[John Byrns]

In article ,
"Arny Krueger" wrote:

"John Byrns" wrote in message

In article ,
"Arny Krueger" wrote:

"John Byrns" wrote in message

In article
, "Ian
Iveson" wrote:

One thing I wonder about. It is common to use a
capacitor in series at the input of a valve power amp,
and this may be used to limit the LF response. If you
use a transformer then arguably you don't need the
series cap for its dc-blocking role. So it may seem
that you can rely on the transformer also for the role
of limiting LF. Would that be wise? I am concerned
about the possibility of ensuing distortion.

I don't see why distortion would become any more of a
problem below the lowest frequency the transformer the
transformer is rated for, assuming the LF signal level
is no higher than the signal level the transformer is
designed for in its specified range.

Distortion is more of a problem at low frequencies
because of core saturation effects:

http://www.rane.com/note159.html

"Core saturation happens when the magnetic field in the
core reaches its maximum possible density, which is what
happens when the applied voltage polarity remains the
same for too long."

Obviously, the applied voltage polarity remains the same
for a longer time at lower frequencies than higher
frequencies.

"Saturation has nothing to do with power delivery: the
onset of saturation depends only on the voltage waveform
applied to the primary."

That quote should be corrected to state that saturation
depends on frequency as well as voltage.

Why? the previous quote already said that once!

Why, because the meaning of the statement "the onset of saturation
depends only on the voltage waveform applied to the primary" is
ambiguous although theoretically correct.

The reason
distortion (saturation) would not be a problem when a
transformer is being used to limit the LF response as the
OP was asking about,

It is the frequency and amplitude of the applied voltage that counts.

Isn't that essentially what I just got through saying in the part of my
post that you snipped out? Please note that there was a typo in that
part of my post when I said "low pass" filter when I meant "high pass"
filter, this typo should have been obvious to the reader since we are
talking about limiting the LF response, which means a high pass filter.

When a
transformer is being used as a high pass filter, its primary is receiving
the applied voltage.

Can you explain how a transformer could act as a high pass filter when
the "primary is receiving the applied voltage", assuming you are not
depending on saturation effects to produce a pseudo low pass filter
effect? To act as a high pass filter the "voltage" can't be "applied"
directly to the transformer's primary, there must be a source impedance
involved in the equation between the source voltage and the transformer
primary. This source impedance could consist of the resistive component
of the impedance of the transformer's primary winding, assuming it is
large enough to create the desired high pass effect in conjunction with
the inductive component of the primary winding's impedance.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Ian Iveson]

John Byrns wrote

Ian Iveson wrote:

One thing I wonder about. It is common to use a
capacitor in series at the input of a valve power amp,
and this may be used to limit the LF response. If you
use a transformer then arguably you don't need the
series cap for its dc-blocking role. So it may seem that
you can rely on the transformer also for the role of
limiting LF. Would that be wise? I am concerned about
the possibility of ensuing distortion.

I don't see why distortion would become any more of a
problem below the lowest frequency the transformer the
transformer is rated for, assuming the LF signal level is
no higher than the signal level the transformer is
designed for in its specified range.

Distortion is more of a problem at low frequencies because of core
saturation effects:

http://www.rane.com/note159.html

"Core saturation happens when the magnetic field in the core
reaches its
maximum possible density, which is what happens when the applied
voltage
polarity remains the same for too long."

Obviously, the applied voltage polarity remains the same for a
longer time
at lower frequencies than higher frequencies.

"Saturation has nothing to do with power delivery: the onset of
saturation
depends only on the voltage waveform applied to the primary."

That quote should be corrected to state that saturation depends on
frequency as well as voltage.

*Magnetising current* is directly responsible for flux density.
Voltage and frequency relations are derived.

The reason distortion (saturation) would
not be a problem when a transformer is being used to limit the LF
response as the OP was asking about, is because what we are talking
about then is a low pass filter where the source resistance driving
the
transformer primary operates in conjunction with the transformer's
primary inductance to roll of the LF response below a specific
point.
This roll off of the primary voltage at lower frequencies prevents
the
core from going into saturation (distortion) at lower frequencies as
would happen if the primary voltage were held constant as the
frequency
decreases.

Not with my maths. Please post yours.

Think of it like this. You have current due to load, and in parallel
you have magnetising current. An increase in magnetising current at
lower frequencies is responsible for the roll-off, given a finite
source resistance. An increase in magnetising current means that the
core traverses a greater part of the BH curve, hence distortion will
increase. In the extreme, saturation will occur if Vs/Rs is great
enough at f=0, ie for DC, when *all* the current is magnetising. If
Vs/Rs is greater than that, then saturation will occur at some
frequency higher than 0.

Yes, effective primary voltage falls with frequency, but not by enough
to hold the magnetising current constant.

If your mathematical argument disagrees with this please post it. So
far you have merely asserted, not demonstrated.

