From gjs@ prophet.pharm.pitt.edu Wed Jan 28 12:28:35 1998 From: "Jon M. Risch" Newsgroups: rec.audio.tech Subject: Latest DIY Interconnect Note, 1998 Date: Tue, 27 Jan 1998 22:14:36 -0800 Message-ID: <34CECCCC.4CF8@cybertron.com> Reply-To: jrisch@cybertron.com ______________________________________________________ LINE LEVEL CABLE CONSTRUCTION AND MATERIAL PREFERENCES by Jon M. Risch Last Updated 1-26-98 jrisch@cybertron.com Information compiled over years of controlled subjective listening tests of cables. Many of the differences heard were subtle, however, taken as a whole, selection of a cable with all the preferred materials/construction can make a significant overall difference. -Unbalanced Connections- Unbalanced connections involve only two separate conductors, where one is considered "hot" and one is considered "ground" (i.e. typical CD player to preamp, preamp to amp using RCA phono style plugs). If the "hot" conductor is earth grounded, the signal is shorted out. If the "ground" conductor is earth grounded, the signal is theoretically unaffected (in practice, ground loops, RF injection, and other undesirable effects can occur if this is done). Classic construction is coaxial, an insulated wire surrounded by a cylinder of conductive material, usually copper braid, or a foil sheath (sometimes both), covered overall in an insulating jacket. Preferred Construction for Unbalanced Connections: After listening to cables with identical materials, and LCR (Inductance, Capacitance and Resistance) parameters within an acceptably similar range, but different physical geometry's, it was determined that a twisted pair cable with overall shield (a telescoping arrangement) was superior to a coaxial or triaxial type. A moderate to high amount of cabling is desirable (cabling is how much twist a wire pair has per distance) depending on the amount of hum rejection necessary and the shield type. The difference is fairly subtle between coaxial and twinaxial, especially when the twinaxial is shielded. -Balanced Connections- A balanced connection nominally involves two conductors, both of which could be considered "hot", but with opposite polarities of signal. If either conductor is earth grounded, theoretically the signal does not short out, but has been unbalanced by this earth connection. As with the unbalanced connection, earth grounding either of the "hot" conductors has it's problems. Since audio signals typically require some sort of shielding from hum, a third conductor, in the form of a conductive cylinder surrounding both "hot" conductors is classically used. This most common construction is called a twisted pair. Preferred Construction for Balanced Connections: It was determined that a twisted pair with overall shield (a telescoping arrangement) was superior to a triaxial type. A coaxial type is normally not used for balanced connections. It was further determined that if it was possible to use the twisted pair without a shield physically present, that this resulted in higher performance. In lieu of no shield, a shield that was spaced away from the twisted pair of conductors performed better than a shield in close or intimate contact with the twisted pair. If a shield was introduced between the pair of wires, the performance suffered greatly, rendering this version inferior to the coaxial style. See Shields for telescopic ground explanation. If a device is designed to be used with a balanced interconnect, it should never be used with unbalanced interconnects unless unavoidable. Examples include: Phono cartridges (sometimes manufacturers ground one side of a balanced cartridge at the cartridge body, or tie the left and right channels together on one side and call it "ground". If this can safely be undone, and the proper cables used, it will result in much better signal transfer), pro microphones, and most pro audio electronics. If a preamp/power amp pair both have balanced outputs and inputs, they would be the preferred hookup method over the unbalanced (RCA) jacks. Even when the signal passes through an extra stage of electronics in order to implement the balanced signal, the benefits of maintaining a balanced connection seem to outweigh all but the most marginal added electronics. -Shields- In coaxial type cables, the shield also carries the audio signal. This may explain the superiority of the twisted pair construction, as when it is shielded, the shield doesn't have to carry signal current. It is much more difficult for a conductive cylinder sheath to provide shielding action when carrying signal currents. If the ground at either end is less than perfect, any hum or interference that the shield is intended to intercept gets mixed with the audio signal. This may occur at a very low level and be "inaudible" in the sense that hum or RF are not heard outright, yet cause a subtle blurring or graininess to be added to the signal. With twisted pair or triaxial cable, the outer conductive sheath known as the shield should only be hard grounded at one end, typically the low