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#1
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Recommend crossover capacitors, values?
I want to recap the crossovers in an old pair of high-end speakers I
own. I've opened up the cabinet and diagramed the circuit, but have a few questions about what I found. Perhaps somebody can help. The first thing I noticed is that many of the "better" caps (polystyrene in this case) are run in parallel with electrolytics to reach the desired value. I spoke with a tech who said that this was done to achieve the filter affect of the combined capacitance while taking advantage of the better signal path through the one quality capacitor in the circuit. Does this make sense? I certainly understand that there is a cost advantage of doing it this way because the circuit uses some very high capacitance values. Replacing these caps with modern, high-end versions would be cost-prohibitive, if not impossible. I just want to compromise as little quality as possible. That leads me to the next question: how do I achieve the desired values and maintain the quality without going broke? The midrange signal is fed through a set of capacitors with a combined value of 75 mfd. That's much higher than I've seen for sale from any high-end capacitor manufacturers, and anything close is prohibitively expensive. The next issue is with matching. I don't own a capacitance meter, so matching the pairs myself is not an option. Is it worth buying matched pairs of replacement caps? And what do I do if I need to add electrolytics into the circuit to achieve the desired value? Can I buy those matched as well? Lastly, what are the preferred brands of capacitors to use? Are there any good web sites that do comparisons, including listening tests? Thanks very much in advance. -- Steve Cohn |
#2
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Recommend crossover capacitors, values?
It's unlikely that the film caps were added to increase the value of the
electrolytics appreciably. Compare the value of the film caps to the 10% (or more) tolerance of the electrolytics. It's done in a bid to combine the quality of the film cap with the capacitance of the electrolytic. The sound of such parallel circuits is pretty unpredictable though - needs experimentation when you change types of components. It's not unusual for an electrolytic to sound better alone than with an extra film cap on top. Intertechnik (http://www.intertechnik.de/) sells "audyn" branded film caps up to rather large values. Very decent sounding parts. The largest film caps are from http://www.eci-capacitors.com/. Never tried them though. Matching to within 10% (eg +/-5% tolerance) is desirable, to make sure the speakers (well, ignoring differences between drive units) remain within 1dB of eachother. |
#3
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Recommend crossover capacitors, values?
Here is a snip from B&Ws FAQ section, it may help....
KE "We usually find that customers who alter crossover components are not fully satisfied with the results. They find that some aspects are improved, but others made worse. A classic case of this is when a polypropylene or other very low-loss type substitutes an electrolytic capacitor. We all know that polypropylene capacitors can sound inherently better, but the change in internal losses changes the response of the filter, which is designed assuming the losses of the electrolytic component. What usually happens when the low loss component is fitted is that the corners of the roll-off are sharpened, giving a peak in the combined response that can make the sound unpleasant in various ways depending on the crossover frequency. One way of getting round this is to wire a small resistor in series with the capacitor to approximate the original losses. I say approximate because the loss factor is a frequency dependent resistance. The actual value you need depends on the original capacitor loss factor and its capacitance value. The larger the value, the lower the resistance for a given loss factor. The formula for the equivalent resistance is: R = d / 2ðfC where R = resistance in ohms, d = loss factor, f = frequency in Hz and C = capacitance in farads. Loss factor is usually expressed as a percentage at 1kHz. For a "low-loss" electrolytic such as the values between 1µF and 20µF found in tweeter circuits, d is of the order of 0.025 (loss factor of 2.5%). For values in the hundreds of microfarads it may be of the order of 0.07 or 7%. Typically therefore a good electrolytic capacitor of 5µF would have an equivalent series resistance of 0.8?. If the capacitor has a much larger resistor in series with it anyway, it's probably not worth altering." "Steve Cohn" wrote in message ... I want to recap the crossovers in an old pair of high-end speakers I own. I've opened up the cabinet and diagramed the circuit, but have a few questions about what I found. Perhaps somebody can help. The first thing I noticed is that many of the "better" caps (polystyrene in this case) are run in parallel with electrolytics to reach the desired value. I spoke with a tech who said that this was done to achieve the filter affect of the combined capacitance while taking advantage of the better signal path through the one quality capacitor in the circuit. Does this make sense? I certainly understand that there is a cost advantage of doing it this way because the circuit uses some very high capacitance values. Replacing these caps with modern, high-end versions would be cost-prohibitive, if not impossible. I just want to compromise as little quality as possible. That leads me to the next question: how do I achieve the desired values and maintain the quality without going broke? The midrange signal is fed through a set of capacitors with a combined value of 75 mfd. That's much higher than I've seen for sale from any high-end capacitor manufacturers, and anything close is prohibitively expensive. The next issue is with matching. I don't own a capacitance meter, so matching the pairs myself is not an option. Is it worth buying matched pairs of replacement caps? And what do I do if I need to add electrolytics into the circuit to achieve the desired value? Can I buy those matched as well? Lastly, what are the preferred brands of capacitors to use? Are there any good web sites that do comparisons, including listening tests? Thanks very much in advance. -- Steve Cohn |
#4
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Recommend crossover capacitors, values?
