[Fai C]

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

[Ian Iveson[_2_]]

On Dec 1, 6:42*pm, Fai C wrote:
Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

The first stage, comprising the left-most two valves, is an anode
follower with an active high-impedance load, resulting in a gain of
around the mu of the bottom valve, and a high output impedance.

The two valves of the second stage operate in push-pull, or you might
prefer to see it as a cathode follower riding on top of an anode-
follower, operating in antiphase. The output impedance is the same as
an ordinary cathode follower AFAICS. The bottom valve is driven
directly by the input signal, and the top half is driven by the first
stage.

Altogether, it seems to me to operate like a mu-stage. Note the two
halves are identical, such that the signal on the first stage's bottom
anode should be the same as that at the same point of the second
stage. If the grid of the second stage's cathode follower were driven
by the anode of the valve underneath it, would that amount to the same
thing as driving it from the first stage? Wouldn't that make the first
stage redundant?

Except for one thing. One way of looking at output impedance is to
consider the effect of driving a signal into the output. As the
circuit is, such a signal would see a cathode above, with an impedance
of a couple of hundred ohms perhaps, in series with the power supply
which should be of negligible impedance. In parallel, looking
downwards, is a resistor and anode, together amounting to several k
ohms. Now, if there were a connection from the anode of the bottom
valve to the grid of the top, then that signal into the output would
also find its way after some attenuation to the grid of the top valve
and drive it. The effect of that would be to increase the impedance of
the cathode, thus increasing the output impedance of the stage.

All in all, it's a mu-follower with the output impedance of a plain
cathode follower.

Could be wrong.

A mu-follower is one of several similar circuits with four-letter
acronyms that I forget. I'm easily confused.

Ian

[flipper]

On Thu, 1 Dec 2011 10:42:29 -0800 (PST), Fai C
wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

It's not a multivibrator.

The first two (vertical) triodes (of each stage) are an SRPP amplifier
and he's buffering it with the second two triodes. The top second
triode is just doing "the same thing" as the previous triode grid it's
connected to and so is the second bottom triode. The idea is to
isolate the load from the signal (first) stage.

Notice at the bottom of the schematic he calls it a "supertotem." It's
also called a Gomes.

See here for more than you probably want to know

http://www.tubecad.com/2004/blog0015.htm

[Alex Pogossov]

"Ian Iveson" wrote in message
...
On Dec 1, 6:42 pm, Fai C wrote:
Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

To achieve gain = mu one needs to load a triode with an infinite load
resistor -- for example, a CCS on MJE340 so loved by Patrick.

But signore Bartolomeo uses a different approach. As a loading, he uses
exactly the same triode with exactly the same cathode resistor (1.82K). As a
result Ra of the loading triode equals Ra of the amplifier triode. Thus gain
= mu/2.

Perhaps there is some sweetness in having the load identical to drive. My
gut feel, it reduces even harmonics (because of sort of symmetry), but would
not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people,
go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think
Patrick's soldering iron is never switched off anyway, even while he is on a
bike ride.)

Regards,
Alex

[Fai C]

AFAIK, group of my friend is interested in revised this Supertotem
driver circuit designed Bartolomeo Aloia to drive the GM70 instead of
211.

Don't you think the possibility having DHT type for the first stage
that consists of 2 x Emission labs 20A and the second stage have 2 x
PX25 invloved per channel rather than 6922 all the way? Or you guys
can think of a better option.

[Ian Iveson[_2_]]

On Dec 2, 12:02*pm, "Alex Pogossov" wrote:
"Ian Iveson" wrote in message

...
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

To achieve gain = mu one needs to load a triode with an infinite load
resistor -- for example, a CCS on MJE340 so loved by Patrick.

But signore Bartolomeo uses a different approach. As a loading, he uses
exactly the same triode with exactly the same cathode resistor (1.82K). As a
result Ra of the loading triode equals Ra of the amplifier triode. Thus gain
= mu/2.

Perhaps there is some sweetness in having the load identical to drive. My
gut feel, it reduces even harmonics (because of sort of symmetry), but would
not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people,
go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think
Patrick's soldering iron is never switched off anyway, even while he is on a
bike ride.)

Regards,
Alex

If grid and cathode were driven by the same small voltage signal, then
the impedance would be the same as if the same signal were applied to
the anode, it seems to me, so the bottom valve would then see a load
of ra. However, in the SRPP, the grid is driven more strongly than the
cathode because of the resistor at the cathode of the top valve, which
senses current. Consequently the active resistance is greater, but it
can't make a very good CCS because there's not enough gain, as Kimmel
pointed out.

***Kimmel mu-stage: http://bit.ly/uL9G86

Develops mu-follower from SRPP, and ends up with a MOSFET on top,
because it makes a stiffer current source than a BJT for the same
reason a pentode would be better than a triode. Since first published,
I think the circuit became commercial and this document was withdrawn.
My criticism of the article is that it condemns SRPP merely on the
grounds that it has a poor current source, without considering that
the top valve, by the same token, must make a contribution to the
quality, as well as the quantity, of distortion. The SRPP offers
endless possibilities for golden-eared tube-rollers.

***SRPP distortion analysis: http://bit.ly/tai8te

cheers,
Ian

[Alex Pogossov]

"Ian Iveson" wrote in message
...
On Dec 2, 12:02 pm, "Alex Pogossov" wrote:
"Ian Iveson" wrote in message

...
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

To achieve gain = mu one needs to load a triode with an infinite load
resistor -- for example, a CCS on MJE340 so loved by Patrick.

But signore Bartolomeo uses a different approach. As a loading, he uses
exactly the same triode with exactly the same cathode resistor (1.82K). As
a
result Ra of the loading triode equals Ra of the amplifier triode. Thus
gain
= mu/2.

Perhaps there is some sweetness in having the load identical to drive. My
gut feel, it reduces even harmonics (because of sort of symmetry), but
would
not help odd harmonics. It is only a gut feel, I am not sure. SPICEd
people,
go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I
think
Patrick's soldering iron is never switched off anyway, even while he is on
a
bike ride.)