Ian

[Arny Krueger]

"John Byrns" wrote in message

In article ,
"Arny Krueger" wrote:

"John Byrns" wrote in message

In article
, "Arny
Krueger" wrote:

"John Byrns" wrote in message

In article
, "Ian
Iveson" wrote:

One thing I wonder about. It is common to use a
capacitor in series at the input of a valve power
amp, and this may be used to limit the LF response.
If you use a transformer then arguably you don't
need the series cap for its dc-blocking role. So it
may seem that you can rely on the transformer also
for the role of limiting LF. Would that be wise? I
am concerned about the possibility of ensuing
distortion.

I don't see why distortion would become any more of a
problem below the lowest frequency the transformer the
transformer is rated for, assuming the LF signal level
is no higher than the signal level the transformer is
designed for in its specified range.

Distortion is more of a problem at low frequencies
because of core saturation effects:

http://www.rane.com/note159.html

"Core saturation happens when the magnetic field in the
core reaches its maximum possible density, which is
what happens when the applied voltage polarity remains
the same for too long."

Obviously, the applied voltage polarity remains the
same for a longer time at lower frequencies than higher
frequencies.

"Saturation has nothing to do with power delivery: the
onset of saturation depends only on the voltage
waveform applied to the primary."

That quote should be corrected to state that saturation
depends on frequency as well as voltage.

Why? the previous quote already said that once!

Why, because the meaning of the statement "the onset of
saturation depends only on the voltage waveform applied
to the primary" is ambiguous although theoretically
correct.

Why did you remove the part of the paragraph that explained the frequency
dependency?

To repeat:

"Core saturation happens when the magnetic field in the
core reaches its maximum possible density, which is
what happens when the applied voltage polarity remains
the same for too long."
Obviously, the applied voltage polarity remains the
same for a longer time at lower frequencies than higher
frequencies

The reason
distortion (saturation) would not be a problem when a
transformer is being used to limit the LF response as
the OP was asking about,

It is the frequency and amplitude of the applied voltage
that counts.

Isn't that essentially what I just got through saying in
the part of my post that you snipped out?

No, that's what you snipped out of my post.

[Ian Iveson]

This might be a bit interesting:

http://www.ivesonaudio.pwp.blueyonde...nByrnsTest.GIF

For what's in the coil and core models:

http://www.ivesonaudio.pwp.blueyonde...byrnstest2.GIF

http://www.ivesonaudio.pwp.blueyonde...byrnstest3.GIF

Ian

[west[_4_]]

"flipper" wrote in message
...
On Thu, 07 Jun 2007 04:03:01 GMT, Eeyore
wrote:



west wrote:

"Eeyore" wrote
Iain Churches wrote:

2. Are they actually better than a passive stepped attenuator
controller?

Better ?

Explain what better is first !

As I've discoverd, in the tube audio world, "better" has no
correlation
with measured technical accuracy / performance is is merely a
subjective
matter.

I fail to see thefore how "better" can be anything other than a
personal
opinion.


Why are you always trying to pick fly **** out of pepper? Maybe you
should
frequent alt.lawyers. Let's stop this bs. I know what he means. I'd
like to
see you post something in his language. Food for thought.

"Better" has no definable meaning.

That's the question he's asking: for an explanation or definition of
why it's supposedly 'better', or by what 'definition one would claim
it's 'better', and why one would use it.


E.g. one often hears here that SET's are better than other amplifiers
types yet
they are demonstrably hugely technically inferior in almost every
respect. If
this is to determine what 'better' means then better = worse.

How about asking a question that has a possible meaningful answer instead
?

He did. You just want to play word games rather than deal with the
intent of the question.


Or alternatively use the word 'nice' so there's no confusion with
technical
accuracy. The statement "SET's are nicer than other types of amplifier"
would be
a more honest expression of opinion than using the word 'better'.

Graham

I believe most of us know what the spirit of the term "better" means in this
case, no matter what the T crossers and the I dotter experts say. If a
potentiometer is placed in the signal path, there is a compromise to the
audio quality. Anything that improves on that compromise is BETTER. Give it
a break. Let's all learn from each other, without the anal retentiveness
nitpicking.

west

[Ian Iveson]

PS Perhaps I should explain that the two graphs show how flux varies
on a linear vertical scale, and how gain varies on a log vertical
scale, on the same horizontal frequency scale.

The model assumes a linear relationship between H and B,
unfortunately. Although the flux plot looks like a BH curve, it isn't.
The apparent saturation is due to the fact that the source resistance
eventually becomes a virtual current source because it is so high
compared to the coil impedance at very low frequencies.

The vertical scale for the flux graph is a bit mysterious. First, to
get the flux density, you would need to divide by the core area (A, in
the model). Then you need to appreciate that "gain" means relative to
the small-signal voltage input (a numerical comparison regardless of
units).

I can't remember what system of units I used. It should be obvious if
magnetic things happen to be fresh in your mind. I constructed the
models ages ago but gave up trying to contrive how to incorporate a
realistic BH curve.

