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Ground Busses
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/210_3470585/NF2D-B-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
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/210_3470585/NF2D-B-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
Re: 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/210 3470585/NF2D-B-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
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/210 3470585/NF2D-B-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
Re: Ground Busses
"Patrick Turner" <info@turneraudio,com .au> wrote in message
news:47CAAC99.9BE36341@turneraudio,com .au...
>
>
> 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
"Patrick Turner" <info@turneraudio,com .au> wrote in message
news:47CAAC99.9BE36341@turneraudio,com .au...
>
>
> 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
Re: Ground Busses
Iain Churches wrote:
>
> "Patrick Turner" <info@turneraudio,com .au> wrote in message
> news:47CAAC99.9BE36341@turneraudio,com .au...
> >
> >
> > 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?
I said 5W, but 25W would be OK.
Because you don't want that R to go open, ever, or the whole audio
circuit
IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
important.
If the B+ becomes shorted to the chassis, you want the fuse to blow
because of that short.
You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
the 0V rail at +500V,
including the OV rail and the speaker wires....
Hope for the best with your amps, but ALWAYS prepare for the worst!
Patrick Turner.
>
> Iain
Iain Churches wrote:
>
> "Patrick Turner" <info@turneraudio,com .au> wrote in message
> news:47CAAC99.9BE36341@turneraudio,com .au...
> >
> >
> > 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?
I said 5W, but 25W would be OK.
Because you don't want that R to go open, ever, or the whole audio
circuit
IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
important.
If the B+ becomes shorted to the chassis, you want the fuse to blow
because of that short.
You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
the 0V rail at +500V,
including the OV rail and the speaker wires....
Hope for the best with your amps, but ALWAYS prepare for the worst!
Patrick Turner.
>
> Iain
Re: Ground Busses
In article <47CBC937.D899D5B8@turneraudio,com .au>,
Patrick Turner <info@turneraudio,com .au> wrote:
> Iain Churches wrote:
> >
> > And why 25W?
>
> I said 5W, but 25W would be OK.
>
> Because you don't want that R to go open, ever, or the whole audio
> circuit
> IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
> important.
>
> If the B+ becomes shorted to the chassis, you want the fuse to blow
> because of that short.
> You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
> the 0V rail at +500V,
> including the OV rail and the speaker wires....
I am having trouble getting my mind around this. I am standing on my
head trying to get a good perspective on the question. Wouldn't it be
-500V on the "OV rail and the speaker wires" if the B+ shorted to the
chassis, or does it just look that way to me because I am standing on my
head?
Regards,
John Byrns
--
Surf my web pages at, http :// fmamradios,com /
In article <47CBC937.D899D5B8@turneraudio,com .au>,
Patrick Turner <info@turneraudio,com .au> wrote:
> Iain Churches wrote:
> >
> > And why 25W?
>
> I said 5W, but 25W would be OK.
>
> Because you don't want that R to go open, ever, or the whole audio
> circuit
> IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
> important.
>
> If the B+ becomes shorted to the chassis, you want the fuse to blow
> because of that short.
> You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
> the 0V rail at +500V,
> including the OV rail and the speaker wires....
I am having trouble getting my mind around this. I am standing on my
head trying to get a good perspective on the question. Wouldn't it be
-500V on the "OV rail and the speaker wires" if the B+ shorted to the
chassis, or does it just look that way to me because I am standing on my
head?
Regards,
John Byrns
--
Surf my web pages at, http :// fmamradios,com /
Re: Ground Busses
John Byrns wrote:
> Patrick Turner <info@turneraudio,com .au> wrote:
> > Iain Churches wrote:
> > >
> > > And why 25W?
> >
> > I said 5W, but 25W would be OK.
> >
> > Because you don't want that R to go open, ever, or the whole audio
> > circuit
> > IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
> > important.
> >
> > If the B+ becomes shorted to the chassis, you want the fuse to blow
> > because of that short.
> > You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
> > the 0V rail at +500V,
> > including the OV rail and the speaker wires....
>
> I am having trouble getting my mind around this. I am standing on my
> head trying to get a good perspective on the question. Wouldn't it be
> -500V on the "OV rail and the speaker wires" if the B+ shorted to the
> chassis, or does it just look that way to me because I am standing on my
> head?
You are correct.
Graham
John Byrns wrote:
> Patrick Turner <info@turneraudio,com .au> wrote:
> > Iain Churches wrote:
> > >
> > > And why 25W?
> >
> > I said 5W, but 25W would be OK.
> >
> > Because you don't want that R to go open, ever, or the whole audio
> > circuit
> > IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
> > important.
> >
> > If the B+ becomes shorted to the chassis, you want the fuse to blow
> > because of that short.