Regards,
Alex

If grid and cathode were driven by the same small voltage signal, then
the impedance would be the same as if the same signal were applied to
the anode, it seems to me, so the bottom valve would then see a load
of ra. However, in the SRPP, the grid is driven more strongly than the
cathode because of the resistor at the cathode of the top valve, which
senses current. Consequently the active resistance is greater, but it
can't make a very good CCS because there's not enough gain, as Kimmel
pointed out.

***Kimmel mu-stage: http://bit.ly/uL9G86
----------------------------
Alex:
You are right -- a triode with a relatively small Rk still is not a great
current source. But being more accurate, an equivalent impedance of an
"active" load, comprising a triode with Rk=1.82K is *exactly* the same as
the output impedance of a common catode stage with Rk=1.82K unbypassed! That
is why, gain is exactly mu/2.

To get used to this concept you might do other mental experiments, e.g.:

1) Assume temporarily that your tubes are say 12AX7s with Rk=0. In this case
the bottom triode will have its cathode literally grounded, and the top
loading triode will have its grid hard soldered to cathode (it will work as
a diode). Would you agree in this case that Ra of the "active" load equals
Ra of a bottom "gain" triode. and consequently, gain=mu/2 ? Obviously you
can not disagree with that.

2) Temporarily imagine that Rks for both tubes are hidden inside the tube
bases or inside the tube envelopes, so you have no access to them. Then this
case will be equivalent to case 1).

3) Imagine that the tubes are weak or poisoned so much, that the resistance
of their cathode coating is 1.82K which just degenerates transconductance.
Then you do need external Rks and the case again resembles case 1).

Regards,
Alex

[Patrick Turner]

On Dec 2, 11:02*pm, "Alex Pogossov" wrote:
"Ian Iveson" wrote in message

...
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

To achieve gain = mu one needs to load a triode with an infinite load
resistor -- for example, a CCS on MJE340 so loved by Patrick.

But signore Bartolomeo uses a different approach. As a loading, he uses
exactly the same triode with exactly the same cathode resistor (1.82K). As a
result Ra of the loading triode equals Ra of the amplifier triode. Thus gain
= mu/2.

Perhaps there is some sweetness in having the load identical to drive. My
gut feel, it reduces even harmonics (because of sort of symmetry), but would
not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people,
go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think
Patrick's soldering iron is never switched off anyway, even while he is on a
bike ride.)

Regards,
Alex

Barto's driver circuits don't work like multibibrators, but uses SRPP
gain stages stages with following cathode follower buffer stage with
active cathode load.
See http://www.audiodesignguide.com/ba/ba211c.jpg

See also the easier to understand http://www.audiodesignguide.com/ba/vtalast.jpg

The driver stages to PP 211 OP stage does not have balancing, and the
rather high THD of the SRPP gain function would affect final THD
measurements, and 6922 would not be optimal IMHO. Better would be
6SN7, and instead of SRPP, bootstrapped follower or mu-follower would
give less THD and be less at risk of arcing etc when used to produce
high drive voltages for 211.
His input stages use a pair of cascaded SRPP, with divider from the
two phases of the two cathode outputs taken to a the grid of second
SRPP; it is a paraphase phase inverter. Anyway, our Italian Tinkerer
uses many more tubes to do what I would using 1 parallel input tube,
and 2 x EL84, and a choke with CT, see sheet 1 at top of page at
http://www.turneraudio.com.au/300w-1...tput-jan06.htm

Nothing wrong with 211 ( or 845 ) based PP OP stages. I believe the
main sonic character is generated in OP stages, and my feeling is that
such high powered stages offer excellent audio sound.

Patrick Turner.

[Alex Pogossov]

"Patrick Turner" wrote

Barto's driver circuits don't work like multibibrators, but uses SRPP
gain stages stages with following cathode follower buffer stage with
active cathode load.
See http://www.audiodesignguide.com/ba/ba211c.jpg

See also the easier to understand
http://www.audiodesignguide.com/ba/vtalast.jpg

Alex:

My understanding is that there is a NFB applied to the cathodes of V5a and
V3a, and a slight positive feedback into the cathodes output tubes.

If this is correct, then I found odd that the feedback is applied to the
cathodes of the amplifier triodes V5a and V3a, but not to the cathodes of
dummy triodes V3b and V5b. (Perhaps it is a drawing mistake or even a
deliberate error intended for those who want to reproduce the design get bad
results.)

This ruins the whole intrinsic symmetry of this "mu/2 amplifier". If the
NFB is deep enough, then the dummy tubes V3b and V5b will be overdriven and
create distortion.

I would connect cathodes of V3a, V3b and V5a, V5b together. Oh, those tube
designers...

Regards,
Alex

[Fai C]

On Dec 4, 4:41*pm, Patrick Turner wrote:
On Dec 2, 11:02*pm, "Alex Pogossov" wrote:









"Ian Iveson" wrote in message

...
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

To achieve gain = mu one needs to load a triode with an infinite load
resistor -- for example, a CCS on MJE340 so loved by Patrick.

But signore Bartolomeo uses a different approach. As a loading, he uses
exactly the same triode with exactly the same cathode resistor (1.82K). As a
result Ra of the loading triode equals Ra of the amplifier triode. Thus gain
= mu/2.

Perhaps there is some sweetness in having the load identical to drive. My
gut feel, it reduces even harmonics (because of sort of symmetry), but would
not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people,
go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think
Patrick's soldering iron is never switched off anyway, even while he is on a
bike ride.)

