I require a set of low capacitance phono leads for turntable to amplifier connection (MM cartridge). The usually suggested suspects for this application include BlueJeans Cable's LC2, around £60 for 6ft (I need a little bit more than 1 meter), some cables by Mogami, around the same price, and Van Damme Silver Series LoCap 55pF - locking RCA Phono cable at around £40 for just over a metre.
https://www.amazon.co.uk/Blue-Jeans-Cable-Stereo-Cables/dp/B00NAJ9I24?th=1
https://www.ebay.co.uk/itm/29314887..._Kf_RsZ0eps-8lqWQI0-NHG9lYQfNqBxoCky4QAvD_BwE
I also have seen that Coax cables usually have fairly low capacitance and assume that any reasonably made Coax would do the job?
The much maligned Audioquest brand also make a (for them) cheap cable, the Tower, which to me, looking at specs also includes a solid core conductor, air foamed insulation and shielding. Would this also be suitable? It looks like it is similar to other Coax's.
https://www.audioquest.com/products...P2NZeluV8lP3m598UWIt_wH5FFOk_mQa1D3WEDWJBYREg
What would you choose or am I over thinking this? Length required perhaps 1.2 to 1.5 meters. I will add a separate ground/chassis wire.
Thanks
https://www.amazon.co.uk/Blue-Jeans-Cable-Stereo-Cables/dp/B00NAJ9I24?th=1
https://www.ebay.co.uk/itm/29314887..._Kf_RsZ0eps-8lqWQI0-NHG9lYQfNqBxoCky4QAvD_BwE
I also have seen that Coax cables usually have fairly low capacitance and assume that any reasonably made Coax would do the job?
The much maligned Audioquest brand also make a (for them) cheap cable, the Tower, which to me, looking at specs also includes a solid core conductor, air foamed insulation and shielding. Would this also be suitable? It looks like it is similar to other Coax's.
https://www.audioquest.com/products...P2NZeluV8lP3m598UWIt_wH5FFOk_mQa1D3WEDWJBYREg
What would you choose or am I over thinking this? Length required perhaps 1.2 to 1.5 meters. I will add a separate ground/chassis wire.
Thanks
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a lot of the RG cables have capacitance below 50pF https://helukabel.de/publication/DE/CATALOGUES/CW/Auswahltabellen_DE/Kap_M_336_347_dt_link.pdf
It is folly to change to low capacitance cables.
MM cartridges are designed to resonate with a preferred load capacitance. Phono preamps take the average phono lead capacitance into account and pad with whatever is necessary. This was a stupid fad, something stereo shops could sell customers. This often leads to reduced high frequency response.
What was done to correct this was read the require capacitance from the cartridge data sheet, measure the leads to the turntable (phono cart. disconnected), and the phono preamp input. Add them up and subtract from the recommended load. Add the required capacitance, now missing.
What you need are leads that are flexible with good shielding with normal capacitance.
MM cartridges are designed to resonate with a preferred load capacitance. Phono preamps take the average phono lead capacitance into account and pad with whatever is necessary. This was a stupid fad, something stereo shops could sell customers. This often leads to reduced high frequency response.
What was done to correct this was read the require capacitance from the cartridge data sheet, measure the leads to the turntable (phono cart. disconnected), and the phono preamp input. Add them up and subtract from the recommended load. Add the required capacitance, now missing.
What you need are leads that are flexible with good shielding with normal capacitance.
Considering what was included as cabling in my hifi components boxes, I'd say: Any cable will do. However for longterm hassle-free use, I do prefer gold plated plugs, and for the look&feel some nicer finish cables. If you can do the soldering yourself, just by a couple of meters of cable and some decent quality plugs.
For good quality cable, take a look at the larger musical instrument sellers, if the cable purchased by the Pros for their studio equipment is good enough for them, it likely will be good enough for you. They have readymade cables, too - for acceptables prices (from my experience, musicians are always short on money, but still prefer good equipment).
For good quality cable, take a look at the larger musical instrument sellers, if the cable purchased by the Pros for their studio equipment is good enough for them, it likely will be good enough for you. They have readymade cables, too - for acceptables prices (from my experience, musicians are always short on money, but still prefer good equipment).
Higher impedance coax has lower capacitance, so 90 ohm is lower capacitance than 50 ohm. However guitar cables are even better than RF-coax since they are designed for the job.
