On Mon, 18 Apr 2005 19:17:01 -0500, (John Byrns) wrote:

The Subject line says it all.

It says only that you have a vivid imagination. Your basic premise,
that hum is lowered by negative feedback, is utterly laughable since
you refuse to use the standard input-related measure.

Your need to twist this idiocy into a personal attack on me shows the
weakness of your position. Pathetic................

--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article , Stewart Pinkerton
wrote:

On Mon, 18 Apr 2005 19:17:01 -0500, (John Byrns) wrote:

The Subject line says it all.

It says only that you have a vivid imagination. Your basic premise,
that hum is lowered by negative feedback, is utterly laughable since
you refuse to use the standard input-related measure.

I don't refuse to use the standard input-related measure, I pointed out
that if you do the sums you will find that except in pathological cases
the only input-related measure that matters is that related to the input
stage of the preamp. You have so far been unable to refute that
contention. You also seem to have limited experience designing and
building real world amplifiers, or you would have long ago noticed that
negative feedback around a power amplifier with marginal power supply
filtering does indeed reduce the hum level heard from the speaker,
although as you say it doesn't so anything for the noise generated by the
input stage of the preamp. Get your nose out of the text books and try it
sometime.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

On Tue, 19 Apr 2005 10:31:28 -0500, (John Byrns) wrote:

In article , Stewart Pinkerton
wrote:

On Mon, 18 Apr 2005 19:17:01 -0500, (John Byrns) wrote:

The Subject line says it all.

It says only that you have a vivid imagination. Your basic premise,
that hum is lowered by negative feedback, is utterly laughable since
you refuse to use the standard input-related measure.

I don't refuse to use the standard input-related measure, I pointed out
that if you do the sums you will find that except in pathological cases
the only input-related measure that matters is that related to the input
stage of the preamp.

Irrelevant, if you're claiming as you did, that NFB reduces the hum
*in a power amp*. Basically, you're just ducking and diving rather
than admit you were flat-out wrong.

You have so far been unable to refute that
contention.

I haven't even tried, since your argument was so pathetic. Power amps
are conventionally designed with nominal input voltages of 1-2 volts
rms for full output, matching nominal preamp output voltages. You are
attempting to score a cheap point by completely altering that
industry-standard gain division - and for no good reason whatever.

You also seem to have limited experience designing and
building real world amplifiers, or you would have long ago noticed that
negative feedback around a power amplifier with marginal power supply
filtering does indeed reduce the hum level heard from the speaker,
although as you say it doesn't so anything for the noise generated by the
input stage of the preamp. Get your nose out of the text books and try it
sometime.

I've designed and built something like fifteen audio power amps, and
none of them had any problems with hum. Having also been a
professional analogue electronics designer for some thirty years, I
suspect that I know rather more than you about the real-world effects
of various circuit configurations. Try reading some of those text
books sometime...............
--

Stewart Pinkerton | Music is Art - Audio is Engineering

In article , Stewart Pinkerton
wrote:

On Tue, 19 Apr 2005 10:31:28 -0500, (John Byrns) wrote:

In article , Stewart Pinkerton
wrote:

On Mon, 18 Apr 2005 19:17:01 -0500, (John Byrns) wrote:

The Subject line says it all.

It says only that you have a vivid imagination. Your basic premise,
that hum is lowered by negative feedback, is utterly laughable since
you refuse to use the standard input-related measure.

I don't refuse to use the standard input-related measure, I pointed out
that if you do the sums you will find that except in pathological cases
the only input-related measure that matters is that related to the input
stage of the preamp.

Irrelevant, if you're claiming as you did, that NFB reduces the hum
*in a power amp*. Basically, you're just ducking and diving rather
than admit you were flat-out wrong.

On the contrary, it is you who are bobbing and weaving, considering that
you haven't offered a single bit of evidence to refute my empirically
verified statement that negative feedback reduces the hum in the output of
an audio power amplifier caused by inadequate filtering of the power
supply feeding the driver stage.

Let me give you an example, and you can tell me what is wrong with my
figuring. Let's take an amplifier like your zero NFB "KISASS", with a
maximum output capability of say 12.5 Watts into 8 Ohms. Let's further
assume that the 12.5 Watt output is delivered with an input of 1 volt.
This gives us a voltage gain of 10x for the amplifier from input to
output. Now let's assume that the input referenced noise level of this
amplifier is 5 uV with a perfectly noiseless power supply. The output
noise level at the speaker terminals will be about 50 uV under this
condition.

