The things you see when ya go lookin'......
 

Keith G wrote:
"Andre Jute" wrote


I think Bob Danielak built a car amp with them. Can't remember the
details now, but it fitted on a shelf behind seat of his Fiat X1/9 or
124 Spyder, something like that. I remember he said the difficult thing
was the power supply design and construction.


http://www.geocities.com/TimesSquare/1965/caramp.html

Thanks for the URL. That's the one I mean. Anyone who wants a tube car
amp might also go on Steve Bench's site and check out a battery tube
amplifier I seem to remember he designed. That might get around the
problem of the difficult switching power supply Bob's HV Car Darling
requires.

Andre Jute
Visit Jute on Amps at http://members.lycos.co.uk/fiultra/
"wonderfully well written and reasoned information
for the tube audio constructor"
John Broskie TubeCAD & GlassWare
"an unbelievably comprehensive web site
containing vital gems of wisdom"
Stuart Perry Hi-Fi News & Record Review

The things you see when ya go lookin'......
 

"Jim Lesurf" wrote in message

In article ,
Serge Auckland wrote:

[snip]

One oddity I've noticed. On the SILK attenuator pages,
they say of conventional resistor attenuators "That's
why at high attenuation level (low signal out, low
listening level) the bandwidth of such volume control is
very poor and the bandwidth is not constant over any
switch position."

Can you give the URL for the page?

http://www.sacthailand.com/transSilkVolume.html

"The benefit of replacing plastic type volume control to stepped attenuator
is obviously the accuracy of tracking and the quality of selector switch
plus low noise resistors can reduce the signal loss to some degrees. However
the regular stepped attenuator featuring resistor type fails to offer better
impedance matching over plastic volume control. That's why at high
attenuation level (low signal out, low listening level) the bandwidth of
such volume control is very poor and the bandwidth is not constant over any
switch position. "


I'm puzzled as I'd
expect the maximum output resistance of a conventional
attenuator to occur at about the -6dB setting, and fall
as the output level is reduced below that. i.e. not have
a "poor bandwidth" at low settings, but at relatively
high ones.

SAC Thailand seems to be challenged both technically and linguistically.

Is there some reason why the transformer referred to
*doesn't* also have a bandwidth that "is not constant" as
the attenuation is altered?

Magic!

If nothing else, I'd assume
that the inductances, capacitances, and resistances,
would all tend to change, and affect the bandwidth...

Of course. We both know the drill...

This is only relevant if using very long
high-capacitance cables. If using cables of normal
capacitance, and of normal domestic lengths, it has no
relevance as the bandwidth is already well in excess of
the audio bandwidth. Although I think a multi-tapped
transformer as an attenuator is a bit of overkill, it is
a theoretically sound solution as the output impedance
will reduce as the attenuation increases.

It's ironic that tapped transformer attenuators have achieved some
popularity in whole-house loudspeaker systems, but resistive attenuators are
making a come back based on wider bandwidth.

Will the input impedance not also tend to change as the
o/p tap is changed?

With transformers, lots of funny stuff happens. One reason why a pro audio
mic preamp with transformers is usually considered to be a kind of EFX box.

The things you see when ya go lookin'......
 

In article , Serge Auckland
wrote:

"Jim Lesurf" wrote in message
...


Nominal impedance 10k. 48dB attentuation in 2dB steps. Inductance 80H.

Since I am unfamiliar with the use of such transformers for audio,
I'll risk asking a few simple questions. :-)

Can you explain what you mean by "10k bridging" in the above? Does it
refer to the input load/arrangement?

For many years now, pro-audio has abandoned the old 600 ohms terminating
(that is, 600 ohms sending impedance, 600 ohms receiving) for the more
modern very low sending impedance (typically less than 50 ohms) into a
high receiving impedance (typically 10kohms) The 10k impedance is
referred to as "bridging" as it can be put across (bridge) a 600 ohm
load without materially affecting the level. The use of the terms is
now something of an anachronism, but is still retained to indicate a
high load impedance, and to distinguish it from the now rarely used 600
ohm terminating imedance.

