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#1
Posted to rec.audio.tubes
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Ground Busses
Patrick posted some interesting facts about ground buss
connections, which I have extracted from another thread and pasted here, because I think the subject is important enough to warrant its own thread. He wrote: The 0V rail of the preamp should be a short buss wire about 100mm long with ends connected to the RCA plug 0V bodies at inputs and outputs. ALL parts with OV connections should be made to this buss, and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case taken to the green/yellow wire to the wall socket so the case can't become live to mains or the B+. There should be NO direct connection of the OV buss to the case. -- I ask: In other words the mains supply case should be bonded to the case, and the 0V (signal grounds) taken to the ground point via a 27 Ohm 5W resistor? Why is this? My experience with ground buss amps is limited. I have never been able to make them quiet enough. I found that the exact position in which a wire was placed on the buss was critical, and that a difference was audible.It may be there is something lacking in my implementation of the buss. I prefer to use a star ground, as follows. Earth (ground) connection from the supply - the only green yellow wire in the amplifier is taken straight to the chassis bonding screw. The input and output RCA signal connectors I used are the isolated type (Neutrik NF2D) http://www.neutrik.com/uk/en/audio/2...-0_detail.aspx I run a separate wire (black) from each of the RCA input and output ground tags to the star ground. Signal wires on the input side have their shields connected at the RCA socket end only. On the psu, I run separate grounds (heavier wire) from each cap separately to the star. They are not linked. The only exception to this is the 1st (reservoir) electrolytic , which is connected directly to the neg terminal of the FW bridge, and then to the star. This is a topology I have seen used on amps that perform well, and has been taught to me as a good solution. It seems to work. My 50W power amp has only 80µV of noise (-108dB) and no audible hum even with the ear against the speaker (Tannoy Gold 15 inch) Regards to all Iain |
#2
Posted to rec.audio.tubes
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Ground Busses
Iain Churches wrote: Patrick posted some interesting facts about ground buss connections, which I have extracted from another thread and pasted here, because I think the subject is important enough to warrant its own thread. He wrote: The 0V rail of the preamp should be a short buss wire about 100mm long with ends connected to the RCA plug 0V bodies at inputs and outputs. ALL parts with OV connections should be made to this buss, and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case taken to the green/yellow wire to the wall socket so the case can't become live to mains or the B+. There should be NO direct connection of the OV buss to the case. -- I ask: In other words the mains supply case should be bonded to the case, and the 0V (signal grounds) taken to the ground point via a 27 Ohm 5W resistor? Why is this? Because chassis can have magnetically induced voltages in them, they should never be used for the 0V rail. And where you have preamp and power amp each with chassis used as the 0V, then you can all too easily have a horrid earth loop with noise injected to the signal path. The use of the 27 ohms is a much higher resistance than the shield of a coax cable which is at 0V, so there won't be a significant signal across this shield wire between to components if the chassis are not strapped to the 0V buss. My experience with ground buss amps is limited. I have never been able to make them quiet enough. I found that the exact position in which a wire was placed on the buss was critical, and that a difference was audible.It may be there is something lacking in my implementation of the buss. It does take some getting right. Especially in MC amps for unbalanced MC cart inputs, but I manage it all easily enough to keep doing it. I prefer to use a star ground, as follows. Earth (ground) connection from the supply - the only green yellow wire in the amplifier is taken straight to the chassis bonding screw. The input and output RCA signal connectors I used are the isolated type (Neutrik NF2D) Nothing wrong with star grounding, ie all bits with a 0V terminal go to ONE point, but in fact you don't have to and a length of thick wire is fine. This buss should never be directly connected to the chassis. Thge chassis ALWAYS MUST be EARTHED via the green/yellow wire. The 0V should be connected indirectly to the chassis but via a lowish resistance which is maybe 100 times the resistance of the coax wire shielding between components. http://www.neutrik.com/uk/en/audio/2...-0_detail.aspx I run a separate wire (black) from each of the RCA input and output ground tags to the star ground. Signal wires on the input side have their shields connected at the RCA socket end only. On the psu, I run separate grounds (heavier wire) from each cap separately to the star. They are not linked. The only exception to this is the 1st (reservoir) electrolytic , which is connected directly to the neg terminal of the FW bridge, and then to the star. After awhile, you realize what 0V wires you really need, and which ones are a must and which are just not a must. This is a topology I have seen used on amps that perform well, and has been taught to me as a good solution. It seems to work. My 50W power amp has only 80µV of noise (-108dB) and no audible hum even with the ear against the speaker (Tannoy Gold 15 inch) If the gain of a power amp is say 20x, or +26dB, then if the noise is determined by the input tube and measured with its grid taken to 0V, and if the input tube has equivalent input grid noise of 4 uV, somewhat noisy really when some good tubes measure 1uV with dc heaters, then your noise will be 80uV at the output. But you're lucky. A preamp may not be any better, and produce 50uV, and this converts to 1,000 uV, or 1 mV. Relative to an average signal level of 1 Vrms you'd have an SNR of only 60dB unweighted. But that's good enough for most folks though; they simply cannot hear that 1mV of noise, ie, hiss and PS hum. Many SS amps fail to be as quiet as ppl think they mostly are. But with better than 60dB unweighted, most tube amps are fine about noise. In fact the howl from the OPT caused by the magnetic currents at audio F are in fact at a much higher sonic level than the noise buried within the signal. SE amps are the worser in this regard. The best OPT have been potted to reduce their howl. Try connection of a dummy R load and turning up the gain with a music signal and you'll see what I mean. The noise of the OPT is as unwanted as are the vibrations from speaker cabinets excited by sound waves inside the cabs. Audio gear that isn't meant to have any sound during operation needs careful design! My latest 845 amp creations tested with less than 1mV of hum in the signal but I sure had to pot the OPT. Then I found the PT was a bit hummy with so many rectifiers on it that have had to place that on a separate chassis and pot it very well. Mains is turned on by a relay in the PSU chassis so NO mains wires go into the power amp chassis and no ac hums in rails either, and no very subtle vibration from the mains tranny shaking the 845 cathodes or other tubes. In such a set up in my 845s, or in my 300 watters as seen at http://www.turneraudio.com.au/300monobloc.html there cannot be star grounding, but noise figures are extremely low, and good. Patrick Turner. Regards to all Iain |
#3
Posted to rec.audio.tubes
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Ground Busses
Iain Churches wrote:
My experience with ground buss amps is limited. I have never been able to make them quiet enough. I found that the exact position in which a wire was placed on the buss was critical, and that a difference was audible.It may be there is something lacking in my implementation of the buss. I guess the order in which connections are made along a bus is significant. If you think of the bus as a resistor, then a high-current return placed furthest from the ground will produce a voltage gradient along the bus. If the next connection is, say, the signal ground from the first gain stage, that voltage could be significant. OTOH, if the connections to the bus are made in order of highest current, the voltages they produce will be minimised. But perhaps there is countervailing argument? If a sensitive connection is close to the ground, then a voltage produced by a high-current connection further along will be attenuated. So perhaps the order is important, but it doesn't matter to which end of the bus the ground is connected? What you don't want is a high-current connection and a sensitive connection both distant from ground. I find a genuine star earth is hard to implement if there are many ground connections to make. Exactly how do you fashion a star? The signal ground must be safe to touch if it is brought out to exposed external connectors. If a resistance is placed between the 0V and chassis ground, then it should be a low enough value and high enough power to ensure that the fuse, and not the resistor, will blow quickly if the signal ground becomes live due to some fault. Perhaps some statutory regulations apply? Not a "pro", or an "expert", as usual, thankfully. Ian |
#4
Posted to rec.audio.tubes
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Ground Busses
"Patrick Turner" wrote in message ... Iain Churches wrote: Patrick posted some interesting facts about ground buss connections, which I have extracted from another thread and pasted here, because I think the subject is important enough to warrant its own thread. He wrote: The 0V rail of the preamp should be a short buss wire about 100mm long with ends connected to the RCA plug 0V bodies at inputs and outputs. ALL parts with OV connections should be made to this buss, and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case taken to the green/yellow wire to the wall socket so the case can't become live to mains or the B+. There should be NO direct connection of the OV buss to the case. -- I ask: In other words the mains supply case should be bonded to the case, and the 0V (signal grounds) taken to the ground point via a 27 Ohm 5W resistor? Why is this? Because chassis can have magnetically induced voltages in them, they should never be used for the 0V rail. And why 25W? Iain |
#5
Posted to rec.audio.tubes
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Ground Busses
