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Hi I posted a few days ago looking for methods to reduce harshness of the highs in my system, and it was suggested (by Al Sekela) that I try a resistive/capacitative device on the ends of the cables. Does anyone know how to make one of these? Do they go on the cables or on the binding posts of the speakers? A stack of very small value parallel caps was suggested totaling 0.01uF; is there any reason why I couldn't try this with a single 0.01uF cap (I happen to have some left over Infinicap bypass caps that are 0.01uF)? Also, just to make sure I understand correctly (sorry, I'm electrically challenged) I should make the following:+speaker wire----cap------resistor----(-)speaker wire
Is that correct?
Thanks so much
Chris
Follow Ups:
Thanks for all the helpful suggestions and info. If all I have at home right now are Ohmite 10ohm resistors left over from a speaker crossover project, could I use those instead?
Thanks
Chris
These are likely to be wire-wound power resistors, with a lot of self-inductance and steel parts.The best resistors I've heard have been the old-style Holco or PRP nonmagnetic resistors Michael Percy sells. If you have a good surplus electronics store handy, you might be able to find some old Dale film resistors that are not magnetic.
My results with cheap resistors, with steel endcaps, were not as good as with the nonmagnetic ones.
Power level is not an issue as long as you keep the capacitor small. Half-watt size is plenty.
Hi Al,
Thanks for the info. This is the description from the Northcreek page, if it helps address whether these might work or not. "Both OHMITE and NORTH power resistors are wirewound of a thermally stable wire alloy in a non-inductive winding pattern over a ceramic core, and are silicone-ceramic conformal coated. Their design has been optimized to provide a purely resistive load under highly dynamic conditions over an extremely large bandwidth. Our OHMITE and NORTH resistors are completely transparent. The gritty texture of virtually all sand cast resistors is eliminated via the wirewounds. The hardness usually associated with metal dome tweeter is simply not there. Our resistors have absolutely no sonic signature whatsoever. Furthermore, they bring to most systems a kind of fine resolution that is only rarely associated with dynamic driver technology."
Sorry to keep bugging you, but I want to see if I can use these before I order some from Michael Percy, since he has a hefty minimum order.
Thank you so much for your help
CHris
The R-C filters on audio cables need to be resistive in the UHF band, not just across the audio band. A winding technique that minimizes inductance may be fine for direct audio purposes such as crossovers, but will still have enough stray inductance to make the resistors look like open-circuits to radio frequency energy.Another problem with these resistors is the insulation. Keep in mind that all dielectrics have some sonic character. Teflon is more benign than most, but some folks cannot tolerate it. The high-temperature silicone-ceramic coating on these resistors is likely to have a bad sonic character compared to the Holco or PRP coatings.
Caddock thin-film resistors are non-inductive and have good sonic character. They are more expensive per piece than the PRP or Holco, but you might find a place that will sell you a couple of pieces to experiment with.
and weigh what you lose against what you gain. In my experience, the losses with any type of Zobel network outweigh the advantages. YMMV, as obviously it does for others in this thread, but look at the model for dielectric absorption in capacitors and see if it doesn't look a lot like what you are asking about ... but mainly, just listen back and forth until you are convinced one way or another.
While Al's theory of RF resonance could indeed be the culprit, a rising speaker system inductance coupled with a low inductance high capacitance speaker cable can send some amps into fits, or just cause a harsh sound.For these kinds of situations, a larger cap value can be of some help.
If you wan to cover all the bases at once, then use three different cap values paralleled together, into a single 10 ohm resistor, with this series R and C paralleled across the speaker terminals.
The cap values?
0.27 to 0.1 uF for the largest value,
0.01 uF for the lower RF range,
0.0047 to 0.001 uF for the upper RF rangeThe 10 ohm resistor MUST be a non-inductive type, and of sufficient wattage to not burn up, as use of the slightly larger cap value will cause a bit more energy to go through the R. Use at least a 2W size, 5W would be better. Most of the "flame-proof" metal oxide types are OK, and the old style carbon composition will also be OK to use.
Jon Risch
I've seen this RC network on the back end of SS amplifiers. 0.1uf-10ohm, usually preceded by a small hash choke across each speaker, L-R terminals. I've used Mills 5w in place of metal films with excellent results. The Mills really smooths things out, removing edginess.
If the amp already has this across it's output's, is it necessary across the speaker inputs?
Also, for the RF arena, wouldn't a silver mica be best (0.001uf)?