Thanks for the reply.
"Bruno Putzeys" wrote: It's unlikely that the film caps were added to increase the value of the electrolytics appreciably... It's done in a bid to combine the quality of the film cap with the capacitance of the electrolytic. Yes, that's what I understood, though perhaps I didn't express it well. Most of the film caps are 5 mfd. Then they're added together, or combined with electrolytics, to reach the desired value. It's not unusual for an electrolytic to sound better alone than with an extra film cap on top. Really? That's interesting. I'll have to experiment. Intertechnik (http://www.intertechnik.de/) sells "audyn" branded film caps up to rather large values. Very decent sounding parts. I don't speak enough German to navigate this site. Do you know of a US distributor who might carry them? Thanks again. -- Steve Cohn |
#5
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Recommend crossover capacitors, values?
Thanks. That was actually quite helpful.
I'd rather not mess with loss values and calculations of the resistance needed to compensate. Sounds like my best bet is to replace the polystyrene capacitors with some higher quality films caps of the same value, and replace the electrolytics with the same as what's already there. Agree? Steve In article , "All Ears" wrote: Here is a snip from B&Ws FAQ section, it may help.... =20 KE =20 "We usually find that customers who alter crossover components are not fu= lly satisfied with the results. They find that some aspects are improved, but others made worse. A classic case of this is when a polypropylene or othe= r very low-loss type substitutes an electrolytic capacitor. We all know tha= t polypropylene capacitors can sound inherently better, but the change in internal losses changes the response of the filter, which is designed assuming the losses of the electrolytic component. What usually happens w= hen the low loss component is fitted is that the corners of the roll-off are sharpened, giving a peak in the combined response that can make the sound unpleasant in various ways depending on the crossover frequency. One way = of getting round this is to wire a small resistor in series with the capacit= or to approximate the original losses. I say approximate because the loss factor is a frequency dependent resistance. The actual value you need depends on the original capacitor loss factor and its capacitance value. = The larger the value, the lower the resistance for a given loss factor. The formula for the equivalent resistance is: R =3D d / 2=F0fC where R =3D resistance in ohms, d =3D loss factor, f =3D frequency in Hz and C = =3D capacitance in farads. Loss factor is usually expressed as a percentage at 1kHz. For a "low-loss= " electrolytic such as the values between 1=B5F and 20=B5F found in tweeter circuits, d is of the order of 0.025 (loss factor of 2.5%). For values in the hundreds of microfarads it may be of the order of 0.07 or 7%. Typical= ly therefore a good electrolytic capacitor of 5=B5F would have an equivalent series resistance of 0.8?. If the capacitor has a much larger resistor in series with it anyway, it's probably not worth altering." =20 "Steve Cohn" wrote in message ... I want to recap the crossovers in an old pair of high-end speakers I own. I've opened up the cabinet and diagramed the circuit, but have a few questions about what I found. Perhaps somebody can help. The first thing I noticed is that many of the "better" caps (polystyren= e in this case) are run in parallel with electrolytics to reach the desired value. I spoke with a tech who said that this was done to achieve the filter affect of the combined capacitance while taking advantage of the better signal path through the one quality capacitor i= n the circuit. Does this make sense? I certainly understand that there is a cost advantage of doing it this way because the circuit uses some very high capacitance values. Replacing these caps with modern, high-end versions would be cost-prohibitive, if not impossible. I just want to compromise as littl= e quality as possible. That leads me to the next question: how do I achieve the desired values and maintain the quality without going broke? The midrange signal is fe= d through a set of capacitors with a combined value of 75 mfd. That's muc= h higher than I've seen for sale from any high-end capacitor manufacturers, and anything close is prohibitively expensive. The next issue is with matching. I don't own a capacitance meter, so matching the pairs myself is not an option. Is it worth buying matched pairs of replacement caps? And what do I do if I need to add electrolytics into the circuit to achieve the desired value? Can I buy those matched as well? Lastly, what are the preferred brands of capacitors to use? Are there any good web sites that do comparisons, including listening tests? Thanks very much in advance. --=20 Steve Cohn --=20 Steve Cohn |
#6
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Recommend crossover capacitors, values?