Regards,
Alex

Barto's driver circuits don't work like multibibrators, but uses SRPP
gain stages stages with following cathode follower buffer stage with
active cathode load.
Seehttp://www.audiodesignguide.com/ba/ba211c.jpg

See also the easier to understandhttp://www.audiodesignguide.com/ba/vtalast.jpg

The driver stages to PP 211 OP stage does not have balancing, and the
rather high THD of the SRPP gain function would affect final THD
measurements, and 6922 would not be optimal IMHO. Better would be
6SN7, and instead of SRPP, bootstrapped follower or mu-follower would
give less THD and be less at risk of arcing etc when used to produce
high drive voltages for 211.
His input stages use a pair of cascaded SRPP, with divider from the
two phases of the two cathode outputs taken to a the grid of second
SRPP; it is a paraphase phase inverter. Anyway, our Italian Tinkerer
uses many more tubes to do what I would using 1 parallel input tube,
and 2 x EL84, and a choke with CT, see sheet 1 at top of page athttp://www.turneraudio.com.au/300w-1+2-schem-input-driver-output-jan0...

Nothing wrong with 211 ( or 845 ) based PP OP stages. I believe the
main sonic character is generated in OP stages, and my feeling is that
such high powered stages offer excellent audio sound.

Patrick Turner.

Dear Pat,
I probably pressing a wrong button and my resppnse didn't show,
hopefully they didn't send my post as email.

From this link:
http://www.audiodesignguide.com/ba/

What they call it a BA211 - the 211 Single Ended Power Amplifier by
Bartolomeo Aloia.

So this is a SE but you said this is a push pull, now I confused.

Thanks!

[Don Pearce[_3_]]

On Sun, 4 Dec 2011 02:11:08 -0800 (PST), Fai C
wrote:

On Dec 4, 4:41*pm, Patrick Turner wrote:
On Dec 2, 11:02*pm, "Alex Pogossov" wrote:









"Ian Iveson" wrote in message

...
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

To achieve gain = mu one needs to load a triode with an infinite load
resistor -- for example, a CCS on MJE340 so loved by Patrick.

But signore Bartolomeo uses a different approach. As a loading, he uses
exactly the same triode with exactly the same cathode resistor (1.82K). As a
result Ra of the loading triode equals Ra of the amplifier triode. Thus gain
= mu/2.

Perhaps there is some sweetness in having the load identical to drive. My
gut feel, it reduces even harmonics (because of sort of symmetry), but would
not help odd harmonics. It is only a gut feel, I am not sure. SPICEd people,
go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I think
Patrick's soldering iron is never switched off anyway, even while he is on a
bike ride.)

Regards,
Alex

Barto's driver circuits don't work like multibibrators, but uses SRPP
gain stages stages with following cathode follower buffer stage with
active cathode load.
Seehttp://www.audiodesignguide.com/ba/ba211c.jpg

See also the easier to understandhttp://www.audiodesignguide.com/ba/vtalast.jpg

The driver stages to PP 211 OP stage does not have balancing, and the
rather high THD of the SRPP gain function would affect final THD
measurements, and 6922 would not be optimal IMHO. Better would be
6SN7, and instead of SRPP, bootstrapped follower or mu-follower would
give less THD and be less at risk of arcing etc when used to produce
high drive voltages for 211.
His input stages use a pair of cascaded SRPP, with divider from the
two phases of the two cathode outputs taken to a the grid of second
SRPP; it is a paraphase phase inverter. Anyway, our Italian Tinkerer
uses many more tubes to do what I would using 1 parallel input tube,
and 2 x EL84, and a choke with CT, see sheet 1 at top of page athttp://www.turneraudio.com.au/300w-1+2-schem-input-driver-output-jan0...

Nothing wrong with 211 ( or 845 ) based PP OP stages. I believe the
main sonic character is generated in OP stages, and my feeling is that
such high powered stages offer excellent audio sound.

Patrick Turner.

Dear Pat,
I probably pressing a wrong button and my resppnse didn't show,
hopefully they didn't send my post as email.

From this link:
http://www.audiodesignguide.com/ba/

What they call it a BA211 - the 211 Single Ended Power Amplifier by
Bartolomeo Aloia.

So this is a SE but you said this is a push pull, now I confused.

Thanks!

It is a simple common cathode triode amplifier. It has no DC feedback
resistor in the cathode, so its operating point will be unstable, not
only during the warm-up period, but over the life of the tube. This
looks to me not so much like a work in progress as a "where shall I
start?".

d

[Patrick Turner]

On Dec 4, 9:11*pm, Fai C wrote:
On Dec 4, 4:41*pm, Patrick Turner wrote:





On Dec 2, 11:02*pm, "Alex Pogossov" wrote:

"Ian Iveson" wrote in message

....
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

[Ian Iveson[_2_]]

On Dec 3, 1:18*am, "Alex Pogossov" wrote:
"Ian Iveson" wrote in message

...
On Dec 2, 12:02 pm, "Alex Pogossov" wrote:





"Ian Iveson" wrote in message

...
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

To achieve gain = mu one needs to load a triode with an infinite load
resistor -- for example, a CCS on MJE340 so loved by Patrick.

But signore Bartolomeo uses a different approach. As a loading, he uses
exactly the same triode with exactly the same cathode resistor (1.82K). As
a
result Ra of the loading triode equals Ra of the amplifier triode. Thus
gain
= mu/2.

Perhaps there is some sweetness in having the load identical to drive. My
gut feel, it reduces even harmonics (because of sort of symmetry), but
would
not help odd harmonics. It is only a gut feel, I am not sure. SPICEd
people,
go ahead and simulate! Patrick, warm up your soldering iron! (Ooops, I
think
Patrick's soldering iron is never switched off anyway, even while he is on
a
bike ride.)

Regards,
Alex

If grid and cathode were driven by the same small voltage signal, then
the impedance would be the same as if the same signal were applied to
the anode, it seems to me, so the bottom valve would then see a load
of ra. However, in the SRPP, the grid is driven more strongly than the
cathode because of the resistor at the cathode of the top valve, which
senses current. Consequently the active resistance is greater, but it
can't make a very good CCS because there's not enough gain, as Kimmel
pointed out.

***Kimmel mu-stage: *http://bit.ly/uL9G86
----------------------------
Alex:
You are right -- a triode with a relatively small Rk still is not a great
current source. But being more accurate, an equivalent impedance of an
"active" load, comprising a triode with Rk=1.82K is *exactly* the same as
the output impedance of a common catode stage with Rk=1.82K unbypassed! That
is why, gain is exactly mu/2.