impedance signal source end. The other end can either be left unconnected, or connected to ground via a 0.01 uF ceramic disc capacitor to aid in RFI suppression. This can be one of the basis for "one way" or "unidirectional" cables. This is known as a telescoping or telescopic ground, due to the "nesting" of the inner conductors within the shield from one end. _________________________________________ _______________________________________________________ ============================================================== _______________________________________________________ _________________________________________ | | ------- --- - -Interconnect Cable Materials- ================================ -Preferred Conductor Materials- In descending order of preference: Bare copper Enameled copper Tinned copper Silver plated copper NOT RECOMMENDED FOR SERIOUS AUDIO USE AT ALL: Cadmium copper, beryllium copper and other copper alloys. Nickel plated copper Silver plated copper clad steel Copper clad steel Tinned steel Bare steel -Insulator Materials- -Inner Conductor Insulation- In descending order of preference: Foamed Teflon (TFE) Solid Teflon (TFE) Foamed FEP Teflon Solid FEP Teflon \ Foamed Polypropylene / These two are real close Solid Polypropylene Foamed Polyethylene NOT RECOMMENDED FOR SERIOUS AUDIO USE AT ALL: Solid Polyethylene Rubber PVC (Polyvinylchoride) \ These two actually attack most conductors Polyurethane / over a period of time, the severity depending on the exact formulation. -Filler or molded insulation- Fillers with lots of air are best. SEE "Inner Conductor Insulation" for order of plastic style fillers Cotton Rayon Nylon The above fibers would all be placed just below foamed polyethylene, but above solid polyethylene. -Shield Materials- In descending order of preference: Bare copper Tinned copper Silver plated copper Foil NOT RECOMMENDED FOR SERIOUS AUDIO USE AT ALL: Double copper braids Foil/braid combinations Cadmium copper, beryllium copper and other copper alloys. Nickel plated copper Silver plated copper clad steel Copper clad steel Tinned steel Bare steel -Jacket Materials- In descending order of preference: Solid Teflon (TFE) Solid FEP Teflon Fluorocopolymer Silicone Rubber EPDM Flamarrest \ Rubber These three are real close Neoprene / NOT RECOMMENDED FOR SERIOUS AUDIO USE AT ALL: PVC (Polyvinylchoride) Polyurethane It would seem that jacket materials could have no possible affect on the audio, due to the shield isolating the signal from the insulators. However, for coaxial cables (or even twisted pairs with braided or served shields), the shield coverage for a braided copper shield maxs out around 95% and often runs 87%-90%, with served copper shields, the shield coverage often runs only 85%. And due to the inherently unbalanced construction of a coaxial cable, and the lack of 100% shielding means that the electric field leaks through the shield and interacts with the surrounding environment, where the jacket is the nearest thing. SPECIFIC RECOMMENDATIONS Some specific recommendations now follow. If some of the recommendations seem contradictory, it is because of conflicting priorities, i.e. bare copper and foamed polypropylene vs. tinned copper and teflon. It must also be kept in mind that the specific recommendations are based on the overall performance of the cable as it is configured, and how it ranked in actual listening tests vs. the other cables. I have looked into the current availability (through Newark) of my favorite cables and have found to my dismay that some of them have been bumped from distributors stock by the rise in usage of LAN and other computer cables. The cable manufacturers can still provide most of them, but only if you purchase a minimum quantity, usually a 1,000 foot spool or more, and are willing to wait till the next time it is convenient for them to run it! So, with that in mind, I will pass along my recommendations with a number of alternatives, in descending order of preference. If the preferred cable is available and in stock at a local distributor, I would recommend getting it ASAP! As for a line level interconnect, I recommend Belden #89259 as my first choice. It is of a coaxial construction, with bare copper braid and shield coverage of 95%, an insulator of foamed Teflon around a 22 Ga. stranded bare copper wire, and an outer jacket of black tint solid Teflon. Capacitance is a low 17.3 pF/ft, which is almost half the capacitance of common interconnect cables. It is superior sonically to many of the expensive/high-end cables sold for hundreds of dollars, and can be terminated with your choice of RCA plug, anything from the nickel plated Switchcraft RCA to the Cardas/Kimber/Tiffany RCA's. It is good enough to be worth using the finest plugs. Available in 100 ($100) and 1000 ($950) foot spools. 