So is "bridging" in this context used to mean "mismatched, but using a high
load impedance to avoid over-loading the source"?

[snip]


Under what conditions of use does the system present (?) 10kOhms?

If a transformer is designed for 10k use, it needs to be presented with
a high load impedance on the secondary. A 10k transformer presented
with a 600ohm load will distort at a much lower level than with a 10k
load, as the core saturates.

In that case I am puzzled by what relevant the specific value "10k" has in
this context. Is the following incorrect for some reason?

The input impedance presented by the transformer to a source connected to
its primary will essentially be the transformed value of the impedance
connected as a load to its secondary.

Thus if the load on the secondary is 'high', the impedance presented by the
primary will be even higher - by the relevant transformation ratio. Given a
load of 600 Ohms on the secondary this implies the load the primary
presents to the source will always be well above 600 Ohms, and vary with
the chosen 'attenuation' setting.

If so, is it the case that the effective load isn't likely to be "10k"?

So the "10k bridging" simply means "a large value that varies with the
chosen attenuation"? If so, why on earth call it "10k"? :-)


Conversely, if a transformer is designed for 600 ohm use is used with a
10k load, it won't saturate or distort, but it could have an
undesirable peak in the treble response, although with a well-designed
transformer, this won't be too serious a problem. Nevertheless, the
cousel of perfection is to terminate transforers with their design
impedance.

I can see that being straightforward with a fixed transformer ratio.
Indeed, I've done that more than once. :-) However how do you do that with
a changing tap of a multi-tap transformer used as an attenuator? Does
anyone do so?


What would be the levels of series resistances, shunt capacitances,
etc, for the above device? You quote '80H' for an inductance, but
don't distinguish the coupled (mutual) value from the uncoupled values.

This will depend on the specific transformer, so I can't answer this....
Iain?

I was wondering if Iain would know the specific values...

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

The things you see when ya go lookin'......
 

In article , Arny Krueger
wrote:
"Jim Lesurf" wrote in message

In article , Serge
Auckland wrote:

[snip]

One oddity I've noticed. On the SILK attenuator pages, they say of
conventional resistor attenuators "That's why at high attenuation
level (low signal out, low listening level) the bandwidth of such
volume control is very poor and the bandwidth is not constant over
any switch position."

Can you give the URL for the page?

http://www.sacthailand.com/transSilkVolume.html

Ok. thanks. :-)

"The benefit of replacing plastic type volume control to stepped
attenuator is obviously the accuracy of tracking and the quality of
selector switch plus low noise resistors can reduce the signal loss to
some degrees. However the regular stepped attenuator featuring resistor
type fails to offer better impedance matching over plastic volume
control. That's why at high attenuation level (low signal out, low
listening level) the bandwidth of such volume control is very poor and
the bandwidth is not constant over any switch position. "

I'll visit the page and see if I can discover how they ensure the source
and load are matched for all transformer settings. :-)

[snip]

Is there some reason why the transformer referred to *doesn't* also
have a bandwidth that "is not constant" as the attenuation is altered?

Magic!

I noticed a 'review' of an (expensive) transformer used as a variable
'volume control' attenuator in a UK mag a few years ago, but didn't follow
up my puzzlement about it at the time...

It is now reminding me of the undergrad we once had doing a 'project'. Part
of the system he had to build was to divide a voltage to half the value.

He used an ADC and a DAC, with the wires between them shifted by one bit.

When we asked why he hadn't used a pair of resistors he gave us a funny
look and it became clear that the idea hadn't occurred to him. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

The things you see when ya go lookin'......
 

"Iain Churches" wrote in message
...

"Stewart Pinkerton" wrote in message
...
On 23 Feb 2006 07:37:16 -0800, "Andre Jute" wrote:


While I would generally hesitate to agree with Jute, he is in this
case quite right. If you really must build a valve amplifier, then the
Lundahl range of transformers does indeed provide excellent
performance at realistic prices. This allows you to go for a more
optimised design than might otherwise be possible, particularly if for
some reason you decide to go down the technically crippled
single-ended route, with its horrific implications regarding core
saturation. Ya need seriously gang-banging iron for those suckers!