Ian

"Ian Iveson" wrote in message
k...
This might be a bit interesting:

http://www.ivesonaudio.pwp.blueyonde...nByrnsTest.GIF

For what's in the coil and core models:

http://www.ivesonaudio.pwp.blueyonde...byrnstest2.GIF

http://www.ivesonaudio.pwp.blueyonde...byrnstest3.GIF

Ian

[John Byrns]

In article ,
"Ian Iveson" wrote:

John Byrns wrote

Ian Iveson wrote:

One thing I wonder about. It is common to use a
capacitor in series at the input of a valve power amp,
and this may be used to limit the LF response. If you
use a transformer then arguably you don't need the
series cap for its dc-blocking role. So it may seem that
you can rely on the transformer also for the role of
limiting LF. Would that be wise? I am concerned about
the possibility of ensuing distortion.

I don't see why distortion would become any more of a
problem below the lowest frequency the transformer the
transformer is rated for, assuming the LF signal level is
no higher than the signal level the transformer is
designed for in its specified range.

Distortion is more of a problem at low frequencies because of core
saturation effects:

http://www.rane.com/note159.html

"Core saturation happens when the magnetic field in the core
reaches its
maximum possible density, which is what happens when the applied
voltage
polarity remains the same for too long."

Obviously, the applied voltage polarity remains the same for a
longer time
at lower frequencies than higher frequencies.

"Saturation has nothing to do with power delivery: the onset of
saturation
depends only on the voltage waveform applied to the primary."

That quote should be corrected to state that saturation depends on
frequency as well as voltage.

*Magnetising current* is directly responsible for flux density.
Voltage and frequency relations are derived.

The reason distortion (saturation) would
not be a problem when a transformer is being used to limit the LF
response as the OP was asking about, is because what we are talking
about then is a low pass filter where the source resistance driving
the
transformer primary operates in conjunction with the transformer's
primary inductance to roll of the LF response below a specific
point.
This roll off of the primary voltage at lower frequencies prevents
the
core from going into saturation (distortion) at lower frequencies as
would happen if the primary voltage were held constant as the
frequency
decreases.

Not with my maths. Please post yours.

Think of it like this. You have current due to load, and in parallel
you have magnetising current. An increase in magnetising current at
lower frequencies is responsible for the roll-off, given a finite
source resistance. An increase in magnetising current means that the
core traverses a greater part of the BH curve, hence distortion will
increase. In the extreme, saturation will occur if Vs/Rs is great
enough at f=0, ie for DC, when *all* the current is magnetising. If
Vs/Rs is greater than that, then saturation will occur at some
frequency higher than 0.

Yes, effective primary voltage falls with frequency, but not by enough
to hold the magnetising current constant.

If your mathematical argument disagrees with this please post it. So
far you have merely asserted, not demonstrated.

My argument depends on two assumptions, please dispute one or the other,
or both if you wish, if you agree with both assumptions then my original
claim stands.

Assumption #1: I am not a transformer engineer, but those who know more
than I do about transformers have told me that for a given degree of
core saturation (distortion), if the frequency is cut in half, then the
voltage applied to the winding must also be cut in half to avoid
saturation. This means that the applied voltage must be made
proportional to the frequency (or lower) if saturation (distortion) is
to be avoided.

Assumption #2: If the transformer is being used to limit the LF
response of the system, then assuming no load on the secondary, the
source resistance feeding the primary of the transformer must be made
equal to the primary inductance at the desired cutoff frequency of the
resulting high pass filter. Below cutoff the voltage out of such a
filter, at the primary of the transformer in this case, falls at rate
that makes the voltage proportional to the frequency. This is exactly
the sort of voltage response we need on the primary to prevent
saturation of the transformer, hence saturation shouldn't be a problem.

So which one of these assumptions is wrong, or if both assumptions are
correct, where did my logic fail?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[John Byrns]

In article ,
"Arny Krueger" wrote:

"John Byrns" wrote in message

In article ,
"Arny Krueger" wrote:

"John Byrns" wrote in message

In article
, "Arny
Krueger" wrote:

"John Byrns" wrote in message

In article
, "Ian
Iveson" wrote:

One thing I wonder about. It is common to use a
capacitor in series at the input of a valve power
amp, and this may be used to limit the LF response.
If you use a transformer then arguably you don't
need the series cap for its dc-blocking role. So it
may seem that you can rely on the transformer also
for the role of limiting LF. Would that be wise? I
am concerned about the possibility of ensuing
distortion.

I don't see why distortion would become any more of a
problem below the lowest frequency the transformer the
transformer is rated for, assuming the LF signal level
is no higher than the signal level the transformer is
designed for in its specified range.

Distortion is more of a problem at low frequencies
because of core saturation effects:

http://www.rane.com/note159.html

"Core saturation happens when the magnetic field in the
core reaches its maximum possible density, which is
what happens when the applied voltage polarity remains
the same for too long."

Obviously, the applied voltage polarity remains the
same for a longer time at lower frequencies than higher
frequencies.

"Saturation has nothing to do with power delivery: the
onset of saturation depends only on the voltage
waveform applied to the primary."

That quote should be corrected to state that saturation
depends on frequency as well as voltage.

Why? the previous quote already said that once!

Why, because the meaning of the statement "the onset of
saturation depends only on the voltage waveform applied
to the primary" is ambiguous although theoretically
correct.