> > You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
> > the 0V rail at +500V,
> > including the OV rail and the speaker wires....
>
> I am having trouble getting my mind around this. I am standing on my
> head trying to get a good perspective on the question. Wouldn't it be
> -500V on the "OV rail and the speaker wires" if the B+ shorted to the
> chassis, or does it just look that way to me because I am standing on my
> head?
You are correct.
Graham
Re: Ground Busses
John Byrns wrote:
>
> In article <47CBC937.D899D5B8@turneraudio,com .au>,
> Patrick Turner <info@turneraudio,com .au> wrote:
>
> > Iain Churches wrote:
> > >
> > > And why 25W?
> >
> > I said 5W, but 25W would be OK.
> >
> > Because you don't want that R to go open, ever, or the whole audio
> > circuit
> > IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
> > important.
> >
> > If the B+ becomes shorted to the chassis, you want the fuse to blow
> > because of that short.
> > You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
> > the 0V rail at +500V,
> > including the OV rail and the speaker wires....
>
> I am having trouble getting my mind around this. I am standing on my
> head trying to get a good perspective on the question. Wouldn't it be
> -500V on the "OV rail and the speaker wires" if the B+ shorted to the
> chassis, or does it just look that way to me because I am standing on my
> head?
>
> Regards,
>
> John Byrns
Indeed you are right, but if the 27R went open, and B+ shorted to the
chassis, then the chassis would try to go +ve, and 0V rail and speakers
etc would try to go
very negative. BUT, if you had a preamp attatched, with coaxial RCA
cable connecting the power amp 0V to preamp 0V, and there was a similar
27 ohms in the preamp
to its chassis and Earth, then the preamp's "ground lifting resistance"
of 27ohms
might also fuse open, and you'd get a high -Ve voltage at the RCA 0V
terminal and speakers
so if you touched this or speakers and the chassis which IS at earth
potential,
you'd get a bad shock.
So hence the need for the ground lift R to be rugged enough so when such
a B+ to ground short
occurs, a mains fuse will blow because of the low load on the power
supply.
Its very unlikely you'd ever get the B+ shorting to the chassis.
Its much more likely that a B+ short to 0V would occur, through a
stuffed output tube,
or from P to S on the OPT, or from an arc across from pin 3 to pin 2 on
octal sockets.
So its likely that the 27R isn't ever exposed to a sudden amount of high
current.
But shit happens, so prepare for it.
The point I was making is that all chassis should be well connected to
EARTH,
and then if ground lift between chassis and 0V rail is the standard way
to lower noise,
then for safety use a high wattage low value
ground lift R which still has MUCH more resistance than the coax outer
shield of an interconnect
to some other component such as preamp or cd player, tuner etc.
Patrick Turner.
> --
> Surf my web pages at, http :// fmamradios,com /
John Byrns wrote:
>
> In article <47CBC937.D899D5B8@turneraudio,com .au>,
> Patrick Turner <info@turneraudio,com .au> wrote:
>
> > Iain Churches wrote:
> > >
> > > And why 25W?
> >
> > I said 5W, but 25W would be OK.
> >
> > Because you don't want that R to go open, ever, or the whole audio
> > circuit
> > IS NOT REFERENCED TO THE CHASSIS AND EARTH, something I feel is
> > important.
> >
> > If the B+ becomes shorted to the chassis, you want the fuse to blow
> > because of that short.
> > You DON'T want a 27 ohm x 1/4 watt R to fuse open in an instant, leaving
> > the 0V rail at +500V,
> > including the OV rail and the speaker wires....
>
> I am having trouble getting my mind around this. I am standing on my
> head trying to get a good perspective on the question. Wouldn't it be
> -500V on the "OV rail and the speaker wires" if the B+ shorted to the
> chassis, or does it just look that way to me because I am standing on my
> head?
>
> Regards,
>
> John Byrns
Indeed you are right, but if the 27R went open, and B+ shorted to the
chassis, then the chassis would try to go +ve, and 0V rail and speakers
etc would try to go
very negative. BUT, if you had a preamp attatched, with coaxial RCA
cable connecting the power amp 0V to preamp 0V, and there was a similar
27 ohms in the preamp
to its chassis and Earth, then the preamp's "ground lifting resistance"
of 27ohms
might also fuse open, and you'd get a high -Ve voltage at the RCA 0V
terminal and speakers
so if you touched this or speakers and the chassis which IS at earth
potential,
you'd get a bad shock.
So hence the need for the ground lift R to be rugged enough so when such
a B+ to ground short
occurs, a mains fuse will blow because of the low load on the power
supply.
Its very unlikely you'd ever get the B+ shorting to the chassis.
Its much more likely that a B+ short to 0V would occur, through a
stuffed output tube,
or from P to S on the OPT, or from an arc across from pin 3 to pin 2 on
octal sockets.
