Kofi Annan said:
It doesn't matter which way you connect the 4/5 and 9 as long as 4/5 are connected together. So in your example 4/5 connected to +ve 6.3V and 9 connected to -ve is good.
Note that in this case 9 is not really -6.3V it's relative 0V.
In the thread where KYW suggested a grounding scheme he suggested connecting the heater -ve to the star ground on the output stage. See this thread post 51 and before. So take a lead from pin 9 to the star ground on the output stage.
This means there will be one lead from the 6.3vfiltered dc supply going to pin 4/5. There will be one lead going from the -ve of the dc filtered supply to pin9. There will be another lead from pin 9 going to the star ground on the output stage.
If you closely follow KYW's scheme on post 50 the grounding arrangements should fall into place quite nicely.
Kev
Kofi Annan said:
I hope I'm helping here, but if we are talking voltage, we are always talking about Relative Voltage. Relative to what?
If your supply is floating, that means it's not connected to an external reference. The external reference could be the earth, your chassis, some point in your circuit at a potential above or below earth ground. And to have a reference, one must have a physical connection to the reference. So back to a floating supply and its two output leads. The only thing you can say is that one lead is positive RELATIVE to the other, and by how much. So you have a supply wherein the potential BETWEEN the leads is 6.3 volts, and there is a positive side and a negative side. But, you don't have a +6.3v lead OR -6.3v lead. IF you connect the positive side to ground, then you have ground and a -6.3v output, relative to ground (or relative to your connection point for the reference. Likewise, IF you connect the negative lead to ground (or another reference) then you have +6.3v relative to the ground (or other reference). Or, let's say you connect two 10k resistors in series between the two leads and then connect the ground (or other reference, blah blah) between the resistors. You then have +3.15 volts and -3.15 volts for the two respective leads (relative to ground or other, etc.,).
Always think in relative terms. This should come as naturally as giving relatives the plum contracts.
Sheldon
Sheldon
Sheldon said:
OK.... OK..... Starting to get it here...
I pride myself on asking the dumb questions that others have too much pride to ask. Even given that, however, I never asked a question pertaining to how what I see as "ground" in the negative supply could really be -6.3V and now I think I get it. (Just for the record here, I don't have a floating supply-- the negative rail of the rectified PSU is tied to ground)
So what you're getting at is that, like all concepts in electronics and politics and online dating, understanding the relative nature of relationships what will ultimately determine how things are perceived.
Put in practical terms, let's say I short pins 4 and 5 and apply the positive rail of the 6.3V supply to it while attaching the GROUNDED negative supply rail to pin 9. The filament now sees 6.3V between 4/5 and 9. If, however, I left the supply floating (no reference for the negative rail) then there would be no telling what the filament would see as there is no specific reference for the positive rail.
Now, if I were to reference the negative rail to a point of negative voltage within the circuit (I don't know why I'd do this, BTW), then the filament would see the difference between the +6.3VDC and the negative reference.
So, in essence, there really is no simultaneous positive and negative reference if one of the rails is referenced to ground. Therefore, if we're using the positive rail for a supply, when we refer to the "negative rail", we're really talking about the whatever-the-hell-the-rail-is-referenced-to supply, right?
If that's the case, then why wouldn't I just ground the filament supply to the second stage star ground and ground pin 9 independently? Given a grounded "negative rail", wouldn't pin 9 be referenced to ground either way? It may be that its necessary to reference the "negative supply" to ground AND pin 9 as well for ground loop reasons, but I'd like a confirmation of this.
Thanks as always for help with the basic concepts that any shmuck would know except for me. Had I an extra contract to offer I would, but some relatives just got into town and needed some cash and well, you know the rest...
Kofi
Hi Kofi
electrical theory shows that current will flow in a conductor when there is a potential difference. Potential as in voltage. You have in your valve heaters a potential difference (PD) of 6.3V, i.e one leg of your heaters is at a potential 6.3V higher than the other, hence current will flow in them.