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#7
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Recommend crossover capacitors, values?
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#9
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Recommend crossover capacitors, values?
In article ,
John Stone wrote: If the existing film caps are polystyrenes, I wouldn't bother replacing them at all. Polystyrenes are about as good as it gets for crossover caps. They are very stable and would not go bad unless the system was heavily overdriven. Well, they look like polystyrenes, but I can't be sure. Even so, they're 20 years old. Don't they degrade over time? Since you have no way of referencing back to the original crossover curves, I'd do as few changes as possible. Actually, I do have an extra set of crossovers to test, but it's true that I don't know what the exact intentions of the designer were. Thanks for your input. I feel like I'm getting close to a decision on which way to take this whole project. -- Steve Cohn |
#10
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Recommend crossover capacitors, values?
in article , Steve Cohn at
wrote on 10/16/03 1:08 PM: In article , John Stone wrote: If the existing film caps are polystyrenes, I wouldn't bother replacing them at all. Polystyrenes are about as good as it gets for crossover caps. They are very stable and would not go bad unless the system was heavily overdriven. Well, they look like polystyrenes, but I can't be sure. Even so, they're 20 years old. Don't they degrade over time? Not really. Good quality film caps (not the wax paper types found in old radios and tv's) pretty much last indefinitely. The main failure mode for older caps was the migration of moisture into the cap causing them to become electrically leaky. If we're talking 20 year old film caps, they're not going to be prone to this kind of failure because they are well sealed. Since you have no way of referencing back to the original crossover curves, I'd do as few changes as possible. Actually, I do have an extra set of crossovers to test, but it's true that I don't know what the exact intentions of the designer were. Thanks for your input. I feel like I'm getting close to a decision on which way to take this whole project. Did you mention anywhere what the speakers actually are? Some here have a lot of familiarity with actual models and may be able to assist you on this. |
#11
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Recommend crossover capacitors, values?
Steve Cohn wrote:
In article , John Stone wrote: If the existing film caps are polystyrenes, I wouldn't bother replacing them at all. Polystyrenes are about as good as it gets for crossover caps. They are very stable and would not go bad unless the system was heavily overdriven. Well, they look like polystyrenes, but I can't be sure. Even so, they're 20 years old. Don't they degrade over time? Most definately. IMO, replacing them every 5-10 years makes a bigger difference than osbessing over what type you use. |
#12
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Recommend crossover capacitors, values?
"Steve Cohn" wrote in message
... Thanks. That was actually quite helpful. I'd rather not mess with loss values and calculations of the resistance needed to compensate. Sounds like my best bet is to replace the polystyrene capacitors with some higher quality films caps of the same value, and replace the electrolytics with the same as what's already there. Agree? Steve Unless you know exactely what you are doing, and has access to proper measuring facilities, I would not recommend fiddling too much with cross overs. We must assume there is a reason for designing the cross over the way it is, if cost is a part of it, we must also assume that a reasonable compromise is done. As long as the things you do can be undone, there is no real harm in experimenting a bit, especially if it is old speakers. KE |
#13
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Recommend crossover capacitors, values?
On 16 Oct 2003 18:08:03 GMT, Steve Cohn
wrote: In article , John Stone wrote: If the existing film caps are polystyrenes, I wouldn't bother replacing them at all. Polystyrenes are about as good as it gets for crossover caps. They are very stable and would not go bad unless the system was heavily overdriven. Well, they look like polystyrenes, but I can't be sure. Even so, they're 20 years old. Don't they degrade over time? Polystyrene caps have not shown any signs of degradation in the past 30 plus years. Since you have no way of referencing back to the original crossover curves, I'd do as few changes as possible. Actually, I do have an extra set of crossovers to test, but it's true that I don't know what the exact intentions of the designer were. Well, that's the problem. As the B&W FAQ points out, their crossovers design in the known limitations of the components employed. Change them for 'better' components at your peril. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#14
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Recommend crossover capacitors, values?
