MC LOADING & STEP UP DEVICE

Wow, Axel thanks a million. Now I am just having a little trouble calculating. What is DCR?

Could we work through a case together so this crystallizes?

Data: Denon Au310 Step up, and 2 cartridges.

#1 Denon Au 310:

Winding wire ratio (pressure-up ratio) 1:10
Primary impedance 40ohms
Secondary impedance 4kohm
Frequency response 20Hz - 40kHz
Deflection (as opposed to 1kHz) Less than ±1dB
Magnetic shield Double
Chord length About 1.2m
Dimensions Width 51x height 53x depth of 181mm
Weight 0.65kg

#2 First Cartridge Supex Super 900
Output .2MV
Impedence 3.5 Ohm

#3 Second Cartridge Madrigal Carnegie one
Output Sensitivity: >0.26mV
Load Impedance: 30 to 50K ohms

So this is the data, now the calculations:

For the first cart:
winding ratio 1:10 of step up,
then Step #1 says-> since 1:10 = 20dB
then step #2 says-> 20*20*47kohm = ?
then step #3 says-> Well I need DCR, Don;t know what it is
now I am lost from here on.

Please help me fill in the blanks. Thanks again for helping me understand. It is greatly appreciated.

31.6 * 31.6 * 47k ohm = 47 ohm for a 30dB trannie

Please explain also, how you get this equality ?
=998.56*47kohms
=46932.32 kohms how is this = 47 ohm ?

Sorry for the silly typo!!!!!
It must read of course:
47k ohm / 31.6 * 31.6 = 47 ohm, for a 30dB trannie

Dfelkai,

"DCR" = "dc resistance," which is usually just a few ohms for low output moving coils, and can be neglected without introducing significant error unless the cartridge is to be loaded to very low values (say below 30 or 40 ohms, or even less if the dcr is particularly low).

Your xfmr has a ten to one turns ratio, so the 0.2mv and 0.26mv cartridge outputs will be stepped up to 2.0mv and 2.6mv respectively, neglecting the dc resistance effect.

That is a little bit less than ideal (ideally I would aim for around 5mv, which a 26db xfmr would provide), but it should be ok if the gain and/or noise performance of the phono stage is not marginal to begin with. You would have to turn the volume control up by 6db, relative to the setting you would use with a 26db xfmr, which is not a huge increase, and typically would not raise noise (background hiss) levels objectionably.

The square of the turns ratio is 100, so the 47K phono stage or preamp input impedance will be seen by the cartridge as 47K/100 = 470 ohms.

The Carnegie One's very wide load impedance specification (30 ohms to 50,000 ohms) is probably intended to indicate that it would be within reason to drive it straight into a 47K phono stage (that provides adequate gain and adequately low noise) with no external resistor, as well as to run it into a high gain step-up xfmr. The 470 ohm reflected load obviously falls within that range, but you may want to try adding resistors of various values to fine-tune the sound to your liking. Keep in mind that adding a resistor in parallel can only lower the 470 ohms; it cannot increase that value. (And adding a resistor in series, which would increase that value, should not be done because it would attenuate the signal seen by the preamp).

According to the data at cartridgedb.com, the SD-900 Super is specified for a load impedance of 2 to 20 ohms, so adding a 20 ohm load resistor on the primary side, or a 2000 ohm load resistor on the secondary side, would appear to be a reasonable way to go. The 47K load impedance of the phono stage or preamp (or 470 ohms as reflected at the primary side of the xfmr) would cause only a negligible lowering of the 2K (or the 20 ohms), so there is no point in bothering to calculate its effects. (OK, I did it anyway: The 20 ohms would be lowered to 19.18 ohms, and the 2000 ohms would be lowered to 1918 ohms).

The Supex's "impedance" of 3.5 ohms probably represents dc resistance, and is small in relation to the 20 ohms so it will not affect the signal level and overload calculations to a significant extent.

Hope that helps,
-- Al

Hi Al,
I think you do make the better teacher then I feel myself, as you have it so well explained.
Let's see if this gets Dfelkai sufficient clarity to proceed.
Thanks again, and let's see what comes up next.