Why did you remove the part of the paragraph that explained the frequency
dependency?

Arny, you are a bald faced liar, go back and read my post again, I did
not remove a single word of your post that I was replying to.

To repeat:

"Core saturation happens when the magnetic field in the
core reaches its maximum possible density, which is
what happens when the applied voltage polarity remains
the same for too long."
Obviously, the applied voltage polarity remains the
same for a longer time at lower frequencies than higher
frequencies

The reason
distortion (saturation) would not be a problem when a
transformer is being used to limit the LF response as
the OP was asking about,

It is the frequency and amplitude of the applied voltage
that counts.

Isn't that essentially what I just got through saying in
the part of my post that you snipped out?

No, that's what you snipped out of my post.

Go back and read my post again, and then go away, I am not going to try
and talk to a liar.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Eeyore]

John Byrns wrote:

Assumption #1: I am not a transformer engineer, but those who know more
than I do about transformers have told me that for a given degree of
core saturation (distortion), if the frequency is cut in half, then the
voltage applied to the winding must also be cut in half to avoid
saturation. This means that the applied voltage must be made
proportional to the frequency (or lower) if saturation (distortion) is
to be avoided.

Correct.

When I was getting into transforemr design for SMPSs a couple of years back I
cane across the term 'volt seconds' which helps explain a lot. The more
volt-seconds, the higher the flux.

Graham

[Ian Iveson]

John Byrns wrote:

Assumption #1: I am not a transformer engineer, but those who know
more
than I do about transformers have told me that for a given degree of
core saturation (distortion), if the frequency is cut in half, then
the
voltage applied to the winding must also be cut in half to avoid
saturation. This means that the applied voltage must be made
proportional to the frequency (or lower) if saturation (distortion)
is
to be avoided.

Assumption #2: If the transformer is being used to limit the LF
response of the system, then assuming no load on the secondary, the
source resistance feeding the primary of the transformer must be
made
equal to the primary inductance at the desired cutoff frequency of
the
resulting high pass filter. Below cutoff the voltage out of such a
filter, at the primary of the transformer in this case, falls at
rate
that makes the voltage proportional to the frequency. This is
exactly
the sort of voltage response we need on the primary to prevent
saturation of the transformer, hence saturation shouldn't be a
problem.

So which one of these assumptions is wrong, or if both assumptions
are
correct, where did my logic fail?


Your assumption #2 is certainly false. It is not a sharp corner
followed by a straight line: -6dB per octave is an asymptote.

Your assumption of no secondary load is not appropriate for a
transformer. However, my simulation uses such a light load that no
load would not make much difference.

I have given one explanation for why the flux flattens at very low f
in my simulation. Translated to your thinking, it gets flatter as your
approximation gets closer to the truth. By that time the damage, as it
were, has been done.

See my maths, and my illustrations, which I trust tally.

Magnetising current is proportional to:

Vs / {Rs + K.f.Lp.(1 + Rs / B.RL)}

whe

K = 2 x pi .
N is the turns ratio
B = the square of the turns ratio
f is the frequency
Vs is the source voltage
Rs is the source resistance
RL is the load resistance
Lp is the primary inductance

Ian

[Phil Allison]

"Ian Iveson"

I don't think it's a question of distortion either,and besides, the
Sowter has a THD of 0.03% at +20dBu at 50Hz.

But what is it for a 2V input at, say 20Hz, or whatever is the lowest
frequency it may encounter?


** +20dBu = 7.75 volts rms so this is the input voltage for 0.03% THD.

Assuming THD is all due to the onset of core saturation ( very likely the
case ) the same THD level will be found at proportionally lower frequencies
and input levels.

Eg:

At 25 Hz with 3.875 volts rms.
At 5 Hz with 775 mV rms.

Typically THD rises dramatically with reducing frequency and fixed input
level, once the onset frequency has been reached.

I had a small 1:1 audio input balancing tranny on hand, rated at 10 kohms
to 10 kohms.

http://www.altronics.com.au/index.as...=item&id=M0706

The following test result were found:

-3 dB bandwidth:

1 Hz to 44kHz

( no mistake, tested with 50 mV rms input and a 250 ohm source )

Saturation:

3% THD at 32 Hz with 2.5 volts rms input.

3% THD at 3.2 Hz with 250 mV rms input.

But circa 50% THD at 25 Hz and 2.5 volts rms input !!!


Conclusion:

Such transformers have very wide small signal bandwidths and do not
inherently roll off sub sonic frequencies - unless driven into gross
saturation and hence gross distortion. A suitable size capacitor can be
fitted in series with the primary winding to prevent this - if large sub
sonic input signals exist.



....... Phil

[Ian Iveson]

Eeyore wrote:

When I was getting into transforemr design for SMPSs a couple of
years back I
cane across the term 'volt seconds' which helps explain a lot. The
more
volt-seconds, the higher the flux.


Useful because they work with switched DC...aka square waves...and low
source resistance.

Less obvious for proper waves, where voltage is variable, and/or when
source resistance is significant.