"Ian Iveson" wrote in message .uk... Iain Churches wrote: My experience with ground buss amps is limited. I have never been able to make them quiet enough. I found that the exact position in which a wire was placed on the buss was critical, and that a difference was audible.It may be there is something lacking in my implementation of the buss. I guess the order in which connections are made along a bus is significant. If you think of the bus as a resistor, then a high-current return placed furthest from the ground will produce a voltage gradient along the bus. If the next connection is, say, the signal ground from the first gain stage, that voltage could be significant. OTOH, if the connections to the bus are made in order of highest current, the voltages they produce will be minimised. But perhaps there is countervailing argument? If a sensitive connection is close to the ground, then a voltage produced by a high-current connection further along will be attenuated. So perhaps the order is important, but it doesn't matter to which end of the bus the ground is connected? What you don't want is a high-current connection and a sensitive connection both distant from ground. Very interesting. Thanks. Next time I build a prototype, I will try this out. I find a genuine star earth is hard to implement if there are many ground connections to make. Exactly how do you fashion a star? My stars are not symnmetrical with the ground point in the middle if that what you mean. On a power amp I put the chassis bonding terminal close to the AC socket, and on a preamp close to input 1. I usually make up the star on the bench, as a cableform, and then fit, trim the loose ends and solder. The signal ground must be safe to touch if it is brought out to exposed external connectors. If a resistance is placed between the 0V and chassis ground, then it should be a low enough value and high enough power to ensure that the fuse, and not the resistor, will blow quickly if the signal ground becomes live due to some fault. Perhaps some statutory regulations apply? Not a "pro", or an "expert", as usual, thankfully. Ditto. But thanks for your thoughts, Ian. This is an interesting business. Regards Iain |
#6
Posted to rec.audio.tubes
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Ground Busses
A star ground is just a circular bus or a very short bus. Grounding is
is tricky and tiresome in inverse proportion to the amount of thought you give it, so I do something between what Iain does and what Patrick does, and I call it a "star-point". Here you can see my star point http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg on my T68bis "Minus Zero" amp. It is the short piece of stiff wire sticking up at the right hand side of the aluminium cased resistor behind the battery boxes in the centre of the top right hand photograph. It's the bleeder resistor to the power supply and the star point is at its 0V end. Notice how the convenitonally drawn schematic http://members.lycos.co.uk/fiultra/t...17acircuit.jpg tells you nothing of this, leaving you to work it out for yourself. All the 0V wires are dropped over this stiff wire and soldered on. Even on such a short bus I take care of the order of the wires as I put them on. From this point a wire is taken to main's earth. The case is connected to mains earth by a wire from very sturdy bolt held in with serrated washers and nuts, which is placed as near as possible to the mains socket; unfortunately it is not too clear in the photograph, but it is just below the switch, near the top right hand corner of the righthand output transformer in the picture. Most schematics don't tell you enough about earthing. Here, for instance: http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg I've shown the star earth being implemented but have not said anything about connecting the case to earth. Mind you, on some of the Lundahl Modular Series 300B schemos I showed all the 0V connections in order, with a note saying "mind the order of the grounding connections", and two people wrote me letters saying that DIYers are not idiots who need their hands held. (I was, when I started, and I'm very grateful to people who made 90 mile round trips to come check over my constructions before I fired them up.) Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review On Mar 2, 12:39*pm, "Iain Churches" wrote: Patrick posted some interesting facts about ground buss connections, which I have extracted from another thread and pasted here, because I think the subject is important enough to warrant *its own thread. He wrote: The 0V rail of the preamp should be a short buss wire about 100mm long with ends connected to the RCA plug 0V bodies at inputs and outputs. ALL parts with OV connections should be made to this buss, and the CHASSIS or CASE connected via a 5 watt 27 ohm R, and the case taken to the *green/yellow wire to the wall socket so the case can't become live to mains or the B+. There should be NO direct connection of the OV buss to the case. -- I ask: In other words the mains supply case should be bonded to the case, and the 0V (signal grounds) taken to the ground point via a 27 Ohm 5W resistor? Why is this? My experience with ground buss amps is limited. I have never been able to make them quiet enough. I found that the exact position in which a wire was placed on the buss was critical, and that a difference was audible.It may be there is something lacking in my implementation of the buss. I prefer to use a star ground, as follows. *Earth (ground) connection from the supply - the only green yellow wire in the amplifier is taken straight to the chassis bonding screw. *The input and output RCA signal connectors I used are the isolated type (Neutrik NF2D) http://www.neutrik.com/uk/en/audio/2...-0_detail.aspx I run a separate wire (black) from each of the RCA input and output ground tags to the star ground. Signal wires on the input side have their shields connected at the RCA socket end only. On the psu, I run separate grounds (heavier wire) from each cap separately to the star. They are not linked. *The only exception to this is the 1st (reservoir) electrolytic , which is connected directly to the neg terminal of the FW bridge, and then to the star. This is a topology I have seen used on amps that perform well, and has been taught to me as a good solution. It seems to work. My 50W power amp has only 80µV of noise (-108dB) and no audible hum even with the ear against the speaker (Tannoy Gold 15 inch) Regards to all Iain |
#7
Posted to rec.audio.tubes
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Ground Busses
This is something I found on the Web. It was apparently posted on the
usenet, perhaps to this group or maybe rec.audio.tech, many years ago, althought I'm unable to find any evidence of the article in the Google archives. I offer the article without comment, and don't make any claims as to its accuracy. Perhaps there is some value to what is written, as quite a few people have linked to or reposted copies on their websites. The author has left his phone number and email address in the signature. If you have any issues, you may wish to contact him there. I would, in fact, be very interested in hearing if anyone manages to contact him that way. -Henry --- BEGIN REPOSTED ARTICLE --- Someone suggested I write an article on power and grounding techniques for equipment construction. This is a topic I can't really do justice to; whole books have been written on the subject. In the spirit of reckless misinformation, I'll try to summarize a few hints. Consider this an introduction for advanced beginners, but bear in mind there is room for expanding and improving the information contained below. -Henry * * * * * * * If circuits worked exactly as they are drawn on schematics, there'd be no need to worry about power and ground topologies or wire routing. Instead, we could just wire up all the components willy-nilly making sure only that all the specified connections were complete. In the real world of electromagnetics, things aren't quite so convenient: 1) Ground isn't really ground. Ideally, ground is a zero-voltage reference that never varies. In fact, every ground bus that carries current has small voltage variations across its length due to small but significant resistance. 2) Stray capacitance. Two parallel conductors form a capacitor across which unexpected AC currents can flow. 3) Electromagnetic induction. By definition, every circuit forms a loop. When a changing magnetic flux (due, perhaps, to the strong field from a transformer or choke) exists in the loop, a current will be induced. Now I'll talk briefly about the consequences of these real-world effects. Ground Loops. A ground loop occurs when a ground circuit encloses a loop and a source of energy causes current to flow through the loop. If the flow of current causes a voltage drop in a sensitive gain stage, the voltage can be amplified and appear as noise. A typical ground loop occurs in the amplifiers I just built. Because I use grounded power cords, the chassis of my monoblocks are joined electrically at the power outlet. The signal grounds are connected (via the input jacks and interconnect cable shields) at the preamp output terminals. The signal grounds are also connected to chassis ground internally in each amplifier. The result is a loop that picks up inductive noise or leakage currents and couples them into the amplifier gain circuitry, causing an audible hum in the speakers. The quick solution is to break the loop by using a three-to-two wire converter on one power cord. A better fix is to "lift" the internal connection between signal and chassis ground in one or both amplifiers and install a 10 Ohm resistor. The resistor is a significant obstacle to the flow of current compared to the stout power cords and effectively breaks the loop. Another sort of ground loop occurs internal to equipment, but for a different reason. In any circuit, one can trace the flow of power from the supply, out to various circuits, and back to ground. Each power supply typically provides current to more than one circuit branches. Topologically speaking, the branches form intermeshing loops that originate and terminate at the power supply. In the regions where the loops overlap (share common conductors), voltage drops in one loop can impose unwanted signals in another. When a circuit loop overlaps on the supply side of a power source, the designer will use parallel capacitors and/or series resistors or inductors to block or shunt away signal currents on the supply rails. The series components keep unwanted signals from leaving their circuit branches, and the parallel caps redirect those that escape to ground. Purifying the supply rails in this manner is called "decoupling". Decoupling also helps to rid the rails of noise that creeps in due to magnetic or electrostatic fields (more on theis later). On the ground side, it's very important to keep the return currents separate from one another as they work their way back to the common power supply terminal. Practically speaking, we want to minimize overlapping loops in the ground circuit. This is done by using a short, thick ground bus of very low resistance and connecting all ground wires to it. The most effective solution is to provide separate conductors for each ground current source and return them all to a single point; this is