To get used to this concept you might do other mental experiments, e.g.:

1) Assume temporarily that your tubes are say 12AX7s with Rk=0. In this case
the bottom triode will have its cathode literally grounded, and the top
loading triode will have its grid hard soldered to cathode (it will work as
a diode). Would you agree in this case that Ra of the "active" load equals
Ra of a bottom "gain" triode. and consequently, gain=mu/2 ? Obviously you
can not disagree with that.

That should be obvious because it is the same point I made, except you
confusingly use the term "Ra" in two different senses in the same
senses. I use Ra for the anode load, and ra for the effective
resistance of the anode.

So when you wrote "Ra of the loading triode equals Ra of the amplifier
triode" I took you to mean that the anode load of the bottom valve is
ra. That is what I corrected.

2) Temporarily imagine that Rks for both tubes are hidden inside the tube
bases or inside the tube envelopes, so you have no access to them. Then this
case will be equivalent to case 1).

Equivalent in some ways but not others...you just put resistors in the
cathodes! I guess all you mean is that the impedance of the top valve/
Rk combination is the same as the bottom. Consequently, if you
perceive the bottom valve/Rk as a voltage source with internal
resistance, then the output voltage will be halved when loaded by an
equal resistance. Thus if the gain were mu with no load, it would be
mu/2 when so loaded.

3) Imagine that the tubes are weak or poisoned so much, that the resistance
of their cathode coating is 1.82K which just degenerates transconductance..
Then you do need external Rks and the case again resembles case 1).

I don't know if I want to agree with "just", but otherwise OK

The key question is whether cathode resistance degenerates mu. If it
doesn't, then your mu/2 is correct, with the proviso that mu, ra, and
gm are not actually constants and all the common equations relating
them seem to me to be shortcut approximations.

Now, if an anode load is a current source, then the gain of the valve
is mu, and Rk has no effect because under constant current conditions
it cannot generate a signal at the cathode. It therefore appears that
the cathode resistor does not degenerate mu, and you are correct.

Actually, the load seen by each valve is quite high, being the sum of
ra, Rk, and Rk(mu+1). This is only true for the second stage if it has
no output load, which could be criticism of the circuit detail because
a significant load would unbalance it.

So if we use mu=33 and ra=2.7k for 6DJ8, then the load for each valve
= 2.7k + 1.82k + 34*1.82k = 66k. That is better than 20 to 1, and gain
for each valve would be fairly close to mu, were the gain not reduced
by its cathode resistor.

As ever, I could be wrong. My initial post didn't point out that the
gain of valves is reduced by their unbypassed cathode resistors. Apart
from that my explanation of the working of the circuit remains
correct.

Some clowns have since muddied the waters. The Butcher in particular
has, as usual, poisoned the thread with nonsense, and misled and
discouraged the OP. I find that behaviour simply too disgusting to
witness, so I shan't be hanging around here much.

cheers, Ian

[Patrick Turner]

On Dec 5, 12:46*am, Ian Iveson wrote:
On Dec 3, 1:18*am, "Alex Pogossov" wrote:





"Ian Iveson" wrote in message

....
On Dec 2, 12:02 pm, "Alex Pogossov" wrote:

"Ian Iveson" wrote in message

....
On Dec 1, 6:42 pm, Fai C wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

"multi" just means it comes with various attachments. Nothing to do
with valve circuits, one hopes.

The circuit probably has a name. Maybe Alex knows? The purpose is to
provide gain and a low impedance output, so it can drive a low
impedance input...maybe triodes in AB2. There are umpteen ways its
operation could be described, depending on how you untangle it.

Alex:
-----------
I do not know what this circuit is called, as I am not an expert in tube
circuits.
But this one can be probably called a "mu/2 amplifier". Let me explain.

[Ian Iveson[_2_]]

On Dec 2, 3:40*am, flipper wrote:
On Thu, 1 Dec 2011 10:42:29 -0800 (PST), Fai C
wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

It's not a multivibrator.

The first two (vertical) triodes (of each stage) are an SRPP amplifier
and he's buffering it with the second two triodes. The top second
triode is just doing "the same thing" as the previous triode grid it's
connected to and so is the second bottom triode. The idea is to
isolate the load from the signal (first) stage.

Notice at the bottom of the schematic he calls it a "supertotem." It's
also called a Gomes.

See here for more than you probably want to know

http://www.tubecad.com/2004/blog0015.htm

Having written of clowns, I feel I should exclude you from the list.

I think it's best to see this as a single, compound SRPP stage in
which the feed from bottom anode to top grid is isolated from the
output. It could be seen in lots of ways though...including a
paraphase splitter and PP stage.

SRPP and mu-follower are essentially the same circuit, but the mu-
follower has a larger current-sense resistance for the current source,
with a tap for the bias, which then calls for AC coupling from bottom
anode to top grid. I'm quite looking forward to experimenting with my
emerging headphone amp, but I'll likely end up with just a single
generous triode and a beautiful output transformer.

Gomes? Somewhere in my search for Kimmel I seem to recall a Gomes. The
Great Revival of valve audio split into camps and many became
commercial, or at least tried. I notice Jones deals with the mu-
follower but doesn't mention the SRPP AFAICS. Too continental,
perhaps.

Ian

[flipper]

On Sun, 4 Dec 2011 11:38:57 -0800 (PST), Ian Iveson
wrote:

On Dec 2, 3:40*am, flipper wrote:
On Thu, 1 Dec 2011 10:42:29 -0800 (PST), Fai C
wrote:

Hello!
My friend just sent me this circuit that is designed by an Italian
builder called Bartolomeo Aloia. The circuit BA211 (see link), I've
discussed with my friend this morning about the driver section of this
211 circuit, it acts like a mutivibrator (pulse generator) for old
tube computer. I wonder why they choose a pulse generator for a driver
stage of the SE amplifier. Any benefits? What is the features from
such driver circuit?

http://www.audiodesignguide.com/ba/

Have Fun!

It's not a multivibrator.

