Hi Intactaudio,
I'm not making this up believe me. Firstly a 30dB trannie has a 1:31.6 ration that gives you a reflected 47ohm since your phono-pre input impedance is 47k
i.e. 47k/31.6^2 ~ 47ohm.
Now to the current. A trannie like a 1:31.6 has a DCR of about 1.5 ohms on primary, and as we calculated 47ohm inductance and with a 13ohm in || a 10.18 ohm impedance.
Now try do the maths and see how much more current will go through the primary than in a non SUT set-up.
On the secondary you have MORE than twenty times the Voltage! Now this can ONLY come from a higher current, right? (ohms law)
Veff= [cart impedance / (trannie impedance + cart DCR)]* Vcart*winding ratio
So a cart like the PW has 0.3mV and 4ohm DCR, and 10ohm impedance.
Veff= [10/(10.18+4)]*0.3*31.6= 6.7mV that the phone-pre will see.
As I said, more than twenty times 6.7/0.3= 22.3
So it is the SUT's primary that enables the cart to deliver 20 time more current than if you are offering 0.3mV to your phono-pre.
I hope this makes some sense.
Greetings,
Axel
I'm not making this up believe me. Firstly a 30dB trannie has a 1:31.6 ration that gives you a reflected 47ohm since your phono-pre input impedance is 47k
i.e. 47k/31.6^2 ~ 47ohm.
Now to the current. A trannie like a 1:31.6 has a DCR of about 1.5 ohms on primary, and as we calculated 47ohm inductance and with a 13ohm in || a 10.18 ohm impedance.
Now try do the maths and see how much more current will go through the primary than in a non SUT set-up.
On the secondary you have MORE than twenty times the Voltage! Now this can ONLY come from a higher current, right? (ohms law)
Veff= [cart impedance / (trannie impedance + cart DCR)]* Vcart*winding ratio
So a cart like the PW has 0.3mV and 4ohm DCR, and 10ohm impedance.
Veff= [10/(10.18+4)]*0.3*31.6= 6.7mV that the phone-pre will see.
As I said, more than twenty times 6.7/0.3= 22.3
So it is the SUT's primary that enables the cart to deliver 20 time more current than if you are offering 0.3mV to your phono-pre.
I hope this makes some sense.
Greetings,
Axel