known as "star" grounding and is standard practice in audio design. In tube gear wired point-to-point, it may be sufficient to route a heavy ground wire around the edge of the circuit and make all connections directly to it at the closest convenient point. Inductive and Capacitive Coupling. Every conductor carrying a signal current generates an electromag- netic field that can couple to other circuit elements. In addition, the environment in which equipment is used is loaded with power line and radio frequency fields that can get into sensitive circuits and cause noise and distortion. I'll give some very quick information on minimizing these problems. Electrostatic fields and capacitive coupling can be reduced by distance and shielding. A grounded metal shield stops a static field in its tracks by imposing an equipotential barrier. To keep the field from sneaking past the shield, the sensitive circuit must be completely enclosed. Capacitance decreases as the reciprocal of the distance between conductors, so separating sensitive wires as much as possible is the other solution to stray electrostatic coupling. Keeping circuit impedances low will help a great deal by raising the frequency at which the coupling becomes a problem (hopefully beyond the bandwidth of the circuit or offending signal source). Shielding with non-ferrous metals is useless against magnetic induction. The answer to induced hum of magnetic origin is to keep circuit loop area to a minimum. The smaller the loop, the smaller the volume of magnetic flux enclosed and the lower the induced current. For this reason, power and signal wires should be twisted tightly with their ground conductors whenever possible. This increases capacitance between the conductors, so watch out in high-impedance signal circuits. Plan the layout of hum-sensitive circuits so that the enclosed area is kept to a minimum. Place transformers, chokes, and high-current conductors as far as possible from these circuits. Iron or mu-metal shields may be of some help, but I wouldn't count on them. It may be better to put the power supply in a separate box for sensitive preamps. In most cases it is good advice to keep wire runs short, to twist conductors carrying opposite currents together (signal and ground, power supply lines, filament wires, etc), to route wires near the chassis, and to physically separate high-gain stages from components and wires that carry high currents. Practical Advice. When laying out your circuit, look at the schematic and identify all of the separate current loops from supply to circuit to ground. Then come up with a scheme to keep these loops as separate as possible on the ground side. The biggest source of ground current in most amplifiers is the power supply ripple in the main filter capacitor. This current, which contains noisy, high-current rectifier current spikes, usually flows back to the power transformer through the secondary center tap. A good strategy is to connect this lead directly to the filter capacitor common terminal. Then run a short stub (could be a half inch) to a second point that will serve as a star ground for the signal circuitry. Another source of high current ground flow in a power amplifier is the common lead from the speaker terminals. You'll want to make sure the low-level signal star ground does not have output ground currents flowing through it or you'll increase the possibility of instability. What I'm describing here is really a "star of stars" grounding scheme. If you view every conductor as a resistor and try to keep associated voltage drops from crossing loops, you'll end up with the best ground scheme. Here's the grounding topology in my tube power amps: The main electrolytic filter caps and driver decoupling caps are all mounted on one circuit board. The three decoupling caps share a common, wide circuit board ground trace. The ground for the main filter cap, for the transformer center tap, and for the decoupling caps all come together in one small area of the circuit board. The driver stage ground points are located close together near the central ground, but "out of the way" of the rectifier current flow. I slotted the copper strategically to "steer" the charging current current away from the driver-stage grounds (defining the stub conductor described above). The following wires attach to the driver-stage ground area on the filter cap board: 1) A single ground wire from a local "star ground" on the driver board that connects the input jack shield, global feedback cable shield, and the input stage bias resistors grounds. 2) A single ground wire carrying the return current from the B- supply. This supply is floating and connected to the driver board by a tightly twisted pair. B- is bypassed locally by electrolytic and film capacitors. A second "star ground" on the driver board connects all the bypass caps. The rationale is that low frequency hum currents are handled by the electrolytics and don't make it off the filter circuit board. Local bypass caps keep RF signals on the supply lines from getting onto the driver board. The current-sourced differential design greatly reduces the coupling of the input and driver signal currents, in the ground leads, justifying the use of a single B- supply and ground wire. I agonized over this layout for a while, but it seems to work quite well. 3) A ground wire from the negative bias board. The bias supply is also floating and connected to the bias board (which also holds the output coupling capacitors) via a twisted pair. There is a 0.47uF film capacitor bypass on the bias board. The common lead from the output tube cathodes connects to a ground point that runs directly to the main star ground without passing through the driver ground node. The power transformer center tap comes in on its own stub directly to the main capacitor common terminal. The two B+ wires to the driver stage are very short and connect directly to the driver board. The output stage B+ is supplied to the output transformer primary center tap from a circuit area close to the main filter cap positive terminal. The power cord ground wire is connected to the chassis at a convenient lug near the back panel AC socket. The filter cap board has a ground wire to a lug on the chassis as well (and perhaps this is why I have a ground loop; I need to experiment with the location of my connection from signal ground to chassis ground). A note on solid-state Class AB amplifiers and power rail routing. The current drawn by the two halves of a Class AB output stage is rectified and has heavy harmonic components. Because solid-state amps draw a lot of current from the rails, there is a good chance of inducing signal-related noise in low-level circuitry unless careful layout is used. A good technique is to twist the positive and negative rail leads together and route them directly to the output devices, keeping them away from low-level conductors. The rails are usually bypassed on the circuit board by electrolytic capacitors which should have a dedicated ground wire for their common terminals. This wire should be kept apart from the small signal ground lead. Care should be taken to keep the negative feedback connection, which typically connects to a node near the output output transistors, from coupling to the power leads. A sophisticated design will use multiple electrolytic capacitors mounted right at the output devices and clever circuit board layout. I believe the famous Analog Devices application note on a wideband current feedback amplifier has some useful notes on this problem (does anyone have a reference?). -- Henry A. Pasternack Member Scientific Staff (514) 761-8734 (phone) Bell Northern Research, Montreal (514) 761-8509 (fax) |
#8
Posted to rec.audio.tubes
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Ground Busses
Andre Jute wrote:
A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. Grounding is is tricky and tiresome in inverse proportion to the amount of thought you give it. I would say the opposite is true. The less you think about grounding, the less tricky it seems. With no thought at all, it becomes as simple as pie. Or fruit tart, for that matter. Just connect all the ground connections together any way you like, and don't worry. It's only when you start to think about it that it truly becomes tricky. Here you can see my star point [URL deleted]. You may be able to see it, but to my eyes the picture is impossibly tiny to reveal any useful details. But, you know I have this problem with photographs. Most schematics don't tell you enough about earthing. Here, for instance: [URL deleted]. I've shown the star earth being implemented but have not said anything about connecting the case to earth. Attempting to connect all the grounds together like that, willy-nilly, is not the right approach. That's because in practice it's nearly impossible to achieve a true equipotential connection for all those wires. Also, there are other performance issues having to do with all those long ground connections running about the amplifier. ... I showed all the 0V connections in order, with a note saying "mind the order of the grounding connections", and two people wrote me letters saying that DIYers are not idiots who need their hands held. Then the DIYers were idiots, because the subject is quite worthy of elaboration. The problem I see with everything you say here is that you fail to address the most important meat of the problem, which is precisely how to determine the "order of the grounding connections" and how this translates into a practical wiring and ground layout. My opinion on this subject is there are many ways to wire an amplifier to minimize hum and noise. Star grounding (and its variants) and bus wiring are two common solutions. Rather than posting fuzzy pictures and vague generalities, if you would like to help your readers, you should teach them the principles involved (you do know them, right?) so they can work out the optimum grounding scheme for each project by themselves. Of course, being a lying psychopath pornographic scumbag, I may not really know what I'm talking about! Feel free to ignore everything I say. In fact, I strongly urge you to do so! :-) -Henry |
#9
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Ground Busses