So far so good, now let's introduce enough power supply ripple into the
driver stage to create 4 mV of hum at the speaker terminals as with your
"KISASS". This 4 mV of hum in the output translates to 0.4 mV of hum when
referenced to the input. Suddenly the input referenced noise level of our
amplifier has jumped from 5 uV to more than 400 uV, a noise increase of 38
dB, due to poor power supply filtering, and unrelated to the inherent
noise level of the input circuit and the first transistor.

Now assume we find this level of hum offensive with our particular
speakers, which are moderately efficient, what can we do? Let's first add
an additional stage configured for a voltage gain of let's say 10x
following the first stage, and using the same transistor as the first
stage. Assuming there is a fair amount of gain in the first stage, the
noise added by the additional stage will be swamped, and we will be left
with an input referenced noise level of close to the original 5 uV, with a
perfectly filtered power supply. The noise level at the speaker output
terminals will now increase from 50 uV to 500 uV due to the increased gain
of the amplifier.

Now lets hook the driver stage up to the inadequately filtered power
supply again and see what we get. The hum in the output will still be 4
mV because the hum was injected at a point in the circuit down stream of
the added gain. The input referenced hum voltage has now decreased from
400 uV to 40 uV because of the increased gain. The input referenced noise
due to the power supply ripple is now only 18 dB greater than the noise
due to the input circuit. The total noise power at the input will be the
RMS value of the sum of the two noise sources, but since we are concerned
with only the hum here, and since the input circuit noise is still 18 dB
lower by measurement, although perhaps not subjectively, we will continue
ignoring the actual input circuit noise, other than to use it as a
reference.

OK, what have we accomplished, we have an amplifier that still has 4 mV of
hum in the output, but has 10 times more gain than the original amplifier
had, and than we wanted, so what to do? Let's put a negative feedback
loop around the amplifier, with enough feedback to reduce the gain to the
original value of 10x voltage gain. But what else happens? Like magic
the hum voltage at the speaker terminals drops from 4 mV to about 0.4 mV,
while the input referenced hum voltage remains at 40 uV. The hum
emanating from the speakers is now tolerable, and all is well with the
world.

So assuming I didn't make any typos, what is wrong with this scenario,
where did my reasoning go wrong? Why do you claim the hum seen at the
speaker terminals didn't drop when a simple experiment will show that it
does?

You have so far been unable to refute that
contention.

I haven't even tried, since your argument was so pathetic. Power amps
are conventionally designed with nominal input voltages of 1-2 volts
rms for full output, matching nominal preamp output voltages. You are
attempting to score a cheap point by completely altering that
industry-standard gain division - and for no good reason whatever.

How did I alter that gain division? I followed the 1 volt input level
requirement precisely in my example above! You are the one that is
beginning to look pathetic, not because of your lack of engineering
skills, but because that sort of name calling is usually resorted to when
a person realizes his argument has no basis.

You also seem to have limited experience designing and
building real world amplifiers, or you would have long ago noticed that
negative feedback around a power amplifier with marginal power supply
filtering does indeed reduce the hum level heard from the speaker,
although as you say it doesn't so anything for the noise generated by the
input stage of the preamp. Get your nose out of the text books and try it
sometime.

I've designed and built something like fifteen audio power amps, and
none of them had any problems with hum.

I don't doubt that the amplifiers had no problem with hum, I am simply
saying that result was achieved either by using a degree of power supply
filtering, and an amplifier circuit with sufficient power supply ripple
rejection to achieve the desired hum level at the speaker terminals, or
was achieved by the application of negative feedback to an amplifier that
would have had excessive hum at the speaker terminals without the
application of NFB.

Having also been a
professional analogue electronics designer for some thirty years, I
suspect that I know rather more than you about the real-world effects
of various circuit configurations. Try reading some of those text
books sometime...............

I don't doubt that you were a "professional analogue electronics designer
for some thirty years", but I can also see why you had to get out of
analogue electronics design and take a job in the mail room.

Note carefully I am not claiming that negative feedback can improve the
noise figure of an amplifier, what I am claiming is that negative feedback
can improve the noise level at the output of the amplifier, which is where
it counts in an audio power amplifier driving a speaker, when hum caused
by power supply ripple is the dominant noise source in the amplifier.