The first two (vertical) triodes (of each stage) are an SRPP amplifier
and he's buffering it with the second two triodes. The top second
triode is just doing "the same thing" as the previous triode grid it's
connected to and so is the second bottom triode. The idea is to
isolate the load from the signal (first) stage.

Notice at the bottom of the schematic he calls it a "supertotem." It's
also called a Gomes.

See here for more than you probably want to know

http://www.tubecad.com/2004/blog0015.htm

Having written of clowns, I feel I should exclude you from the list.

I think it's best to see this as a single, compound SRPP stage in
which the feed from bottom anode to top grid is isolated from the
output. It could be seen in lots of ways though...including a
paraphase splitter and PP stage.

SRPP and mu-follower are essentially the same circuit, but the mu-
follower has a larger current-sense resistance for the current source,
with a tap for the bias, which then calls for AC coupling from bottom
anode to top grid. I'm quite looking forward to experimenting with my
emerging headphone amp, but I'll likely end up with just a single
generous triode and a beautiful output transformer.

Gomes? Somewhere in my search for Kimmel I seem to recall a Gomes. The
Great Revival of valve audio split into camps and many became
commercial, or at least tried. I notice Jones deals with the mu-
follower but doesn't mention the SRPP AFAICS. Too continental,
perhaps.

Ian

You wouldn't need to search for Gomes if you simply read the link I
provided.

[Ian Iveson[_2_]]

On Dec 5, 4:21*am, flipper wrote:

Gomes? Somewhere in my search for Kimmel I seem to recall a Gomes. The
Great Revival of valve audio split into camps and many became
commercial, or at least tried. I notice Jones deals with the mu-
follower but doesn't mention the SRPP AFAICS. Too continental,
perhaps.

Ian

You wouldn't need to search for Gomes if you simply read the link I
provided.

I didn't search for Gomes. I didn't need to.

Ian

[Patrick Turner]

Ian scribed........

SRPP and mu-follower are essentially the same circuit, but the mu-
follower has a larger current-sense resistance for the current source,
with a tap for the bias, which then calls for AC coupling from bottom
anode to top grid.

Well, SRPP and mu-foll do have "totem pole" config but that's where
the similarity ends. The SRPP can only be really called PP when there
is substantial work on the load done by BOTH top AND bottom tube, and
the load is such that the top Rk generates enough load current from
bottom tube to give Vgk applied to top tube which is nearly equal to
the Vgk applied to the bottom tube from a signal source.
Suppose one had a pair of EL86 in triode ( similar to EL84 in triode,
but Ra = 1k2 ) in SRPP circuit, and for each tube Ea = 150V, Ia =
60mAdc, and phones of 32 ohms were connected to top cathode, then one
probably could get about +/- 50mA peak Ia change in load to give 39mW
of power into 32 ohms which to the tubes looks like a short circuit,
because an ideal class A load would be 1k2, with each tube "seeing"
close to 2k4, or R x Ra.
EL86 has u = 10 approx, and gain with EL86 is low with load of about
64 ohms, and THD is high, so you'd need a shirt&trouser load of NFB to
straighten out the mess you have without an OPT.

But suppose you had a mu-foll, with say 6AS7/6080 with Ea = 100V and
Ia 200mA, with choke between cathode and 0V. The cathode voltage would
have a cap to keep Idc from the phones, say 2,200uF.
The driver tube can be set up like a normal common cathode gain stage
except that its dc RL is a pair of resistors to B+ with junction
bypassed to 6AS7 cathode with say 470uF, ie, top of choke, and also
the signal output for the phones. This means the output voltage from
"top" tube 6AS7 is in series with bottom tube anode supply resistance,
and this resistance is barely aware there is any load connected; and
in fact the load resistance is "bootstrapped" and appears to the drive
tube as a much higher R than it actually is, so the driver tube
provides low THD drive to the OP tube. With 200mA in the 6AS7 at idle,
load current can be maybe +/- 150mA giving 0.35 Watts which is enough
to deafen our Ian if the Rolling Stones is played that loud.

So the mu-follower has very little load current produced in its bottom
tube and this is also true in a preamp situtation such as at
http://www.turneraudio.com.au/Line-preamp-2003.htm

The use of mu-foll as opposed to SRPP is to AVOID load current sensing
between top and bottom tubes and to promote the top tube to being an
almost pure cathode follower, and then have the bottom tube operating
with a very high effective RL which its THD becomes much lower than
SRPP, or a normal tube with non bootstrapped resistance for dc to
anode.


I'm quite looking forward to experimenting with my
emerging headphone amp, but I'll likely end up with just a single
generous triode and a beautiful output transformer.

In the last headhone amp I used EL84 in triode with OPTs taken from a
Fisher AM/FM receiver.
The load was about 5k : 16, and for headphones, ANY load is about OK,
you'll have enough power/voltage headroom.

I used 1/2 6CG7 to drive EL84 with 12dB NFB.

The customer is extremely happy.

Noise is the main problem to overcome, so I suggest all trannys are
potted, and DC is applied to all heaters; an external PSU is a good
idea. Even then, tube noise can be present. One should aim for noise
to be less than 0.05mV, or 50uV. You may find this impossible achieve,
but you get say 0.25mV. Well, a simple resistance divider across the
16 ohm winding, say 39 ohms plus 8.2 ohms will give mean the tube
signal level will have to be about 6 times higher, but the R divider
divides the noise down so SNR is improved by 6 times. Most headphone
outlets on power amps and receivers have such a divider which allows
tubes or transistors to see a high value load and hence give low THD,
while being able to still give oodles of voltage for headphones.

The phones amp I built for my customer in 2009 is fully integrated,
has hi & low level outputs, and can be used as a normal preamp with
superb performance.

A lot of ppl try to avoid OPTs in phone amps while insisting on tubes
to give OTL type of power. Its not good practice, but a pair of
complementary source follower mosfets could easily be used with a +/-
12V supply
and Ia at 0.5 amps, and then one drives both gates from a C&R coupled
triode of some sort. The secret is to have the voltage amping done
linearly, and also the current amping, and class A mosfets in source-
foll mode will be remarkably linear, even if the phones are 4 ohms.
6AS7 with a PP OPT would also be OK.
But once you go to tubes and OPT, the OPT allows a normal amp to be
made, and loading and linearity becomes much better than without OPT.