"Andre Jute" wrote in message ... A star ground is just a circular bus or a very short bus. Grounding is is tricky and tiresome in inverse proportion to the amount of thought you give it, so I do something between what Iain does and what Patrick does, and I call it a "star-point". Here you can see my star point http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg on my T68bis "Minus Zero" amp. It is the short piece of stiff wire sticking up at the right hand side of the aluminium cased resistor behind the battery boxes in the centre of the top right hand photograph. It's the bleeder resistor to the power supply and the star point is at its 0V end. Notice how the convenitonally drawn schematic http://members.lycos.co.uk/fiultra/t...17acircuit.jpg tells you nothing of this, leaving you to work it out for yourself. All the 0V wires are dropped over this stiff wire and soldered on. Even on such a short bus I take care of the order of the wires as I put them on. From this point a wire is taken to main's earth. The case is connected to mains earth by a wire from very sturdy bolt held in with serrated washers and nuts, which is placed as near as possible to the mains socket; unfortunately it is not too clear in the photograph, but it is just below the switch, near the top right hand corner of the righthand output transformer in the picture. Most schematics don't tell you enough about earthing. Here, for instance: http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg I've shown the star earth being implemented but have not said anything about connecting the case to earth. Mind you, on some of the Lundahl Modular Series 300B schemos I showed all the 0V connections in order, with a note saying "mind the order of the grounding connections", and two people wrote me letters saying that DIYers are not idiots who need their hands held. (I was, when I started, and I'm very grateful to people who made 90 mile round trips to come check over my constructions before I fired them up.) Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review Great illustration. Did you have those schematics/illustrations professionally made or is there a particular program you used? Thanks. west |
#10
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Ground Busses
I remember the guy that originally posted that article, he used to post
on the usenet newsgroup "rec.audio.high-end", it seems unlikely you would have found it on the web. Regards, John Byrns In article , Henry Pasternack wrote: This is something I found on the Web. It was apparently posted on the usenet, perhaps to this group or maybe rec.audio.tech, many years ago, althought I'm unable to find any evidence of the article in the Google archives. I offer the article without comment, and don't make any claims as to its accuracy. Perhaps there is some value to what is written, as quite a few people have linked to or reposted copies on their websites. The author has left his phone number and email address in the signature. If you have any issues, you may wish to contact him there. I would, in fact, be very interested in hearing if anyone manages to contact him that way. -Henry --- BEGIN REPOSTED ARTICLE --- Someone suggested I write an article on power and grounding techniques for equipment construction. This is a topic I can't really do justice to; whole books have been written on the subject. In the spirit of reckless misinformation, I'll try to summarize a few hints. Consider this an introduction for advanced beginners, but bear in mind there is room for expanding and improving the information contained below. -Henry * * * * * * * If circuits worked exactly as they are drawn on schematics, there'd be no need to worry about power and ground topologies or wire routing. Instead, we could just wire up all the components willy-nilly making sure only that all the specified connections were complete. In the real world of electromagnetics, things aren't quite so convenient: 1) Ground isn't really ground. Ideally, ground is a zero-voltage reference that never varies. In fact, every ground bus that carries current has small voltage variations across its length due to small but significant resistance. 2) Stray capacitance. Two parallel conductors form a capacitor across which unexpected AC currents can flow. 3) Electromagnetic induction. By definition, every circuit forms a loop. When a changing magnetic flux (due, perhaps, to the strong field from a transformer or choke) exists in the loop, a current will be induced. Now I'll talk briefly about the consequences of these real-world effects. Ground Loops. A ground loop occurs when a ground circuit encloses a loop and a source of energy causes current to flow through the loop. If the flow of current causes a voltage drop in a sensitive gain stage, the voltage can be amplified and appear as noise. A typical ground loop occurs in the amplifiers I just built. Because I use grounded power cords, the chassis of my monoblocks are joined electrically at the power outlet. The signal grounds are connected (via the input jacks and interconnect cable shields) at the preamp output terminals. The signal grounds are also connected to chassis ground internally in each amplifier. The result is a loop that picks up inductive noise or leakage currents and couples them into the amplifier gain circuitry, causing an audible hum in the speakers. The quick solution is to break the loop by using a three-to-two wire converter on one power cord. A better fix is to "lift" the internal connection between signal and chassis ground in one or both amplifiers and install a 10 Ohm resistor. The resistor is a significant obstacle to the flow of current compared to the stout power cords and effectively breaks the loop. Another sort of ground loop occurs internal to equipment, but for a different reason. In any circuit, one can trace the flow of power from the supply, out to various circuits, and back to ground. Each power supply typically provides current to more than one circuit branches. Topologically speaking, the branches form intermeshing loops that originate and terminate at the power supply. In the regions where the loops overlap (share common conductors), voltage drops in one loop can impose unwanted signals in another. When a circuit loop overlaps on the supply side of a power source, the designer will use parallel capacitors and/or series resistors or inductors to block or shunt away signal currents on the supply rails. The series components keep unwanted signals from leaving their circuit branches, and the parallel caps redirect those that escape to ground. Purifying the supply rails in this manner is called "decoupling". Decoupling also helps to rid the rails of noise that creeps in due to magnetic or electrostatic fields (more on theis later). On the ground side, it's very important to keep the return currents separate from one another as they work their way back to the common power supply terminal. Practically speaking, we want to minimize overlapping loops in the ground circuit. This is done by using a short, thick ground bus of very low resistance and connecting all ground wires to it. The most effective solution is to provide separate conductors for each ground current source and return them all to a single point; this is known as "star" grounding and is standard practice in audio design. In tube gear wired point-to-point, it may be sufficient to route a heavy ground wire around the edge of the circuit and make all connections directly to it at the closest convenient point. Inductive and Capacitive Coupling. Every conductor carrying a signal current generates an electromag- netic field that can couple to other circuit elements. In addition, the environment in which equipment is used is loaded with power line and radio frequency fields that can get into sensitive circuits and cause noise and distortion. I'll give some very quick information on minimizing these problems. Electrostatic fields and capacitive coupling can be reduced by distance and shielding. A grounded metal shield stops a static field in its tracks by imposing an equipotential barrier. To keep the field from sneaking past the shield, the sensitive circuit must be completely enclosed. Capacitance decreases as the reciprocal of the distance between conductors, so separating sensitive wires as much as possible is the other solution to stray electrostatic coupling. Keeping circuit impedances low will help a great deal by raising the frequency at which the coupling becomes a problem (hopefully beyond the bandwidth of the circuit or offending signal source). Shielding with non-ferrous metals is useless against magnetic induction. The answer to induced hum of magnetic origin is to keep circuit loop area to a minimum. The smaller the loop, the smaller the volume of magnetic flux enclosed and the lower the induced current. For this reason, power and signal wires should be twisted tightly with their ground conductors whenever possible. This increases capacitance between the conductors, so watch out in high-impedance signal circuits. Plan the layout of hum-sensitive circuits so that the enclosed area is kept to a minimum. Place transformers, chokes, and high-current conductors as far as possible from these circuits. Iron or mu-metal shields may be of some help, but I wouldn't count on them. It may be better to put the power supply in a separate box for sensitive preamps. In most cases it is good advice to keep wire runs short, to twist conductors carrying opposite currents together (signal and ground, power supply lines, filament wires, etc), to route wires near the chassis, and to physically separate high-gain stages from components and wires that carry high currents. Practical Advice. When laying out your circuit, look at the schematic and identify all of the separate current loops from supply to circuit to ground. Then come up with a scheme to keep these loops as separate as possible on the ground side. The biggest source of ground current in most amplifiers is the power supply ripple in the main filter capacitor. This current, which contains noisy, high-current rectifier current spikes, usually flows back to the power transformer through the secondary center tap. A good strategy is to connect this lead directly to the filter capacitor common terminal. Then run a short stub (could be a half inch) to a second point that will serve as a star ground for the signal circuitry. Another source of high current ground flow in a power amplifier is the common lead from the speaker terminals. You'll want to make sure the low-level signal star ground does not have output ground currents flowing through it or you'll increase the possibility of instability. What I'm describing here is really a "star of stars" grounding scheme. If you view every conductor as a resistor and try to keep associated voltage drops from crossing loops, you'll end up with the best ground scheme. Here's the grounding topology in my tube power amps: The main electrolytic filter caps and driver decoupling caps are all mounted on one circuit board. The three decoupling caps share a common, wide circuit board ground trace. The ground for the main filter cap, for the transformer center tap, and for the decoupling caps all come together in one small area of the circuit board. The driver stage ground points are located close together near the central ground, but "out of the way" of the rectifier current flow. I slotted the copper strategically to "steer" the charging current current away from the driver-stage grounds (defining the stub conductor described above). The following wires attach to the driver-stage ground area on the filter cap board: 1) A single ground wire from a local "star ground" on the driver board that connects the input jack shield, global feedback cable shield, and the input stage bias resistors grounds. 