Question about loading with an SUT

I use five different carts and use one SUT currently wired at 1:10.

@theflattire If you hear differences between the cartridges its likely got more to do with loading the transformer correctly than anything else.

@adam8179 That method I mentioned is daunting! Jensen Transformers did a lot of this work and so they have a pdf file you have to ask about that shows the loading their transformers are expecting, depending on the cartridge  used.

Plan B: place a 100K variable resistance across the output of the transformer while its plugged into your phono section. Find an LP of which you also have a CD or digital source. Play the CD or file. Compare to the LP and vary the control until the two sound very similar. Its likely that the LP won't sound as bright... At any rate disconnect the potentiometer and measure its value using a Digital Voltmeter on the Ohms scale and find a fixed resistor of the same value or very close.

Right here is actually the biggest weakness of LP reproduction as opposed to digital; not noise floor, dynamic range, distortion or any of that. Its setup and that is likely a huge part of why digiphiles prefer digital; they just really haven't heard an LP set up properly and no shame in that.

I’m wondering if there would really be much of a difference if I had an SUT with the exact ratio and loading that is specified rather than "getting close?"

@adam8179 Transformers will ’ring’ (distort) if insufficiently loaded and will roll off if loaded too much. So the answer is yes. You can hear it and its easily measured.

The correct loading value varies with the source impedance (the cartridge).

Transformers transform impedance; they do not isolate impedance, so the output impedance of the transformer varies with the source impedance.

Don’t worry about what is ’ideal’ for any LOMC cartridge- loading such cartridges for sound quality is a myth. Your main concern is making sure the transformer isn’t modifying the sound by being incorrectly loaded (although all SUTs make distortion and limit bandwidth even if loaded correctly).

This is tricky since the capacitance of the tonearm cable and that of the cable between the transformer and phono section plays a role. Quite literally this should be done with a square wave generator, an oscilloscope and a variable resistance. With the cartridge in place the square wave (of very low amplitude) is applied to the input side of the transformer and the output observed on the ’scope. The variable resistance is placed across the output (which is connected to the phono section) and varied until the ’scope shows something that looks as close to the square wave as possible. If this does not make sense to you find a technician to do it for you.

This value of resistance is called ’critical damping’.

Obviously this is tricky (in most cases will have to be done by a technician) and is one reason I prefer using a phono section that does not need an SUT; one competently designed so I don’t have to worry about ’cartridge loading’ (which is for the benefit of the phono section, not the cartridge); just plug and play.