You might want to think for a moment what it is you are trying to say.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

John Byrns wrote:

In article , Stewart Pinkerton
wrote:

On Tue, 19 Apr 2005 10:31:28 -0500, (John Byrns) wrote:

In article , Stewart Pinkerton
wrote:

On Mon, 18 Apr 2005 19:17:01 -0500, (John Byrns) wrote:

The Subject line says it all.

It says only that you have a vivid imagination. Your basic premise,
that hum is lowered by negative feedback, is utterly laughable since
you refuse to use the standard input-related measure.

I don't refuse to use the standard input-related measure, I pointed out
that if you do the sums you will find that except in pathological cases
the only input-related measure that matters is that related to the input
stage of the preamp.

Irrelevant, if you're claiming as you did, that NFB reduces the hum
*in a power amp*. Basically, you're just ducking and diving rather
than admit you were flat-out wrong.

On the contrary, it is you who are bobbing and weaving, considering that
you haven't offered a single bit of evidence to refute my empirically
verified statement that negative feedback reduces the hum in the output of
an audio power amplifier caused by inadequate filtering of the power
supply feeding the driver stage.

Let me give you an example, and you can tell me what is wrong with my
figuring. Let's take an amplifier like your zero NFB "KISASS", with a
maximum output capability of say 12.5 Watts into 8 Ohms. Let's further
assume that the 12.5 Watt output is delivered with an input of 1 volt.
This gives us a voltage gain of 10x for the amplifier from input to
output. Now let's assume that the input referenced noise level of this
amplifier is 5 uV with a perfectly noiseless power supply. The output
noise level at the speaker terminals will be about 50 uV under this
condition.

So far so good, now let's introduce enough power supply ripple into the
driver stage to create 4 mV of hum at the speaker terminals as with your
"KISASS". This 4 mV of hum in the output translates to 0.4 mV of hum when
referenced to the input. Suddenly the input referenced noise level of our
amplifier has jumped from 5 uV to more than 400 uV, a noise increase of 38
dB, due to poor power supply filtering, and unrelated to the inherent
noise level of the input circuit and the first transistor.

Now assume we find this level of hum offensive with our particular
speakers, which are moderately efficient, what can we do? Let's first add
an additional stage configured for a voltage gain of let's say 10x
following the first stage, and using the same transistor as the first
stage. Assuming there is a fair amount of gain in the first stage, the
noise added by the additional stage will be swamped, and we will be left
with an input referenced noise level of close to the original 5 uV, with a
perfectly filtered power supply. The noise level at the speaker output
terminals will now increase from 50 uV to 500 uV due to the increased gain
of the amplifier.

Now lets hook the driver stage up to the inadequately filtered power
supply again and see what we get. The hum in the output will still be 4
mV because the hum was injected at a point in the circuit down stream of
the added gain. The input referenced hum voltage has now decreased from
400 uV to 40 uV because of the increased gain. The input referenced noise
due to the power supply ripple is now only 18 dB greater than the noise
due to the input circuit. The total noise power at the input will be the
RMS value of the sum of the two noise sources, but since we are concerned
with only the hum here, and since the input circuit noise is still 18 dB
lower by measurement, although perhaps not subjectively, we will continue
ignoring the actual input circuit noise, other than to use it as a
reference.

OK, what have we accomplished, we have an amplifier that still has 4 mV of
hum in the output, but has 10 times more gain than the original amplifier
had, and than we wanted, so what to do? Let's put a negative feedback
loop around the amplifier, with enough feedback to reduce the gain to the
original value of 10x voltage gain. But what else happens? Like magic
the hum voltage at the speaker terminals drops from 4 mV to about 0.4 mV,
while the input referenced hum voltage remains at 40 uV. The hum
emanating from the speakers is now tolerable, and all is well with the
world.

So assuming I didn't make any typos, what is wrong with this scenario,
where did my reasoning go wrong? Why do you claim the hum seen at the
speaker terminals didn't drop when a simple experiment will show that it
does?

You have so far been unable to refute that
contention.

I haven't even tried, since your argument was so pathetic. Power amps
are conventionally designed with nominal input voltages of 1-2 volts
rms for full output, matching nominal preamp output voltages. You are
attempting to score a cheap point by completely altering that
industry-standard gain division - and for no good reason whatever.