2) A single ground wire carrying the return current from the B- supply. This supply is floating and connected to the driver board by a tightly twisted pair. B- is bypassed locally by electrolytic and film capacitors. A second "star ground" on the driver board connects all the bypass caps. The rationale is that low frequency hum currents are handled by the electrolytics and don't make it off the filter circuit board. Local bypass caps keep RF signals on the supply lines from getting onto the driver board. The current-sourced differential design greatly reduces the coupling of the input and driver signal currents, in the ground leads, justifying the use of a single B- supply and ground wire. I agonized over this layout for a while, but it seems to work quite well. 3) A ground wire from the negative bias board. The bias supply is also floating and connected to the bias board (which also holds the output coupling capacitors) via a twisted pair. There is a 0.47uF film capacitor bypass on the bias board. The common lead from the output tube cathodes connects to a ground point that runs directly to the main star ground without passing through the driver ground node. The power transformer center tap comes in on its own stub directly to the main capacitor common terminal. The two B+ wires to the driver stage are very short and connect directly to the driver board. The output stage B+ is supplied to the output transformer primary center tap from a circuit area close to the main filter cap positive terminal. The power cord ground wire is connected to the chassis at a convenient lug near the back panel AC socket. The filter cap board has a ground wire to a lug on the chassis as well (and perhaps this is why I have a ground loop; I need to experiment with the location of my connection from signal ground to chassis ground). A note on solid-state Class AB amplifiers and power rail routing. The current drawn by the two halves of a Class AB output stage is rectified and has heavy harmonic components. Because solid-state amps draw a lot of current from the rails, there is a good chance of inducing signal-related noise in low-level circuitry unless careful layout is used. A good technique is to twist the positive and negative rail leads together and route them directly to the output devices, keeping them away from low-level conductors. The rails are usually bypassed on the circuit board by electrolytic capacitors which should have a dedicated ground wire for their common terminals. This wire should be kept apart from the small signal ground lead. Care should be taken to keep the negative feedback connection, which typically connects to a node near the output output transistors, from coupling to the power leads. A sophisticated design will use multiple electrolytic capacitors mounted right at the output devices and clever circuit board layout. I believe the famous Analog Devices application note on a wideband current feedback amplifier has some useful notes on this problem (does anyone have a reference?). -- Henry A. Pasternack Member Scientific Staff (514) 761-8734 (phone) Bell Northern Research, Montreal (514) 761-8509 (fax) -- Surf my web pages at, http://fmamradios.com/ |
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Ground Busses
On Mar 2, 8:33*am, Patrick Turner wrote:
Good Stuff. Patrick, reducing your and Iain's post to a very few salient points, am I correct in deriving "best practice" as follows: a) The chassis must be grounded to the mains ground b) The circuit ground should be separate and isolated from the chassis/ case, connected via the 27ohm@5W resistor. c) The circuit ground should be as short as possible and loops (such as connecting signal-shields at both ends) are to be avoided. I see safety addresssed by grounding the chassis directly to the mains ground. I see any excess potentials within the circuit bleeding to the case. I also see isolating the circuit from the case helping when other components are connected (and grounded). It seems that this solution is the one that was actually put into place on the humming pre-amp... Thanks in advance. Peter Wieck Wyncote, PA |
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Ground Busses
"John Byrns" wrote in message
... I remember the guy that originally posted that article, he used to post on the usenet newsgroup "rec.audio.high-end", it seems unlikely you would have found it on the web. http://ai.kaist.ac.kr/~suh/DIY/ground |
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Ground Busses
Henry Pasternack wrote:
Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# In power amps this is relatively easy to achieve and running a thick bus from the PSU 0V past the power section to the preamp section should work just a s well since the power currents will not flow through any of the preamp sections of the bus. In separate pre-amps or mic pre-amps or tube mixers where the supply is remote from the pre-amp this is clearly not possible and there is the added problem of separating power currents from input/output signal currents (unless floating transformer inputs and outputs are used). One solution I have seen is to have a local pre-amp power supply - indeed this was very common practice in many tube based recording mixers of the 50s and 60s. Each pre-amp would have its own mains transformer and PSU along with balanced floating inputs and outputs. All earth loop problems were therefore local to the pre-amp and you could connect them together however you liked to build a mixer without ever having to worry about ground loops. An expensive option to be sure, but one that worked very well. Cheers ian |
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Ground Busses
Ian Thompson-Bell wrote: Henry Pasternack wrote: Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# In power amps this is relatively easy to achieve and running a thick bus from the PSU 0V past the power section to the preamp section should work just a s well since the power currents will not flow through any of the preamp sections of the bus. But still a compromise. In separate pre-amps or mic pre-amps or tube mixers where the supply is remote from the pre-amp this is clearly not possible and there is the added problem of separating power currents from input/output signal currents (unless floating transformer inputs and outputs are used). One solution I have seen is to have a local pre-amp power supply - indeed this was very common practice in many tube based recording mixers of the 50s and 60s. Each pre-amp would have its own mains transformer and PSU along with balanced floating inputs and outputs. All earth loop problems were therefore local to the pre-amp and you could connect them together however you liked to build a mixer without ever having to worry about ground loops. An expensive option to be sure, but one that worked very well. Far simpler is to have 2 (or more) stars and use these to direct current flow. In particular, the PSU should have its own star and this is where ALL ripple currents must flow. This can now be tied to the input 'star' with a *non-current-carrying conductor* (or at least carrying only the B- smoothed DC). It is *essential* to keep power and signal paths separate for hum free operation. Graham |
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Ground Busses
"Ian Thompson-Bell" wrote in message
... The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# True. But a better practical arrangement is to create a "star of stars". The real key, IMHO, is to start with the schematic and draw out all of the current loops in the circuit, from power supply out to the signal circuitry and back, and also the input and output currents. Then you find places where separate current loops share common paths, and then separate out these loops so they meet at (to the greatest extent possible) single points. The connection to the chassis is done for electrostatic shielding. It's done at a single point on the circuit's ground net. Where that point should be is a subject for debate. To understand the implications, you have to visualize the effects of currents flowing though and in the chassis walls due to external potentials and electrostatic/electromagnetic fields. Not easy if you really want to take it to the "next level". And that's why that fellow in the article reposted said whole books can be written on the subject. If you try to follow a single technique from rote and vague instructions, your results may be hit-and-miss. Always better, I say, to understand the problem from first principles. -Henry |
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Ground Busses
Henry Pasternack wrote: "Ian Thompson-Bell" wrote The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# True. But a better practical arrangement is to create a "star of stars". The real key, IMHO, is to start with the schematic and draw out all of the current loops in the circuit, from power supply out to the signal circuitry and back, and also the input and output currents. Then you find places where separate current loops share common paths, and then separate out these loops so they meet at (to the greatest extent possible) single points. 100% correct. If you try to follow a single technique from rote and vague instructions, your results may be hit-and-miss. Always better, I say, to understand the problem from first principles. I couldn't agree more. With grounding it's almost all about directing current flow in an appropriate way. Graham |
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Ground Busses
In article ,
"Henry Pasternack" wrote: "John Byrns" wrote in message ... I remember the guy that originally posted that article, he used to post on the usenet newsgroup "rec.audio.high-end", it seems unlikely you would have found it on the web. http://ai.kaist.ac.kr/~suh/DIY/ground I meant originally, I assume this is one of the many copies on the web that you said existed? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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Ground Busses
Andre Jute wrote:
A star ground is just a circular bus or a very short bus. Grounding is is tricky and tiresome in inverse proportion to the amount of thought you give it, so I do something between what Iain does and what Patrick does, and I call it a "star-point". Here you can see my star point http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg on my T68bis "Minus Zero" amp. It is the short piece of stiff wire sticking up at the right hand side of the aluminium cased resistor behind the battery boxes in the centre of the top right hand photograph. It's the bleeder resistor to the power supply and the star point is at its 0V end. Notice how the convenitonally drawn schematic http://members.lycos.co.uk/fiultra/t...17acircuit.jpg Given the topic of the thread, shouldn't the ground commection under the rectifier be after the choke, not before? -- Nick |
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Ground Busses
