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How important is the cable between the SUT and phono pre?

I know when using a cable between a MM cartridge and the phono pre it's very important to take into account the capacitance of the cable for cartridge loading.

I don't recall seeing a discussion on the importance of using low capacitance cables between a SUT and  phono pre.  

I picked up a Denon Au-340 to replace my Denon AU-320 in my system and the AU-320 has built in cables that run to the phono pre, hence my question.

Is there a way to figure out the capacitance requirement for this cable or is it not that important? Will a good shielded cable work fine?

I don't want suggestions on some high dollar cables, that will never happen. I have about 15 or 20 pairs of cables that I picked up over the years, I can always go through the pile and measure the capacitance if necessary.

Thanks

 

BillWojo

billwojo
billwojo OP
397 posts
 

@mulveling

 

"MC are said to not be sensitive to capacitance, but the problem with a SUT is that it reflects the capacitance of its output cable times the SQUARE of its turns ratio. That’s enough capacitance that it WILL start to affect the MC cartridge."

 

Can you point me to some more information on this? I was searching for information and found nothing to indicate that this was a problem. I've read that the cables from cartridge to SUT didn't need to be particularly low capacitance but nobody talks about the cables from SUT to phono pre.

Thanks

 

BillWojo
 

 

millercarbon's avatar
millercarbon
12,531 posts
 

You have multiple cables. In the time spent asking for guesses here you could hook them up and know. Then let us know. Why not try them all, let us know what you tried, how it sounded?

mulveling's avatar
mulveling
2,190 posts
 

@billwojo

I am probably not the kind of expert you need here. But look at this page which I found very interesting:

http://www.hagtech.com/loading.html

The first section deals specifically with loading MM cartridges with capacitance. However, the formula Fr = 1 / (2*PI*SQRT(L * C)) works equally for MC and MM cartridges. This formula defines the cart’s resonant frequency based on its inherent inductance and the downstream (cable) capacitance. The resonance is often accompanied by a sharp peak and followed by rolloff. Generally you want this frequency as high as possible, well out of the audible band (> 20kHz). This generally requires low capacitance OR low inductance (as per the formula). MC cartridges get the low inductance (that’s the L in the formula) for "free". Normally this is enough that they need not concern themselves with phono cable capacitance. HOWEVER with a SUT reflecting the output cable’s capacitance times the square of its turns ratio (look this up elsewhere), capacitance could suddenly become large enough to drop the resonant frequency back near or into audible range and become a concern. For example: say you (unwisely) choose a fat audiophile interconnect run with 200 pF capacitance. And your SUT is a 30x. 30 * 30 * 200pF = 180,000 pF. Wow. Say your MC has an inductance of 1mH. Using the calculator in that Hagerman page I linked, the resonance is now at 3,800 Hz. You’re gonna have a bad time! Choose a cable with 40pF and now it’s at 26,000 Hz. Much better!

jpjones3318's avatar
jpjones3318
149 posts
 

@jasonbourne52, it's not quite that simple for MM as increasing capacitance will also move the resonant frequency down, depending on the electrical characteristics of the generator, of course.  This is why on a cartridge like the AT150MLX, if you want flat response, the cartridge cannot see more than 150pF.  Also why that cartridge has such a maligned reputation for exaggerated HF response.

@mulveling, looking at transformer equivalent circuits I don't see reflected capacitance.  Reflect impedance, reflected leakage inductance, but not capacitance.  Do you have cite for this?

@billwojo, capacitance on the secondary with load R will form a zobel, which can tune the response of the transformer.  For best performance every SUT should be tuned this way, but as it is cartridge, transformer, and upstream phono stage dependent, it's not practical for the average person.  Just know that changing C on the secondary can have an audible effect, but it's to do with the transformer response itself.  

At the bottom of this page is a tech note from Morgan Jones: https://www.sowter.co.uk/specs/8055.htm

 

 

 

mijostyn's avatar
mijostyn
8,570 posts
 

@billwojo , The single most important factor is to keep the cable as short as possible. I would use a high bandwidth balanced cable like Canare Da206. 

I use Sowter transformers which I mounted inside the phono stage with a switch to go back and forth between MM and MC. Doing this depends on how much real estate is available inside the phono stage. The transformers are very small. 

https://www.sowter.co.uk/acatalog/E_A_Sowter_Ltd_PHONO_CARTRIDGE_TRANSFORMERS_30.html

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