OK - so this thread was promted by some comments on another thread - not wanting to hijack that thread I created this one...
ISSUE: some high current designed amps have an issue with speaker cables that have a high capacitance. - the amp can be driven to self destruction because of internal oscilation caused by the high capacitance of the speaker cable - this does NOT apply to Tube amps - i.e. to my knowledge
The amps I know of that are affected in this way are Ayre, Gryphon and NAIM - only NAIM warns of this up front AND instruct their dealers to let customers know about it
So why don’t other brands warn about the possibility?
QUESTION: - would it put you off? - would you select a different amp if the manufacturer warned of this "issue" up front?
I tend to agree with anhwy61, shadome, almarg and others that feel there is no reason for high capacitance in a cable.
The only "reason" as such, pertains to adopting a particular cable geometry in order best to combat cable related noise issues.
The cable geometry used in one CARDAS cable having high capacitance is a very low noise design - effective at attaining the "black background "
The "side effect" of that particular geometry is high capacitance - which is not an issue with tube amps - and is only an issue with SOME high current solid state amp designs
Can you acjieve the same black bakground with a different geometry? - I believe so - but they may be more complex to manufacture
There’s are many ways to "skin a cat" - in the end - it all boils down to cost.
@cheeg While I’m not an expert by any means, I have been an audio enthusiast for more than 35 years and have had the opportunity of owning or extensively auditioning some very nice equipment - speakers, amps, cables and accessories - some combinations working very well together and some not. Regarding cables, IMO that there is little to no reason to use high capacitance cables for any system, regardless of speakers and whether powering with a ss amp (particularly a high currant ss amp) or tubes. I have one set of low capacitance, highly conductive (individual strands of polyethylene insulated Oxy free pure copper)) cables, that I now use always, regardless of what I trade in and out of my system, knowing that they will allow me to hear subtle differences in everything else without adding a character or coloration of their own. I have no worries of them raising havoc with any of my high currant amps and they work equally well with tubes. My RCA interconnect cables are short run, low C pure silver and I have no desire to change them either.....just some thoughts...Jim
Thanks for starting this thread-I had no idea that this was a potential issue with my system! I completely agree with @elizabeth that it is both the amp and cable manufactures’ responsibility to warn the public if there is a potential issue with their product.
Unfortunately, much of the electrical discussion I find to be extremely dense. It would be a great service to the audio community if someone would provide a layman’s rule of thumb for determining whether their system may be subject to harmful isolation to to a poor match between amp and cables.
I tend to agree with anhwy61, shadome, almarg and others that feel there is no reason for high capacitance in a cable. To Al's statement "A cable having extreme and/or unusual parameters would be a non-starter for me" - I say "DITTO". The amps mentioned in the OP are neither cheep nor poorly designed. Over the years, I've come to the conclusion that the three main attributes of good cables is: high conductivity, low capacitance and low inductance. Beyond that, IMO, there are a lot of very expensive gimmicks out there that do nothing more than alter or degrade the the original signal. Signal loss and degradation is also the reason that high capacitance cables do not work for high speed data processing....Jim
Thanks for taking time to reply. No need to apologize for the length. Appreciate your efforts to be thorough. Still digesting, though on the initial read-through you've provided worthwhile elaboration on BJC's comments. Performance not simply a function of conductivity as influenced by gauge, but metallurgy, and geometry too. I think your idea of separating to reduce locally generated "intra cable" interference is practiced by mftrs. producing "flat" cables like Wireworld and Mapleshade (others too, no doubt). Thanks again.
@ghosthouse - I don’t profess to be an expert or anywhere near that, since I have only been "tinkering" with the effects of cable design and geometries for about the past 4 years,
WRT...
I wonder if their, "...barring a really odd design, which may introduce various undesirable effects...." is tacit acknowledgement of the oscillation risk you raise
In short - yes, I believe so to.
But I would interpret "odd design" to be a reference to the diealectric attributes of the insulation used, and cable geometry, because they too are a factor in the capacitance of the cable.
But there are a couple of points in the text you posted that I believe should be expanded upon, e.g. ...
The first point...
speaker cables are, for all practical purposes, immune from interference from EMI or RFI,
When EMI/RFI is introduced into the conversation it is generally with respect to external EMI/RFI influences.
