How can I calculate my phono chain's capacitance?

I got a new preamp and not just the loading but the capacitance can be configured. I'm wondering how I can calculate my chain's capacitance in order to set my phono preamp to the right settings,

I have a Morrow Audio PH3 cable coming which rates at 294pf. I own a VPI Prime with a 20X2L cart and the 3D-printed 10" tonearm.

 

Capacitance has really no influence on this cartridge, not at frequencies we possibly can hear.

 

Do You mean it has?

 

294 pF for the PH3 cable seems very high. The PH1 cable has only 98 pF. It seems like Morrow’s website would make note of the effect on MM cartridges.

 

Yes, this is something that effects the sound of a cart.

 

The minimal effect of capacitance on a low output moving coil cartridge is explained here.

Hagerman Technology LLC: Cartridge Loading

 

I'm quoting the number directly from their website. The pF rating only increases as we go up in phono cable caliber. To moot, their most expensive reference cable has a pF rating of 980 for a 1-meter cable. Half that for a 0.5m cable. So I'm understandably confused. Some websites seem to indicate the lower the better but why would this well regarded company make people spend hundreds and thousands of dollars and keep increasing its phono cable capacitance in the process the higher up you go in their cable line if it's so bad?

But how? Seems that finding a link explaining these concepts in basic simple plain English is quite challenging!

I thank you for the link but I'm no mathematician nor engineer so this stuff is way too granular for me. Is it possible to boil it down to a simple concept, please? What effect would having an MC cart have on capacitance? Is the rating I quoted from Morrow Audio valid in my application? If not, again, how can I approximately deduce my capacitance to appropriately calibrate my new phono preamp?

 

In my experience, with phono connections, the lower the capacitance, the better. I buy interconnects that are "low capacitance".

 

Moving Coil Cartridges are essentially immune to capacitance loading, but are greatly affected by resistive loading.

Moving Magnet Cartridges are sensitive to both capacitance and resistive loading.

 

If you venture on to EBay
You will see Capitance meters for sale.
If your headshell if detachable. Then it makes it simple. Connect meter to the phono plug that connects to then phono pre, and read off capitance.
You can also measure your interconnects, and check out dodgy capacitors .

 

For MMs it helps if the capacitance suits the inductance, not getting the res too low. For MCs, like in this case, the res will be so high up in freq not even a bat will hear it.

 

Thanks for clearing that up in a succinct fashion. The question remains, however, as to how can I determine the capacitance so I can properly set my phono preamp to the right setting?

So why would Morrow Audio's phono cables boast a higher-the-better capacitance rating the more money you throw at their cable line? Makes no sense, does it?

 

What's "the right setting"? Does Dynavector suggest a total capacitance value? If not I'm not sure how calculating the total capacitance helps you. Set capacitance to 0 and sleep well.

 

As others have noted, the reason capacitance matters with phono carts is because the inductance of the phono cart and the resistance and capacitance of the cable and phono stage loading the cart together form an oscillating circuit with a resonance at a certain frequency and a steep roll off of frequencies above the resonant frequency.

However, with MC carts, the inductance is so low that the resonant frequency with any amount of capacitance you're going to run into, is going to be way up beyond the audible frequency range, even way up beyond dog whistle range. Unless you have a problem with radio frequency oscillating or something, you can pretty much ignore the capacitance of the phono cable and phono stage with a low inductance cartridge.

With MM carts, the inductance is high enough that the capacitance and resistance loading will alter the frequency response of the system -- capacitance will tune the frequency of the resonance -- more capacitance will tune it lower, less capacitance will tune it higher; resistance will affect the amplitude of it -- the lighter the load the more the resonance will ring. And with MM's the resonance is pretty much always in the audible range so R and C tuning will impact what you hear.

How can you calculate the capacitance load on your cart?

Well, you need to add together the capacitance of the tonearm cable, then the capacitance of the cable between the turntable and the first active device -- the phono preamp -- plus the capacitance of the connectors, plus the load capacitance of the phono stage.

So you need to know the capacitance of the tonearm cable -- does VPI provide a spec?, the capacitance of the interconnect, the capacitance of the interconnect's RCAs, and the load capacitance of the phonostage.

You've only mentioned the cable capacitance of 294 pF (which I'm guessing also included the capacitance of the connectors). So you need to add the phono cable capacitance to that (that's probably only a foot or so of cable at like 30 pF/ft but VPI would have to tell you). And I'm guessing what you're wondering is what to set your phono stage capacitance to, because it has adjustable capacitance, yes?

Zero if possible or as low as possible. There's no reason not to go as low as possible anyway in this circumstance, unless you have some kind of ultra high frequency squealing as a result, but you'll have already loaded down that cart with a lot of capacitance by the time you hit the phono stage.