Ian

[John Byrns]

In article ,
"Ian Iveson" wrote:

John Byrns wrote:

Assumption #1: I am not a transformer engineer, but those who know
more
than I do about transformers have told me that for a given degree of
core saturation (distortion), if the frequency is cut in half, then
the
voltage applied to the winding must also be cut in half to avoid
saturation. This means that the applied voltage must be made
proportional to the frequency (or lower) if saturation (distortion)
is
to be avoided.

Assumption #2: If the transformer is being used to limit the LF
response of the system, then assuming no load on the secondary, the
source resistance feeding the primary of the transformer must be
made
equal to the primary inductance at the desired cutoff frequency of
the
resulting high pass filter. Below cutoff the voltage out of such a
filter, at the primary of the transformer in this case, falls at
rate
that makes the voltage proportional to the frequency. This is
exactly
the sort of voltage response we need on the primary to prevent
saturation of the transformer, hence saturation shouldn't be a
problem.

So which one of these assumptions is wrong, or if both assumptions
are
correct, where did my logic fail?

Your assumption #2 is certainly false. It is not a sharp corner
followed by a straight line: -6dB per octave is an asymptote.

My assumption #2 has nothing to do with transformers directly, so it is
the one assumption of the two that I know to be actually true. I am
aware that it is not a sharp corner, but so what I believe that it all
works out anyway, and if it doesn't we could just spec the transformer
with a tiny bit of extra margin. Let's think about an example, I'm
doing this in my head so a mistake is possible. Say we want the -3 dB
point of our high pass to be at 25 Hz. We pick the source resistance
and the primary inductance of the transformer to achieve that turn over
point. Then we determine the maximum level we wish to handle and spec.
the transformer so that it can handle that level at 25 Hz assuming the
source impedance is zero.

When we check we find that we have an extra margin of 3 dB to the
saturation point at 25 kHz, and the level asymptotically approaches the
line representing the saturation point from assumption #1 as the
frequency is decreased.

Your assumption of no secondary load is not appropriate for a
transformer. However, my simulation uses such a light load that no
load would not make much difference.

I was simply trying not to complicate the model in order to help promote
understanding, but the secondary load is irrelevant, we can simply
reflect it back to the primary side of the transformer and incorporate
it into the source impedance. Besides changing the effective source
impedance seen by the primary, this also slightly complicates picking
the required operating level of the transformer because we must take the
resulting voltage divider effect into account when specifying the
required operating level of the transformer.

I have given one explanation for why the flux flattens at very low f
in my simulation. Translated to your thinking, it gets flatter as your
approximation gets closer to the truth. By that time the damage, as it
were, has been done.

What damage is already done? If you found any damage then you didn't
pick the maximum operating level of the transformer correctly, see my
comment on this above.


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

[Phil Allison]

"Phil Allison"

** Typo:

http://www.altronics.com.au/index.as...=item&id=M0706

The following test result were found:

-3 dB bandwidth:

1 Hz to 84 kHz


Not " 44 kHz" as previously posted.




...... Phil

[Eeyore]

Ian Iveson wrote:

Eeyore wrote:

When I was getting into transforemr design for SMPSs a couple of
years back I cane across the term 'volt seconds' which helps explain a lot.
The
more volt-seconds, the higher the flux.

Useful because they work with switched DC...aka square waves...and low
source resistance.

Less obvious for proper waves, where voltage is variable, and/or when
source resistance is significant.

Since where was a square wave not 'proper' ?

You just can't help saying daft things can you ?

Graham

[Iain Churches]

"Arny Krueger" wrote in message
. ..
"Iain Churches" wrote in message
i.fi

http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg

Butt-ugly amplfier if there ever was one.
Arny. I would be *very* worried indeed if *you* liked it:-)
But most other people do, and that's what *really* matters.

Cordially,
Iain

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote in message

I thought volume controls are usually inside the amplifier because it's
simply convenient to put them there.

In these days of high level sources, no preamp is actually
required, so one can mount a pair stepped attenuators in
the power amp chassis, and feed the CD player direct.

http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg

For many decades I didn't own a preamp. Everything of mine had line level
outs
anyway (including my turntable).

The current one only qualifies as a preamp since it has a phono input but
in
reality it's just a source switcher the way I use it.

Yes. You could also fit the input selector (source switcher) to the power
amp also, to make it a line level integrated amplifier. I use a separate
phono stage mounted close to the turntable with balanced line output.

Iain

[Iain Churches]

"Eeyore" wrote in message
...


Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

There's *no way* a variable R costs as much as tapped transformers in the
real
world.

The TKD stereo attenuator costs about Euro 270 plus tax and shipping.
The transformers are about UKP 90 each. Not a lot of difference


For a simple source selector and volume control I'd use a pot followed
by
a high-performance op-amp buffer of course. Tubist might consider
replacing
the op-amp with a cathode follower, which is about as blameless as tube
audio
gets.

Yep. That's the concept on which my own preamp is based.

I was toying with the idea of a DC battery powered CF stage actually.
Rechargeable via a wall wart.