2nd choice: Belden #82259 Same as above except with a Flamarrest jacket. May be more flexible than the above, have not handled a sample. Available only in 1000 foot spools ($750). These two are head and shoulders above most of the overpriced interconnects out there. As for other commercial coaxial alternatives, their performance is a big step down from these. It must be kept in mind that these have such excellent performance due to the top rated materials; it is a shame that this combination of materials is not available in a twinaxial cable. ---------------------------Update------------------------ Since first posting my DIY interconnect cable recipe (I also have a speaker cable recipe note as well, available upon request, or search dejanews using my e-mail address and cables, DIY and 89259 as keywords) I have discovered a way to improve upon the raw 89259. It is labor intensive, and more expensive (about 3X) but the results come close to matching almost anything out there at any price. You need to start with twice as much 89259 as for the stock cable, e.g., if your need is a 10 foot pair of interconnects, instead of two 10 foot pieces of coax, you need four eleven foot pieces. You also need two 11 foot sections of another coaxial cable with a larger diameter than the #89259, to use the braided shield from, the shield can be either tinned or bare copper, but must be a copper braided type. Either separate braided shield such as Belden #8668 for a small cable bundle (no extra insulation) or Belden #8661 (for a shield used with extra spacer insulation) or a full coaxial cable such as Belden #9259, can be stripped of it's jacket and the braid loosened off the center insulation/wire. Either the braid or the 9259 cable cost about $40 for a 100 foot spool. Now, you disassemble the 89259, removing the jacket, and cutting or sliding the coaxial shield off of the center insulated conductor. When you are done, you will have cut jackets (discard), cut or slipped off braid (may find useful) and a piece of foamed FEP teflon insulated bare stranded copper wire. Take the pieces of insulated center conductor, and twist (as tightly as you can) them together for the length of the wires. Try to twist each side equally, or one side will come up short. More initial length is needed to account for twisting. You have now created a twisted pair! It should be tightly held in the tight twist, do not let it unravel or become loose if at all possible. Some polyolefin heatshrink spaced every 6-8 inches will help here. Shield it with the larger shield braid from the other cable mentioned, and ground the shield at one end only, insulating the other end from the RCA plug. If you really want the best, find some "filler" material to pad the sides and keep the larger shield spaced away from the twisted pair. Cotton string works OK, but a higher quality insulator, such as the center insulator guts (preferably teflon) from another cable, would be even better. The end result is slightly stronger bass, and a slight improvement in the smoothness in the highs. Exactly where Mr. Green in RAHE found very minor weaknesses compared to $1000 interconnects. -------------------- The best commercial twinaxial cable I know of is Belden #89207. It has a tinned copper braid shield of 95% coverage (about the max for a braided shield), one tinned copper 20 Ga. conductor and one bare copper conductor with FEP Teflon insulation, and a jacket of black tint Teflon (the cable looks really nice, sort of a bronze overall effect). The capacitance between conductors is 14 pF/ft. It is fairly stiff, but can be bent to hold a shape fairly well. It is relatively free of microphonics, but can generate noises when moved or handled, depending on the impedance (low Z has negligible noise) of the circuit. 2nd choice: Belden #89272 As above except shield coverage is 93%, and both conductors are tinned copper, and jacket is blue tint Teflon (looks kind of different!). Capacitance between conductors is 16.9 pF/ft. 3rd choice: Belden #89999 As above except shield coverage 85%, and jacket is light beige FEP Teflon. Capacitance between conductors is 18.9 pF/ft. This is more flexible than the two above, but has less resistance to hum pickup due to lower percentage of shield coverage. May have slightly less handling noise in some applications. Is nominally intended for use as a LAN cable, so it should be available from distributors. If flexibility is a big concern, then the best all-around twisted pair cable I know of, with extremely low handling noise, and better than average sonic performance is Belden #83393. It has a special foil shield 100% (foil bonded to paper instead of plastic for low handling noise) with a stranded tinned copper shield drain wire, 20 Ga. stranded tinned copper insulated with FEP Teflon and the overall pair wrapped in noise reducing tape (a cloth tape impregnated with high resistance conductive compound to eliminate triboelectric effects), and a bright yellow silicone rubber jacket. Capacitance between conductors is 22 pF/ft. It is fairly flexible, but has a slight spring to it, sometimes called lay (or lack of it). The only other down side is that the silicone rubber jacket is not very rugged physically. It is prone to cut or split damage, as when a rack might get rolled over it. To this day, every sample of this cable I have given out for evaluation by studio personnel or guitarists has not come back! I quit "giving away" my personal stock years ago! 2nd Choice: Belden #83394 As above, except 22 Ga. conductors and a red silicone rubber jacket. This jacket is proportionally thinner than the 83393 yellow jacket and even more easily damaged. OK if it is not run over or abraded. 