However, I believe the Proximity Effect, which is EMI/RFI between the conductors within a cable has a far greater impact than people are led to believe.
From that perspective, speaker cables are probably affected the most due to the higher voltages and current they are subject too..
An "experiment" that I tried - which I believe demostrates the impact of the Proximity Effect in speaker cables - like the D352...
I listened to the D352 as is - then I seperated the two conductors and allowed about 2" of space between the conductors.
The impact of simply seperating the two conductors was a significant improvement in sound quality across the board,...
- better bass control and depth - improved image - improved clarity - improved dynamics
The second point...
The answer to keeping conductivity high is simple: the larger the wire, the lower the resistance, and the higher the conductivity.
I feel this is also not the entire story - so let’s disect it a little further.
According to the International Annealed Copper Standard - IACS
As atoms get larger however, more and more electrons are between the nucleus and valence shell, shielding the outermost electrons from the nucleus’ influence. This is why silver is a better conductor than copper, it is a larger atom with a more strongly shielded nucleus.
But since the valence electrons in silver are less influenced by the nucleous it takes far less force to have them switch between atoms.
The net resuilt of all this science - not only is silver a better conductor - i.e. from a resistance perspective) - it is a FASTER conductor.due to the shielded valence electrons
So - it is not JUST the size of the cable, but the material the conductor is made from.
FYI: in my tinkering with cables, I have tried cables of of various sizes and cables that are just copper and cables that are silver coated copper.
Personally I liked the speed and details of the siver coated cables.
The larger gauge did seem to convey deeper more well controlled bass frequencies than lighter gauge i.e. with cables that used a simple cable geometry.
HOWEVER - all that changed once I made cables with a HELIX cable geometry.
The HELIX Cable provided better performance across the board, especially improved bass depth and control, However, it did so using lighter gauge conductors
In my case... - I was using a 10 gauge Van den Hul D352 speaker cable (silver plated) - I now use a cable with --- a 16 gauge Silver plated signal conductor and --- a 13 guage tinned neutral conductor
SO... - selecting a heavier gauge cable is a simplistic approach. - I believe selecting cable with a well designed geometry is a far better solution.
One such cable is the QED Silver Spiral. - please note that I have not personally tried this cable, - BUT the geometry of this cable is similar to my own HELIX design and should make this cable a very good performer. - I have also heard from others that seem to like this cable very much
It is my belief that most large cable manufacturers are aware of the cable capacitance issue and they may not publish the capacitance values because... - the capacitance of their cables do NOT pose a problem. - also, they fear it may just "muddy the waters" for many consumers.
Hats off to companies like CARDAS and Van den Hul, for ensuring capacitance values for their cables are published.
Yes - it would ne nice if ALL cable companies posted full cable attributes
But - l beileve it is up to the manufacturer of the amplifiers likely to be affected by the wrong cable choice, to make their consumers aware of this issue, like NAIM does
I saw this thread and recalled a review of the Schiit Vidar amp when it first came out. I think it was the computer audiophile site, and when the reviewer tried his 9 gauge cables, the amp started having issues.
The reviewer sent the amp back to Schiit, they did some investigating and decided to make a change to the amp as a result. Personally I don't see the need to ever employ 9 gauge speaker cables in any of my systems, but there you go.
Unsound, thank you kindly for the gracious response. Cycles2, separating the two conductors as you describe will result in capacitance being very low, although not zero. However, it will cause inductance to be considerably higher than if the conductors were in close proximity. And in a speaker cable inductance is much more likely to be a significant factor than capacitance, aside from the situation that has been discussed in which cable capacitance is ultra-high and the amplifier is sensitive to that.
High inductance is particularly likely to have significant sonic consequences if speaker impedance at high frequencies is low (such as in the case of most electrostatic speakers) and cable length is long. That is because the impedance presented by an inductance is directly proportional to frequency, and cable inductance is directly proportional to length.
I thought I could count on you to illuminate this topic. Let me say that I am humbled that you went out of your way to research the hidden links, and offer your considered thoughts on the subject. I sincerely appreciate it; thank you.