Patrick Turner.

[Ian Iveson[_2_]]

On Dec 8, 10:31*am, Patrick Turner wrote:
Ian scribed........

SRPP and mu-follower are essentially the same circuit, but the mu-
follower has a larger current-sense resistance for the current source,
with a tap for the bias, which then calls for AC coupling from bottom
anode to top grid.

Well, SRPP and mu-foll *do have "totem pole" config but that's where
the similarity ends.

The difference is as I have described it. The difference in how you
envisage the operation of the two circuits is up to you.

Alex has already pointed out that the gain of a symmetrical SRPP must
be mu/2 and I have agreed with him, giving supporting analysis. I
provided a link to Kimmel's original paper which develops the mu-
follower from the SRPP.

Do keep up.

The SRPP can only be really called PP when there
is substantial work on the load done by BOTH top AND bottom tube, and
the load is such that the top Rk generates enough load current from
bottom tube to give Vgk applied to top tube which is nearly equal to
the Vgk applied to the bottom tube from a signal source.
Suppose one had a pair of EL86 in triode ( similar to EL84 in triode,
but Ra = 1k2 ) in SRPP circuit, and for each tube Ea = 150V, Ia =
60mAdc, and phones of 32 ohms were connected to top cathode, then one
probably could get about +/- 50mA peak Ia change in load to give 39mW
of power into 32 ohms which to the tubes looks like a short circuit,
because an ideal class A load would be 1k2, with each tube "seeing"
close to 2k4, or R x Ra.
EL86 has u = 10 approx, and gain with EL86 is low with load of about
64 ohms, and THD is high, so you'd need a shirt&trouser load of NFB to
straighten out the mess you have without an OPT.

It would be easier for you to simply link to Kimmel's paper. Except
it's already been done.

But suppose you had a mu-foll, with say 6AS7/6080 with Ea = 100V and
Ia 200mA, with choke between cathode and 0V. The cathode voltage would
have a cap to keep Idc from the phones, say 2,200uF.
The driver tube can be set up like a normal common cathode gain stage
except that its dc RL is a pair of resistors to B+ with junction
bypassed to 6AS7 cathode with say 470uF, ie, top of choke, and also
the signal output for the phones. This means the output voltage from
"top" tube 6AS7 is in series with bottom tube anode supply resistance,
and this resistance is barely aware there is any load connected; and
in fact the load resistance is "bootstrapped" and appears to the drive
tube as a much higher R than it actually is, so the driver tube
provides low THD drive to the OP tube. With 200mA in the 6AS7 at idle,
load current can be maybe +/- 150mA giving 0.35 Watts which is enough
to deafen our Ian if the Rolling Stones is played that loud.

So the mu-follower has very little load current produced in its bottom
tube and this is also true in a preamp situtation such as athttp://www.turneraudio.com.au/Line-preamp-2003.htm

The use of mu-foll as opposed to SRPP is to AVOID load current sensing
between top and bottom tubes and to promote the top tube to being an
almost pure cathode follower,

Had you read my original post on this thread, you would realise that
the the circuit under discussion does exactly that.

and then have the bottom tube operating
with a very high effective RL which its THD becomes much lower than
SRPP, or a normal tube with non bootstrapped resistance for dc to
anode.

I'm quite looking forward to experimenting with my
emerging headphone amp, but I'll likely end up with just a single
generous triode and a beautiful output transformer.

In the last headhone amp I used EL84 in triode with OPTs taken from a
Fisher AM/FM receiver.
The load was about 5k : 16, and for headphones, ANY load is about OK,
you'll have enough power/voltage headroom.

Yes. In my case 5k : 62R

I'm still dithering on the sec. 4 x 4R or 1 x 62. If only I could
predict the effect on leakage.

I used 1/2 6CG7 to drive EL84 with 12dB NFB.

With 6CH6 in triode I would have more or less unity gain, and enough
headroom. It would be nice to try a proper triode though. If I can do
without feedback, that's what I'll stick with.

The customer is extremely happy.

Lots of headphone amps are rubbish. Not many ppl used to care because
even poor headphones can sound much clearer than a poor room system.
There's a huge market for headphones now, although much of the top end
is functionalist rather than functional. Within that market, a new
generation of discerning audiophiles is emerging.

Noise is the main problem to overcome, so I suggest all trannys are
potted, and DC is applied to all heaters; an external PSU is a good
idea. Even then, tube noise can be present. One should aim for noise
to be less than 0.05mV, or 50uV. You may find this impossible achieve,
but you get say 0.25mV. Well, a simple resistance divider across the
16 ohm winding, say 39 ohms plus 8.2 ohms will give mean the tube
signal level will have to be about 6 times higher, but the R divider
divides the noise down so SNR is improved by 6 times. Most headphone
outlets on power amps and receivers have such a divider which allows
tubes or transistors to see a high value load and hence give low THD,
while being able to still give oodles of voltage for headphones.

Noise is indeed the biggest...actually the only...problem to be
overcome.

I'll start with as much as possible and then reluctantly add bits
until the noise is gone. That way I'll know what I can't hear.

The phones amp I built for my customer in 2009 is fully integrated,
has hi & low level outputs, and can be used as a normal preamp with
superb performance.

A lot of ppl try to avoid OPTs in phone amps while insisting on tubes
to give OTL type of power. Its not good practice, but a pair of
complementary source follower mosfets could easily be used with a +/-
12V supply
and Ia at 0.5 amps, and then one drives both gates from a C&R coupled
triode of some sort. The secret is to have the voltage amping done
linearly, and also the current amping, and class A mosfets in source-
foll mode will be remarkably linear, even if the phones are 4 ohms.
6AS7 with a PP OPT would also be OK.
But once you go to tubes and OPT, the OPT allows a normal amp to be
made, and loading and linearity becomes much better than without OPT.