So its likely that the 27R isn't ever exposed to a sudden amount of high
current.
But shit happens, so prepare for it.
The point I was making is that all chassis should be well connected to
EARTH,
and then if ground lift between chassis and 0V rail is the standard way
to lower noise,
then for safety use a high wattage low value
ground lift R which still has MUCH more resistance than the coax outer
shield of an interconnect
to some other component such as preamp or cd player, tuner etc.
Patrick Turner.
> --
> Surf my web pages at, http :// fmamradios,com /
Re: Ground Busses
On Mar 2, 8:33 am, Patrick Turner <i...@turneraudio,com .au> 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
On Mar 2, 8:33 am, Patrick Turner <i...@turneraudio,com .au> 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
Re: Ground Busses
"Peter Wieck" <pfjw@aol,com > wrote in message
news:7bc45853-7ac6-419c-91bc-24e786a53a91@s37g2000prg.googlegroups,com ...
On Mar 2, 8:33 am, Patrick Turner <i...@turneraudio,com .au> 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
Most books seem to stress this, and the amp builders
I have know seem to have always paid particular attention to it.
It is critical for safety.
> b) The circuit ground should be separate and isolated from the chassis/
> case, connected via the 27ohm@5W resistor.
I have seen boards in a setero amp with the grounds separated
by a 10 Ohm resistor, but this is the first time I recall hearing about
this excellent 27 Ohm 5W solution. I would like to try it.
c) The circuit ground should be as short as possible and loops (such
as connecting signal-shields at both ends) are to be avoided.
A friend of mine in the UK was I was young was a prototype
wireman. He used to make up all sort of interesting circuits for
the studio where he worked. He taught me that the input wirirng
should be grounded at the input connector (connector isolated
from the chassis)
> 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).
There seem to be several ways to build a quiet hum-free amp.
Most people seem to be happy with an amplifier with no hum
or hiss audible from the listening position. With careful work,
it is possible to build an amplifier which is dead silent even with
your ear against the speaker.
http :// www .kolumbus.fi/iain.churches/Pics/HomeAudioSystem/C50_002.jpg
Regards to all
Iain
"Peter Wieck" <pfjw@aol,com > wrote in message
news:7bc45853-7ac6-419c-91bc-24e786a53a91@s37g2000prg.googlegroups,com ...
On Mar 2, 8:33 am, Patrick Turner <i...@turneraudio,com .au> 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
Most books seem to stress this, and the amp builders
I have know seem to have always paid particular attention to it.
It is critical for safety.
> b) The circuit ground should be separate and isolated from the chassis/
> case, connected via the 27ohm@5W resistor.
I have seen boards in a setero amp with the grounds separated
by a 10 Ohm resistor, but this is the first time I recall hearing about
this excellent 27 Ohm 5W solution. I would like to try it.
c) The circuit ground should be as short as possible and loops (such
as connecting signal-shields at both ends) are to be avoided.
A friend of mine in the UK was I was young was a prototype
wireman. He used to make up all sort of interesting circuits for
the studio where he worked. He taught me that the input wirirng
should be grounded at the input connector (connector isolated
from the chassis)
> 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).
There seem to be several ways to build a quiet hum-free amp.
Most people seem to be happy with an amplifier with no hum
or hiss audible from the listening position. With careful work,
it is possible to build an amplifier which is dead silent even with
your ear against the speaker.
http :// www .kolumbus.fi/iain.churches/Pics/HomeAudioSystem/C50_002.jpg
Regards to all
Iain
Re: Ground Busses
Iain Churches wrote:
> "Peter Wieck" <pfjw@aol,com > 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
But it doesn't have to be if your transformer and other mains wiring meets
Class II.
Bear in mind that safety earthing isn't universal even in Europe. I gather
that Denmark ? in particular has many unearthed outlets.
Graham
Iain Churches wrote:
> "Peter Wieck" <pfjw@aol,com > 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
But it doesn't have to be if your transformer and other mains wiring meets
Class II.
Bear in mind that safety earthing isn't universal even in Europe. I gather
that Denmark ? in particular has many unearthed outlets.
Graham
Re: Ground Busses
In article <47CD538F.E19AE3A2@hotmail,com >,
Eeyore <rabbitsfriendsandrelations@hotmail,com > wrote:
> Iain Churches wrote:
>
> > "Peter Wieck" <pfjw@aol,com > 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
>
> But it doesn't have to be if your transformer and other mains wiring meets
> Class II.
>
> Bear in mind that safety earthing isn't universal even in Europe. I gather
> that Denmark ? in particular has many unearthed outlets.