THe absolute voltage becomes referenced to earth when one of the legs is grounded. Therefore if the +ve leg is grounded the heater still has a PD of 6.3V but the -ve side will be -6.3V refernced to earth. If the -ve leg is grounded, as is the convention, then the heater +ve is at 6.3V but there is still a PD of 6.3V across the heater terminals.
Now consider this, if you have the heater supply grounded at the power end, and at the heater pin end, e.g.if you tie to ground the rectifier and connect pin9 to the star point ground at the ouput stage, you will have the heater supply grounded at 2 ground points. BAD IDEA, VERY VERY BAD IDEA
You need to follow the grounding scheme that KYW outlined. The reason is simple, you have currents flowing in wires to the ground points, the current flowing through the ground points will cause a PD because every wire will have some resistance and Ohms law says that current flowing through a resistance will cause a voltage. If that voltage causes a PD at the input stage of the phono amp, or any gain stage, the high gain will amplify it causing hum. It is very important that all currents of each stage are considered, and arranged to cancel out wherever possible, in order to minimise any PD which cause earth loop currents, which cause hum. KYW considered this in the design hence his grounding scheme.
Believe me I'm no expert, but I believe what I've just written is essentially correct and in all these things there is more to be learned. Grounding power supply points, signal points, chassis and mains is a complex but important area of building electronic circuits. Getting it right gives an inky black background to the music, getting it wrong causes hum and hiss.
Kev
electrical theory shows that current will flow in a conductor when there is a potential difference. Potential as in voltage. You have in your valve heaters a potential difference (PD) of 6.3V, i.e one leg of your heaters is at a potential 6.3V higher than the other, hence current will flow in them.
THe absolute voltage becomes referenced to earth when one of the legs is grounded. Therefore if the +ve leg is grounded the heater still has a PD of 6.3V but the -ve side will be -6.3V refernced to earth. If the -ve leg is grounded, as is the convention, then the heater +ve is at 6.3V but there is still a PD of 6.3V across the heater terminals.
Now consider this, if you have the heater supply grounded at the power end, and at the heater pin end, e.g.if you tie to ground the rectifier and connect pin9 to the star point ground at the ouput stage, you will have the heater supply grounded at 2 ground points. BAD IDEA, VERY VERY BAD IDEA
You need to follow the grounding scheme that KYW outlined. The reason is simple, you have currents flowing in wires to the ground points, the current flowing through the ground points will cause a PD because every wire will have some resistance and Ohms law says that current flowing through a resistance will cause a voltage. If that voltage causes a PD at the input stage of the phono amp, or any gain stage, the high gain will amplify it causing hum. It is very important that all currents of each stage are considered, and arranged to cancel out wherever possible, in order to minimise any PD which cause earth loop currents, which cause hum. KYW considered this in the design hence his grounding scheme.
Believe me I'm no expert, but I believe what I've just written is essentially correct and in all these things there is more to be learned. Grounding power supply points, signal points, chassis and mains is a complex but important area of building electronic circuits. Getting it right gives an inky black background to the music, getting it wrong causes hum and hiss.
Kev
Kofi Annan said:
Yup
Kofi Annan said:
The two legs of the filament would still see a voltage across them of 6.3V. What you don't know is what the voltage potential between the filaments and the cathode is. This can be important for hum issues. Say your cathode is sitting a +5v above circuit ground. If you connect the negative filament terminal to ground, the grounded filament end would be at -5v relative (here they come again) to the cathode. The positive ends of the filament would be at +1.3V relative to the cathode (+6.3v - 5V= +1.3v). With AC filament heating, some electrons could flow from the cathode to the filament. So you'd like the entire filament at about 30v or so above the cathode and you'd connect the negative end of the filament supply to a voltage source that is about 30v above the cathode. I don't know how important this is in DC heated filaments, but it couldn't hurt.
Kofi Annan said:
Nope. See above. There would still be 6.3 volts across the filament. However, at least part of the filament (all of it, if the reference voltage were more than 6.3V negative) would be at a negative potential relative (again) to "ground". And since the cathode is usually positive, the filament would be negative relative to the cathode. You usually don't want that.