How did I alter that gain division? I followed the 1 volt input level
requirement precisely in my example above! You are the one that is
beginning to look pathetic, not because of your lack of engineering
skills, but because that sort of name calling is usually resorted to when
a person realizes his argument has no basis.

You also seem to have limited experience designing and
building real world amplifiers, or you would have long ago noticed that
negative feedback around a power amplifier with marginal power supply
filtering does indeed reduce the hum level heard from the speaker,
although as you say it doesn't so anything for the noise generated by the
input stage of the preamp. Get your nose out of the text books and try it
sometime.

I've designed and built something like fifteen audio power amps, and
none of them had any problems with hum.

I don't doubt that the amplifiers had no problem with hum, I am simply
saying that result was achieved either by using a degree of power supply
filtering, and an amplifier circuit with sufficient power supply ripple
rejection to achieve the desired hum level at the speaker terminals, or
was achieved by the application of negative feedback to an amplifier that
would have had excessive hum at the speaker terminals without the
application of NFB.

Having also been a
professional analogue electronics designer for some thirty years, I
suspect that I know rather more than you about the real-world effects
of various circuit configurations. Try reading some of those text
books sometime...............

I don't doubt that you were a "professional analogue electronics designer
for some thirty years", but I can also see why you had to get out of
analogue electronics design and take a job in the mail room.

Note carefully I am not claiming that negative feedback can improve the
noise figure of an amplifier, what I am claiming is that negative feedback
can improve the noise level at the output of the amplifier, which is where
it counts in an audio power amplifier driving a speaker, when hum caused
by power supply ripple is the dominant noise source in the amplifier.

You might want to think for a moment what it is you are trying to say.

Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

John, your convoluted reasoning is difficult to follow.

If that porcine idiot Oinkerton were to have built and tested
his nasty little SS contraption, you'd have all your answers about
what hum gets produced and where, and how it does/does not
get cancelled/reinforced by the FB.

In general though, rail hum that leaks into the output of an amp
in open loop is reduced when NFB is applied in one form or another unless the hum

is solely due to applied input noise and is external to the loop of NFB.
This is very evident in tube circuits.

Patrick Turner.

In article , Patrick Turner
wrote:

John, your convoluted reasoning is difficult to follow.

Sorry, I was just trying to follow your example.

If that porcine idiot Oinkerton were to have built and tested
his nasty little SS contraption, you'd have all your answers about
what hum gets produced and where, and how it does/does not
get cancelled/reinforced by the FB.

I already know where hum gets produced in Stewart's design. The problem
is that while the output stage has a degree of power supply rejection, the
driver or voltage amplifier stage has none, and the power supply for that
stage is not all that well filtered. When I pointed that out to Stewart,
and suggested bolstering the two filter capacitors involved to improve the
situation, Stewart said it wasn't necessary, and quoted a rather gross
number for the ripple voltage in the output of the amplifier.
Interestingly the number he came up with was in the same ball park as my
estimate, so I think we are probably pretty close, Stewart just seems to
have a Tin Ear accepting more hum than me. There is no feedback in
Stewart's amplifier, so there is no hum reduction from that effect.

In general though, rail hum that leaks into the output of an amp in open
loop is reduced when NFB is applied in one form or another unless the hum

is solely due to applied input noise and is external to the loop of NFB.
This is very evident in tube circuits.

Yes, you know that, and I know that, but when I mentioned it in a post to
Stewart he said I was full of it and that I didn't have a clue. That's
what the argument is about, my claim that negative feedback can reduce the
hum at the speaker terminals of a power amplifier, tube or transistor
doesn't matter, while Stewart says feedback doesn't reduce hum. Clearly
Stewart has been living under a rock somewhere, either that or he has
never actually played with the circuitry of an amplifier.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

On Tue, 19 Apr 2005 17:40:47 -0500, (John Byrns) wrote:

In article , Stewart Pinkerton
wrote:

On Tue, 19 Apr 2005 10:31:28 -0500, (John Byrns) wrote:

In article , Stewart Pinkerton
wrote:

On Mon, 18 Apr 2005 19:17:01 -0500, (John Byrns) wrote:

The Subject line says it all.

It says only that you have a vivid imagination. Your basic premise,
that hum is lowered by negative feedback, is utterly laughable since
you refuse to use the standard input-related measure.

I don't refuse to use the standard input-related measure, I pointed out
that if you do the sums you will find that except in pathological cases
the only input-related measure that matters is that related to the input
stage of the preamp.