Basically, always buy a trannie that will handle a little more power
than you are designing for, rather than a little less. Your bottom end
will be eternally grateful...................
--

Keith has a good alternative to Lundahl, and practically on his doorstep.
- AE Sowter Ltd.

Iain


Hi Iain,
Dunno if its the same now but Sowter's used to just build to order and
didn't carry stock. Unless things have changed there could be a bit of a
wait.
Top class mains and output transformers imo, also used in my 120w monoblocs.

Mike

Mike

The things you see when ya go lookin'......
 

"Keith G" wrote in message
...

Those of you with a predilection for copious amounts of glass and iron in
your amplifiers go scrute this site thoroughly:

http://www.sacthailand.com/



Those of you who like copious amounts of wood on your amps go see he

http://www.edgar.sk/index.php?id=8&lng=ENG


Czech where this stuff comes from!!

(No market for valves anywhere much, these days.....!! ;-)

The things you see when ya go lookin'......
 

"Jim Lesurf" wrote in message
...
In article , Serge Auckland
wrote:

"Jim Lesurf" wrote in message
...


Nominal impedance 10k. 48dB attentuation in 2dB steps. Inductance 80H.

Since I am unfamiliar with the use of such transformers for audio,
I'll risk asking a few simple questions. :-)

Can you explain what you mean by "10k bridging" in the above? Does it
refer to the input load/arrangement?

For many years now, pro-audio has abandoned the old 600 ohms terminating
(that is, 600 ohms sending impedance, 600 ohms receiving) for the more
modern very low sending impedance (typically less than 50 ohms) into a
high receiving impedance (typically 10kohms) The 10k impedance is
referred to as "bridging" as it can be put across (bridge) a 600 ohm
load without materially affecting the level. The use of the terms is
now something of an anachronism, but is still retained to indicate a
high load impedance, and to distinguish it from the now rarely used 600
ohm terminating imedance.

So is "bridging" in this context used to mean "mismatched, but using a
high
load impedance to avoid over-loading the source"?

[snip]

Yes, matching isn't really relevant, as the source impedance is low, and the
load is high. The relevance of the term "bridging" is that the impedance is
sufficiently high (greater than 10k usually) that is can be placed across a
output without significantly loading down the output level regardless of
source impedance (provided it is low). So, with a source impedance of 0-600
ohms, and a bridging load of 10k, the level drop will be well below 1dB.


Under what conditions of use does the system present (?) 10kOhms?

In the present case of a transformer-based attenuator, if the load on the
secondary is high (again say 10k) then the impedance into the primary will
be 10k x the square of the turns ratios, so many times 10k. Worse case, when
the transformer is at 1:1, the input impedance of the attenuator presented
to the source will be 10k (or whatever the secondary load is). This means
that the source will be very lightly loaded at all times.

If a transformer is designed for 10k use, it needs to be presented with
a high load impedance on the secondary. A 10k transformer presented
with a 600ohm load will distort at a much lower level than with a 10k
load, as the core saturates.

In that case I am puzzled by what relevant the specific value "10k" has in
this context. Is the following incorrect for some reason?

The input impedance presented by the transformer to a source connected to
its primary will essentially be the transformed value of the impedance
connected as a load to its secondary.

Thus if the load on the secondary is 'high', the impedance presented by
the
primary will be even higher - by the relevant transformation ratio. Given
a
load of 600 Ohms on the secondary this implies the load the primary
presents to the source will always be well above 600 Ohms, and vary with
the chosen 'attenuation' setting.

If so, is it the case that the effective load isn't likely to be "10k"?

It is 10k to the secondary. As you rightly say, the impedance seen looking
into the primary will be many times that.

