Tonearm wiring capacitance

doctorcilantro

I'm looking at some Soundsmith cartridges which come in a 100pf or 400pf version.

My buddy who helped me with my custom XLR tonearm setup stated that the capacitance wouldn't matter due to a voltage divider situation.

Any thoughts? I'm looking at running the new moving iron cart. at 35K and trying to figure out which version of the cart. to get.

I'm pretty much a Luddite with regard to capacitance; my tonearm wiring is about 34awg solid core silver and it's about 2feet and wired via XLR to connect to the mic preamp at 35K.

Internal Tonearm Wire (Solid Core Pure Silver Litz)
Ultra-Fine 34AWG tonearm wire constructed of 3 individually enameled“Real” Solid Core Pure Silver conductors which are tightly twisted using our H-Wound Litz TM technique. Our H-Wound Litz TM method involves Slow Feed High Pitch Precision Twisting of each of the wires into an almost horizontal conguration. Advanced low dielectric loss enamel to reduce overall weight and eliminate static build up. Designed for the most demanding tonearms and cartridges on the market.
Design: Proprietary Horizontal Wound
Conductor: Solid Pure Silver 99.999% (not plated)
Double Polyurethane Enamel Temp Res: 155C°
Overall Diameter: 0.2mm/wire
Weight per 60cm of wire is 0.5grams
Features: Advanced low dielectric loss enamel film Directly solderable with enamel coating acting as a flux Moisture resistant

Available in 0.6M PACK

Richard: I figure 12 inches for the tonearm + table internal wiring + 12 inches for exterior
so 414.8/30*2=27.7 ohms
your grado has a dcr of 2 ohms


5:03 PM
Would 33.5 AWG make much of a difference? 14.11 ohms

5:07 PM
Richard: Actually now that I think about it it won't matter with your pre. The cable resistance forms a voltage divider network with both the cart resistance and the pre load resistance, and the 38k dominates everything else and so there's negligible loss. But if the pre weer loading at 100 ohms instead, that 27 ohms would cost you dearly.

5:09 PM
Richard: like I said.. voltage divider. the cart generator sees 2 ohms, then 14, then 38k, then 14 in turn

so the voltage the pre sees is between the ends of the 38k resistance, and (google voltage divider) (38K+14)/(38K+2*14+2) ~~ 1 for all practical purposes

5:10 PM
so, no, the cart isn't going to see the cable load - all it will be seeing is the pre

quadzilla

The question is what is the capacitance on the input of your pre? Tonearm wiring is fairly negligible in this regard. Input load and capacitance should be set at the pre. It basically depends on how rolled off you want the highs to sound.

doctorcilantro

Had another discussion with my buddy last night on other topics, and only just touched on this again.

I think what I'm gathering, is that since I'm loading at 35K, and the tonearm capacitance is generally low, it simply won't matter; the cart will see the preamp load. Also due to the cart's 2ohm DCR and 2mH inductance?

But the point is that I'm looking at the Soundsmith carts, which come in 100pF and 400-600pF. Still waiting for the master (PL) to get back to me on that.

quadzilla

Yes, and that capacitance needs to be matched at the pre. The wiring doesn't really matter.

doctorcilantro

quadzilla wrote: »

Yes, and that capacitance needs to be matched at the pre. The wiring doesn't really matter.

What do picofarads represent here? The input DCR of the preamp is at 35K? I'm not sure what needs to be matched.

hearingimpared

Doc, your cartridge specs should tell you what the target load capacitance in your preamp should be set to. Just an FYI on my Spectral pre I have a space for custom capacitance & custom resistive loads. Check your preamp specs to see if you have the same.

Since I've been using MC cartridges the last few years I've not had to tweak capacitance but it is nice having a custom space to place a custom load to tweak you load. For instance; my cartridge calls for a 100 ohm resistive load. After tweaking I've found the best sound is achieved with 88.8 ohms. I used to do the same with MM cartridges back in the day and it really does make a world of difference being able to custom set your loads.

I don't think you have anything to worry about concerning the capacitance of your tonearm wire. Besides, if you did, I'm sure Soundsmith would have made note of it in the specs sheets or setup specs.

doctorcilantro

Okay, I'm just not clear on the terminology because Grado has never listed a target load capacitance. The state 47K for the input resistive? load at the preamp.

Soundsmith offers a 100pF and another custom 200-400pF.

The only thing Grado lists is internal resistance at 2ohms and 2mH inductance.

I found a bunch of other folks loading their Grados at 35-38K and I'll need to hear from Soundsmith as to which cart. they recommend as I'd llike to keep using the stock 35K on my preamp.

hearingimpared

doctorcilantro wrote: »

Okay, I'm just not clear on the terminology because Grado has never listed a target load capacitance. The state 47K for the input resistive? load at the preamp.

Soundsmith offers a 100pF and another custom 200-400pF.

The only thing Grado lists is internal resistance at 2ohms and 2mH inductance.

I found a bunch of other folks loading their Grados at 35-38K and I'll need to hear from Soundsmith as to which cart. they recommend as I'd llike to keep using the stock 35K on my preamp.

My terminology Doc. Target load = preamp load! Sorry for the confusion. 47K ohm is the norm for MM carts, some moving iron and even some MC cartridges. MM carts and some moving iron carts are very sensitive to the capacitive load and have an across the board resistive load of 47k Ohms. I guess that didn't to be stated though.;)

doctorcilantro

I don't know what this 100pF is.

My thought was the opposite, in that MCs with their low loads at pre would need carts with really low internal resistance.

It's well known that you can even effectively load a mm or mi at even 10K, well like the low output Grados which have 2ohm internal resistance, maybe even 1K (might not sound great of course).

So I'm not clear on why one maker of moving iron carts just states yo uneed that 47K load at your preamp, and SS goes for to discuss capacitance. If the tonearm wire doesn't matter? What does? Is this pF some kind of measure of the cart's resistance and inductance?

I have some reading to do it seems.

hearingimpared

pF is pico farads. Here's a link explaining Farrads. Units of measure for capacitors. Along the same lines as ohms for resistors and henrys for inductors.

http://en.wikipedia.org/wiki/Farad