Choosing the right SUT for my setup

Denon made the AU305

6 moons primer

https://6moons.com/audioreviews/stepup/primer.html

think about future changes now:

separate control of gain and impedance is most flexible,

to leave your cables alone:

pass for MM bypass is a nice feature, leave SUT in-line bypassing it's transformer

multiple front selectable inputs is good for multiple arms

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impedance guidance: coil impedance x 10 = _____?

that’s the ’guidance’ impedance you want ’shown’ to your MM phono input. (MM Phono input is typically 47,000, verify yours). then go up/dn from there, it’s just guidance. (nothing wrong, but, frequency response can be effected)

your choices: coil 12 x 10 = 120; coil 14 x 10 = 140, close, so: avg 130. ’guidance.

formula: 47,000 divided by x-factor squared = the impedance that will be shown to the MM Phono input (change 47,000 if yours is different)

now, working backwards to find a desired x factor: 47,000 divided by "what x factor squared?" will be close to 130. 47,000 divided by the goal of 130 = 361 for a desired x factor squared.

x factor 18 sq. = 324. x factor 19 sq. = 361.

Note: it’s inverse: up the x factor thus up the x factor squared, higher number yields LOWER impedance that will be ’shown’

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NOW, that x factor yields what signal strength? enough? overload?

one choice is .25mv x 19 = 4.75mv, allow some loss, say 4.5mv

other .4mv x 19 = 7.6mv, allow some loss, say 7mv.

So, if settings are NOT independant, look for a SUT setting withan x factor of 19 or just a bit lower.

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from an old chart I found:

Denon AU-320 offers too low, or too high xf 10 or xf 36

Denon AU300LC has only xf 10

Fidelity Research FRT-4, 3 inputs + PASS for MM Thruput; offers 4 optional x-factors, one is 18,27 (it’s 30 ohm setting), +25db; another is x factor 20.68 (it’s 10 ohm setting) +26db.

EAR MC4 one of 4 settings is xf 18.

EAR MC3, one of 3 settings is xf 20, +26db

Entre ET 100, 3 inputs + PASS for MM thruput; 3 optional loads

Input impedance: 3, 10 or 40 ohms select, you would use the 10 ohm setting.

Gain:
3 ohm -- 32dB
10 ohm -- 26dB
40 ohm -- 20dB

It’s Tricky.

 

@audioguy85 

 

SUT is a 1/10 version does not necessarily mean the cartridge will see 470 ohms. Here is an example, my Jensen mc-2rr-L has a 430 ohm impedance that the cartridge will see, while my Rothwell mcx SUT, also 1/10, presents a 100 ohm loading.

So you have $$$ tied up into 2 SUT’s rather than one. Yes, Different loadings can be done with the use of resistors. I made loading plugs which did the same. Bent SUT was set up for loading pliugs. But you STILL have an extra component and cable rather than the shortest path.

Also, load is important as it changes the character or response of cartridge

Yes, I understand that. But its NOT a positive thing for the cartridge according to Ralph @ Atmasphere. The loading stiffens the cantilever and is necessary for the preamp so it does not ring like the cheaper ones generally do @ 47K. FWIW I have been running my .LOMC at 47K for about 15 yrs. I have loading plugs to make any value I want. But I chose 47K because it sounds best

It is also better to use a SUT for a low output m/c rather than a preamp with m/c capability. The reason being most preamps rely on j-fets to boost the signal.

That may be true with some but I doubt all of them, especially tubes. I have an SS which I use the 47K loading. So i find your assertion at least questionable. But even if so, you still haven’t dealt the the addition to the signal path. I suspect whatever gains may be made using your idea are then lost with the addition of an extra component and cable.

That said, I appreciate your response. I just disagree mostly. But if you like what you are doing, great. I’d be glad to listen with you.

The individual with the Sculpture A SUT's made it known the Company is willing to wind a Transformer to a Bespoke Ratio. 

Guess it comes down to do what ever sounds good to you. I tried it both ways...sounds better with SUT in the chain. The extra cable is very low capacitance...makes no difference or detriment to sound. 

Also, I did not pull any of this from my A$$, WHAT I "assert" is fact. A good SUT will not add anything to the character of the sound. I disagree also about loading not being important. Too little or too much will effect both the high frequency response and the bass....that is why cartridge manufactures have a recommended load.