Irrelevant, if you're claiming as you did, that NFB reduces the hum
*in a power amp*. Basically, you're just ducking and diving rather
than admit you were flat-out wrong.

On the contrary, it is you who are bobbing and weaving, considering that
you haven't offered a single bit of evidence to refute my empirically
verified statement that negative feedback reduces the hum in the output of
an audio power amplifier caused by inadequate filtering of the power
supply feeding the driver stage.

Let me give you an example, and you can tell me what is wrong with my
figuring. Let's take an amplifier like your zero NFB "KISASS", with a
maximum output capability of say 12.5 Watts into 8 Ohms. Let's further
assume that the 12.5 Watt output is delivered with an input of 1 volt.
This gives us a voltage gain of 10x for the amplifier from input to
output. Now let's assume that the input referenced noise level of this
amplifier is 5 uV with a perfectly noiseless power supply. The output
noise level at the speaker terminals will be about 50 uV under this
condition.

So far so good, now let's introduce enough power supply ripple into the
driver stage to create 4 mV of hum at the speaker terminals as with your
"KISASS". This 4 mV of hum in the output translates to 0.4 mV of hum when
referenced to the input. Suddenly the input referenced noise level of our
amplifier has jumped from 5 uV to more than 400 uV, a noise increase of 38
dB, due to poor power supply filtering, and unrelated to the inherent
noise level of the input circuit and the first transistor.

Now assume we find this level of hum offensive with our particular
speakers, which are moderately efficient, what can we do? Let's first add
an additional stage configured for a voltage gain of let's say 10x
following the first stage, and using the same transistor as the first
stage. Assuming there is a fair amount of gain in the first stage, the
noise added by the additional stage will be swamped, and we will be left
with an input referenced noise level of close to the original 5 uV, with a
perfectly filtered power supply. The noise level at the speaker output
terminals will now increase from 50 uV to 500 uV due to the increased gain
of the amplifier.

Now lets hook the driver stage up to the inadequately filtered power
supply again and see what we get. The hum in the output will still be 4
mV because the hum was injected at a point in the circuit down stream of
the added gain. The input referenced hum voltage has now decreased from
400 uV to 40 uV because of the increased gain. The input referenced noise
due to the power supply ripple is now only 18 dB greater than the noise
due to the input circuit. The total noise power at the input will be the
RMS value of the sum of the two noise sources, but since we are concerned
with only the hum here, and since the input circuit noise is still 18 dB
lower by measurement, although perhaps not subjectively, we will continue
ignoring the actual input circuit noise, other than to use it as a
reference.

OK, what have we accomplished, we have an amplifier that still has 4 mV of
hum in the output, but has 10 times more gain than the original amplifier
had, and than we wanted, so what to do? Let's put a negative feedback
loop around the amplifier, with enough feedback to reduce the gain to the
original value of 10x voltage gain. But what else happens? Like magic
the hum voltage at the speaker terminals drops from 4 mV to about 0.4 mV,
while the input referenced hum voltage remains at 40 uV. The hum
emanating from the speakers is now tolerable, and all is well with the
world.

So assuming I didn't make any typos, what is wrong with this scenario,
where did my reasoning go wrong? Why do you claim the hum seen at the
speaker terminals didn't drop when a simple experiment will show that it
does?

What's wrong with that scenario? Your original article claimed that
NFB reduces hum, and you referred that to *adding* NFB to an existing
amplifier. When I pointed out how laughable was that claim, you now
duck and dive to an artificially created scenario where you *add* a
gain stage to an amplifier in order to prove your wrong-headed point.

Real designers just make a proper power supply in the first place, or
configure the amp to have good PSU rejection.

You have so far been unable to refute that
contention.

I haven't even tried, since your argument was so pathetic. Power amps
are conventionally designed with nominal input voltages of 1-2 volts
rms for full output, matching nominal preamp output voltages. You are
attempting to score a cheap point by completely altering that
industry-standard gain division - and for no good reason whatever.

How did I alter that gain division? I followed the 1 volt input level
requirement precisely in my example above! You are the one that is
beginning to look pathetic, not because of your lack of engineering
skills, but because that sort of name calling is usually resorted to when
a person realizes his argument has no basis.

The pathetic one is the one who adds extra gain stages just to 'prove'
a lost cause. Attempting to distract attention from what you did first
time around the loop doesn't help.