Kofi Annan said:
It's all relative (not relative(s), as in the case with contracts). Positive and negative in the filament supply just refers to the direction that current will flow in the supply (always goes from negative to positive). If you connect the negative rail of the supply to ground, the other end will be positive relative to ground. If you connect the positive rail of the supply to ground, the other end will be negative relative to ground. Either way, you'd have 6.3v across the filament and it would get hot.
Kofi Annan said:
Correct, you would be referenced to ground. And yes you can do it in such a way as to create ground loops. I don't have the circuit diagram, so can't comment further. Safe bet would be to bring filament supply ground and pin 9 ground to the same point.
Kofi Annan said:
Maybe next time?
Sheldon
Konnichiwa,
Actually, in the case of the Phonostage being discussed it would hurt, unless you use a very large bypass capacitor to ground.
The output valve's cathode is at ground and the Input stage is at around 0.5V and heaters are DC. Referencing the heater negative voltage "hard" to ground is quietest in this type of arrangement.
However, it is essential to limit the connections between heater and audio circuit to a single point and a single connection.
As a reminder for all in this discussion, here the post with the schematic:
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
Sayonara
Sheldon said:
Actually, in the case of the Phonostage being discussed it would hurt, unless you use a very large bypass capacitor to ground.
The output valve's cathode is at ground and the Input stage is at around 0.5V and heaters are DC. Referencing the heater negative voltage "hard" to ground is quietest in this type of arrangement.
However, it is essential to limit the connections between heater and audio circuit to a single point and a single connection.
As a reminder for all in this discussion, here the post with the schematic:
http://www.diyaudio.com/forums/showthread.php?postid=335624#post335624
Sayonara
Thanks for that Kuei. I'm not much further along than Kofi. I couldn't find the schematic earlier.
Sheldon
ps; Kuei if you are still tuned in I have another question (sorry for the thread diversion). Earlier in the thread you mentioned the value of multiple RC cells (as compared to LC) for pre-amp power supplies. I assume the same might apply for low power single ended amps, at least at very low power. Any thoughts as to final cap size vs bias current (or whatever would be the controlling variables)?
Sheldon
ps; Kuei if you are still tuned in I have another question (sorry for the thread diversion). Earlier in the thread you mentioned the value of multiple RC cells (as compared to LC) for pre-amp power supplies. I assume the same might apply for low power single ended amps, at least at very low power. Any thoughts as to final cap size vs bias current (or whatever would be the controlling variables)?
Being the King of Bad Ideas, I might have expected this. One issue, however:
Since the PSU will be in another enclosure entirely, I initially thought that I would just ground the PSU in its enclosure and only bring over the B+ and the filament supply, leaving the grounds in the PSU box.
I was corrected, however, by KYW. He advised that the I should pass the ground references over from the PSU box to the phono stage box. It only dawns on me now that it seems I should not ground the PSU or the filament in the PSU box. I should merely PASS the grounds from the PSU box to the phono stage box and ground them according to KYW's grounding scheme in the phono box only.
Is this right? Well, of course it isn't right, Kofi. But tell me why it isn't right and maybe I'll learn something.
Maybe.
Kofi
Konnichiwa,
First, both LC and RC and mixed LCRC supplies can be used to provide whatever ripple rejection and supply impedance are needed.
LC Filters invariably include significant resonances, which can make them problematic if you cannot use the exact parts used during tuning.
With RC supplies you have no resonance but the supplies DCR becomes significant which is a problem for stages with varying supply current demands.
A nice item of the RC supply is that the phase of the hum remaining is such that you can use a "badly filtered" +B to cancel AC heated DHT's hum.
The final filter capacitor is best considered as coupling capacitor for the load, that then sets the minimum required.
Sayonara
Sheldon said:
First, both LC and RC and mixed LCRC supplies can be used to provide whatever ripple rejection and supply impedance are needed.
LC Filters invariably include significant resonances, which can make them problematic if you cannot use the exact parts used during tuning.
With RC supplies you have no resonance but the supplies DCR becomes significant which is a problem for stages with varying supply current demands.
A nice item of the RC supply is that the phase of the hum remaining is such that you can use a "badly filtered" +B to cancel AC heated DHT's hum.