3rd Choice: Belden #83396 As above, except four 22 Ga. conductors allow cross-wiring ala Canare cables. Actually performs better than 83394 (when cross-connected), but is stiffer. Cross-connected it is fairly resistant to hum for a foil shielded cable, however capacitance climbs to 40 pF/ft with the cross-connection (also known as a star-quad hookup). Not recommended for guitar use, OK for studio/hi-fi use. Higher performance than above, but stiffer foil shielded twisted pair: Belden #89182 Like 89207, except foamed FEP Teflon insulation, 22 Ga. conductors, and foil/polyester shield w/drain wire. 28.9 pF/ft. Belden #88761 As above, except red tint Teflon jacket, 35 pF/ft. This is the Teflon version of the classic 8761 used in studios world-wide for years as a cheap but good twisted pair. Belden #87761 As above except Red fluorocopolymer jacket. Belden #82761 As above except Flamarrest jacket. Belden #88641 Like 88761, except 24 Ga. conductors and 31 pF/ft. Belden #82641 As above except Flamarrest jacket. -Special Note- CABLES WITH STEEL CONDUCTORS, COPPER COVERED STEEL, OR SILVER PLATED COPPER COVERED STEEL, TENDED TO SOUND VERY POOR. ALSO, CABLES INSULATED WITH PVC WERE FOUND TO BE VERY POOR AS WELL. NOTE: COPPERWELD IS ANOTHER NAME FOR COPPER COVERED STEEL. Belden #'s for these types of cables are listed below. If you are currently using one of these types of cables, a very significant difference in audio performance can be had by upgrading to one of the recommended types. This list is for informational purposes only. 9456, 8421, 8417, 9454, 8416, 9239, 9223, 9224, 9264. 8446, 9686, 9685, 8788, 8434, 8413, 9399 8411, 8401, 8413, 8406, 9396, 9399, 8410, 8420. 9397, 9398, 1812A, 1813A. This list is NOT all inclusive; if you have commercial cables in use in your studio, home stereo, etc. check the specs for that particular cable, WHATEVER BRAND IT MAY BE, and make sure it does not have steel or PVC in it! There are some who will take issue with the method used to obtain this data (subjective listening tests), however, none of the recommendations violates any of the commonly accepted classical approaches to the quality of materials. For instance, the recommendations for insulator materials just happens to follow the ranking (more or less) of those same materials for their dielectric constants, i.e., teflon has the lowest dielectric constant, and PVC has one of the highest. By the same token, the conductor ranking generally follows the ranking of conductivity. So you can choose to follow these recommendations whether you have one particular belief system or not, in either case the data will be very likely to lead you towards better performance of your audio system. ADDENDUM Different Cable Configurations: Belden 82248, is a foamed teflon insulated coaxial which can have the 18 gauge solid bare copper center used for twisted pair interconnect or multiple conductor speaker cable. For interconnects: Cut away and discard the outer shield and jacket, twist a pair of foam insulated solid conductors tightly around one another, place a piece of high grade heatshrink over the two ends to keep the pair twisted, and slip a copper braid over the pair for shielding. It is recommended that this shield be hard grounded at one end only, typically the source end. If you have heavy RFI or suspect interference problems, instead of leaving the other end float, use a 0.01 uF ceramic capacitor to make a connection between the shield and that end's ground. Belden 1506A has a solid 20 gauge bare copper center with foamed teflon insulation that can be used as the guts of a twisted pair. This solid center contrasts with the stranded conductor on the 89259. Cut away and discard the outer shield and jacket, twist the pair of foam insulated solid conductors tightly around one another, place a piece of high grade heatshrink over the two ends to keep the pair twisted, and then take some of the center insulation, the foamed teflon, and remove the copper conductor from the insulation. The easiest method is to slit the insulation down one side, and remove the copper wire. Now use this insulation only to fit in next to the twisted pair in the crack between the spiraled tubes of insulation, and then slip a copper braid over the whole assembly for shielding. To dress out the outer braid, get some heatshrink to cover the braid, or use some dippable/paintable PVC in the color of your choice. Digital Interconnects, 75 Ohm SP/DIF format using BNC or RCA connectors. Belden 89259 is 75 ohm impedance, and makes an excellent digital interconnect. I recommend adding an additional shield of copper braid over the teflon jacket, and hard grounding it at the source end, and ground the other end of the braid via a 0.01 uF ceraminc disc capacitor. The additional shielding minimizes noise pickup. Belden 1506A, a solid 20 gauge bare copper wire, with foamed teflon insulation, and a Duofoil and 95% coverage tinned copper braid shield. 