You also seem to have limited experience designing and
building real world amplifiers, or you would have long ago noticed that
negative feedback around a power amplifier with marginal power supply
filtering does indeed reduce the hum level heard from the speaker,
although as you say it doesn't so anything for the noise generated by the
input stage of the preamp. Get your nose out of the text books and try it
sometime.

I've designed and built something like fifteen audio power amps, and
none of them had any problems with hum.

I don't doubt that the amplifiers had no problem with hum, I am simply
saying that result was achieved either by using a degree of power supply
filtering, and an amplifier circuit with sufficient power supply ripple
rejection to achieve the desired hum level at the speaker terminals, or
was achieved by the application of negative feedback to an amplifier that
would have had excessive hum at the speaker terminals without the
application of NFB.

The first two are always a good idea, the last is a pathetic joke.

Having also been a
professional analogue electronics designer for some thirty years, I
suspect that I know rather more than you about the real-world effects
of various circuit configurations. Try reading some of those text
books sometime...............

I don't doubt that you were a "professional analogue electronics designer
for some thirty years", but I can also see why you had to get out of
analogue electronics design and take a job in the mail room.

I see that you've run out of real arguments. Quelle surprise..........

Note carefully I am not claiming that negative feedback can improve the
noise figure of an amplifier, what I am claiming is that negative feedback
can improve the noise level at the output of the amplifier, which is where
it counts in an audio power amplifier driving a speaker, when hum caused
by power supply ripple is the dominant noise source in the amplifier.

Well of course it bloody can - by reducing the system gain. Never
argued, and utterly pointless.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Tue, 19 Apr 2005 22:12:54 -0500, (John Byrns) wrote:

In article , Patrick Turner
wrote:

John, your convoluted reasoning is difficult to follow.

Sorry, I was just trying to follow your example.

Now now kiddies, play nicely............ :-)

If that porcine idiot Oinkerton were to have built and tested
his nasty little SS contraption, you'd have all your answers about
what hum gets produced and where, and how it does/does not
get cancelled/reinforced by the FB.

I already know where hum gets produced in Stewart's design.

Strangely enough, so do I. It's an inevitable result of the design
constraints.

The problem
is that while the output stage has a degree of power supply rejection, the
driver or voltage amplifier stage has none, and the power supply for that
stage is not all that well filtered. When I pointed that out to Stewart,
and suggested bolstering the two filter capacitors involved to improve the
situation, Stewart said it wasn't necessary, and quoted a rather gross
number for the ripple voltage in the output of the amplifier.

Stop telling lies. I said that *I* had no problem with the resulting
hum level, and I agreed that if *you* wanted an inky-black noise
floor, then bigger caps would certainly do it.

Interestingly the number he came up with was in the same ball park as my
estimate, so I think we are probably pretty close, Stewart just seems to
have a Tin Ear accepting more hum than me. There is no feedback in
Stewart's amplifier, so there is no hum reduction from that effect.

Not a tin ear, I just don't get all that distracted by a steady-state
low-level hum. Different matter if it's modulated, as would happen in
a Class AB design. As you've noted, I am perfectly well aware of the
KISASS hum level, and how to reduce it if desired.

In general though, rail hum that leaks into the output of an amp in open
loop is reduced when NFB is applied in one form or another unless the hum

is solely due to applied input noise and is external to the loop of NFB.
This is very evident in tube circuits.

Yes, you know that, and I know that, but when I mentioned it in a post to
Stewart he said I was full of it and that I didn't have a clue.

Bull****, I simply pointed out that reducing hum by reducing overall
gain, is hardly an achievement.

That's
what the argument is about, my claim that negative feedback can reduce the
hum at the speaker terminals of a power amplifier, tube or transistor
doesn't matter, while Stewart says feedback doesn't reduce hum. Clearly
Stewart has been living under a rock somewhere, either that or he has
never actually played with the circuitry of an amplifier.

Clearly, you are determined to keep lying and distorting on the basis
of your rubbish argument. I'm sure our gentle readers can decide who's
making sense here.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

John Byrns wrote:

In article , Patrick Turner
wrote:

John, your convoluted reasoning is difficult to follow.

Sorry, I was just trying to follow your example.

If that porcine idiot Oinkerton were to have built and tested
his nasty little SS contraption, you'd have all your answers about
what hum gets produced and where, and how it does/does not
get cancelled/reinforced by the FB.