Dynamic loading of cables was invented before WWII: I saw it discussed in an old EE text somewhere.I had an InnerSound ESL-300 amp with L-R-C networks on the output leads to the speaker terminals, and found improvement by adding R-C networks to the amp ends of the speaker cables. Keep in mind that the output binding posts represent an impedance change and reflection point to RF noise on the cable, so internal networks are not completely effective.
You can use R-C networks at the speakers only, or at both ends of the speaker cables. Using a network at each end of the cable improves the damping.
Silver-mica capacitors have the best sonic character of any that I've tried, but I haven't tried Teflon due to expense. They do have resonant frequencies comparable to axial-lead film types, so I recommend using a parallel collection of caps a decade apart: 10,000, 1000, 100, and 10 pF, or a similar collection, would work well into the UHF band where the cables typically have resonant harmonics.
........"I had an InnerSound ESL-300 amp with L-R-C networks on the output leads to the speaker terminals, and found improvement by adding R-C networks to the amp ends of the speaker cables"If I infer this correctly, on the inside of the amp chassis, there was an L-R-C network applied to the speaker output terminals, to stabilize the amp I would surmize, and then on the outside of the amp chassis, U placed an addition R-C network on the speaker cables?
Would this not setup a Tank circuit?
Cheers,
~kenster
So it probably resonates far above any meaningful amp gain bandwidth.The resistor in the R-C network is there to damp things. It needs to be a resistor type with low inductance.
It is in the form and general size of a Zoble, but the values I recomend are larger R and larger C than what a true Zobel would be.If a power amp has a seires inductor, and then a Zobel across the outputs, this is specifically for the amp to be stable to the amp terminals.
Once you add in a speaker cable and a loudspeaker load, it may be necessary to add an additional RC network at the speaker terminals, to take care of what the speaker cable is doing, and if the loudspeaker input Z has a rising impedance at HF's. All of this would be necesary ONLY if the power amp is NOT unconditionally stable.
Yes, a Mill's R would be good here for general purpose audio use, but I am not sure about their RF behavior.
As for the small cap (o.ooo1uF), yes, a silver mica would be a good choice, as would a polystyrene or PP F&F.
Jon Risch
And the cap/resistor goes ACROSS the speaker terminals. Like an EQ network Balancing the impedance spikes along the frequency range of the speaker.I am not 100% familiar with the technique (seen it done...never did it) , but watch the voltage/wattage ratings, speakers can be high voltage/current devices.
Mike z
www.geocities.com/mzisserson
It sounds as tho you're describing a "snubber" which is used to drain RFI & EMI to ground. In the matter of the spkr. snubber it should consist of a 0.01 uF non-inductive cap with about an 8 ohm carbon comp. R in series accross the spkr. terminals.
While I certainly don't mean or intend to step on any toes here and have respect for both Al and Bart and the suggestion they have provided, are U sure your harshness problem is not coming from somewhere else?If the quality of your incoming AC power that feeds your system is poor/noisy, it can manifest itself as a harshness or irritating quality to the sound.
A system component mismatch can also cause harshness.
Just my .02 cents worth speaking from experience.
Cheers,
~kenster
It is easy to lose track of the big picture when discussing specific tweaks. The harshness problem experienced by cporada may have nothing to do with speaker cables. There are plenty of other possible causes.IIRC, his original post mentioned an experience with increased harshness upon changing cables. This suggests RF resonance within the cables, but may also be due to increased stiffness of the cables. Cables that are stiff and difficult to fit into the space behind a system can conduct mechanical vibration into the components, no matter how well the support isolates the components from the shelves/racks.
The R-C filter tweak is cheap and easy to try, so little money or time is lost if it does not help. It may help in unexpected ways even if it does not cure the original problem.
as that's the area you could spend the most $$ on (see transparent, MIT, nordost, and you'll find me correct).spend a few weeks working on addressing AC (get a transformer based conditioner for your line level gear) & vibration control (sand boxes work great) and you may be shocked how much harshness you remove like this.
rc
First, the R-C tweak Al describes is very effective and dirt cheap! If you do it the easy way it takes all of 5 minutes.Second, there are R-C versions for parallel filtering that DO work wonders on AC and are also dirt cheap. BE CAREFUL; ELECTRICITY CAN KILL!!