16.1 pF/foot, 75 ohms impedance. The additional shielding afforded by the Duofoil seems to help minimize jitter due to noise pickup by a digital interconnect. For the ultimate in shielding, add an additional shield by slipping a copper braid over the cable jacket, and hard grounding it at the source end, and ground the other end of the braid via a 0.01 uF ceraminc disc capacitor. NOT recommended for analog audio use due to the fact that the Duofoil and tinned copper shield do not make as good of a ground return path as the bare copper shield in the 89259. Cable Costs and Availability: The various Belden cables I recommend are not run of the mill Ham radio coaxial cable. In most cases, the local Belden distributor will have to order a spool from Belden to get it for you. In order to give you a better idea of availablity, and costs, I have called around and worked up some figures. I will list both the price Newark charges, and the lowest price from a local distributor. Newark can be found on the web at: http://www.newark.com/ I have found that Anixter is nationwide, and has some of the lowest prices and an amazing depth of stock. Many local Anixter distributors in major metropolitan areas will cut to length, or at least sell a leftover portion of a cut roll. A list of Belden distributors can be found at: http://www.belden.com/distributors/DISTLOC1.htm and a list of distributors that will cut to length certain model cables is at: http://www.belden.com/products/rhtheatp.htm This site is a listing of Belden recommended cables for use in video and home theater installations. These recommendations are not based on listening tests, and do not match mine. Belden 89259, My highest recommended multi-purpose audio cable, coaxial. Can be used for interconnects, speaker cable and digital cables. Available in 100 foot spools which only weigh 5 pounds for minimal shipping charges. Usually in stock or only a few weeks from availability at Belden, so your distributor can usually get it quickly. Newark: 100 feet $142 plus S&H Best Local Price: $0.92/foot cut to length (small local shop had some leftover, not typically available at this price) Typical Price, 100 foot spool: $108 Belden 82259, 89259 without the teflon jacket, OK for interconects, not recommended for use as speaker cable. Available only in 1000 foot spools Newark: $797 Best Local Price: $580 Belden 89207, twisted pair, 100 foot spool Newark: $120 Best Local Price: $80 Belden 89272, twisted pair, avaialble in 500 foot spool Newark: $593 Best Local price: $399 Belden 1506A, used for digital coax 75 ohm, available in 500 foot spool Newark: $399 Best Local Price: $303 Belden 82248, center only used for twisted pair interconnect or multiple conductor speaker cable , available in 1,000 foot spool. Newark: $743 Best Local Price: $550 Belden 89292, center used for speaker cable, available in 500 foot spool. Newark: $970 Best Local Price: $785 ****************************************************************** Possible Substitutions (These cables have not been listened to): West Penn Wire (all available only in 1,000 foot spools) 25825, similar to Belden 82259, except solid center wire of 25 gauge, bare copper with bare copper 95% coverage shield and foamed teflon center insulation. 17 pF/foot. Jacket is a flame retardant low-smoke PVC, similar to Belden's Flamearrest. 25815, similar to Belden 82259, except solid center wire of 20 gauge, bare copper 95% coverage shield and foamed teflon center insulation. Jacket is a flame retardant low-smoke PVC, similar to Belden's Flamearrest. 16.5 pF/foot. - - - - - - - - - - - - - - - - - - - - - - American Insulated Wire Corp. A55515, similar to Belden 89207 A55514, similar to Belden 89272 - - - - - - - - - - - - - - - - - - Carol Wire and Cable, 500 foot spools C8050, similar to Belden 89207 C8055, similar to Belden 89272 - - - - - - - - - - - - - - - - - - Consolidated Wire and Cable 4798, similar to Belden 89207 FYI, There is a companion note for DIY speaker cable, just e-mail me or search Dejanews for a copy. ********************************************************************* Copyright Jon M. Risch 1998, all rights reserved, except transmission by USENET and like facilities granted. Any use or inclusion in print or other media are specifically prohibited. The informational content is not warrantied in any way or form, and any use of said content are at the reader's own risk, the author shall not be held responsible in any way for any damages or injuries arising from the content of this post. Common safety practices are encouraged at all times. Do not fold, spindle or mutilate. *********************************************************************