My conclusion reading all of this is that I wouldn’t worry about his allegation that the resistor value chosen by Goertz is not ideal. As he even said, based on his simulations: (Comments shown in brackets are mine):
Even 100nF in series with 10 ohms restores the amplifier phase margin to normal.... 4.7 ohms is preferable, but the phase margin is barely affected. The speaker end response has a small ’lump’ with 10 ohms [between about 5 and 10 MHz!], and phase goes ’wobbly’ at above 20MHz. This is probably not a concern, and you will almost certainly get away with it.
I don’t, however, see any reason to doubt his statement that:
It is very evident that this particular cable [Goertz MI 1] should never be used without a Zobel at the speaker end....
Don’t want to sidetrack this thread into a defense of Paul Laudati and Clear Day Cable though I will say I’m inclined to take him at his word. Paul has been around a while and it would be a fairly easy task to "autopsy" one of his cables and refute his solid silver claim if it were bogus. To my knowledge, that has not happened. I can report the Double Shotguns were better with my gear than Morrow Audio SP-4 silver plated copper...and not by a little bit. They are also preferred in one amp/speaker combination I have over Cardas Parsec cable. The review at the link below, while largely anecdotal, might be of interest.
If bi-wiring, how would these capacitance numbers work...simply additive? or something else??
Parallel doubles capacitance and halves inductance and resistance.
Bi-wiring separates the load into two parts. Response for each part differs from a single drive.
Don't know a thing about Clear Day and they provide no technical information. From reading their information, it seems their product comes from 'messing about' and may be very specific or just generic. Solid core will be stiff. Price seems too low for pure silver of a reasonable gauge, say 18. That's about 4oz of pure silver ~$65. 18ga solid silver hookup wire is about $9/ft. 32 feet for two 8' runs is ~$288. Add in connectors, heat shrink and labor and the price is too low.
Speaker Cable: Speaker cable is a bit different from a lot of the interconnect cables we handle, in several respects. Because speakers are driven at low impedance (typically 4 or 8 ohms) and high current, speaker cables are, for all practical purposes, immune from interference from EMI or RFI, so shielding isn't required. The low impedance of the circuit, meanwhile, makes capacitance, which can be an issue in high-impedance line or microphone-level connections practically irrelevant. The biggest issue in speaker cables, from the point of view of sound quality, is simply conductivity; the lower the resistance of the cable, the lower the contribution of the speaker cable's resistance to the damping factor, and the flatter the frequency response will be. While one can spend thousands of dollars on exotic speaker cable, in the end analysis, it's the sheer conductivity of the cable, and (barring a really odd design, which may introduce various undesirable effects) little else that matters. The answer to keeping conductivity high is simple: the larger the wire, the lower the resistance, and the higher the conductivity.
Hello Steve - I copied the above from the Blue Jeans site. I wonder if their, "...barring a really odd design, which may introduce various undesirable effects...." is tacit acknowledgement of the oscillation risk you raise (among other things, I suppose). In reply to your original question, knowing an amp was susceptible to high capacitance induced oscillation would not put me off from buying that amp (assuming it was desirable to begin with) BUT I would certainly exercise care with the speaker cables attached to it.
Thanks for the Cardas info. By contrast to the high capacitance number for their Clear spkr. cable I note their Parsec cable is 30 pf/ft.
If bi-wiring, how would these capacitance numbers work...simply additive? or something else??
Anyone have an idea about capacitance of the Clear Day Double Shotgun speaker cable?
By comparison - The Van den Hul D352 is
32.5 pF / meter. so that's about 100 pF for a 10 ft cable
Don't let that put you off Cardas - some of their cables are much lower
At least Cardas makes the capacitance of their cables knowm - which makes me think they are aware of the issue - and feel the audiophile should know about it
^While I agree with your point, there’s no need to even consider replacing one’s amplification. As I’ve said before: there’s no sound reason not to use the provided RC networks (zobels).
Selecting a different amp to suit your cables is like buying a new car because you can't get spark plugs for the old one in your favourite brand.
If the amp is a good one, toss the cables, There are lots of cables out there but finding a really good sounding power amp can take patience (and money).
The authors suggest that the supplied RC networks values for the MI 2's could be improved upon, perhaps someone might be able to confirm or refute this. Furthermore, I would be most appreciative(!) if instructions for construction of the ideal zobels for the MI 3's could be provided.