What does Europe have to do with this issue, I thought that the presence
of "safety earthing", or lack thereof, was mostly an issue of how old
the building is, or are you saying that in Europe there was a directive
that all outlets without "safety earthing" must be upgraded?
Regards,
John Byrns
--
Surf my web pages at, http :// fmamradios,com /
In article <47CD538F.E19AE3A2@hotmail,com >,
Eeyore <rabbitsfriendsandrelations@hotmail,com > wrote:
> Iain Churches wrote:
>
> > "Peter Wieck" <pfjw@aol,com > 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
>
> But it doesn't have to be if your transformer and other mains wiring meets
> Class II.
>
> Bear in mind that safety earthing isn't universal even in Europe. I gather
> that Denmark ? in particular has many unearthed outlets.
What does Europe have to do with this issue, I thought that the presence
of "safety earthing", or lack thereof, was mostly an issue of how old
the building is, or are you saying that in Europe there was a directive
that all outlets without "safety earthing" must be upgraded?
Regards,
John Byrns
--
Surf my web pages at, http :// fmamradios,com /
Re: Ground Busses
John Byrns wrote:
> What does Europe have to do with this issue
Most of us live here !
Graham
John Byrns wrote:
> What does Europe have to do with this issue
Most of us live here !
Graham
Re: Ground Busses
On Mar 4, 8:24 am, "Iain Churches" <Iai...@kolumbus.fi> wrote:
> With careful work,
> it is possible to build an amplifier which is dead silent even with
> your ear against the speaker.
Aren't they all supposed to be that way?
Peter Wieck
Wyncote, PA
On Mar 4, 8:24 am, "Iain Churches" <Iai...@kolumbus.fi> wrote:
> With careful work,
> it is possible to build an amplifier which is dead silent even with
> your ear against the speaker.
Aren't they all supposed to be that way?
Peter Wieck
Wyncote, PA
Re: Ground Busses
"Peter Wieck" <pfjw@aol,com > wrote in message
news:7d131625-6278-4a3b-ad84-79afd71d91db@s19g2000prg.googlegroups,com ...
On Mar 4, 8:24 am, "Iain Churches" <Iai...@kolumbus.fi> wrote:
>> With careful work,
>> it is possible to build an amplifier which is dead silent even with
>> your ear against the speaker.
> Aren't they all supposed to be that way
Indeed they are "supposed" to be.
Iain
"Peter Wieck" <pfjw@aol,com > wrote in message
news:7d131625-6278-4a3b-ad84-79afd71d91db@s19g2000prg.googlegroups,com ...
On Mar 4, 8:24 am, "Iain Churches" <Iai...@kolumbus.fi> wrote:
>> With careful work,
>> it is possible to build an amplifier which is dead silent even with
>> your ear against the speaker.
> Aren't they all supposed to be that way
Indeed they are "supposed" to be.
Iain
Re: Ground Busses
"Iain Churches" <IainNG@kolumbus.fi> wrote in message
news:D5fzj.306080$6m3.178365@reader1.news.saunalahti.fi...
>
>
> "Peter Wieck" <pfjw@aol,com > wrote in message
> news:7d131625-6278-4a3b-ad84-79afd71d91db@s19g2000prg.googlegroups,com ...
> On Mar 4, 8:24 am, "Iain Churches" <Iai...@kolumbus.fi> wrote:
>
>>> With careful work,
>>> it is possible to build an amplifier which is dead silent even with
>>> your ear against the speaker.
>
>> Aren't they all supposed to be that way
>
> Indeed they are "supposed" to be.
> Iain
PS I recently saw an "English language manual" for a
Chinese amp. It was a single sheet of folded A4)
At the bottom of the page it said:
"There may be some, but not considerable humble from the
loodspeaker".
There was indeed "considerable humble from the loodspeaker"
at both 50 and 100Hz.
Iain
"Iain Churches" <IainNG@kolumbus.fi> wrote in message
news:D5fzj.306080$6m3.178365@reader1.news.saunalahti.fi...
>
>
> "Peter Wieck" <pfjw@aol,com > wrote in message
> news:7d131625-6278-4a3b-ad84-79afd71d91db@s19g2000prg.googlegroups,com ...
> On Mar 4, 8:24 am, "Iain Churches" <Iai...@kolumbus.fi> wrote:
>
>>> With careful work,
>>> it is possible to build an amplifier which is dead silent even with
>>> your ear against the speaker.
>
>> Aren't they all supposed to be that way
>
> Indeed they are "supposed" to be.
> Iain
PS I recently saw an "English language manual" for a
Chinese amp. It was a single sheet of folded A4)
At the bottom of the page it said:
"There may be some, but not considerable humble from the
loodspeaker".
There was indeed "considerable humble from the loodspeaker"
at both 50 and 100Hz.
Iain