Sounds like a fun project:-) How is it progressing??
I chose a separate regulated psu.

Iain

[Patrick Turner]

Iain Churches wrote:

"Arny Krueger" wrote in message
. ..
"Iain Churches" wrote in message
i.fi

http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg

Butt-ugly amplfier if there ever was one.
Arny. I would be *very* worried indeed if *you* liked it:-)
But most other people do, and that's what *really* matters.

Cordially,
Iain

Are there tubes in the "heatsink" on top of the chassis?
How does such an amount of surrounding metal help keep the tubes cool?

Most audiophiles would immediately search for the screws holding down
such a cover, remove them all,
and throw away the offending metalwork, so they'd get a more "open
sound".

And perhaps less smoke.

Patrick Turner.

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote

Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

That doesn't really answer the question.


There's *no way* a variable R costs as much as tapped transformers in the
real world.

The TKD stereo attenuator costs about Euro 270 plus tax and shipping.
The transformers are about UKP 90 each. Not a lot of difference

Sounds to me like ripoff pricing.

There's plenty of accurate attenuators out there that I've come across. The
better ones use thick film resistors screened onto what's effectively a
multi-pole switch manufactured using potentiometer technology.


For a simple source selector and volume control I'd use a pot followed
by a high-performance op-amp buffer of course. Tubist might consider
replacing the op-amp with a cathode follower, which is about as blameless
as tube audio gets.

Yep. That's the concept on which my own preamp is based.

I was toying with the idea of a DC battery powered CF stage actually.
Rechargeable via a wall wart.

Sounds like a fun project:-) How is it progressing??
I chose a separate regulated psu.

Just a concept that crossed my mind as I was reading these posts. It would be
trivially simple to make one.

I thought the battery powered bit would appeal to the audiophools. The batteries
could feed the heater directly but it would need a tiny inverter for the B+.

Graham

[Iain Churches]

"Patrick Turner" wrote in message
...

http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg

Are there tubes in the "heatsink" on top of the chassis?
How does such an amount of surrounding metal help keep the tubes cool?

It is a cooling stack. Aluminium plates spaced 10mm apart,
(narrower than the smallest finger) which do quite a good job of
dissipating the heat. The tubes are cooled by convection, through
the bottom of the chassis and up the sides of the tubes.

Most audiophiles would immediately search for the screws holding down
such a cover, remove them all,
and throw away the offending metalwork, so they'd get a more "open
sound".

In this part of the world, the safety regs, and also domestic insurance,
require a cage or metal protection for the tubes in Class I amplifiers,
which can only be removed by the use of a tool (so press fit cages are
taboo)

Whether or not the owner removes the cage, is entirely his/her own
affair, and the responsibility , if the cage is removed and
someone burns themselves, is transferred from builder to owner.


And perhaps less smoke.

A number of these amps have been built. The oldest is now seven years
old. They are owned by responsible people who know how to check
the bias. None have developed faults to date.

Iain

[Patrick Turner]

Iain Churches wrote:

"Patrick Turner" wrote in message
...

http://www.kolumbus.fi/iain.churches...-30%20SA01.jpg

Are there tubes in the "heatsink" on top of the chassis?
How does such an amount of surrounding metal help keep the tubes cool?

It is a cooling stack. Aluminium plates spaced 10mm apart,
(narrower than the smallest finger) which do quite a good job of
dissipating the heat. The tubes are cooled by convection, through
the bottom of the chassis and up the sides of the tubes.

Most audiophiles would immediately search for the screws holding down
such a cover, remove them all,
and throw away the offending metalwork, so they'd get a more "open
sound".

In this part of the world, the safety regs, and also domestic insurance,
require a cage or metal protection for the tubes in Class I amplifiers,
which can only be removed by the use of a tool (so press fit cages are
taboo)

Whether or not the owner removes the cage, is entirely his/her own
affair, and the responsibility , if the cage is removed and
someone burns themselves, is transferred from builder to owner.

And perhaps less smoke.

A number of these amps have been built. The oldest is now seven years
old. They are owned by responsible people who know how to check
the bias. None have developed faults to date.

Iain

Sugden class A solid state amps had horrible heatsinks with
fins 10mm apart, about 50mm long, and running along the length
of the side of the box, and flat, like yours, and thus greatly reducing
any possible natural air flow.
They ran scorching hot, and MUCH hotter than if the same fin area was
mounted so the
fins were vertical, thus generating a much faster effective air flow,
such as in Quad 405.

So the way you have your heatsink provides compliance with safety regs,
but very poor
air flow, and lousy heat removal compared to what could have been
achieved with more
intelligent design of the metal work, ie, with radial but verical fins,
and an open mesh
cover over the lot, or no damn fins anywhere, and just a decent cage,
like Quad 40,
but with lots of 6mm holes around where the tube sockets
BOLT SOLIDLY TO THE CHASSIS, and with well perforated bottom plate.
This allows air flow in through the bottom, and up around the tubes, and
out the mesh with very low restrictions.

In Oz where room temps are 30C on summer days often, good natural
cooling for amps is a MUST.