While Zo (denoting characteristic impedance) = ( L / C )^0.5 is an equation that is widely used in various EE applications, I don’t recall ever seeing a **simple** derivation of it. The Wikipedia writeup I referred to on Characteristic Impedance, in conjunction with the Telegrapher’s Equations writeup it links to, provides a derivation, although it is rather complex. Another derivation is shown at this link in the first answer to someone’s question.
Note that in both derivations the bottom line equation which includes series resistance R and shunt conductance G reduces to Zo = ( L / C )^0.5 when R and G are zero, and therefore to a close approximation of that equation when R and G are small enough to be negligible (on the same per unit length basis that is used for L and C). And under those circumstances Zo becomes essentially independent of frequency. Keep in mind also, as you probably realize, that characteristic impedance is essentially independent of length.
Actually, I've never seen the formula Z = ( L / C )^0.5. Where does it originate?
1) 25 foot length as that is what was shown on the MI/AG site in Fig 4.
3) I mistyped. Conceptually, the cable LR are in series and the C is parallel with the load.
4) I understand characteristic impedance. A 75Ω cable is designed to be driven by 75Ω source and terminate in 75Ω load impedances. I dealt with PCB impedances for years in high speed digital and have fixed innumerable CATV issues by changing splitters or terminating open jacks with 75Ω loads for friends and family.
Given that a speaker cable can't be hurt to have a CI matching that of the speaker, its reasonable to expect that the amp should be stable with such a speaker cable. That's why I say that designers have to accept that.
I’m afraid I have to question or disagree with several things in your analysis:
1)I’ll start with the least significant of the issues that I see. What length are you assuming in your calculation that resulted in 0.05 ohms at 1 kHz? Plugging the numbers for the particular cable into your methodology I find that the result at 1 kHz is almost completely dominated by resistance, with the result therefore being not much different than the cable’s resistance spec of 0.00098 ohms per foot (x2 conductors, presumably, although that isn’t made clear in the table).
2)Your equation "Z=1/(1/(ZL+ZR)+1/ZC) * Length" would reflect the parallel combination of (ZL + ZR) and (ZC), yet as you correctly state L and R are in series, while C is in parallel.
3)Related to that, specifically to the fact that L and R are in series, I don’t see the basis for your statement that "this impedance is in parallel with the amp and speaker." Certainly the amp is not being loaded with 0.05 ohms!
4)Most significantly, I believe you are conflating "impedance," derived as a combination of the individual impedances of R, L, and C at a given frequency, with "characteristic impedance," which is not the same thing.
I recognize that the two terms are sometimes used interchangeably, but that is incorrect and potentially confusing. (Even the heading in the Goertz table that I referred to makes that mistake, although the writeup above the table makes clear that they are referring to characteristic impedance). For example, a 75 ohm coaxial cable has a "characteristic impedance" of 75 ohms, but at most frequencies certainly does not have a 75 ohm "impedance" based on any series and/or parallel combination of the individual impedances of R, L, and C at each frequency.
"Characteristic impedance" is essentially independent of frequency, assuming, as I alluded to earlier, that conductor resistance per unit length and dielectric conductance per unit length would not affect a calculation based on the square root of (L/C) significantly. See the Wikipedia writeup on "Characteristic Impedance," which is consistent with my understanding of the matter.
I conceptualize cables as a (SERIES LR with PARALLEL C) x Length. First sum the LR impedances and then add the inverse of the LR sum to the inverse of the C impedance. Z=1/(1/(ZL+ZR)+1/ZC) * Length. It's actually more complicated because ½L is in each lead and R is in both leads with the cap between them
Using the numbers on the link for Divinity, 4nH .98mΩ 1.5nF / ft, I come up with ~0.05Ω @ 1KHz. The impedance is impressively flat relative to a 2 wire standard, but nowhere near 4Ω.
This impedance is in parallel with the amp and speaker. Since the value is so low relative to the speaker impedance, the impedance remains low well past the audio band and can cause some amplifiers problems, particularly if the speaker has a very low Z minima.
A ’benefit’ of plain old speaker cable is its impedance is rising, thus preventing amp problems. The downside is the rising impedance, quadrupling in the region where the ear is most sensitive, is reacting negatively in terms of phase.
