2. analog
  3. 173274-124530

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

Showing 2 responses by atmasphere

atmasphere's avatar
atmasphere
11,615 posts
 

However, transformers do not reflect secondary load C to the primary.   

@jpjones3318 

Transformers transform impedance and impedance includes capacitance. However, things are not as simple as just that. You have to also consider how a parallel capacitance interacts with the inductance of the transformer- and here we are talking about a resonance. This is also occurring on the primary side! Of course, I'm saying the same thing that Dave @intactaudio just did in different words.

If your EE friends tell you this isn't a thing, here's an EE that is telling you it is, just FWIW... but 'multiplied back to the source' is only correct in that there is a fractional factor involved, variable with frequency. This is really one reason I stay away from SUTs if I can help it 😁

As a general rule of thumb, the best advice is to use low capacitance cables. If you do this right, the electrical resonances involved will be so high that on the cartridge side it will be well outside the transformer's bandwidth. If loaded properly on the secondary side (such that there is no ringing) again you're off the hook. At any rate don't think for a minute that the loading on the secondary side (including capacitive effects) can't be measured on the primary side!

 

atmasphere's avatar
atmasphere
11,615 posts
 

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?

@jpjones3318 Transformers are called that because they transform impedance. They do not isolate it!

So a load on the output of the transformer very much affects the source on the input side. This is part of why the transformer must be loaded correctly. Incorrect loading of the transformer can have other effects too- for example all transformers have inter-winding capacitance. If the transformer is too 'lightly loaded' (output load impedance is way too high) the inter-winding capacitance will begin to affect frequency response, perhaps manifesting as a hump in the frequency response rather than being flat.

More to discover