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SUTs and Resistive Loading Questions

Hello, I have a few questions about SUTs and adding parallel resistors to reduce the load impedance.

I have a SUT with a 1:15 turns ratio. As we know, the load for a 1:15 SUT through a MM/47,000 phono preamp would be: 47,000/15/15 = 209 ohms.

However, I want a load impedance of 100 ohms for the MC cart I'm using. To calculate the value of the resistor I need to add in parallel to do so:

100 ohms = Z/15/15 for a SUT with a 1:15 turns ratio. Solving for Z = 22,500 ohms.

Resistor Value Needed = 1/((1/22,500 ohms) - (1/47,000 ohms)) = 43,164 ohms.

So now, my questions...

If my phono preamp has a 100 ohms load setting, can I use that (instead of the 47,000 ohms setting and the above calculations for adding parallel resistor) to essentially get the 100 ohms load impedance I want?

Also, is there any difference in damping using the first method versus the second method? I would think not, but not completely sure.

Thanks for your insight.
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larryi
3,984 posts
 

Regardless of the theoretical issues, there is no harm at all in just trying different loading. 

I experimented with primary side loading by making RCA loading plugs and an RCA T splitter.  I used cheap resistors for the experiment, with the intention of buying the good stuff of the right value when I was done experimenting.  I planned to solder the right resistors on to the back of the input jack of my phono stage (it has a built in SUT), between the hot pin and the ground lug.  As it turned out, I just preferred no additional loading, but, it was sort of fun just making a few plugs and trying them out.

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edwyun OP
244 posts
 
Larry, thats what I intend to try. It is easy enough.

Lew thanks for describing the other options on the primary side. I will look into it further.

As for the need for a SUT, my pre has sufficuent gain for a MC but my experience is that using a SUT with a MM pre has benefits.

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rauliruegas
13,057 posts
 
Dear @edwyun : "  my pre has sufficuent gain for a MC but my experience is that using a SUT with a MM pre has benefits. "

That statement makes no sense to me other that the MC stage in your preamp be a bad design, that could be but I can't know because I don't know wich unit you own.

I said that makes no sense because: how or why can you think that adding an external SUT and additional IC cables and connectors can improve or gives benefits to the quality level performance of the same cartridge signal?

Look, if I assume that your preamp has an active gain MC stage and is a " decent " design then what you posted can't be true because those additional external devices you are talking about and in a " perfect audio world " ( that does not exist. ) the best it can do is no cartridge signal degradation and NEVER an improvement in any way.

Those additional devices you want to use only can degrade the cartridge signal and NEVER can improve it: that different levels of degradation are name it DISTORTIONS, additional distortions.

If you like those additional distortions is not the main audio subject here.


Regards and enjoy the music,
R.
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edwyun OP
244 posts
 
I agree less is more (and thus don’t like using more connections, resistors, etc, than necessary), but this is about trying different loading with a cart/SUT/phono setup to see what sounds best. If the resistors make a difference, then I would most likely change to a different SUT with different loading characteristics.

But I disagree that adding a SUT alone to a phono stage would lead to sound degradation. To me, the benefit of a SUT is not just gain.  YMMV.




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rauliruegas
13,057 posts
 
Dear @edwyun : It's your privilege to disagree.

R.
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