If you have a phono-preamp close to the turntable the cable isn't important, setting the load capacitance in the preamp is... Optimal total capacitance depends on the cartridge so its best to have a selectable capacitance preamp and check datasheet of the cartridge you are using...
Hi Mark,
Patently untrue! Try RG-174A or similar. Normal cable TV wire is too stiff. You want something pliable, many low capacitance cables for turntables are very thick and also very stiff. Avoid thick cable, too much stress on the shield when bending near any clamp or connector.
What is important is % shield coverage and a good dielectric to avoid distortion. Some musical instrument cable is good, some terrible. Wire user in test equipment is always very good. Typically 50 ohm, but that is an RF impedance, at audio frequencies the characteristic impedance is not important at all.
Patently untrue! Try RG-174A or similar. Normal cable TV wire is too stiff. You want something pliable, many low capacitance cables for turntables are very thick and also very stiff. Avoid thick cable, too much stress on the shield when bending near any clamp or connector.
What is important is % shield coverage and a good dielectric to avoid distortion. Some musical instrument cable is good, some terrible. Wire user in test equipment is always very good. Typically 50 ohm, but that is an RF impedance, at audio frequencies the characteristic impedance is not important at all.
The RF characteristic impedance is √(L/C), where L is the inductance per unit length and C the capacitance per unit length.
The speed of propagation is 1/√(LC). It depends only on the dielectric, as it is also equal to c/√(epsilonr mur), where c is the speed of light in vacuum, epsilonr the relative dielectric constant (or whatever that's called nowadays) of the dielectric, and mur its relative permeability, which is usually 1.
All in all, when you know the cable length and type of dielectric, you can calculate the capacitance from the RF characteristic impedance.
The speed of propagation is 1/√(LC). It depends only on the dielectric, as it is also equal to c/√(epsilonr mur), where c is the speed of light in vacuum, epsilonr the relative dielectric constant (or whatever that's called nowadays) of the dielectric, and mur its relative permeability, which is usually 1.
All in all, when you know the cable length and type of dielectric, you can calculate the capacitance from the RF characteristic impedance.
The characteristic impedance is another way of expressing the capacitance and inductance per unit length, so its very pertinent. The capacitance per unit length of coax is given by (2*pi*e) / ln(b/a) where e is the permitivity of the dielectric, b and a are radii of outer and inner conductors. The inductance formula is u * ln(b/a) / (2*pi), where u is the permeability of free space. characteristic impedance is sqrt (L/C), or Z = (ln(b/a) / (2*pi)) * sqrt (u/e).
This means C is proportional to 1 / Z for the same dielectric, 90 ohm cable will have 55% of the capacitance of 50 ohm cable.
With a polythene dielectric in fact 90 ohm will have b/a = 9.3, C = 55pF/m, 50 ohm coax b/a = 3.45, C = 99pF/m
Dielectric choice is indeed important as dielectrics that absorb moisture (such as PVC) have very ill-defined permitivities, and thus variable capacitance (and losses). The best dielectric for low capacitance is probably foamed PE or foamed PTFE. 75ohm coax for video often uses foamed PE dielectric.
I guess don't buy the terrible guitar cables. Buy the good ones. Guitar cables are usually very flexible, that's one reason to recommend them - if you want good braid coverage the cable will be stiffer, there's simply no way to avoid this. Put the preamp near the turntable and use short cables as I said - then the cables are less critical.
To my knowledge most thin RF coax is 50 ohm, it would be nice to find 90 ohm thin coax, but the inner conductor would be very thin indeed thinking about it, an issue for fitted connectors... Thinner cables are much more flexible (even 20% thinner makes a big difference).
So a thin guitar cable with foamed dielectric is going to tick all the boxes except ease of fitting connectors.
This means C is proportional to 1 / Z for the same dielectric, 90 ohm cable will have 55% of the capacitance of 50 ohm cable.
With a polythene dielectric in fact 90 ohm will have b/a = 9.3, C = 55pF/m, 50 ohm coax b/a = 3.45, C = 99pF/m
Dielectric choice is indeed important as dielectrics that absorb moisture (such as PVC) have very ill-defined permitivities, and thus variable capacitance (and losses). The best dielectric for low capacitance is probably foamed PE or foamed PTFE. 75ohm coax for video often uses foamed PE dielectric.