As to this question of a three foot phono cable with 294 pF of capacitance. I think that's a stupid design idea. It won't matter much with very low inductance carts, but it would completely alter the sound of higher inductance carts. I'd reject it out of hand myself.

Also I see Morrow has those cables marked as directional? Are these twinax cables with a shield that's floating at one end. I like that kind of geometry in hifi and I make cables like that myselff, but not in a connection between a cart and a phono stage. I've found that's a noisy way to go in that application.

I think Morrow is bundling lots of individually insulated wires together, hence the high capacitance, yes? If you want that sort of geometry, you might want to try true Litz cables, which are individually insulated by twisted in such a way to lower inductance (they're really designed to address skin effect, but that not an issue at audio frequencies over short runs at the gauges of cable we use). KAB makes an interconnect, the Spiral Air, with Cardas Litz cable and ETI gold over copper (instead of gold over brass) connectors and teflon and cotton dielectric (for a capacitance of 35 pF/ft, vs. this Morrow cable which seems to have a capacitance of 90 ish pF/ft). It's only $100 for a 3- foot pair. I haven't heard it but it might be worth checking out.

 

Go to the bottom of the page for specifications.

Dynavector 20X2 H/L | MC Phono Cartridge

Here are the specs of my phono preamp.

Decade < Phono Stages < Lehmannaudio

 

No mention of a suggested capacitance.

 

The lowest setting on my phono preamp is 47pF. Just confused about all this as you'd expect the capacitance number to go DOWN the higher the caliber of cable you buy from Morrow Audio but it goes UP.

I'm wondering if it'd benefit the sound to set it at a higher setting matching as close as possible the capacitance rating Morrow Audio assigns to the PH3 cable which is 294pF. Unless all of that is pointless and that rating is only applicable to MM carts so I should set my preamp to the lowest capacitance setting of 47pF, then?

 

There's no inductance spec for the cart on the cart specs. That's what you need to cacluate the resonant frequency of the RLC circuit, which is what you're dealing with when you're dealing with cart loading. But a 0.3 mV output cart is going to have an inductance in the 10-30 uH range. If you have 300 pF of capacitance in line with that, and a 30 ohm resistance load as per the recommendation, the resonant frequency of the system is going to be at higher than 1.9 MHz, we're talking radio frequencies here, miles above the audible range. If you add a little more or a little less capacitance to that circuit, it's not going to make a damn bit of difference.

 

Most preamps load to 100 - 150pf
So most turntables have st least 100 - 150 pf
So, you are already up to 250 pf.
Now if your turntable has captive leads
you can add by using a y connector and a loading plug.
But you cannot take away. If the turntable ie Project, is without leads then you can chose low capitance
Leads.
MC however is not affect to any great extent by capitance, but it is by loading .say the cartridge has internal impedance of 120 ohms the we would load at 1/10 ie 12 ohms.
Although one is free to experiment.
As you progress up to 47K the sound will be brighter.

 

Like I said, it doesn't matter. You can try it at all the darn settings the preamp has, whatever you set it at, the action is going to be taking place at radio frequencies. Unless you're having RF oscillation, it's not going to make any difference.

 

Cable capacitance is not a measure of quality one way or another. And in electrical terms, in most of our home hifi gear we have very low source impedances, very high load impedances and we're using very short runs of cable, so the capacitance isn't really coming into play too much -- except with MM phono carts.

I don't understand why anyone would design unbalanced analog audio cable to have more and more individually insulated strands with higher and higher capacitances, other than to charge more and more for them. I'm not sure what performance gains are realized, in theory or practice, with short runs of audio cable following this design philosophy. But people do seem to like these cables.

 

So basically, it's all about whatever sounds best to me? If so, what tonal differences should I expect if I raise or lower the capacitance setting on my phono preamp?

 

When he said "it's not going to make a damn bit of difference", what he meant was "you will not hear tonal differences as you raise or lower the capacitance setting on your phono preamp". At least not with a moving coil cartridge.

Personally, even with MM cartridges I think this is a bit overblown. A lot of Ortofon and Audio Technica MM's suggest recommended capacitance that wouldn't be possible for the majority of their customers to achieve (think 100pf-150pf - you'd basically have to solder a phono preamp to the back of your tonearm). I didn't hear any Bad Stuff by having reasonable length cables into a reasonable phono stage. I think what the capacitance warnings (along with captive wires on turntables) are there to do is keep people from running 50 foot wires from the turntable in their living room into their bedroom or something.

 

With a very low inductance MC cart? None. But maybe some people would think you'd hear infintessimally more or less body or shrillness to HF character. But honestly, with a that kind of inductance, as I and others have been saying, that capacitance loading shouldn't make any audible difference. The expectation should be no difference.