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#15
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Recommend crossover capacitors, values?
(Mkuller) wrote:
(Nousaine) wrote: Several years ago I conducted a controlled listening experiment where 8 mFd WonderCaps were compared as input coupling capacitors (a commonly recommended practice) to an assemblage of 3 Radio Shack ($0.99) electrolytic non-polar capacitors to attain a capacitance value within 10% of the actual value of the WonderCap as measured with a capacitance meter. No one was able to reliably identify one from the other using the headphone jack on the direct coupled Bryston amplifier. Indeed in the era cited for the Jung/Marsh work I obtained high quality 10 mFd capacitors and believed they improved the sound of an amplifier when substituted for the original electrolytics. Until that fateful day when a friend asked to hear "that capacitor experiment again." I happily accomodated him but was aghast to later find I had forgotten that the "wrong" capacitor had been re-inserted. Yet, he reported the same improvements as before. This prompted me to repeat this experiment with my son operating the controls and not telling me which caps were in-circuit. I then found that even I could not reliably tell them apart when I didn't know beforehand which was in-circuit. I have no doubt you were unable to hear capacitor differences, but many high end equipment manufacturers listen and compare the sound of the exotic capacitors before they decide which to put in their equipment. They tell me they hear differences and sometimes pay extra for one brand over another because of those differences. As an audiophile, one brand of capacitor looks the same to me as another. The sound I hear is all that matters so don't tell me it's just marketing. Regards, Mike I'm not telling you anything except I've put these claims to the test on several occasions and, so far, no one has been able to distinguish capacitors by dialectric at audio frequencies in typical circuit topology under listening bias conditions. Walt Jung and Dick Marsh have made these claims, which I originally bought, but neither have ever conducted a controlled test to support these beliefs. Indeed, other than John Atkinson, I'm probably the ONLY person who has directly compared capacitor dialectric in a straightforward manner. Although the Atkinson liberally misinterpreted his data that experiment conclusively showed that subjects were unable to "hear" capacitors by dialectric with regard to sound alone. My experiments showed this to be true as well. |
#16
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Recommend crossover capacitors, values?
On 16 Oct 2003 20:08:12 GMT, "All Ears" wrote:
"Steve Cohn" wrote in message ... Thanks. That was actually quite helpful. I'd rather not mess with loss values and calculations of the resistance needed to compensate. Sounds like my best bet is to replace the polystyrene capacitors with some higher quality films caps of the same value, and replace the electrolytics with the same as what's already there. Agree? Steve Unless you know exactely what you are doing, and has access to proper measuring facilities, I would not recommend fiddling too much with cross overs. We must assume there is a reason for designing the cross over the way it is, if cost is a part of it, we must also assume that a reasonable compromise is done. As long as the things you do can be undone, there is no real harm in experimenting a bit, especially if it is old speakers. This is certainly true, and B&W even include the point in their FAQ, that crossovers are *designed* with the capacitor losses taken into account (surprise!), so replacing with 'superior' components won't necessarily improve the sound. BTW, you can't replace polystyrene caps by 'higher quality' components, because polystyrene caps are the best available. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#17
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Recommend crossover capacitors, values?
On 16 Oct 2003 20:07:42 GMT, Joseph Oberlander
wrote: Steve Cohn wrote: In article , John Stone wrote: If the existing film caps are polystyrenes, I wouldn't bother replacing them at all. Polystyrenes are about as good as it gets for crossover caps. They are very stable and would not go bad unless the system was heavily overdriven. Well, they look like polystyrenes, but I can't be sure. Even so, they're 20 years old. Don't they degrade over time? Most definately. IMO, replacing them every 5-10 years makes a bigger difference than osbessing over what type you use. For film caps, this is absolutely untrue. Anything made in the last 25 years or so has an almost indefinite lifetime, while electrolytics of the same vintage only 'dry out' if they are in a hot environment such as a tube amplifier. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#18
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Recommend crossover capacitors, values?
