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"Low Capacitance" Cables?

markanini

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Capacitance is a huge issue for turntable interconnects - particularly if the turntable is to use high inductance cartridges (MM / MI) not so much an issue for MC cartridges.
Do cartridge manufacturers specify an optimal pF value? How about the cables between the cartridge and interconnects?
 

Speedskater

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For long analog RCA unbalanced single-ended interconnect cables (say well longer than 15 feet/5 meters). The best cables have a very heavy shield. Like the BJC LC-1 and a few similar cables. These will reduce Common Impedance Coupling Current noise. For a long run there can be a 20dB difference between these and a poorly chosen cable. (per Bill Whitlock)
 

Angsty

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Capacitance is a huge issue for turntable interconnects - particularly if the turntable is to use high inductance cartridges (MM / MI) not so much an issue for MC cartridges.
Yes - I got interested in low capacitance cables when I was using a MM cartridge. Now I have a MC…

I appreciate what @solderdude said. Even in my MM phono setup, I’d rather have a bit more capacitance than to get noise coming through unshielded cables. BJC makes note that their testing concluded that double braid shielded coax was most effective for audio use.

LC-1 can be a bit more expensive than other Belden coax varieties; it is exclusive to BJC and requires rarer Taversoe plugs instead of Canare. Yet, it may perform no better when minimum capacitance is not warranted, such as for line level connections.
 

Angsty

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Do cartridge manufacturers specify an optimal pF value? How about the cables between the cartridge and interconnects?
This post contains info on how to calculate the optimal capacitance for your cartridge.

 

dlaloum

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Do cartridge manufacturers specify an optimal pF value? How about the cables between the cartridge and interconnects?
They typically provide a "recommended range" - indicatively AT MM cartridges do best with total C between 100 and 200pf (with optimal, from experience, being 100pf!) - but the capacitive loading interacts with the resistive loading - and although the standard "recommendation" is 47kohm - period cartridge manuals suggest a range of between 27k and 70k ... and when combined with capacitance, that can make an enormous difference to the voicing!!! (it is basically tuning an EQ filter to match the cartridge)

Manufacturers have avoided fixed loading specs for MM, as it would put customers off, as there is no standard, and phono stages are so varied, that whatever you set as your spec, is likely to exclude a large % of the marketplace - so they get vague and waffly!!!
 

dlaloum

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The most reliable solution is to keep the cable between cart and phono pre as short as possible
And that can result in some awkward positioning issues.... (words of wisdom from someone who shortened the interconnect to 50cm.... and then had trouble finding a spot for his phono pre! - but I did manage to get total capacitance down to 60pf)
 

markanini

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The most reliable solution is to keep the cable between cart and phono pre as short as possible
It's paralleled in electric guitars, though most players like the coloration in the audible band. For those that don't, or wish for more precise control, some products offer a solution in the shape of an opamp circuit to buffer the signal, and you can use any length cable you want! Installation can be either at the output jack. Or, if built into the pickup, a differential configuration can be used to cancel out RF and EMI noise at the source. I wonder why this hasn't been used on turntables.
 
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levimax

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It's paralleled in electric guitars, though most players like the coloration in the audible band. For those that don't, or wish for more precise control, some products offer a solution in the shape of an opamp circuit to buffer the signal, and you can use any length cable you want! Installation can be either at the output jack. Or, if built into the pickup, a differential configuration can be used to cancel out RF and EMI noise at the source. I wonder why this hasn't been used on turntables.
For TT it works out well to do the same thing. Short run from TT to phono pre amp and then you can run longer from phono pre to pre amp.
 

dlaloum

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For TT it works out well to do the same thing. Short run from TT to phono pre amp and then you can run longer from phono pre to pre amp.
If at all possible, mostly for DIY.... you build the phono pre into the turntable.... then you can get the raw capacitance down to below 50pf (potentially circa 30pf) - with additions made via resistive and capacitive "plugs"
 

egellings

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If at all possible, mostly for DIY.... you build the phono pre into the turntable.... then you can get the raw capacitance down to below 50pf (potentially circa 30pf) - with additions made via resistive and capacitive "plugs"
That's a good idea, so long as the TT motor and its electronics, if any, do not radiate noise into it. With low output impedance moving coil carts, cable capacitance from normal-length cables will not matter.
 

levimax

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That's a good idea, so long as the TT motor and its electronics, if any, do not radiate noise into it. With low output impedance moving coil carts, cable capacitance from normal-length cables will not matter.
With MC carts you don't need to worry much about loading but depending on the environment noise pick-up can be an issue with longer cables. For me I find trying to put the phono-pre inside the TT to not be worth the trouble but using short cables (less than 12") from TT to phono pre whether MM or MC to be very helpful.
 