"Eeyore" wrote in message
... Henry Pasternack wrote: True. But a better practical arrangement is to create a "star of stars". The real key, IMHO, is to start with the schematic and draw out all of the current loops in the circuit, from power supply out to the signal circuitry and back, and also the input and output currents. Then you find places where separate current loops share common paths, and then separate out these loops so they meet at (to the greatest extent possible) single points. 100% correct. Your posting that said essentially the same thing arrived on my server slightly after I wrote the above, although the date shows you posted it earlier... Apologies for making the same point twice. I couldn't agree more. With grounding it's almost all about directing current flow in an appropriate way. And bearing in mind that current always finds its way to ground, and learning to think about all the sneaky ways it does so, and the voltage drops it creates along the way... -Henry |
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Ground Busses
"John Byrns" wrote in message
... I meant originally, I assume this is one of the many copies on the web that you said existed? I found the posting today on the Web. -Henry |
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Ground Busses
In article ,
Ian Thompson-Bell wrote: Henry Pasternack wrote: Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# In my experience it is not the input filter cap that is important here, but rather that it is the final filter cap in the main PSU filter that must be connected to the "star point" or its equivalent. In power amps this is relatively easy to achieve and running a thick bus from the PSU 0V past the power section to the preamp section should work just a s well since the power currents will not flow through any of the preamp sections of the bus. In separate pre-amps or mic pre-amps or tube mixers where the supply is remote from the pre-amp this is clearly not possible and there is the added problem of separating power currents from input/output signal currents (unless floating transformer inputs and outputs are used). One solution I have seen is to have a local pre-amp power supply - indeed this was very common practice in many tube based recording mixers of the 50s and 60s. Each pre-amp would have its own mains transformer and PSU along with balanced floating inputs and outputs. All earth loop problems were therefore local to the pre-amp and you could connect them together however you liked to build a mixer without ever having to worry about ground loops. An expensive option to be sure, but one that worked very well. And in other 50s and 60s systems a whole rack full of microphone preamps were powered from a common power supply without problems because only power currents flowed through the wires from the power supply, the signal input and output currents were isolated from the common power wires by input and output transformers. Oops on proof reading, I see that you already mentioned this in parenthesis, oh well. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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Ground Busses
In article ,
"Henry Pasternack" wrote: "John Byrns" wrote in message ... I meant originally, I assume this is one of the many copies on the web that you said existed? I found the posting today on the Web. Are you saying it wasn't originally posted on usenet? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
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Ground Busses
On Mar 2, 2:13*pm, "West" wrote:
"Andre Jute" wrote in message ... A star ground is just a circular bus or a very short bus. Grounding is is tricky and tiresome in inverse proportion to the amount of thought you give it, so I do something between what Iain does and what Patrick does, and I call it a "star-point". Here you can see my star pointhttp://members.lycos.co.uk/fiultra/KISS%20192%20T68MZ417A.jpg on my T68bis "Minus Zero" amp. It is the short piece of stiff wire sticking up at the right hand side of the aluminium cased resistor behind the battery boxes in the centre of the top right hand photograph. It's the bleeder resistor to the power supply and the star point is at its 0V end. Notice how the convenitonally drawn schematichttp://members.lycos.co.uk/fiultra/t68mzwe417acircuit.jpg tells you nothing of this, leaving you to work it out for yourself. All the 0V wires are dropped over this stiff wire and soldered on. Even on such a short bus I take care of the order of the wires as I put them on. From this point a wire is taken to main's earth. The case is connected to mains earth by a wire from very sturdy bolt held in with serrated washers and nuts, which is placed as near as possible to the mains socket; unfortunately it is not too clear in the photograph, but it is just below the switch, near the top right hand corner of the righthand output transformer in the picture. Most schematics don't tell you enough about earthing. Here, for instance:http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg I've shown the star earth being implemented but have not said anything about connecting the case to earth. Mind you, on some of the Lundahl Modular Series 300B schemos I showed all the 0V connections in order, with a note saying "mind the order of the grounding connections", and two people wrote me letters saying that DIYers are not idiots who need their hands held. (I was, when I started, and I'm very grateful to people who made 90 mile round trips to come check over my constructions before I fired them up.) Andre Jute Visit Jute on Amps athttp://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review Great illustration. Did you have those schematics/illustrations professionally made or is there a particular program you used? Thanks. west Pillock: You can do all of that using "Word" and the extra symbols chart. Most word-processing programs are capable of all of that and more. On a Mac, it is that much easier. So, you could finally furnish that long- promised schematic on your "Slow B+" as the wherewithall is likely already resident on your computer. Peter Wieck Wyncote, PA |
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Ground Busses
Eeyore wrote:
Ian Thompson-Bell wrote: Henry Pasternack wrote: Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# In power amps this is relatively easy to achieve and running a thick bus from the PSU 0V past the power section to the preamp section should work just a s well since the power currents will not flow through any of the preamp sections of the bus. But still a compromise. In separate pre-amps or mic pre-amps or tube mixers where the supply is remote from the pre-amp this is clearly not possible and there is the added problem of separating power currents from input/output signal currents (unless floating transformer inputs and outputs are used). One solution I have seen is to have a local pre-amp power supply - indeed this was very common practice in many tube based recording mixers of the 50s and 60s. Each pre-amp would have its own mains transformer and PSU along with balanced floating inputs and outputs. All earth loop problems were therefore local to the pre-amp and you could connect them together however you liked to build a mixer without ever having to worry about ground loops. An expensive option to be sure, but one that worked very well. Far simpler is to have 2 (or more) stars and use these to direct current flow. In particular, the PSU should have its own star and this is where ALL ripple currents must flow. This can now be tied to the input 'star' with a *non-current-carrying conductor* (or at least carrying only the B- smoothed DC). Presumably you mean no *signal* current carrying conductor. This still leaves a common mode conductor carrying output signal current which is of course supplied by the power supply. I am not clear how multiple local stars solve the problem. It is *essential* to keep power and signal paths separate for hum free operation. Which can only be achieved with transformers? Cheers Ian |
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Ground Busses
Ian Thompson-Bell wrote: Eeyore wrote: Ian Thompson-Bell wrote: Henry Pasternack wrote: Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# In power amps this is relatively easy to achieve and running a thick bus from the PSU 0V past the power section to the preamp section should work just a s well since the power currents will not flow through any of the preamp sections of the bus. But still a compromise. In separate pre-amps or mic pre-amps or tube mixers where the supply is remote from the pre-amp this is clearly not possible and there is the added problem of separating power currents from input/output signal currents (unless floating transformer inputs and outputs are used). One solution I have seen is to have a local pre-amp power supply - indeed this was very common practice in many tube based recording mixers of the 50s and 60s. Each pre-amp would have its own mains transformer and PSU along with balanced floating inputs and outputs. All earth loop problems were therefore local to the pre-amp and you could connect them together however you liked to build a mixer without ever having to worry about ground loops. An expensive option to be sure, but one that worked very well. Far simpler is to have 2 (or more) stars and use these to direct current flow. In particular, the PSU should have its own star and this is where ALL ripple currents must flow. This can now be tied to the input 'star' with a *non-current-carrying conductor* (or at least carrying only the B- smoothed DC). Presumably you mean no *signal* current carrying conductor. Well ... if there's no current, then there'll be no signal too for sure. What I meant basically was a link to simply ensure that the 2 stars are at the same potential. This still leaves a common mode conductor carrying output signal current which is of course supplied by the power supply. I am not clear how multiple local stars solve the problem. It is *essential* to keep power and signal paths separate for hum free operation. Which can only be achieved with transformers? Not necessary. Transfomers introduce their own problems. Graham |
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Ground Busses
Henry Pasternack wrote:
"Ian Thompson-Bell" wrote in message ... The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# True. But a better practical arrangement is to create a "star of stars". The real key, IMHO, is to start with the schematic and draw out all of the current loops in the circuit, from power supply out to the signal circuitry and back, and also the input and output currents. Then you find places where separate current loops share common paths, and then separate out these loops so they meet at (to the greatest extent possible) single points. The problem I see with that is that all output currents must flow from the power supply, through the load and back to the PSU 0V but they share a common ground with the inputs. How do you separate these? The connection to the chassis is done for electrostatic shielding. It's done at a single point on the circuit's ground net. Where that point should be is a subject for debate. To understand the implications, you have to visualize the effects of currents flowing though and in the chassis walls due to external potentials and electrostatic/electromagnetic fields. Not easy if you really want to take it to the "next level". And that's why that fellow in the article reposted said whole books can be written on the subject. If you try to follow a single technique from rote and vague instructions, your results may be hit-and-miss. Always better, I say, to understand the problem from first principles. No argument about that! Cheers Ian |
#27
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Ground Busses
John Byrns wrote:
In article , Ian Thompson-Bell wrote: Henry Pasternack wrote: Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# In my experience it is not the input filter cap that is important here, but rather that it is the final filter cap in the main PSU filter that must be connected to the "star point" or its equivalent. In power amps this is relatively easy to achieve and running a thick bus from the PSU 0V past the power section to the preamp section should work just a s well since the power currents will not flow through any of the preamp sections of the bus. In separate pre-amps or mic pre-amps or tube mixers where the supply is remote from the pre-amp this is clearly not possible and there is the added problem of separating power currents from input/output signal currents (unless floating transformer inputs and outputs are used). One solution I have seen is to have a local pre-amp power supply - indeed this was very common practice in many tube based recording mixers of the 50s and 60s. Each pre-amp would have its own mains transformer and PSU along with balanced floating inputs and outputs. All earth loop problems were therefore local to the pre-amp and you could connect them together however you liked to build a mixer without ever having to worry about ground loops. An expensive option to be sure, but one that worked very well. And in other 50s and 60s systems a whole rack full of microphone preamps were powered from a common power supply without problems because only power currents flowed through the wires from the power supply, the signal input and output currents were isolated from the common power wires by input and output transformers. I am not clear about that. The output signal currents (internal to the transformer isolated circuit) flow from the psu through the output stage and transformer primary and thence to the PSU 0V, so presumably each needs a separate connection to/from the PSU? Oops on proof reading, I see that you already mentioned this in parenthesis, oh well. Sort of, except I was assuming separate PSUs rather than one feeding a rack of mic preamps. Cheers Ian Regards, John Byrns |
#28
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Ground Busses
Ian Thompson-Bell wrote: The problem I see with that is that all output currents must flow from the power supply, through the load and back to the PSU 0V but they share a common ground with the inputs. How do you separate these? Clever local decoupling can achieve this for all but very low frequencies. A technique used at Neve in fact. Graham |
#29
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Ground Busses
Eeyore wrote:
Ian Thompson-Bell wrote: Eeyore wrote: Ian Thompson-Bell wrote: Henry Pasternack wrote: Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. The key phrase here is 'reducing the resistance of the common ground bus to zero'. it is all very well connecting all grounded leads to a single point but if you then connect that by a single wire to the zero volts point of the power supply you have immediately introduced a long no zero common ground bus. So a star ground really only works if the star point IS the 0V point of the PSU i.e the ground of the input filter cap.# In power amps this is relatively easy to achieve and running a thick bus from the PSU 0V past the power section to the preamp section should work just a s well since the power currents will not flow through any of the preamp sections of the bus. But still a compromise. In separate pre-amps or mic pre-amps or tube mixers where the supply is remote from the pre-amp this is clearly not possible and there is the added problem of separating power currents from input/output signal currents (unless floating transformer inputs and outputs are used). One solution I have seen is to have a local pre-amp power supply - indeed this was very common practice in many tube based recording mixers of the 50s and 60s. Each pre-amp would have its own mains transformer and PSU along with balanced floating inputs and outputs. All earth loop problems were therefore local to the pre-amp and you could connect them together however you liked to build a mixer without ever having to worry about ground loops. An expensive option to be sure, but one that worked very well. Far simpler is to have 2 (or more) stars and use these to direct current flow. In particular, the PSU should have its own star and this is where ALL ripple currents must flow. This can now be tied to the input 'star' with a *non-current-carrying conductor* (or at least carrying only the B- smoothed DC). Presumably you mean no *signal* current carrying conductor. Well ... if there's no current, then there'll be no signal too for sure. What I meant basically was a link to simply ensure that the 2 stars are at the same potential. But that link carries common mode current from one star to the PSU 0V so how does that solve the problem? This still leaves a common mode conductor carrying output signal current which is of course supplied by the power supply. I am not clear how multiple local stars solve the problem. It is *essential* to keep power and signal paths separate for hum free operation. Which can only be achieved with transformers? Not necessary. Transfomers introduce their own problems. Graham So how do you isolate signal currents from power supply ones? given that output currents flow from the PSU through the load and back to the PSU 0V with or without transformers? Cheers Ian |
#30
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Ground Busses
Eeyore wrote:
Ian Thompson-Bell wrote: The problem I see with that is that all output currents must flow from the power supply, through the load and back to the PSU 0V but they share a common ground with the inputs. How do you separate these? Clever local decoupling can achieve this for all but very low frequencies. A technique used at Neve in fact. Graham Please elaborate. I can see local B+ decoupling is practical not to say fairly common, but how do you locally decouple grounds? Cheers Ian |
#31
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Ground Busses
"Eeyore" wrote in message
... Ian Thompson-Bell wrote: The problem I see with that is that all output currents must flow from the power supply, through the load and back to the PSU 0V but they share a common ground with the inputs. How do you separate these? Clever local decoupling can achieve this for all but very low frequencies. A technique used at Neve in fact. Once again, agreed. The way I do it is as follows: The main capacitor board has a short ground bus running through it. The power transformer center tap connects at one end of this bus. All the charging currents associated with the rectifier are contained at this end. The other end of the ground bus faces the signal circuitry. The B+ lead to the output transformer comes off the first filter cap. Current flows to the transformer, through the output tube(s), plate to cathode, and back to the filter cap ground bus. The wires in this circuit are routed close together (or twisted) to minimize loop area. The second filter cap (or set of filter caps, or whatever) sits on an extension of the ground bus/ No output stage current flows in this extension. The far end of the extension is the input/driver circuit ground reference. On the B+ side, RC or preferably LC decoupling is used to isolate the two loops at signal frequencies. The input jacks are electrically isolated from the chassis and connected to the input circuit using a twisted pair. A separate ground bus runs the length of the input/driver stage. The input twisted pair ground is connected to this bus at the input tube end, and a wire connects the driver stage end (or the signal circuit bus itself is extended) to the cap board signal ground. There is a solid connection from the rectifier side of the power supply ground bus to the chassis. Then, the input jack grounds are optionally connected to the chassis by small (0.01uF) capacitors with short leads. These (in principle) bypass RF currents on the input cable shields to the chassis. This is a pretty good approach that has worked well for me. A major source of hum is unbalanced capacitance between the power transformer windings and ground. With this arrangement, these currents flow through the chassis and back into the supply through the rectifier side of the power supply ground bus, avoiding the signal circuitry. Sometimes, though, in spite of careful design, the damned thing still hums. In that case, you have to experiment until you find the cause of the problem. -Henry |
#32
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Ground Busses
Ian Thompson-Bell wrote: Eeyore wrote: Ian Thompson-Bell wrote: The problem I see with that is that all output currents must flow from the power supply, through the load and back to the PSU 0V but they share a common ground with the inputs. How do you separate these? Clever local decoupling can achieve this for all but very low frequencies. A technique used at Neve in fact. Please elaborate. I can see local B+ decoupling is practical not to say fairly common, but how do you locally decouple grounds? It helps somewhat when using twin supply op-amp circuitry. You place a resistor (say 100 ohms) in both supply rails and a cap (say 100 uF) from each pin of the op-amp to local ground. The local ground is returned to the central 'star point' or earth bus via the non-curent-carrying' conductor. This local decoupling results in output currents (these are really the only ones of concern) circulating locally to the op-amp, at least at all but low frequencies. I suppose something similar can be achieved with single supply working too. Imagine the series R being a very high value and you'll see that it approximates to an individual local supply for each such decoupled stage. Graham |
#33
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Ground Busses