So the "10k bridging" simply means "a large value that varies with the
chosen attenuation"? If so, why on earth call it "10k"? :-)

Because the secondary is designed to be loaded by 10k


Conversely, if a transformer is designed for 600 ohm use is used with a
10k load, it won't saturate or distort, but it could have an
undesirable peak in the treble response, although with a well-designed
transformer, this won't be too serious a problem. Nevertheless, the
cousel of perfection is to terminate transforers with their design
impedance.

I can see that being straightforward with a fixed transformer ratio.
Indeed, I've done that more than once. :-) However how do you do that
with
a changing tap of a multi-tap transformer used as an attenuator? Does
anyone do so?

Probably not, but in the case of Iain's transformer, each secondary is
designed to be terminated in 10k. Of course what impedance each secondary
actually sees depends on whether he is switching between secondaries, or, as
I think more likely by the description of the transformer, he is adding
secondaries as he increases the volume. This shows that transformer design
terminations are very nominal, and good transformers will work well outside
their nominal ratings. Nevertheless, if a transformer is designed for a
secondary load of 10k, it would be foolish to load it with 600 ohms, but
whether it is 10k, 20k, 50k or even down to 5k, it won't make any
difference.


What would be the levels of series resistances, shunt capacitances,
etc, for the above device? You quote '80H' for an inductance, but
don't distinguish the coupled (mutual) value from the uncoupled values.

This will depend on the specific transformer, so I can't answer this....
Iain?

I was wondering if Iain would know the specific values...


S.

The things you see when ya go lookin'......
 

"Mike Gilmour" wrote in message
...

"Iain Churches" wrote in message
...

"Stewart Pinkerton" wrote in message
...
On 23 Feb 2006 07:37:16 -0800, "Andre Jute" wrote:


While I would generally hesitate to agree with Jute, he is in this
case quite right. If you really must build a valve amplifier, then the
Lundahl range of transformers does indeed provide excellent
performance at realistic prices. This allows you to go for a more
optimised design than might otherwise be possible, particularly if for
some reason you decide to go down the technically crippled
single-ended route, with its horrific implications regarding core
saturation. Ya need seriously gang-banging iron for those suckers!

Basically, always buy a trannie that will handle a little more power
than you are designing for, rather than a little less. Your bottom end
will be eternally grateful...................
--

Keith has a good alternative to Lundahl, and practically on his doorstep.
- AE Sowter Ltd.

Iain


Hi Iain,
Dunno if its the same now but Sowter's used to just build to order and
didn't carry stock. Unless things have changed there could be a bit of a
wait.
Top class mains and output transformers imo, also used in my 120w
monoblocs.

Mike

Hi Mike, They seem to have stock of "popular items" and of course of all
the broadcast stuff. Their bespoke service is pretty quick.

Iain

The things you see when ya go lookin'......
 

"Serge Auckland" wrote in message
...

"Jim Lesurf" wrote in message
...
In article , Serge Auckland
wrote:

"Jim Lesurf" wrote in message
...


Nominal impedance 10k. 48dB attentuation in 2dB steps. Inductance
80H.

Since I am unfamiliar with the use of such transformers for audio,
I'll risk asking a few simple questions. :-)

Can you explain what you mean by "10k bridging" in the above? Does it
refer to the input load/arrangement?

For many years now, pro-audio has abandoned the old 600 ohms terminating
(that is, 600 ohms sending impedance, 600 ohms receiving) for the more
modern very low sending impedance (typically less than 50 ohms) into a
high receiving impedance (typically 10kohms) The 10k impedance is
referred to as "bridging" as it can be put across (bridge) a 600 ohm
load without materially affecting the level. The use of the terms is
now something of an anachronism, but is still retained to indicate a
high load impedance, and to distinguish it from the now rarely used 600
ohm terminating imedance.

So is "bridging" in this context used to mean "mismatched, but using a
high
load impedance to avoid over-loading the source"?

[snip]

Yes, matching isn't really relevant, as the source impedance is low, and
the load is high. The relevance of the term "bridging" is that the
impedance is sufficiently high (greater than 10k usually) that is can be
placed across a output without significantly loading down the output level
regardless of source impedance (provided it is low). So, with a source
impedance of 0-600 ohms, and a bridging load of 10k, the level drop will
be well below 1dB.


