Where to insert the step up transformer


Hello
I've just picked up my first MC cartridge. An unused Ortofon MC10 with step up transformer.
Since the RCA interconnects on my HK T60 are removeable, is there a best place to insert the transformers?
To clarify
The choices are
Turntable -RCA Cables- Transformer-MM Phono Input
or
Turntable-Transformer-RCA Cables-MM Phono input

All advice appreciated.

Cucurello

PS
Any one know of a source for additional headshells for the Harmon Kardon T-series tables?
cucurello
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.
Hi,
as Dertonarm said, THE BEST is to have the trannie right inside the phono-pre ---- unfortunately most often there's not enough space unless you want to dismantle the trannie.
Of course that would give you the least capacitance issues with the out-put connection, and presumably including very good screening.

DerTonarm knows his FR products, and if you look at e.g. an FR XF-1 you know what I mean with regard to space needed.

Cheers,
Axel
PS: I now use an MM and have none of that issue either :-)
Hey Gregm, Axlewahl, Almarg, & Dertonarm
Thanks for your input.
But I gotta tell you it did not work.

Not the cartridge/transformer hookup, I have not tried that yet.
What I mean is that no matter how hard you try you'ze guys won't scare me away with a barrage of opinion

I have read every word of it.
Understood some and probably misunderstood as much again.
I really appreciate the energy you are all putting into this.

Here are some reactions/replies
- The cartridge & transformes ARE a manufacturer's match
- The transformers are passive "in-line" devices
- It will require a 4'cable to go from TT to MM Phono input

Gregm's suggestion to try both ways appeals to me as I am most comfortable with the "aural" comparison.

I will be biased toward Dertonarm's advice.
It just seems to make sense that the signal should be amplified before travelling the distance.
Shielding however is something that I'd not considered.
Do you guys/gals think these transformers and the cable run ought to be shielded?
If so. With what material?

That's it for now.

Thanks again to all

Cucurello