In early tubed electronics in aircraft, they had tubes clamped in metal
heat sinks, and exposed to cooling air flow.
As planes went higher and faster, they had to refrigerate the air flow
because speed increases air temp.
Failures of tubes become far more common if T is allowed to be high.
In domestic hi-fi, naked tubes but with surround holes for good airflow
and cage for safety is all thats needed,
and if buyers can see the tubes at night easily through the mesh covers
they won't remove them.

Patrick Turner.

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote

Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

That doesn't really answer the question.

High end tube audiophiles expect certain brand name components
to be used. DACT stepped attenuators are high on the list.
Some insist on TKD. If a manufacturer want to sell to in this
market, he must meet the expectations of the customer.

There's *no way* a variable R costs as much as tapped transformers in
the
real world.

The TKD stereo attenuator costs about Euro 270 plus tax and shipping.
The transformers are about UKP 90 each. Not a lot of difference

Sounds to me like ripoff pricing.
That's the reality I am afraid. Quality comes at a price.

There's plenty of accurate attenuators out there that I've come across.
The
better ones use thick film resistors screened onto what's effectively a
multi-pole switch manufactured using potentiometer technology.

Yes. DACT use Elma switches, IIRC. There are some other good
SA's using switches from Grayhill.

I was toying with the idea of a DC battery powered CF stage actually.
Rechargeable via a wall wart.

Sounds like a fun project:-) How is it progressing??
I chose a separate regulated psu.

Just a concept that crossed my mind as I was reading these posts. It would
be
trivially simple to make one.

I thought the battery powered bit would appeal to the audiophools. The
batteries
could feed the heater directly but it would need a tiny inverter for the
B+.

There are preamps and phono stages available like this already.

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote

Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

That doesn't really answer the question.

High end tube audiophiles expect certain brand name components
to be used.

That's their problem not mine.

Brand name =/= any guarantee of performance / quality etc.

In fact it's the ultimate fool's paradise.

Graham

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote in message

I was toying with the idea of a DC battery powered CF stage actually.
Rechargeable via a wall wart.

Sounds like a fun project:-) How is it progressing??
I chose a separate regulated psu.

Just a concept that crossed my mind as I was reading these posts. It would
be trivially simple to make one.

I thought the battery powered bit would appeal to the audiophools. The
batteries could feed the heater directly but it would need a tiny inverter
for the
B+.

There are preamps and phono stages available like this already.

I suspected as much.

No doubt they cost megabucks.

It would be fun to burst their balloon by offering one just as good for say
$200.

Graham

[Eeyore]

Iain Churches wrote:

Some insist on TKD.

What exactly do TDK offer that others don't ?

Nothing I expect.

Graham

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote in message

There's plenty of accurate attenuators out there that I've come across.
The better ones use thick film resistors screened onto what's effectively a
multi-pole switch manufactured using potentiometer technology.

Yes. DACT use Elma switches, IIRC. There are some other good
SA's using switches from Grayhill.

None of these use potentiometer technology.

Graham

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote

Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

That doesn't really answer the question.

High end tube audiophiles expect certain brand name components
to be used.

That's their problem not mine.

Brand name =/= any guarantee of performance / quality etc.

In fact it's the ultimate fool's paradise.

Graham


I agree entirely, but if a maker wants to sell a product,
any product, he must give the customer what they (think they)
want.

Iain

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote in message

I was toying with the idea of a DC battery powered CF stage
actually.
Rechargeable via a wall wart.

Sounds like a fun project:-) How is it progressing??
I chose a separate regulated psu.

Just a concept that crossed my mind as I was reading these posts. It
would
be trivially simple to make one.

I thought the battery powered bit would appeal to the audiophools. The
batteries could feed the heater directly but it would need a tiny
inverter
for the
B+.

There are preamps and phono stages available like this already.

I suspected as much.

No doubt they cost megabucks.

It would be fun to burst their balloon by offering one just as good for
say
$200.

IIRC the ones I have seen were Chinese, and cheap as chips.

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote in message
Iain Churches wrote:
"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote

Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

That doesn't really answer the question.

High end tube audiophiles expect certain brand name components
to be used.

That's their problem not mine.

Brand name =/= any guarantee of performance / quality etc.

In fact it's the ultimate fool's paradise.

I agree entirely, but if a maker wants to sell a product,
any product, he must give the customer what they (think they)
want.

If it's simply a large price tag, I'm all for that !

More fool the purchaser.

Graham

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:

There are preamps and phono stages available like this already.

I suspected as much.

No doubt they cost megabucks.

It would be fun to burst their balloon by offering one just as good for
say $200.

IIRC the ones I have seen were Chinese, and cheap as chips.

So, are they any good ?

Any links ?

Graham

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

Some insist on TKD.

What exactly do TDK offer that others don't ?

Nothing I expect.

Graham


It has forty steps, in contrast to the more common
24 steps. Some makers have 60 step attenuators
but these are available only in OEM quantities.

The DACT has an open construction. The TKD
reminds one of a smaller version of the
fully-enclosed studded rotary faders you used
to see in studio equipment.