Porno Pas wrote: This is something I found on the Web. SNIP some soppy crap The author has left his phone number and email address in the signature. If you have any issues, you may wish to contact him there. I would, in fact, be very interested in hearing if anyone manages to contact him that way. -Henry --- BEGIN REPOSTED ARTICLE --- Someone suggested I write an article on power and grounding techniques for equipment construction. SNIP some stuff probably more at home on rec.audio.opinion. -- Henry A. Pasternack Member Scientific Staff (514) 761-8734 (phone) Bell Northern Research, Montreal (514) 761-8509 (fax) Isn't he the fellow who was fired by Bell not too long after that? I wonder why. Considering the article posted, it is not difficult to guess. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review |
#34
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Ground Busses
Ian Thompson-Bell wrote: So how do you isolate signal currents from power supply ones? given that output currents flow from the PSU through the load and back to the PSU 0V with or without transformers? Explained in my other reply. Graham |
#35
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Ground Busses
Here we go with the old Magnequest Scum methods again. What happens is
that Porno Pas, unable technically to fault what I write, rephrases what I say in a slightly different manner and then pretends that what I say is wrong. It's bull****. And the rest is just Porno Pas claiming that whatever I say is white is really black. It is beneath contempt, not worth answering. That's quite aside from the fact that I don't hold cosy chats with child molesers. -- Andre Jute Henry "Porno" Pasternack wrote: Andre Jute wrote: A star ground is just a circular bus or a very short bus. Not really, ANDRE. *A star ground is the abstract notion of a purely equipotential (equal voltage) single point connection that eliminates ground loops by reducing the resistance of the common ground bus to zero. *It's impossible to achieve in practice, though, and trying to take the approach too literally is likely to cause more harm than good. Grounding is is tricky and tiresome in inverse proportion to the amount of thought you give it. I would say the opposite is true. *The less you think about grounding, the less tricky it seems. *With no thought at all, it becomes as simple as pie. *Or fruit tart, for that matter. *Just connect all the ground connections together any way you like, and don't worry. *It's only when you start to think about it that it truly becomes tricky. Here you can see my star point [URL deleted]. You may be able to see it, but to my eyes the picture is impossibly tiny to reveal any useful details. *But, you know I have this problem with photographs. Most schematics don't tell you enough about earthing. Here, for instance: [URL deleted]. *I've shown the star earth being implemented but have not said anything about connecting the case to earth. Attempting to connect all the grounds together like that, willy-nilly, is not the right approach. *That's because in practice it's nearly impossible to achieve a true equipotential connection for all those wires. *Also, there are other performance issues having to do with all those long ground connections running about the amplifier. ... I showed all the 0V connections in order, with a note saying "mind the order of the grounding connections", and *two people wrote me letters saying that DIYers are not idiots who need their hands held. Then the DIYers were idiots, because the subject is quite worthy of elaboration. *The problem I see with everything you say here is that you fail to address the most important meat of the problem, which is precisely how to determine the "order of the grounding connections" and how this translates into a practical wiring and ground layout. My opinion on this subject is there are many ways to wire an amplifier to minimize hum and noise. *Star grounding (and its variants) and bus wiring are two common solutions. *Rather than posting fuzzy pictures and vague generalities, if you would like to help your readers, you should teach them the principles involved (you do know them, right?) so they can work out the optimum grounding scheme for each project by themselves. Of course, being a lying psychopath pornographic scumbag, I may not really know what I'm talking about! *Feel free to ignore everything I say. *In fact, I strongly urge you to do so! *:-) -Henry |
#36
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Ground Busses
Andre Jute wrote: Here we go with the old Magnequest Scum methods again. What happens is that Porno Pas, unable technically to fault what I write, rephrases what I say in a slightly different manner and then pretends that what I say is wrong. It's nothing like what you wrote you bloody idiot. Henry actually understands the fine detail of what he's talking about instead of posting 'design by rote' guides. Graham |
#37
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Ground Busses
On Mar 2, 7:13*pm, "West" wrote:
"Andre Jute" wrote in message ... A star ground is just a circular bus or a very short bus. Grounding is is tricky and tiresome in inverse proportion to the amount of thought you give it, so I do something between what Iain does and what Patrick does, and I call it a "star-point". Here you can see my star pointhttp://members.lycos.co.uk/fiultra/KISS%20192%20T68MZ417A.jpg on my T68bis "Minus Zero" amp. It is the short piece of stiff wire sticking up at the right hand side of the aluminium cased resistor behind the battery boxes in the centre of the top right hand photograph. It's the bleeder resistor to the power supply and the star point is at its 0V end. Notice how the convenitonally drawn schematichttp://members.lycos.co.uk/fiultra/t68mzwe417acircuit.jpg tells you nothing of this, leaving you to work it out for yourself. All the 0V wires are dropped over this stiff wire and soldered on. Even on such a short bus I take care of the order of the wires as I put them on. From this point a wire is taken to main's earth. The case is connected to mains earth by a wire from very sturdy bolt held in with serrated washers and nuts, which is placed as near as possible to the mains socket; unfortunately it is not too clear in the photograph, but it is just below the switch, near the top right hand corner of the righthand output transformer in the picture. Most schematics don't tell you enough about earthing. Here, for instance:http://members.lycos.co.uk/fiultra/Jute-EL34-SEntry.jpg I've shown the star earth being implemented but have not said anything about connecting the case to earth. Mind you, on some of the Lundahl Modular Series 300B schemos I showed all the 0V connections in order, with a note saying "mind the order of the grounding connections", and two people wrote me letters saying that DIYers are not idiots who need their hands held. (I was, when I started, and I'm very grateful to people who made 90 mile round trips to come check over my constructions before I fired them up.) Andre Jute Visit Jute on Amps athttp://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review Great illustration. Did you have those schematics/illustrations professionally made or is there a particular program you used? Thanks. west Good golly, no, I don't send out for simple art. Graphic arts is one of my professions, though at the higher levels we called typopgraphers or reprographers because it as much about technicalities as about art. Here are some introductory books in a series of which I am general editor: http://members.lycos.co.uk/fiultra/T...%20GDitCA.html and see also my key text for advanced designers "Grids" (Rotovision, Switzerland, 1996) he http://members.lycos.co.uk/fiultra/T...re%20Jute.html The programme I use for schematics is QuarkXPress, a professional page makeup programme; I just drew the symbols in it and duplicate them on the "pasteboard". It really isn't worth buying QXP--- it is a fair chunk over a thousand dollars in price --- or investing the substantial time necessary to master the programme, just to draw schematics. Try Microsoft Word's drawing module. Andre Jute "I was at a board meeting for the LA Chapter of the Audio Engineering Society last night on XM Satellite radio audio and data transmission. Sadly, we missed you there, and at the SMPTE and Acoustical Society recent meetings as well. Everyone was asking, 'Where is that wonderful Andre Jute? The world just doesn't rotate without him...'" -- John Mayberry, Emmaco |
#38
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Ground Busses
John Byrns wrote:
I meant originally, I assume this is one of the many copies on the web that you said existed? I found the posting today on the Web. Are you saying it wasn't originally posted on usenet? Guys, please, this is the most futile, petty and puerile bout of bickering I've ever seen. Truly. I even feel stupid for reading it. You're undermining the quality of rat squabbling. People expect better than flyweight finger-poking. Ian |
#39
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Ground Busses
On Mar 2, 9:39*pm, Nick Gorham wrote:
Andre Jute wrote: A star ground is just a circular bus or a very short bus. Grounding is is tricky and tiresome in inverse proportion to the amount of thought you give it, so I do something between what Iain does and what Patrick does, and I call it a "star-point". Here you can see my star point http://members.lycos.co.uk/fiultra/K...0T68MZ417A.jpg on my T68bis "Minus Zero" amp. It is the short piece of stiff wire sticking up at the right hand side of the aluminium cased resistor behind the battery boxes in the centre of the top right hand photograph. It's the bleeder resistor to the power supply and the star point is at its 0V end. Notice how the convenitonally drawn schematic http://members.lycos.co.uk/fiultra/t...17acircuit.jpg Given the topic of the thread, shouldn't the ground commection under the rectifier be after the choke, not before? -- Nick I published a wiring diagram as well. If you wire as instructed for this little amp, all 0V ends are led directly to a single point. In that case it doesn't matter where the earth is shown on the circuit diagram (on which there isn't space to show the star point) because there is a wiring schemo as well. HTH. Andre Jute Visit Jute on Amps at http://members.lycos.co.uk/fiultra/ "wonderfully well written and reasoned information for the tube audio constructor" John Broskie TubeCAD & GlassWare "an unbelievably comprehensive web site containing vital gems of wisdom" Stuart Perry Hi-Fi News & Record Review |
#40
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Ground Busses
On Mar 2, 9:53*pm, John Byrns wrote:
In article , *"Henry Pasternack" wrote: "John Byrns" wrote in message ... I meant originally, I assume this is one of the many copies on the web that you said existed? I found the posting today on the Web. Are you saying it wasn't originally posted on usenet? It might not be Google at fault when the original of the article in question cannot be found. The author might have withdrawn it from the net when Bell Canada fired him because of it. Regards, John Byrns -- Surf my web pages at, *http://fmamradios.com/ HTH. Andre Jute Thumbs well clear of the bricks |
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