Best loading for Audio Technica OC-09 using 1:10 SUT

Status
Not open for further replies.
Jump to Latest
#21
Jensen JT-44K-DX
Primary DC resistance of that SUT is 3 ohm.
Secondary DC resistance in 1:10 mode is 950 ohm.
Now we can calculate the extra load (actually the copper loss), which is the (square of the step up ratio x primary DC resistance) + secondary DC resistance.
In our example the extra load is (10² x 3) + 950 = 1250 ohm.
Now, to calculate a real 100 ohm load resistance, these 1250 ohm must be added to the (simplistic) 10k (10k is 100 (load impedance) x 10² (square of step up ratio).
So we must present the cartridge through the SUT with a load of 10k + 1250 ohm = 11250 ohm.
To get this resistance the standard 47k input resistor of the phono preamp must be parallelled with a 14790 ohms nearest standard value 14700 ohms.
 
#22
merlin el mago said:
Andy my maths for 100 ohms load

With a gain of 1:10, you need an impedance of 10000 ohms on yor Moving Magnet input (10^2*100).

The resistors must have a value equal to:

Rload = 1/(1/R1 - 1/R2)

Where
R1 is the impedance you want for your Moving Magnet input and R2 is the actual impedance of your Moving Magnet input


Rload = 1/(1/10000 - 1/47000) = 12658 ohms

If you don't want to post here please send me a PM with your maths.
Click to expand...

You were actually correct the first time - 12,702 in parallel with 47K gives 10,000 ohms.

I said what I said because you used the word 'added' (rather than parallelled).

However, I suggest life becomes much easier if you use a ss head amp - not a SUT - to give your LOMC the signal level it needs to feed an MM phono stage. Then you are simply parallelling 47K ... not having to take into account the resistance of the secondary.

And as Pieter wrote - it's not an absolute that the cart will sound its best at a particular loading. So if the mfr says '100 ohms' ... you may prefer 120 or 150 ohms.

Andy
 
Status
Not open for further replies.
Top Bottom