Iain

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote in message
Iain Churches wrote:
"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote

Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

That doesn't really answer the question.

High end tube audiophiles expect certain brand name components
to be used.

That's their problem not mine.

Brand name =/= any guarantee of performance / quality etc.

In fact it's the ultimate fool's paradise.

I agree entirely, but if a maker wants to sell a product,
any product, he must give the customer what they (think they)
want.

If it's simply a large price tag, I'm all for that !

More fool the purchaser.

A high end dealer, a good friend of mine, tells me that he
thinks that PQ (perceived quality) is 40% of the purchasing
decision!

Iain

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:

There are preamps and phono stages available like this already.

I suspected as much.

No doubt they cost megabucks.

It would be fun to burst their balloon by offering one just as good for
say $200.

IIRC the ones I have seen were Chinese, and cheap as chips.

So, are they any good ?

Can't say. I noticed the lack of a CE mark, and put it down again:-)

Any links ?'

A local shop sells them. I will try to get some info.



Graham

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote in message
Iain Churches wrote:

Some insist on TKD.

What exactly do TDK offer that others don't ?

Nothing I expect.


It has forty steps, in contrast to the more common
24 steps. Some makers have 60 step attenuators
but these are available only in OEM quantities.

The DACT has an open construction. The TKD
reminds one of a smaller version of the
fully-enclosed studded rotary faders you used
to see in studio equipment.

Used to being the operative phrase.

No studio equipment today would use such a deficient design. In fact, the last
time I saw studded attenutors was in 1969 and they were being scrapped at that
time. No-one wanted to buy them since a P&G conductive plastic fader was simply
so much better.

Graham

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote

Actually, even if you buy from the most expensive maker
in the UK, a pair of transformers cost about the same as the
TKD variable attenuator, which for many is a standard
choice.

Whose standard ?

The people who want to have stepped attenuators of course.

That doesn't really answer the question.

High end tube audiophiles expect certain brand name components
to be used.

That's their problem not mine.

Brand name =/= any guarantee of performance / quality etc.

In fact it's the ultimate fool's paradise.

I agree entirely, but if a maker wants to sell a product,
any product, he must give the customer what they (think they)
want.

If it's simply a large price tag, I'm all for that !

More fool the purchaser.

A high end dealer, a good friend of mine, tells me that he
thinks that PQ (perceived quality) is 40% of the purchasing
decision!

I don't doubt you (or him).

The question has to be, where do they get these ideas about perceived value from
?

It's a nice con-trick whilst you can continue to play it.

Graham

[Eeyore]

Iain Churches wrote:

"Eeyore" wrote
Iain Churches wrote:
"Eeyore" wrote
Iain Churches wrote:

There are preamps and phono stages available like this already.

I suspected as much.

No doubt they cost megabucks.

It would be fun to burst their balloon by offering one just as good for
say $200.

IIRC the ones I have seen were Chinese, and cheap as chips.

So, are they any good ?

Can't say. I noticed the lack of a CE mark, and put it down again:-)

LOL ! If it's battery operated it arguably doesn't need one. The CE marking
regulations are far from being clear on such points. Certainly, if battery
powered, it wouldn't need to comply with the 'low voltage directive' (low
voltage meaning basically wall socket type volts). It ought to have to comply
with the EMC Directive though.


Any links ?'

A local shop sells them. I will try to get some info.

Thank you kindly.

Graham

[Sander deWaal]

Eeyore said:


No studio equipment today would use such a deficient design. In fact, the last
time I saw studded attenutors was in 1969 and they were being scrapped at that
time. No-one wanted to buy them since a P&G conductive plastic fader was simply
so much better.


Please define "better". ***grin***

--

- Maggies are an addiction for life. -

[Iain Churches]

"Eeyore" wrote in message
...


Iain Churches wrote:

"Eeyore" wrote in message
Iain Churches wrote:

Some insist on TKD.

What exactly do TDK offer that others don't ?

Nothing I expect.


It has forty steps, in contrast to the more common
24 steps. Some makers have 60 step attenuators
but these are available only in OEM quantities.

The DACT has an open construction. The TKD
reminds one of a smaller version of the
fully-enclosed studded rotary faders you used
to see in studio equipment.

Used to being the operative phrase.

No studio equipment today would use such a deficient design. In fact, the
last
time I saw studded attenutors was in 1969 and they were being scrapped at
that
time. No-one wanted to buy them since a P&G conductive plastic fader was
simply
so much better.

Following stud rotary faders came the Paignton "quadrant"
design, - long before P+G. Hifi amps still have rotary attenuators
amd TKD is considered one of the best. (they also manufacture
conductive plastic faders for studio consoles)

Iain

[Eeyore]

Sander deWaal wrote:

Eeyore said:

No studio equipment today would use such a deficient design. In fact, the last
time I saw studded attenutors was in 1969 and they were being scrapped at that
time. No-one wanted to buy them since a P&G conductive plastic fader was simply
so much better.

Please define "better". ***grin***

LOL.

Well..... effectively infinite resolution for one thing plus noiseless operation.

Graham