take this C load and leave it in, when using an SUT it will become 10nF -> 10mF and it 'kills' the treble stone dead.

So that is beyond reasonable in deed. But you can see what happens if you use a capacitive IC from trannie to phono input...

Now as to the resonance frequency. As the MAIN factor needs you to know the correct inductance of the cart ---- Ortofon, and I asked them in person, never even measures it!
Also, there is the SUT --- Ortofon? Don't know, so to be practical we have to experiment.

Depending on the SUT it MAY want some damping too. In this case you'd hear some 'papery chirp' in the treble...

If so, secondary loading will be the first best thing to try.
Bearing in mind that any parallel secondary loading is reflected / by the winding ratio squared as seen by the cart and as mentioned.
Example: 30dB = 1:31.6 ratio, 47k ohm phono input with 18k ohm secondary load = 13 ohm the cart will see on primary, intead of 47 ohm. (You know the maths)

If this makes everything too dull somehow, we consider primary loading to get an impedance match. I used ~ 2.5 x DC coil resistance MC 10 = 3 ohms according http://www.cartridgedb.com/results_2.asp
so somewhere around 10 ohm, i.e. a 13 ohm resistor in case of a 30dB SUT with 'natural impedance' of 47 ohm.

OK, now we are in this territory when I said earlier Cucurello needs more information than he'd care for :-)

The last thing, is getting any resonance of the SUT combined cart sorted, by putting an RC of suitable size on secondary to shunt any resonances around >20kHz...

If Cucurello has a T10, that came with the MC 10 none of this aught to any issue at all, and that's the good news :-)

Axel

Dear Cucurello, if the MC output is very low and the phonoamp is far away, do amplify the signal as early as possible and use a low capacitance phono cable. To keep solder joints and connectors to the minimum possible, I would however - whenever possible - integrate the transformer into the phono-input section (especially so as most step-up transformers do furthermore benefit from the additional shielding of the preamps cabinet and the input of the phono/RIAA-preamp can easily adjusted (with tubes.... sometimes with JFets too) to perfectly match teh secondary of the transformer.
Cheers,
D.