I have several sets of cables at home, my favorite are high count twisted litz. These cables definitely qualify as high capacitance. This capacitance problem is also effected by the speaker crossover itself that is attached to the cable. So depending on crossover design and layout combined with cable, a problem with speaker cables capacitance can occur with amplifiers that have a lot of feedback and some high-feedback push-pull tube amps. A capacitive load can drive the feedback phase far enough to lead to oscillation, sometimes at ultrasonic frequencies. You might not hear it, but soon there's smoke coming out of your tweeter.
As I’m sure you are aware, characteristic impedance can be calculated to a close approximation as the square root of (L/C), using those parameters on a per unit length basis and provided that conductor resistance per unit length and dielectric conductance per unit length are insignificant. The L and C values shown in the table appear to be consistent with the indicated characteristic impedances, which range from "~1.7" to "~4" ohms.
Adding a network to an amplifier to correct for a cable is a tailspin, just adding eq to eq.
I’d like to see how Goertz calculates a Z of 4 or 8Ω at audio frequencies from their geometry.
SS amplifier outputs are a tiny fraction of 8Ω which is what gives rise to large damping factors. Characteristic impedances are beneficial when the source and load impedances are matched. Almost no speaker is a flat 4 or 8Ω impedance, largely negating any supposed benefit. Typical impedance variations of 4:1 are common and 10:1 is not uncommon.
See Cable Snake Oil Antidote Amplifier Output to see how amplifier output impedance can interact with cables.
^I’m not sure if they still do. When I got mine the RC networks were separate. I’ve since read that some have them directly integrated into the cables. I’m not sure, but I seem to recall that separate RC network replacements were available for $20, but I also seem to recall that some might have received them gratis. Some have even made their own.
Kalali, that’s an excellent question, and I’ve wondered the same thing myself. While I’ve seen a number of reports over the years of solid state amplifiers self-destructing as a result of having to drive cables having ultra-high capacitance, I don’t think I’ve ever seen a report of an amp being damaged from having to drive an electrostatic speaker.
But while I’m not sure how to explain that, if I were to hazard a guess I’m thinking it may be related to the presence of the step-up transformer that I believe is used at the input of nearly all ESLs. Perhaps the bandwidth limitations and/or other characteristics of the transformer cause the amp to see a load impedance that is much less capacitive at ultrasonic and RF frequencies than it is at audible frequencies, and in comparison with the impedance of a highly capacitive cable at ultrasonic and RF frequencies.
And my suspicion is that the destructive oscillations which have been reported to result from the use of high capacitance cables typically occur at ultrasonic or RF frequencies, not at audible frequencies.
Also, I believe that the few ESL designs which don’t have a step-up transformer at their input, such as some older Acoustat models, have a built-in amplifier to step up the input voltage. In those cases presumably the built-in amp provides a relatively non-capacitive input impedance.
The point about ESL speakers and the significant capacitive load, as compared to the load from the cable, they present to the amplifiers has been mentioned twice and I see no explanation as why amplifiers seem to be able to suck that (load) up without self destruction. what gives?
Because someone told me when I bought the Odyssey that the Goertz cables can possibly make the amp oscillate. I didn't own Goertz so it wasn't an issue.
Zobel network seems a solution to a deliberate poor cable design so consumer pays more than once Factual equivalent of alpha core with zobel is just simple power wire half buck per foot
The Goertz cables are flat and the conductors are closely coupled so as to increase the capacitance.
This is done to reduce the Characteristic Impedance of the cable. Their cables approach 4 and 8 ohms (depending on cable selection) and so reduce reflections in the cable depending on the impedance of the speaker.
Some may suggest that reflections at audio frequencies are a non-issue, but measurements that I and a team I was associated with (using a Time Delay Reflectometer) suggest that if you can get the cable to have a low CI, it will be more revealing.
So there can be a reason for high capacitance cables, and amp designers need to suck it up. The old Polk Audio wire was high capacitance and did mess with unstable amps of the era. But as at least one pointed out here, ESLs are capacitive as well and are often driven by amplifiers :)
@kiganki "then amp that oscillates was likely designed with shortcuts to improve specifications (or poorly designed).". It is obvious you know nothing about Odyssey amps. They are more honest than most audio manufacturers. Visit them at one of the audio shows and you will be singing an entirely different tune.
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