Third, most power conditioners have a mixed reputation, because of what they do to dynamics, regardless of price. And when you look inside some of these expensive jobs, as some inmates have and have posted the pix, you'd laugh at what you're paying for. But Al posted how to use an ordinary transformer with another R-C on the secondaries to make a cheap parallel AC filtering device that is quite effective.
How do I know this? I've been using them on my rig since Al showed me how to make them and they damn well work exactly as he says they do.
I do agree with you wholly that AC filtering done correctly and vibration controls are indeed great on sonics. So are room acoustical tweaks, which you didn't mention. These don't negate the R-Cs on the speaker terminals - the impact is cumulative and worth the effort.
no disagreements w/ anything you said; tranny based conditioners are often undersized---should've made that clear in my original post (mine is 3.0 kva, so no worries). room treatments, esp at 1st reflection, can make a world of difference.i guess the overarching rec i have is---cables should be last as process of elimination; harshness comes in many guises, and equip/cables is only one.
also, you mentioned al showed you how to put a parallel AC filter after the 2ndarys of a tranny; can you elaborate or post? (emailing me is fine as well.)
best
rc
Actually I'd be really interested in seing how to make an AC filter according to Al's designs as well. If you could post, that would be great
Thanks
Chris
The basic idea is to load the AC line with resistance, but without burning up a lot of power.All cables, including the ones used to connect your house power outlets to your breaker panel, have a characteristic impedance. Their DC resistance may be very low, but RF noise sees an impedance determined by the inductance and capacitance of the cable. When RF noise encounters a change in impedance, it is somewhat reflected. This is why simple capacitor filters are not as effective as resistor-capacitor filters. The simple capacitor filters reflect some of the noise and it can buld up to higher levels somewhere else.
A straightforward approach would be to attach a resistor in series with a capacitor to an AC plug. The problem with this is that you need to use a proper capacitor and resistor to withstand AC voltage spikes without burning your house down. Surge protectors help, but do not completely eliminate AC spikes.
It turns out that transformers are good at reducing the magnitudes of AC spikes. Their cores have a limited ability to pass high frequency energy and this tames the spikes. Their cores are also good at dissipating high frequency energy instead of reflecting it back into the AC wiring.
A simple filament transformer can be used to make a parallel R-C filter. The larger and simpler the transformer, the higher its core losses and the more effective it will be. Thus, do not use toroidal transformers if cheaper square ones are available.
The math required to determine the R and C values is fairly simple. We want a resistance that looks like 120 ohms (I measured some Romex-type cable and got 120 ohms for the characteristic impedance) to the AC line. Transformers transform voltage by the turns ratio N and impedance by the square of the turns ratio. Thus, a transformer with 120-volt primary and 12-volt secondary has an N value of 10 and N-squared of 100. One needs a 1.2-ohm resistor on the secondary to look like 120 ohms at the AC input to the primary.
The capacitor is used to keep the 60 Hz power out of the resistor. Without a capacitor, the 1.2-ohm resistor in our example would dissipate 120 watts! This would require a very large transformer and heat up the room.
The size of the capacitor determines the actual power dissipated in the resistor. If we use, say, a half-watt size resistor, we want to keep the power down to a quarter of a watt or less to avoid overheating the resistor. The resistor power is the resistor value times the square of the current, so 0.25 watts in a 1.2-ohm resistor means the current has to be less than 0.45 amperes.
We can ignore the phase angle issues for this calculation, as the capacitor impedance will be much larger than the resistor at 60 Hz. The size of capacitor needed to deliver 0.45 amperes at 12 volts is determined by Ohm's Law: I = V/Xc, where Xc is the capacitor impedance at 60 Hz. Thus, we need a magnitude of Xc of 26.3 ohms.
Capacitor impedance is the inverse of [the angular frequency times the capacitance]. The angular frequency is 2 times Pi (3.14159...) times the frequency in Hz. For 60 Hz, the capacitor impedance is 1/(377*C), or 0.0027/C, where C is in farads. Thus, to get 26.3 ohms impedance at 60 Hz, we need a capacitance of 0.0027/26.3, or 100 microfarads.
Using a smaller capacitor will further reduce the power in the resistor but raise the frequency for which the resistor becomes effective. Please do not use an electrolytic capacitor for AC service: these are polarized and cannot withstand significant reverse voltage. They can explode if used incorrectly!
Oil-filled motor capacitors can be used. If the capacitor is too small, there will be little benefit. The transformer core will stop responding at a frequency lower than the effective frequency for the R-C filter.
If you build one of these, put some sort of fuse or circuit breaker on the primary side to prevent a fire if the capacitor or transformer windings should fail.