The final filter capacitor is best considered as coupling capacitor for the load, that then sets the minimum required.
Sayonara
Konnichiwa,
Yup, thta is recommended. You do need the Earth connection (via antiparallel diodes) somewhere in your phonostage, but at the same time you need all metal chassis parts linked with very low impedance, so all of the phonostage and PSU case need to be earthed but the signal circuit MUST not make any electrical contact with the case EXCEPT at the star ground via our diodes and possibly a 100 Ohm resistor (may be made switchable).
Implemented like this you are both safe and avoid hum.
Sayonara
Kofi Annan said:
Yup, thta is recommended. You do need the Earth connection (via antiparallel diodes) somewhere in your phonostage, but at the same time you need all metal chassis parts linked with very low impedance, so all of the phonostage and PSU case need to be earthed but the signal circuit MUST not make any electrical contact with the case EXCEPT at the star ground via our diodes and possibly a 100 Ohm resistor (may be made switchable).
Implemented like this you are both safe and avoid hum.
Sayonara
Wait, wait, wait...
The AC from the wall will be coming in to the PSU box and NOT
the phono stage. If I need to have an "Earth" ground point in the
phonostage box, then won't I need to run an additional "Earth" wire from
the PSU box to the phono stage box?
In other words, if I need to connect the Earth ground (third
prong on the three-prong receptacle) to the phono stage chassis and the
Earth ground will only be in the PSU box, then don't I have to bring the
Earth ground from the PSU box into the phono stage box and ground it to
the phono stage chassis via anti-parallel diodes?
Every time I think I understand this...
Kofi
The AC from the wall will be coming in to the PSU box and NOT
the phono stage. If I need to have an "Earth" ground point in the
phonostage box, then won't I need to run an additional "Earth" wire from
the PSU box to the phono stage box?
In other words, if I need to connect the Earth ground (third
prong on the three-prong receptacle) to the phono stage chassis and the
Earth ground will only be in the PSU box, then don't I have to bring the
Earth ground from the PSU box into the phono stage box and ground it to
the phono stage chassis via anti-parallel diodes?
Every time I think I understand this...
Kofi
You need to bond the incoming earth wire to the power supply chassis for safety. You then need to connect the 2 chassis together electrically. This is then the earth bonding point in the amp chassis that you connect the "69" diodes to.
The wire that connects the 2 chassis together should be at least the same gauge as the earth wire in the power cord and needs to make good electrical connections at both ends.
Kev
The wire that connects the 2 chassis together should be at least the same gauge as the earth wire in the power cord and needs to make good electrical connections at both ends.
Kev
Konnichiwa,
Yes, I tend to use 4 length of coaxial cable (solid core copper conductor - usually RG223) to cary the heater and +B voltages and returns. The screens of these are the earth conductor.
The way this works is based on two principles:
1) Electrical safety demands that all exposed metal parts of a mains powered device are either strongly insulated (safety insulated - don't even go there with DIY Gear) from the mains or that they are earthed via a low resistance connection.
2) Hum free and good sound require no or as little as possible connection to earth from the signal circuit EXCEPT at the Power Amplifier.
By linking phonostage chassis, umbilical cable screen and the PSU Box to the earth terminal we make sure you and Mrs. Annan are safe from electrocution.
By linking the Phonostage chassis via anti-parallel diodes to the signal circuit we keep the siignal circuit first of all screened but secondly disconnected from the earth until fault voltages reac around 0.5V (if they do - worry). Adding 100 Ohm in parallel with the diodes makes sure the signal circuit still has a good earth reference IF it is used entierely with safety insulated gear.
The other option would be to tie the phonostage chassis to signal ground and place the anti parallel diodes in the Powersupply case. Both approaches make sense.
It is easy, just think what current flows where and via what path (including unwanted, parasitical currents) and design your current loops to keep the "good" (signal) currents away from the bad (parasitic, PSU currents) as much as possible while remaining within the mains safety code.
Sayonara
Kofi Annan said:
Yes, I tend to use 4 length of coaxial cable (solid core copper conductor - usually RG223) to cary the heater and +B voltages and returns. The screens of these are the earth conductor.
