Interconnects with Step up transformer

The overriding consideration is the capacitance of the cable itself. The goal is to keep it under 100pf. Longer single ended cables with capacitance higher than this could cause high frequency roll-off depending on the other capacitances in the phono signal path. Brand mixing does not matter.

Nominal cable capacitance is 30pf/ft, limiting length to 3 ft or less. I use Belden 1505A cable, a video cable. Capacitance is 17pf/ft. I limit my phono section cable lengths to less than 2 ft. I typically measure a capacitance of 50pf or less, including connectors.

If you DIY your cables, this is an easy result. If you don't, I would find out or measure this value for other single ended cable types.

The above argument is strictly true for mm cartridges, but is also important for mc cartridges as well. See the Hagerman discussion referenced below.

The output of the phono preamp does not need such low capacitance. I would advise though, to keep the capacitance of that cable and all other single ended cables to less than 150pf. Balanced cables can be far longer.

Hagerman has a great cable loading discussion on the website.

@chrisocr 

"Wow , appreciate the informative responses. My rega turntable does not have a DIN connection so the cable is fixed to the RB330 tone arm , and I see Rega sells the same interconnect that can be used throughout the signal chain , I believe the cable is called Rega connect 3 cable made by the same UK company that supplies to Rega to use in their tonearms , now I myself have heard a sound change when swapping out the cable out from SUT to my parasound jc3 plus , and from the parasound to rogue audio preamp I’m using a kimber Carbon cable , now onto would love to use the same carbon cable on my SUT but it’s not insulated so hum will occur . Using three different cable brand in my analog chain does not make sense to me ."

It should always be easy to hear the differences between other manufacturer's components in the signal chain, just confirms that nothing in between them is altering the signal in any way. Interconnect, speaker cables and power leads shouldn't alter the sound in any way though most hobbyists want to believe they do. The Rega Couple 3 you mentioned in your post and I underlined, would not be a bad choice. It's made of very high-quality ingredients from Klotz and Neutrik, is very well assembled and should last as long as you'd ever want it to. I have two pair of the long-discontinued Couple 2 as well as one pair of the Couple 3. They do exactly what's written on the can which is very little and except when I'm in the mood to mix and match components in my system I mostly forget about them.

When looking to learn if a real value is able to be had for exchanging a cable, I have monoblock Power Amp's able to be fed a cable from a Source Direct. The same can be done with a owned pre-amp with a separate VC for each channel.

My own evaluations is that there is only occasionally a notable difference able to be detected, but that is when changing a wire used for the signal path. For example, OFC to OCC, or the same types to PC Triple C or a D.U.C.C.

Swapping out Cables using the same signal wire has not convinced me much is on offer from Cables with a commonly used construction method,

As stated in the earlier post, swapping out a same cable type for different lengths has not presented a change to an end sound considered different.

I have used a MC Cart' direct into the MM circuit, what was required to achieve a typical volume for a replay was an increased Volume Level. A  very Rich in Tone end sound was very noticeable as the change to the Cart's sonic if used through the MC circuit. I have used SUT's that have added a similar Richness of Tone.

SUT's are generally injecting a Tonal Richness, where one perceives enough is  added is their unique choice, hence many recommend different models as their preferred sonic trait.

It is also worth suggesting,  if there is an interest in experiencing different Step Up Tranxs, arranging for a experience of a Head Amp will also be beneficial to have a perception that transparency is the sonic trait.   

@chrisocr you should be using purpose built phono cables which are low capacitance between your SUT and phono stage.