That's why I'm using an OPT. Otherwise, Nat Semi does a very nice
headphone buffer chip and I wouldn't need valves at all.

Ian

[Patrick Turner]

On Dec 10, 7:22*am, Ian Iveson wrote:
On Dec 8, 10:31*am, Patrick Turner wrote:

Ian scribed........

SRPP and mu-follower are essentially the same circuit, but the mu-
follower has a larger current-sense resistance for the current source,
with a tap for the bias, which then calls for AC coupling from bottom
anode to top grid.

Well, SRPP and mu-foll *do have "totem pole" config but that's where
the similarity ends.

The difference is as I have described it. The difference in how you
envisage the operation of the two circuits is up to you.

Alex has already pointed out that the gain of a symmetrical SRPP must
be mu/2 and I have agreed with him, giving supporting analysis. I
provided a link to Kimmel's original paper which develops the mu-
follower from the SRPP.

Do keep up.

I have my own views, and will state them independantly to other
websites if I see fit.

I might say that regardless of how a triode is used, if the loading
gives gain = µ/2, then that load is TOO LOW.
Take a pair of EL84 in triode. µ = 20, and for nice clean class A gain
might be 17. But your saying for SRPP, gain could be 10, and I would
say that is preposterous, ie, stoopid, and to be avoided at all
costs.

The SRPP can only be really called PP when there
is substantial work on the load done by BOTH top AND bottom tube, and
the load is such that the top Rk generates enough load current from
bottom tube to give Vgk applied to top tube which is nearly equal to
the Vgk applied to the bottom tube from a signal source.
Suppose one had a pair of EL86 in triode ( similar to EL84 in triode,
but Ra = 1k2 ) in SRPP circuit, and for each tube Ea = 150V, Ia =
60mAdc, and phones of 32 ohms were connected to top cathode, then one
probably could get about +/- 50mA peak Ia change in load to give 39mW
of power into 32 ohms which to the tubes looks like a short circuit,
because an ideal class A load would be 1k2, with each tube "seeing"
close to 2k4, or R x Ra.
EL86 has u = 10 approx, and gain with EL86 is low with load of about
64 ohms, and THD is high, so you'd need a shirt&trouser load of NFB to
straighten out the mess you have without an OPT.

It would be easier for you to simply link to Kimmel's paper. Except
it's already been done.





But suppose you had a mu-foll, with say 6AS7/6080 with Ea = 100V and
Ia 200mA, with choke between cathode and 0V. The cathode voltage would
have a cap to keep Idc from the phones, say 2,200uF.
The driver tube can be set up like a normal common cathode gain stage
except that its dc RL is a pair of resistors to B+ with junction
bypassed to 6AS7 cathode with say 470uF, ie, top of choke, and also
the signal output for the phones. This means the output voltage from
"top" tube 6AS7 is in series with bottom tube anode supply resistance,
and this resistance is barely aware there is any load connected; and
in fact the load resistance is "bootstrapped" and appears to the drive
tube as a much higher R than it actually is, so the driver tube
provides low THD drive to the OP tube. With 200mA in the 6AS7 at idle,
load current can be maybe +/- 150mA giving 0.35 Watts which is enough
to deafen our Ian if the Rolling Stones is played that loud.

So the mu-follower has very little load current produced in its bottom
tube and this is also true in a preamp situtation such as athttp://www.turneraudio.com.au/Line-preamp-2003.htm

The use of mu-foll as opposed to SRPP is to AVOID load current sensing
between top and bottom tubes and to promote the top tube to being an
almost pure cathode follower,

Had you read my original post on this thread, you would realise that
the the circuit under discussion does exactly that.

Reading your waffle is difficult. You are a great waffler which few
ppl understand, and now you complain ppl don't read you right, or
fully. BE CLEARER using less words.

and then have the bottom tube operating
with a very high effective RL which its THD becomes much lower than
SRPP, or a normal tube with non bootstrapped resistance for dc to
anode.

I'm quite looking forward to experimenting with my
emerging headphone amp, but I'll likely end up with just a single
generous triode and a beautiful output transformer.

In the last headhone amp I used EL84 in triode with OPTs taken from a
Fisher AM/FM receiver.
The load was about 5k : 16, and for headphones, ANY load is about OK,
you'll have enough power/voltage headroom.

Yes. In my case 5k : 62R

If you had a 5k0 : 16 OPT, and the sec load was 62 ohms, the primary
load is 19k4, and the two EL84 see a pure class A load of high value
and their gain approaches 20, or µ, and you get excellent fidelity.

So in your case, and I guess, because you ain't supplied enough
details, that you should have said "in my case 19k4 : 62r."


I'm still dithering on the sec. 4 x 4R or 1 x 62. If only I could
predict the effect on leakage.

The loading of 16 ohms may give a -3dB pole due to LL at say 50kHz.
With loading = 62 ohms, or near enough to 4 times the load ohms, the
-3dB due to LL is raised to 200kHz.
But the primary shunt C may possible prevent any such -3dB HF at
200kHz, and in fact shunt C and LL will form a seond order filter of
some sort and give a peaked response unless some sort of a zobel is
used to provide the LC circuit with a critical damping R value. The
R&C values may be estimated, then tried out when you make the amp,
then altered to whatever flatttens response, without adversely loading
the amp at HF or provoking HF instability.

I used 1/2 6CG7 to drive EL84 with 12dB NFB.

With 6CH6 in triode I would have more or less unity gain, and enough
headroom. It would be nice to try a proper triode though. If I can do
without feedback, that's what I'll stick with.

The customer is extremely happy.

Lots of headphone amps are rubbish. Not many ppl used to care because
even poor headphones can sound much clearer than a poor room system.

Indeed. Headphone loadings usually cause the amp output devices to
work in class A and increase their gain thus boosting effective NFB
and reducing all forms of distertion. Because only a tiny poofteenth
if a an output voltage is required with phones, even with a noise
reducing R divider present, phones can give a cleaner signal than any
supplied to a speaker.