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I use my 3 foot BJC LC-1 cables to my phono with no issues for MM or MC. In my case, I traded for a slightly longer, well shielded, low capacitance cable to put the phono further away from other electronics that might cause hum. That’s worked well for both of my phonos.

I’d be concerned that proximity to the motor of a turntable in an integrated phono, or transformers in other components, would be a bigger harm than a few dozen more pF.
 

Killingbeans

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You could wrap it in mu-metal. But a longer cable is definitely a cheaper solution :D
 

Speedskater

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I would think that for most MM cartridges and pre-amp input stages a 3 foot BJC LC-1 cable would have less than ideal total capacitance.
Don't know if you could hear the difference, but it could be measured at above audio frequencies, as peaking or ringing.
 

levimax

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I would think that for most MM cartridges and pre-amp input stages a 3 foot BJC LC-1 cable would have less than ideal total capacitance.
Don't know if you could hear the difference, but it could be measured at above audio frequencies, as peaking or ringing.
Don't forget about cable inside the tone arm and the connectors and phono pre-amp. It is pretty hard to get capacitance too low for an AT cart.
 

Angsty

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The capacitance of LC-1 is 12.2 pF/ft. I calculated the optimal capacitance for my MM using the calculator I referenced earlier; it’s good.
 

dlaloum

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I use my 3 foot BJC LC-1 cables to my phono with no issues for MM or MC. In my case, I traded for a slightly longer, well shielded, low capacitance cable to put the phono further away from other electronics that might cause hum. That’s worked well for both of my phonos.

I’d be concerned that proximity to the motor of a turntable in an integrated phono, or transformers in other components, would be a bigger harm than a few dozen more pF.
One of the joys of turntables - so damn many variables!

But yes, that too can be a problem, more so with MC, less so with MM, and very heavily dependent on the motor and motor control tech used!
 

dlaloum

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The capacitance of LC-1 is 12.2 pF/ft. I calculated the optimal capacitance for my MM using the calculator I referenced earlier; it’s good.
To give an idea of the impact of loading - both C and R.... here are some measurements I made about ten years ago, using an AT150ea body, with a 440MLa stylus fitted

I tested the frequency response at 60pf, 296pf, 422pf, and 535pf, each with R loadings of 10k, 21k, 43k, 83k and 97k

I also modeled the theoretical "electrical" response - which are the smooth lines of colours matching the measurement lines... the modeled plots assume a theoretical "perfect" cantilever within infinitely low mass, and therefore no resonance within the range....

The main difference between the model and the plots is in fact the combined imperfections/distortions of the magnetic system (the generator/magnets... eddy currents etc...), and the needle / cantilever (primarily cantilever resonance...) - combining the two (model and measured) allows for interesting analysis of different styli... (!!)

For this specific cartridge/stylus combination... the optimal loading would be somewhere around 30k, with 60pf... if the capacitance is higher, optimal R would start to drop... at 296pf... the 21k R loading is pretty damn good... but you could opt to flatten the 3k to 10k zone, in exchange for a slightly rising top end... (everything is a compromise!) - by going up to an R loading in the mid 30k (at a guess).

As can be seen, there is NO capacitance at which this combination would achieve anything approaching a flat F/R with the "standard" 47K loading

(applying Digital EQ changes the game of course!)

THe AT440 body is slightly different, as it has inductance of 480mH as opposed to the AT150 body which has 340mH... so if you have a number of bodies within the family, you can use that as another variable, in aiming for perfection.... but roughly speaking the results for the AT440 body with the ATN440MLa stylus were pretty similar.

The AT cartridges tend to like a low capacitance, as well as a resistive loading lower than the standard 47k for best results

How does this tally with you calculator method?

results were:
AT150-440mla - 60pf.jpg


AT150-440mla - 296pf.jpg


AT150-440mla - 422pf.jpg


AT150-440mla - 535pf.jpg
 
OP
MattHooper

MattHooper

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Hey folks, thought I'd drop in a cable question here:

At what point do mismatched cable lengths matter to the stereo signal, and what could be affected?

I presume that, for instance, connecting unbalanced RCA cables between a pre-amp to an amp, using a 3 foot cable for the Right channel and 6 foot for the Left channel would be unlikely to produce any audible issues. But then, at what point WOULD there be issues? How much longer would the Right channel cable have to be before problems arise? I presume one problem could be you hit high frequency roll off by sheer length. But, any other issues? Like a mismatch of the timing of the signal between left and right signals to the amp?

Same question goes to mismatched length of speaker cables.

Thanks.
 
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