Kofi Annan said:
The way this works is based on two principles:
1) Electrical safety demands that all exposed metal parts of a mains powered device are either strongly insulated (safety insulated - don't even go there with DIY Gear) from the mains or that they are earthed via a low resistance connection.
2) Hum free and good sound require no or as little as possible connection to earth from the signal circuit EXCEPT at the Power Amplifier.
By linking phonostage chassis, umbilical cable screen and the PSU Box to the earth terminal we make sure you and Mrs. Annan are safe from electrocution.
By linking the Phonostage chassis via anti-parallel diodes to the signal circuit we keep the siignal circuit first of all screened but secondly disconnected from the earth until fault voltages reac around 0.5V (if they do - worry). Adding 100 Ohm in parallel with the diodes makes sure the signal circuit still has a good earth reference IF it is used entierely with safety insulated gear.
The other option would be to tie the phonostage chassis to signal ground and place the anti parallel diodes in the Powersupply case. Both approaches make sense.
Kofi Annan said:
It is easy, just think what current flows where and via what path (including unwanted, parasitical currents) and design your current loops to keep the "good" (signal) currents away from the bad (parasitic, PSU currents) as much as possible while remaining within the mains safety code.
Sayonara
OK, so let's see if I got it this time:
PSU box:
Earth grounded (third prong of 3-prong plug tied to chassis), and the B+ and filament negative supply are NOT grounded in the PSU box, but passed to the phono stage box.
Per your advice, Kuei, I am using a 4-prong Speak-on connector to pass the B+, filament, and both grounds to the phono stage. Since there are no more available ports on the Speak-on, I will need to pass the Earth separately.
Phono stage box:
Accepts the B+ supply and ground, the filament positive and negative supply and the Earth ground. The B+ and filament negative are tied to the second stage star ground and the Earth ground is attached to the chassis.
Is the signal ground also attached to the chassis and then attached to the Earth ground location with the anti-parallel diodes? This doesn't sound right-- it sounds more like I should have the signal ground from the phono stage insulated from the chassis and the insulated signal ground attached to the Earth ground via anti-parallel diodes.
Wow. There's so many ways I could be wrong here. Just pick a few and let me know why I can't get this through my thick skull.
Kofi
PSU box:
Earth grounded (third prong of 3-prong plug tied to chassis), and the B+ and filament negative supply are NOT grounded in the PSU box, but passed to the phono stage box.
Per your advice, Kuei, I am using a 4-prong Speak-on connector to pass the B+, filament, and both grounds to the phono stage. Since there are no more available ports on the Speak-on, I will need to pass the Earth separately.
Phono stage box:
Accepts the B+ supply and ground, the filament positive and negative supply and the Earth ground. The B+ and filament negative are tied to the second stage star ground and the Earth ground is attached to the chassis.
Is the signal ground also attached to the chassis and then attached to the Earth ground location with the anti-parallel diodes? This doesn't sound right-- it sounds more like I should have the signal ground from the phono stage insulated from the chassis and the insulated signal ground attached to the Earth ground via anti-parallel diodes.
Wow. There's so many ways I could be wrong here. Just pick a few and let me know why I can't get this through my thick skull.
Kofi
Konnichiwa,
In that case ground the phonostage chassis at the signal circuit star ground. Make sure the negative +B wire has a good deal of crossection.
PSU Box is connected to mains earth. Place the diodes (and switch and 100R resistor) into the PSU Box (between case and negative line of +B). Heaters remain completely floating except for one connection to signal star ground from the heater negative wire.
Sayonara
Kofi Annan said:
In that case ground the phonostage chassis at the signal circuit star ground. Make sure the negative +B wire has a good deal of crossection.
PSU Box is connected to mains earth. Place the diodes (and switch and 100R resistor) into the PSU Box (between case and negative line of +B). Heaters remain completely floating except for one connection to signal star ground from the heater negative wire.
Sayonara
Do you mean use a nice, thick 10AWG wire for the B+ ground in the phono stage box?