On 16 Oct 2003 23:09:29 GMT, (Mkuller) wrote:
(Nousaine) wrote: Several years ago I conducted a controlled listening experiment where 8 mFd WonderCaps were compared as input coupling capacitors (a commonly recommended practice) to an assemblage of 3 Radio Shack ($0.99) electrolytic non-polar capacitors to attain a capacitance value within 10% of the actual value of the WonderCap as measured with a capacitance meter. No one was able to reliably identify one from the other using the headphone jack on the direct coupled Bryston amplifier. Indeed in the era cited for the Jung/Marsh work I obtained high quality 10 mFd capacitors and believed they improved the sound of an amplifier when substituted for the original electrolytics. Until that fateful day when a friend asked to hear "that capacitor experiment again." I happily accomodated him but was aghast to later find I had forgotten that the "wrong" capacitor had been re-inserted. Yet, he reported the same improvements as before. This prompted me to repeat this experiment with my son operating the controls and not telling me which caps were in-circuit. I then found that even I could not reliably tell them apart when I didn't know beforehand which was in-circuit. I have no doubt you were unable to hear capacitor differences, but many high end equipment manufacturers listen and compare the sound of the exotic capacitors before they decide which to put in their equipment. They tell me they hear differences and sometimes pay extra for one brand over another because of those differences. As an audiophile, one brand of capacitor looks the same to me as another. The sound I hear is all that matters so don't tell me it's just marketing. It's a combination of marketing, wishful thinking and very poor test protocols on the part of those manufacturers, most of whom couldn't design their way out of a paper bag.................. BTW, what measures do you take to eliminate bias in your 'reviews'? -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#19
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Recommend crossover capacitors, values?
"Mkuller" wrote in message
... Steve Cohn wrote: I'd rather not mess with loss values and calculations of the resistance needed to compensate. Sounds like my best bet is to replace the polystyrene capacitors with some higher quality films caps of the same value, and replace the electrolytics with the same as what's already there. Agree? While I'm no expert in this area, I can give you some information. Capacitor quality and sound became well known to the audiophile community from a series of articles by Marsh and Jung in Audio magazine in about 1980-81. Peter Moncrieff of IAR took this a step further and had his Wonder Caps made to his specs for high end equipment (Audio Research used them among others). Having taken to heart P.T. Barnum's words, that there's a sucker born every minute. Since that time there have been many brands of exotic capacitors made which are used in many high end products. One of the things Moncrieff recommended in the early 1980s was to bypass electrolytic caps with small value polypropylene or polystyrene, say 1/100th or 1/10th (or both using two smaller low value caps) of the value of the larger cap. That was because larger value, high quality caps were not available or were very expensive then. This was recomended so Moncrief could sell caps. And as another poster mentioned, by bypassing the bigger, poorer quality caps with smaller value higher quality caps, the theory was that you get the some of the benefits without the high cost. Sonic Frontiers (now Anthem) in Canada used to have a subsidiary called The Parts Connection that stocked all of the exotic caps. I believe it's gone or operating under another name now. Perhaps someone could help you find their successor. Regards, Mike Unfortunately for Moncrief, he never demonsttrated any sonic benefits from his "Wonder" caps. |
#20
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Recommend crossover capacitors, values?
Stewart Pinkerton wrote:
For film caps, this is absolutely untrue. Anything made in the last 25 years or so has an almost indefinite lifetime, while electrolytics of the same vintage only 'dry out' if they are in a hot environment such as a tube amplifier. You'd be amazed at how much older equipment used electroyltics. Oh - ozone/smog hurts them as well. |
#21
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Recommend crossover capacitors, values?
On 18 Oct 2003 00:30:21 GMT, Joseph Oberlander
wrote: Stewart Pinkerton wrote: For film caps, this is absolutely untrue. Anything made in the last 25 years or so has an almost indefinite lifetime, while electrolytics of the same vintage only 'dry out' if they are in a hot environment such as a tube amplifier. You'd be amazed at how much older equipment used electroyltics. Oh - ozone/smog hurts them as well. I've been an electronics engineer for 35 years - I'm very familiar with older equipment! Besides, you specifically stated that you change *film* capacitors. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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