I guess don't buy the terrible guitar cables. Buy the good ones. Guitar cables are usually very flexible, that's one reason to recommend them - if you want good braid coverage the cable will be stiffer, there's simply no way to avoid this. Put the preamp near the turntable and use short cables as I said - then the cables are less critical.
To my knowledge most thin RF coax is 50 ohm, it would be nice to find 90 ohm thin coax, but the inner conductor would be very thin indeed thinking about it, an issue for fitted connectors... Thinner cables are much more flexible (even 20% thinner makes a big difference).
So a thin guitar cable with foamed dielectric is going to tick all the boxes except ease of fitting connectors.
Hi Mark,
Larger diameter cable puts more stress on the shield as it is bent near the clamp or RCA connector. This has everything to do with diameter and not stiffness. Remember, I repair this stuff for a living and have for 50 years. I have seen just about every fad and results of people monkeying around with just about everything. I also work in the Test and Measurement industry.
At audio frequencies, RF characteristics don't really matter unless they are so bad the affect low frequencies and you would never, ever see them used in test equipment of good audio gear. Want to talk about effects at 1 MHz up, okay. But it doesn't relate to a phono preamp and cartridge in any way, shape or form. So keep comments relevant to the application please.
Guitar cables are flexible as they are moved a lot. The typical connector is a 1/4" phone plug with has very good strain relief on the cable. It is meant to be pulled as so often happens. Your normal RCA cable does have nearly as good a starin relief - if any at all. Phono cables are not designed to withstand several strong pulls. Each type of wire is designed (well) for it's intended purpose. The problem I have seen with guitar cables with RCA plugs is that over time the shield connections can fail - or the signal lead depending on how tight it was made during installation. This is due to gravity and constant tension. Cables with fine wires often fail where normal ones wouldn't. Just repaired a pair of expensive specialty cables. They were expensive garbage, a "Litz" type. Each with insulation (not enamel).
It boils down to this. Try to get cute or fancy, you end up with problems.
Yes, dielectric is critical (which is why I recommended RG-174A or similar). But a phono circuit doesn't care if the characteristic impedance is 50 R, 62R, 75R or 110R (or anything else within reason). The cartridge cares about the capacitance it sees, along with resistive load. That determines the response curve. Dielectric determines distortion, shield coverage is all about hum pickup. You have to balance these things. I see very little point in arguing the minutia, the OP just simply wants good leads. Then, he has to live with having those wires. Thick ones will break.
The cartridge requires enough capacitance that you can use about the same length as the original wire. You will have to pad it somewhere, normally the preamp input. Want the most from your cartridge? Measure the total lead capacitance, the preamp input capacitance and refer to the recommended cartridge load. Make the total equal that. It is no more complicated than this, assuming you are using decent wire for this application.
Larger diameter cable puts more stress on the shield as it is bent near the clamp or RCA connector. This has everything to do with diameter and not stiffness. Remember, I repair this stuff for a living and have for 50 years. I have seen just about every fad and results of people monkeying around with just about everything. I also work in the Test and Measurement industry.
At audio frequencies, RF characteristics don't really matter unless they are so bad the affect low frequencies and you would never, ever see them used in test equipment of good audio gear. Want to talk about effects at 1 MHz up, okay. But it doesn't relate to a phono preamp and cartridge in any way, shape or form. So keep comments relevant to the application please.
Guitar cables are flexible as they are moved a lot. The typical connector is a 1/4" phone plug with has very good strain relief on the cable. It is meant to be pulled as so often happens. Your normal RCA cable does have nearly as good a starin relief - if any at all. Phono cables are not designed to withstand several strong pulls. Each type of wire is designed (well) for it's intended purpose. The problem I have seen with guitar cables with RCA plugs is that over time the shield connections can fail - or the signal lead depending on how tight it was made during installation. This is due to gravity and constant tension. Cables with fine wires often fail where normal ones wouldn't. Just repaired a pair of expensive specialty cables. They were expensive garbage, a "Litz" type. Each with insulation (not enamel).
It boils down to this. Try to get cute or fancy, you end up with problems.
Yes, dielectric is critical (which is why I recommended RG-174A or similar). But a phono circuit doesn't care if the characteristic impedance is 50 R, 62R, 75R or 110R (or anything else within reason). The cartridge cares about the capacitance it sees, along with resistive load. That determines the response curve. Dielectric determines distortion, shield coverage is all about hum pickup. You have to balance these things. I see very little point in arguing the minutia, the OP just simply wants good leads. Then, he has to live with having those wires. Thick ones will break.