There's a huge market for headphones now, although much of the top end
is functionalist rather than functional. Within that market, a new
generation of discerning audiophiles is emerging.

Yeah, but ppl are crammed close to a PC in a bedroom, and room sound
is always going to be worse,
and then there are neighbours close by in small dwelings. And the vast
majority are listening to MP3 crap and programme is pop, and much
processed digital sound, and the number of audiophiles conceived in
this process of crapology is very small indeed. Phone uses have always
"been emerging" for 100Years, but real audio nutters want good room
sound where the source is an analog recording of an acoustic
instrument of singer, all without much processing. That ideal is
virtually never the case, and whatmost ppl use for source recordings
is digital in origin, so audiophiles then have to discern between crap
digital and good digital, and its a never ending search for the
perfect sound.

Noise is the main problem to overcome, so I suggest all trannys are
potted, and DC is applied to all heaters; an external PSU is a good
idea. Even then, tube noise can be present. One should aim for noise
to be less than 0.05mV, or 50uV. You may find this impossible achieve,
but you get say 0.25mV. Well, a simple resistance divider across the
16 ohm winding, say 39 ohms plus 8.2 ohms will give mean the tube
signal level will have to be about 6 times higher, but the R divider
divides the noise down so SNR is improved by 6 times. Most headphone
outlets on power amps and receivers have such a divider which allows
tubes or transistors to see a high value load and hence give low THD,
while being able to still give oodles of voltage for headphones.

Noise is indeed the biggest...actually the only...problem to be
overcome.

I'll start with as much as possible and then reluctantly add bits
until the noise is gone. That way I'll know what I can't hear.

Say you have a typical 2mV of noise across the 16 ohm winding from a
pair of EL84 in triode. If you just connect phones to speaker
terminals, that 2mV is clearly audible. In fact, strapping headphones
across speaker terminals of any amp is a good way to monitor noise
from a power amp and discern what it might be, ie, mains harmonics, or
just hiss, or rectifier pulses, or all 3.

I like to see less than 0.05mV of phone noise, so noise at 16 ohms
should be reduced to 0.5mV, then a 10:1 resistance divider used. The
audible noise within the measured 2mV may be a lot less than 2mV,
typically 0.5mV at 16 ohms. So you can usually get way with a lower R
diver ratio.

The phones amp I built for my customer in 2009 is fully integrated,
has hi & low level outputs, and can be used as a normal preamp with
superb performance.

A lot of ppl try to avoid OPTs in phone amps while insisting on tubes
to give OTL type of power. Its not good practice, but a pair of
complementary source follower mosfets could easily be used with a +/-
12V supply
and Ia at 0.5 amps, and then one drives both gates from a C&R coupled
triode of some sort. The secret is to have the voltage amping done
linearly, and also the current amping, and class A mosfets in source-
foll mode will be remarkably linear, even if the phones are 4 ohms.
6AS7 with a PP OPT would also be OK.
But once you go to tubes and OPT, the OPT allows a normal amp to be
made, and loading and linearity becomes much better than without OPT.

That's why I'm using an OPT. Otherwise, Nat Semi does a very nice
headphone buffer chip and I wouldn't need valves at all.

Opamps OPA234 plus a couple of source follower mosfets in class A and
a loop of NFB will also sound well,
but it could be argued the SS will omit the spirit of the music.......

Patrick Turner.

[Alex Pogossov]

"Patrick Turner" wrote in message
...

Opamps OPA234 plus a couple of source follower mosfets in class A and
a loop of NFB will also sound well...

Alex:
Are you serious?
OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate is
simply not suitable for Hi-Fi audio.
LM358 which costs under 10c will "sound" even better.

[Don Pearce[_3_]]

On Mon, 12 Dec 2011 23:05:24 +1100, "Alex Pogossov"
wrote:


"Patrick Turner" wrote in message
...

Opamps OPA234 plus a couple of source follower mosfets in class A and
a loop of NFB will also sound well...

Alex:
Are you serious?
OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate is
simply not suitable for Hi-Fi audio.
LM358 which costs under 10c will "sound" even better.


Alex, could I ask a favour? Will you restore your newsreader's
attribution settings to their default. The way you have it right now
threads are screwed and impossible to follow the moment you post.

Thanks

Don

[Doug Bannard]

"Alex Pogossov" wrote in message
...

"Patrick Turner" wrote in message
...

Opamps OPA234 plus a couple of source follower mosfets in class A and
a loop of NFB will also sound well...

Alex:
Are you serious?
OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate is
simply not suitable for Hi-Fi audio.
LM358 which costs under 10c will "sound" even better.


Hi Alex:

Patrick must have meant OPA2134.

Best Regards: Doug Bannard

[Alex Pogossov]

"Doug Bannard" wrote in message
m...

"Alex Pogossov" wrote in message
...

"Patrick Turner" wrote in message
...

Opamps OPA234 plus a couple of source follower mosfets in class A and
a loop of NFB will also sound well...

Alex:
Are you serious?
OPA234 with only 350kHz unity gain bandwidth and only 0.2V/us slew rate
is simply not suitable for Hi-Fi audio.
LM358 which costs under 10c will "sound" even better.


Hi Alex:

Patrick must have meant OPA2134.

Best Regards: Doug Bannard

This op-amp is a really good one!

[Patrick Turner]

Someone said, in my defense......
Patrick must have meant OPA2134.

Best Regards: Doug Bannard

This op-amp is a really good one!-

Indeed. I did in fact mean the OPA2134PA.

I used some to make a very low THD oscillator this time last year. I
got 0.001% at 5Vrms at 1kHz, an improvement over what I had been
using.

I spent a month being unwell then, and I used that unwell time to
farnarkle with non pay dirt activities such as re-making a wien bridge
oscillator.

The OPA2134PA is listed at Jaycar electronic stores for $8.95. Its
described as a "Audio high performance op-amp". But I cooked two to
death very easily. But ya gotta let smoke out sometimes, even though
smoke won't go back in, to be able to learn by doing.

Patrick Turner.