I already know where hum gets produced in Stewart's design. The problem
is that while the output stage has a degree of power supply rejection, the
driver or voltage amplifier stage has none, and the power supply for that
stage is not all that well filtered. When I pointed that out to Stewart,
and suggested bolstering the two filter capacitors involved to improve the
situation, Stewart said it wasn't necessary, and quoted a rather gross
number for the ripple voltage in the output of the amplifier.
Interestingly the number he came up with was in the same ball park as my
estimate, so I think we are probably pretty close, Stewart just seems to
have a Tin Ear accepting more hum than me. There is no feedback in
Stewart's amplifier, so there is no hum reduction from that effect.

If the SE transistor drive amp rail has 1 mV of hum then it is all applied
to the output stage because the collector resistance is very high.
But the output stage is unity gain, so 1 mV of hum appears in the output.
That would be disastrous for horn speakers.

There is a huge amount of NFB in Oinkie's amp,
but its not global, and if it was that 1 mV would be reduced by about the
amount of global FB


In general though, rail hum that leaks into the output of an amp in open
loop is reduced when NFB is applied in one form or another unless the hum

is solely due to applied input noise and is external to the loop of NFB.
This is very evident in tube circuits.

Yes, you know that, and I know that, but when I mentioned it in a post to
Stewart he said I was full of it and that I didn't have a clue. That's
what the argument is about, my claim that negative feedback can reduce the
hum at the speaker terminals of a power amplifier, tube or transistor
doesn't matter, while Stewart says feedback doesn't reduce hum. Clearly
Stewart has been living under a rock somewhere, either that or he has
never actually played with the circuitry of an amplifier.

He does not have serious respect for us as a group, he thinks tubes are ****e,
and he said he wasn't going to build his paper amp.

He is like the pork salesman in the synagogue.

I wish you well in your discussions with the man,
but it just may not lead anywhere.

Meanwhile I have respect for those who actually build something
regardless of whether its SS or tube, and I would bid them
respect us in return.

Patrick Turner.



Regards,

John Byrns

Surf my web pages at, http://users.rcn.com/jbyrns/

I said.....
If that porcine idiot Oinkerton were to have built and tested
his nasty little SS contraption, you'd have all your answers about
what hum gets produced and where, and how it does/does not
get cancelled/reinforced by the FB.


JB said....
I already know where hum gets produced in Stewart's design.

Oinkerton said.......

Strangely enough, so do I. It's an inevitable result of the design
constraints.

The only thing really constraining the design is the
inexperienced mind of Oinkerton.

We have to strain our ears to hear the Oinkish squeals and grunts from the
bottom
of the hole its so deep

In article , Stewart Pinkerton
wrote:

What's wrong with that scenario? Your original article claimed that
NFB reduces hum, and you referred that to *adding* NFB to an existing
amplifier. When I pointed out how laughable was that claim, you now
duck and dive to an artificially created scenario where you *add* a
gain stage to an amplifier in order to prove your wrong-headed point.

In my "original article" I simply quoted the hum level of a particular
amplifier, and pointed out that the amplifier achieved the stated result
without even using any negative feedback. You then asked me why feedback
would affect hum level, and I offered my explanations, which you seem take
exception with. It is obvious that you are taking exception to this well
known use of feedback simply to create controversy, so this seems an
expeditious point to end the discussion. I will only comment that your
argument that the application of feedback doesn't reduce hum at the
speaker terminals, applies equally to using feedback to reduce the
distortion at an amplifier's output. I have noticed that most SS
amplifiers use gobs of feedback, I guess their designers aren't too bright
since feedback doesn't reduce either hum or distortion. The irony is that
you have succeeded in proving that the SE tube contingent has had it right
all along, feedback is not useful in audio amplifiers.

Real designers just make a proper power supply in the first place, or
configure the amp to have good PSU rejection.

"Real designers"? I guess that means you aren't a real designer since you
designed the amplifier that had enough ripple on the voltage amplifier
power supply rail to cause a rather gross 4 mV of ripple at the speaker
terminals!


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

In article , Stewart Pinkerton
wrote:

On Tue, 19 Apr 2005 22:12:54 -0500, (John Byrns) wrote:

In article , Patrick Turner
wrote:

If that porcine idiot Oinkerton were to have built and tested
his nasty little SS contraption, you'd have all your answers about
what hum gets produced and where, and how it does/does not
get cancelled/reinforced by the FB.