The cartridge requires enough capacitance that you can use about the same length as the original wire. You will have to pad it somewhere, normally the preamp input. Want the most from your cartridge? Measure the total lead capacitance, the preamp input capacitance and refer to the recommended cartridge load. Make the total equal that. It is no more complicated than this, assuming you are using decent wire for this application.
I am also of the firm belief that captive phono leads from the 1970s and 1980s are pretty much all in need of replacement, regardless of how they "look".
Most went through nasty cable grip clamps which have caused more trouble than just about anything else. Plenty of Japanese shielded cable has internally deteriorated and gone green and sticky. Sansui cables are one of the worst. They actually turn back to oil inside! Molded RCA plugs seep a liquid and the internal soldered connections in the sealed plug get flaky.
Measure the capacitance at the RCA plug AND measure the cable run for resistance to the cart/headshell wires, assuming your TT doesn't short/mute the output when "off".
Most went through nasty cable grip clamps which have caused more trouble than just about anything else. Plenty of Japanese shielded cable has internally deteriorated and gone green and sticky. Sansui cables are one of the worst. They actually turn back to oil inside! Molded RCA plugs seep a liquid and the internal soldered connections in the sealed plug get flaky.
Measure the capacitance at the RCA plug AND measure the cable run for resistance to the cart/headshell wires, assuming your TT doesn't short/mute the output when "off".
As Mark and I have tried to explain, there is a direct relation between RF characteristic impedance and capacitance per unit length. For a given dielectric, the higher the RF characteristic impedance, the smaller the capacitance per unit length.
The sum of the cable capacitance and the preamplifier input capacitance has to be approximately equal to the recommended load capacitance. When the recommended load capacitance is small and there is some practical reason why the cable has to be fairly long, you need a low-capacitance-per-unit-length cable, when the recommended load capacitance is large and the cable is short, you don't.
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Hi Marcel,
Why did you even say that? This is painfully obvious, and I covered it by recommending the original cable length, then measuring and compensating for any difference. You don't need a smith chart to figure this out. Sure the characteristic impedance has a factor, but does it matter if you're going to measure and compensate?
Do not focus on having a higher characteristic impedance. It is completely pointless at audio frequencies. Since when at audio over short lengths do we ever worry about reflection and termination in the same impedance as the source or load?? the short factual answer is that we do not. We are only concerned with the total capacitance and resistive load presented to the cartridge - is that not a true statement?
As I've made clear a few times now, using a low capacitive cable forces you to add capacitance, usually at the preamp input. Fair? So, if you spent more for a cable that is equivalent, but lower capacitance, is it also fair to say you wasted money?
Let's keep this discussion limited to the audio bandwidth, which is lower than 50 KHz in a phono cartridge. Otherwise we end up discussing factors that, although are true, have no real bearing at these frequencies. Tell me where that is useful beyond having an academic argument.
Why did you even say that? This is painfully obvious, and I covered it by recommending the original cable length, then measuring and compensating for any difference. You don't need a smith chart to figure this out. Sure the characteristic impedance has a factor, but does it matter if you're going to measure and compensate?
Do not focus on having a higher characteristic impedance. It is completely pointless at audio frequencies. Since when at audio over short lengths do we ever worry about reflection and termination in the same impedance as the source or load?? the short factual answer is that we do not. We are only concerned with the total capacitance and resistive load presented to the cartridge - is that not a true statement?
As I've made clear a few times now, using a low capacitive cable forces you to add capacitance, usually at the preamp input. Fair? So, if you spent more for a cable that is equivalent, but lower capacitance, is it also fair to say you wasted money?
Let's keep this discussion limited to the audio bandwidth, which is lower than 50 KHz in a phono cartridge. Otherwise we end up discussing factors that, although are true, have no real bearing at these frequencies. Tell me where that is useful beyond having an academic argument.
Because his input is actually a very useful summation without a whole lot of superfluous verbiage and BS.
We've been here since 2004. Marcel joined before both of us two. Give him credit where credit is due.
Now it is "painfully obvious" while just a little while ago it was "patently untrue!".