Under what conditions of use does the system present (?) 10kOhms?

In the present case of a transformer-based attenuator, if the load on the
secondary is high (again say 10k) then the impedance into the primary
will be 10k x the square of the turns ratios, so many times 10k. Worse
case, when the transformer is at 1:1, the input impedance of the
attenuator presented to the source will be 10k (or whatever the secondary
load is). This means that the source will be very lightly loaded at all
times.

If a transformer is designed for 10k use, it needs to be presented with
a high load impedance on the secondary. A 10k transformer presented
with a 600ohm load will distort at a much lower level than with a 10k
load, as the core saturates.

In that case I am puzzled by what relevant the specific value "10k" has
in
this context. Is the following incorrect for some reason?

The input impedance presented by the transformer to a source connected to
its primary will essentially be the transformed value of the impedance
connected as a load to its secondary.

Thus if the load on the secondary is 'high', the impedance presented by
the
primary will be even higher - by the relevant transformation ratio. Given
a
load of 600 Ohms on the secondary this implies the load the primary
presents to the source will always be well above 600 Ohms, and vary with
the chosen 'attenuation' setting.

If so, is it the case that the effective load isn't likely to be "10k"?

It is 10k to the secondary. As you rightly say, the impedance seen looking
into the primary will be many times that.

So the "10k bridging" simply means "a large value that varies with the
chosen attenuation"? If so, why on earth call it "10k"? :-)

Because the secondary is designed to be loaded by 10k


Conversely, if a transformer is designed for 600 ohm use is used with a
10k load, it won't saturate or distort, but it could have an
undesirable peak in the treble response, although with a well-designed
transformer, this won't be too serious a problem. Nevertheless, the
cousel of perfection is to terminate transforers with their design
impedance.

I can see that being straightforward with a fixed transformer ratio.
Indeed, I've done that more than once. :-) However how do you do that
with
a changing tap of a multi-tap transformer used as an attenuator? Does
anyone do so?

Probably not, but in the case of Iain's transformer, each secondary is
designed to be terminated in 10k. Of course what impedance each secondary
actually sees depends on whether he is switching between secondaries, or,
as I think more likely by the description of the transformer, he is adding
secondaries as he increases the volume. This shows that transformer design
terminations are very nominal, and good transformers will work well
outside their nominal ratings. Nevertheless, if a transformer is designed
for a secondary load of 10k, it would be foolish to load it with 600 ohms,
but whether it is 10k, 20k, 50k or even down to 5k, it won't make any
difference.


What would be the levels of series resistances, shunt capacitances,
etc, for the above device? You quote '80H' for an inductance, but
don't distinguish the coupled (mutual) value from the uncoupled
values.

This will depend on the specific transformer, so I can't answer this....
Iain?

I was wondering if Iain would know the specific values...


S.


Jim. The specification comes straight from an EBU manual.
Serge was able to describe the device more lucidly than I, without
having to refer to the broadcast handbook. The inductance, is a design
value in the spec. "80H or better" My units are were slightly less.

Iain

The things you see when ya go lookin'......
 

In article , Iain Churches
wrote:

[big snip]

Jim. The specification comes straight from an EBU manual. Serge was able
to describe the device more lucidly than I, without having to refer to
the broadcast handbook. The inductance, is a design value in the spec.
"80H or better" My units are were slightly less.

OK, thanks.

I was curious about this as result of the strange claims made by 'Silk'
comparing the transformer attenuator with a simple potential divider. So
far as I can see, both types can be expected to have a setting-dependent
bandwidth, despite the implication of what Silk have been quoted as saying.
Hence it seems odd for them to give this as a reason for all the extra cost
and complications.

This then prompted me to wonder about the uncoupled inductances, parasitic
capacitances, etc, that would allow someone to estimate the actual
bandwidth in use of the transformers. Since you quoted the 80H I wondered
if you knew the other relevant values for your transformer...

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html