I already know where hum gets produced in Stewart's design.

Strangely enough, so do I. It's an inevitable result of the design
constraints.

Hardly, there was/is no such design constraint. The "KISASS" design is
easily modified to improve the power supply ripple rejection of the
voltage amplifier stage. All that need be done is to replace the 150 Ohm
resistor in the collector circuit of the voltage amplifier stage with a
current source of about 200 mA, and then reconnect the 150 Ohm resistor
from the collector of the voltage amplifier transistor to ground.

That is only one of several possible ways to increase the power supply
rejection of the voltage amplifier stage in the "KISASS". No wonder you
took a job in the mail room.


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/

On Wed, 20 Apr 2005 22:45:00 -0500, (John Byrns) wrote:

In article , Stewart Pinkerton
wrote:

On Tue, 19 Apr 2005 22:12:54 -0500, (John Byrns) wrote:

In article , Patrick Turner
wrote:

If that porcine idiot Oinkerton were to have built and tested
his nasty little SS contraption, you'd have all your answers about
what hum gets produced and where, and how it does/does not
get cancelled/reinforced by the FB.

I already know where hum gets produced in Stewart's design.

Strangely enough, so do I. It's an inevitable result of the design
constraints.

Hardly, there was/is no such design constraint. The "KISASS" design is
easily modified to improve the power supply ripple rejection of the
voltage amplifier stage. All that need be done is to replace the 150 Ohm
resistor in the collector circuit of the voltage amplifier stage with a
current source of about 200 mA, and then reconnect the 150 Ohm resistor
from the collector of the voltage amplifier transistor to ground.

That would add another active device, and would reduce the KIS aspect
which is central to the design requirement. Turner already bitched
about the output emitter-followers, imagine what he (and probably you)
would have said about an added CCS! I certainly considered the use of
such a device for the exact reason you state, and I commonly use it in
my 'real' designs, but I rejected it on simplicity grounds, and I
consider KISASS to have achieved what it set out to do.

That is only one of several possible ways to increase the power supply
rejection of the voltage amplifier stage in the "KISASS". No wonder you
took a job in the mail room.

Typical pathetic ad hominem attack in lieu of a real argument.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Wed, 20 Apr 2005 22:41:08 -0500, (John Byrns) wrote:

In article , Stewart Pinkerton
wrote:

What's wrong with that scenario? Your original article claimed that
NFB reduces hum, and you referred that to *adding* NFB to an existing
amplifier. When I pointed out how laughable was that claim, you now
duck and dive to an artificially created scenario where you *add* a
gain stage to an amplifier in order to prove your wrong-headed point.

In my "original article" I simply quoted the hum level of a particular
amplifier, and pointed out that the amplifier achieved the stated result
without even using any negative feedback. You then asked me why feedback
would affect hum level, and I offered my explanations, which you seem take
exception with. It is obvious that you are taking exception to this well
known use of feedback simply to create controversy, so this seems an
expeditious point to end the discussion.

What is 'obvious' is that you made up a ludicrously artificial
scenario, and then tried to duck and dive your way out of it.

I will only comment that your
argument that the application of feedback doesn't reduce hum at the
speaker terminals, applies equally to using feedback to reduce the
distortion at an amplifier's output. I have noticed that most SS
amplifiers use gobs of feedback, I guess their designers aren't too bright
since feedback doesn't reduce either hum or distortion. The irony is that
you have succeeded in proving that the SE tube contingent has had it right
all along, feedback is not useful in audio amplifiers.

Typical idiocy from you, Byrns, as SS amps are generally designed with
lots of open-loop gain and then brought back to the standard 1V rms
for full output by the use of NFB. That does of course reduce all
outout error signals including hum, but is *not* the same scenario as
your original post, however much you keep lying about it.

Real designers just make a proper power supply in the first place, or
configure the amp to have good PSU rejection.

"Real designers"? I guess that means you aren't a real designer since you
designed the amplifier that had enough ripple on the voltage amplifier
power supply rail to cause a rather gross 4 mV of ripple at the speaker
terminals!

Yep, and it doesn't bother *me* at all. If it bothers *you*, I already
told you how to fix it.
--

Stewart Pinkerton | Music is Art - Audio is Engineering