🙄
Hi poldaaudio,
When I responded to Mark, I was more concerned with the fact that guitar cable is often higher capacitance and that argument wasn't applicable. He made a point for a low capacitance cable, then a higher capacitance cable was immediately recommended. That was a side argument that didn't apply to the issue at hand. Had he recommended a guitar cable, without going into capacitance - fine. That cable does tend to be thick, that is a problem.
Look. It is this simple. Within reason, the absolute amount of capacitance a cable has is immaterial for the phono. You change the wire type, time to measure the capacitance and correct for any change. It is no more complicated than that. The other factor is that thick wires without special RCA connectors is more likely to fail over time just hanging there. This approach costs more, has zero benefit.
Just to make it clear, I do respect Marcel, but not due to his tenure here, but his technical contributions. I did get frustrated over the discussion turning into an academic argument more than helpful information that would better suit the OP. I don't think anyone can disagree with the practical points I made.
Hi John,
As for verbiage, I only try to explain more fully because many people read these threads that aren't even members. The rationale is as important as the answer some times. They may read only one post, or a couple.
When I responded to Mark, I was more concerned with the fact that guitar cable is often higher capacitance and that argument wasn't applicable. He made a point for a low capacitance cable, then a higher capacitance cable was immediately recommended. That was a side argument that didn't apply to the issue at hand. Had he recommended a guitar cable, without going into capacitance - fine. That cable does tend to be thick, that is a problem.
Look. It is this simple. Within reason, the absolute amount of capacitance a cable has is immaterial for the phono. You change the wire type, time to measure the capacitance and correct for any change. It is no more complicated than that. The other factor is that thick wires without special RCA connectors is more likely to fail over time just hanging there. This approach costs more, has zero benefit.
Just to make it clear, I do respect Marcel, but not due to his tenure here, but his technical contributions. I did get frustrated over the discussion turning into an academic argument more than helpful information that would better suit the OP. I don't think anyone can disagree with the practical points I made.
Hi John,
As for verbiage, I only try to explain more fully because many people read these threads that aren't even members. The rationale is as important as the answer some times. They may read only one post, or a couple.
I find it very practical to know that cable capacitance is cable delay divided by RF characteristic impedance, and that cable delay depends on the length of the cable and the speed of propagation of electromagnetic waves in the cable dielectric. For one thing, it means that all polyethylene-filled 75 ohm cables of a certain length have the same capacitance, and that that capacitance is less than that of 50 ohm cables of the same length.
In particular, it means that the thin and flexible 75 ohm cables used for video and S/PDIF connections are fairly good low-capacitance cables (about 67 pF/m) if they have polyethylene dielectric. (The same holds for the much thicker coaxial cables that are usually used for television, but those are less practical for mechanical reasons, like you already wrote.)
The recommended load capacitance is very different for different cartridges. Some cartridges require a low load capacitance and some turntables have remarkably high internal wiring capacitances, leaving very little capacitance for the cable from the turntable to the preamplifier and the preamplifier itself. For an example, see post #31 of https://www.diyaudio.com/community/...split-from-opa1656-thread.377331/post-6786832
Hi Marcel,
I agree - at RF frequencies. It doesn't matter to an audio signal, and both channels are the same so there is no delay to worry about either between them.
Absolutely! Many cartridges have varying capacitance loads. That's why I find it astounding the "high end" market pushes low capacitance cables and very few even pay attention to the cartridge load (beyond being 47K). Anyone buying a good cartridge (normally expensive) doesn't even check the loading requirements. "Technicians" used are often completely clueless as well. Therefore the poor customer searching for the best performance is hampered before they even start. How many "cartridge shootouts" do you think are never set up properly?
Cool fact, I didn't know that. I have never had to deal with this. Thank you. Makes sense of course, just never needed to think of it that way.
I agree - at RF frequencies. It doesn't matter to an audio signal, and both channels are the same so there is no delay to worry about either between them.
Absolutely! Many cartridges have varying capacitance loads. That's why I find it astounding the "high end" market pushes low capacitance cables and very few even pay attention to the cartridge load (beyond being 47K). Anyone buying a good cartridge (normally expensive) doesn't even check the loading requirements. "Technicians" used are often completely clueless as well. Therefore the poor customer searching for the best performance is hampered before they even start. How many "cartridge shootouts" do you think are never set up properly?
To that I would add low-triboelectric effect. Teflon turned out to maybe not be the best choice of insulator.