AWG and length unspecified.
There's a version of this that works very well for AC cables too and for parallel AC filtering. But you have to be carful to use only X or X2 rated caps for safety reasons, as these are made for AC current and the silver micas and others are definitely NOT!The combination in my system of the R-Cs for speaker cables, R-Cs as parallel filters in AC outlets and on my PCs works cumulatively and is really a delicious difference.
Al has taught me that RFI intermodulation needs to be controlled at many points. All of them good and all of them work together IME.
Perhaps a replacement for ceramic disk caps and other uses.
http://www.mouser.com/catalog/628/677.pdf
Mouser part#:75-MKP1841310635
http://www.vishay.com/docs/26019/mkp1841.pdf
A single 0.01 microfarad capacitor will work in some applications.However, all real capacitors have some parasitic inductance, and the combination of the inductance and capacitance results in a resonant frequency. The device acts like a capacitor up to the resonant frequency, then like an inductor above it. Generally, the smaller the capacitor, the smaller the parasitic inductance, and the higher the resonant frequency.
The point of these filters is to let the higher frequency noise energy on the cable go into the resistor, so a capacitor with a low resonant frequency will not allow higher frequency noise to be dissipated in the resistor. I measured some 0.01 microfarad capacitors and found resonant frequencies from 15 to 21 MHz. Cable resonant frequencies start at about 50 MHz for a one-meter cable and go up from there. The fundamental is inversely proportional to the length, so a two-meter cable starts at 25 HMz, a four-meter at 12.5 MHz, etc. There are many harmonics above these, so 15 to 21 MHz limitation from the capacitor is not very good for filtering these things, even with a long cable.
One way around this is to use a series of smaller capacitors in parallel with the big one. Each smaller capacitor maintains its capacitive behavior to its higher resonant frequency, so the parallel combination works like a better-quality capacitor. I like the sound of silver-mica caps in this service, and these are available in sizes as small as a few picofarads. I would use three or four in a series like 10,000, 1000, 100, and 10 pF, or any similar set of convenient values.
The resistor must also not have much stray inductance, so a metal film or metal foil type is best. Use a value equal to the characteristic impedance of your cable, if you know what it is, or ten ohms if you don't. If the resistor is much larger than ten ohms, scale the capacitor down accordingly so the product of R and C is about the same as 10 ohms times 0.01 microfarads.
A really luxurious installation would use a separate resistor for each capacitor, as this would avoid interactions among the capacitors.
The cleanest way to install these is to solder them to the ends of the cables. However, if you want to preserve the resale value of fancy cables, solder the R-C networks to silver spades and clamp them above the speaker cable spades under the binding post nuts.
As bartc said, you can simply stick the wires under the nuts to see if this tweak is going to do any good before you commit to the spades or soldering to the cables.
A carbon comp R used in the 'snubber' tends to dissipate the high frequencies drained off by the cap due to the C.C.'s "lossiness.
I shoudld have read your responce before giving mine... I see what you are doing! Nice trick, I will have to try it sometime for fun...
Mike z
www.geocities.com/mzisserson
He really has this down. As it happens there are several ways to play with caps, but in the end some experimentation will help. Al does have a formula he posted here for determining some optimum valuaes of capacitance and resistance for these R-Cs; you do have to know the inductance (I think) of your cable. If he gave you starting values, I'd use them.Soooo, you can use one cap or more than one. If you use more than one, as Al has explained to me, you can cover more than one frequency range of potential RFI intermodulation. One may do it for you. Just try it and see what happens.
You can experiment very easily using a small wire nut to link the cap to the resistor in the middle. You end up with a free lead coming out of the cap, a free lead coming out of the resistor, and a lead of the cap wirenutted to a lead of the resistor in the middle. Put the free lead of the cap into one binding post with the speaker cable lead; the other free lead of the resistor into the other binding post with the other speaker cable lead. Use the same values for R-Cs on both ends of each speaker cable, speaker end and amp end, 4 of these little devices in all. Let it burn in for a while, but if it works in your system you should start hearing the effects of cleaner HF pretty quickly.
This is not the ideal way to construct these, but it probably will be enough for you to get started in experimenting. Al says that he prefers the R and C soldered in the middle and silver spades on the leads. Obviously, if you use the right values and you use the array rather than the single cap you will get the best sounding result.
The sound of removing RFI intermodulation is usually subtle but noticeable.
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