Wait-- I know the PSU box will be earthed, but how do the diodes work here? I thought I would go AC to switch to fuse to diodes to chassis. Now it sounds like I should involve the B+ ground / negative somehow? I thought I would just pass the B+ negative / ground to the phono stage chassis and ground it there.
Go that one. I got it... but should I still connect the chassiseseses of the PSU box and the phono stage box together? Sounds like I should for safety reasons.
Well... you always think you're done answering questions, but I'm like the perpetual damsel in distress. You can also think of me as the mildly-retarded character in "Of Mice and Men", if you'd like a literary allegory.
Hey Lenny! Uhhh... what's a ground?!?
Kofi
Konnichiwa,
I'd say > 16 Gauge. 10 Gauge may be excessive.
NO. ABSOLUTELY NOT.
I think this either needs drawing out or you need to start to follow my command "think where the current will flow".
Remember, current flows always in closed loops. In your Phonostage you have the loop involving the heater supply positive and negative line, the loop involving the high tension (+B) supply positive and negative line, the loops involving signal and signal-return (often falsely called "ground") per channel one each for input and output and actually a third interstage one and finally a parasitary earth loop involving the eatrh connection which is needed for electrical safety.
Each loop should be as seperate as possible, so the good elite (and imaginary) electrons from our signal don't get associated with the peopn worker electrons in the powersupply and so that both are kept away from the criminal elements in the earth loop.
Basically, for electrons we definitly want "Apartheit".
Hence each current loop is kept fully separate.
But in order to make sure everything is solidly referenced to the same place we connect signal return, heater supply return (negative heater line) and power supply return (negative HT line) together at the "star-ground".
Observe that although each current loop is joined to the star-ground ideally no current flows into or out of the starground but all are contained in their own respective loops.
Finally, as we do not have a seperate earth connector in our Neutrik speakon we need to make the earth connection somehow. We now tie the Phonostage chassis also to the star ground.
In the powersupply case the case is connected directly to earth (more preciceley the PEN - Protecteive Earth Neutral) but heater and HT supplies are NOT connected anywhere, EXCEPT for the back to back diodes which link the HT negative line and chassis.
What this does is to keep the earth connection in effect disconnected from the HT supply if the difference in potential is small, so the earth loop normally introduced is in effect broken.
I hope this helps, if not, please draw out what I have written above on paper and try to get your head around it.... It is not that difficult really.
Ciao T
Kofi Annan said:
I'd say > 16 Gauge. 10 Gauge may be excessive.
Kofi Annan said:
NO. ABSOLUTELY NOT.
I think this either needs drawing out or you need to start to follow my command "think where the current will flow".
Remember, current flows always in closed loops. In your Phonostage you have the loop involving the heater supply positive and negative line, the loop involving the high tension (+B) supply positive and negative line, the loops involving signal and signal-return (often falsely called "ground") per channel one each for input and output and actually a third interstage one and finally a parasitary earth loop involving the eatrh connection which is needed for electrical safety.
Each loop should be as seperate as possible, so the good elite (and imaginary) electrons from our signal don't get associated with the peopn worker electrons in the powersupply and so that both are kept away from the criminal elements in the earth loop.
Basically, for electrons we definitly want "Apartheit".
Hence each current loop is kept fully separate.
But in order to make sure everything is solidly referenced to the same place we connect signal return, heater supply return (negative heater line) and power supply return (negative HT line) together at the "star-ground".
Observe that although each current loop is joined to the star-ground ideally no current flows into or out of the starground but all are contained in their own respective loops.
Finally, as we do not have a seperate earth connector in our Neutrik speakon we need to make the earth connection somehow. We now tie the Phonostage chassis also to the star ground.
In the powersupply case the case is connected directly to earth (more preciceley the PEN - Protecteive Earth Neutral) but heater and HT supplies are NOT connected anywhere, EXCEPT for the back to back diodes which link the HT negative line and chassis.
What this does is to keep the earth connection in effect disconnected from the HT supply if the difference in potential is small, so the earth loop normally introduced is in effect broken.
I hope this helps, if not, please draw out what I have written above on paper and try to get your head around it.... It is not that difficult really.
Ciao T
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