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What differentiates good audio xmfrs from bad ones?

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Guest

Wed Jan 09, 2019 6:45 pm   



I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?
It must be some sort of physical attribute. The way they are wound,
insulation, etc.
Is there a way to tell using just an oscilloscope? I'm just
curious. I am very happy with the way my tube amp sounds.
Thanks,
Eric

gregz
Guest

Thu Jan 10, 2019 9:45 am   



<etpm_at_whidbey.com> wrote:
Quote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?
It must be some sort of physical attribute. The way they are wound,
insulation, etc.
Is there a way to tell using just an oscilloscope? I'm just
curious. I am very happy with the way my tube amp sounds.
Thanks,
Eric


Frequency response delivering full power is what I think. Some trick
winding process is likely to cost more.

Greg

pfjw@aol.com
Guest

Thu Jan 10, 2019 3:45 pm   



Some things:

Quality of the core material.
Care and bulk of wiring.
Frequency range to be covered.
Power requirements.

After which, like anything else, all about materials wound on the thighs of virgins on Walpurgis Night.

Peter Wieck
Melrose Park, PA

Paul Drahn
Guest

Thu Jan 10, 2019 9:45 pm   



On 1/9/2019 9:38 AM, etpm_at_whidbey.com wrote:
Quote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?
It must be some sort of physical attribute. The way they are wound,
insulation, etc.
Is there a way to tell using just an oscilloscope? I'm just
curious. I am very happy with the way my tube amp sounds.
Thanks,
Eric

The capacitance of the windings will limit the high frequency response.
Perhaps the best will have the secondary wire in parallel with the
primary wire. Never had one to take apart.


Paul

Look165
Guest

Thu Jan 10, 2019 11:45 pm   



The parasistic elements. (copper, iron...).

etpm_at_whidbey.com a écrit le 09/01/2019 à 18:38 :
Quote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?
It must be some sort of physical attribute. The way they are wound,
insulation, etc.
Is there a way to tell using just an oscilloscope? I'm just
curious. I am very happy with the way my tube amp sounds.
Thanks,
Eric


whit3rd
Guest

Thu Jan 10, 2019 11:45 pm   



On Wednesday, January 9, 2019 at 9:32:20 AM UTC-8, et...@whidbey.com wrote:
Quote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?


The core of a transformer has laminations, because a solid metal lump
would have electrical conduction losses (eddy currents) to cause large
heat losses (and reduce output efficiency). A power transformer
has thick laminations (60 Hz losses are small anyhow, but at 60 kHz,
that would be inefficient), and a switchmode transformer is made of
high-electrical-resistivity ferrite (at 60 kHz, the size can be small, though
such a low-magnetization material wouldn't be great for lower
frequency power).

Audio transformers are most efficient when made from very thin laminations of
soft iron, which is a more expensive construction than is used for either
60 Hz or 60 kHz power transformers. It just has more small parts.


Guest

Fri Jan 11, 2019 6:45 pm   



On Thu, 10 Jan 2019 14:19:27 -0800 (PST), whit3rd <whit3rd_at_gmail.com>
wrote:

Quote:
On Wednesday, January 9, 2019 at 9:32:20 AM UTC-8, et...@whidbey.com wrote:
I see really expensive audio output and power transformers for sale
as well as cheap ones. And lots of folks really want older ones
because they are better than the new crop. So what is the difference?

The core of a transformer has laminations, because a solid metal lump
would have electrical conduction losses (eddy currents) to cause large
heat losses (and reduce output efficiency). A power transformer
has thick laminations (60 Hz losses are small anyhow, but at 60 kHz,
that would be inefficient), and a switchmode transformer is made of
high-electrical-resistivity ferrite (at 60 kHz, the size can be small, though
such a low-magnetization material wouldn't be great for lower
frequency power).

Audio transformers are most efficient when made from very thin laminations of
soft iron, which is a more expensive construction than is used for either
60 Hz or 60 kHz power transformers. It just has more small parts.

Thanks for the edifying reply.
Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted. So I guess this was a perfect example
of the xmfr being made in a way that was unsuitable for audio.
Thanks Again,
Eric

whit3rd
Guest

Sat Jan 12, 2019 12:45 am   



On Friday, January 11, 2019 at 9:07:33 AM UTC-8, et...@whidbey.com wrote:

Quote:
Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted.


That can happen because of saturation and remanence: the addition of a load on
the low voltage side (like, a light bulb) will help greatly. The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).

Phil Allison
Guest

Sat Jan 12, 2019 12:45 am   



et...@whidbey.com wrote:
Quote:



Audio transformers are most efficient when made from very thin laminations of
soft iron,


** Soft iron has not been used since the days of Michael Faraday.

Thin laminations of silicon steel is the norm.




Quote:
Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted.


** You exaggerate.



..... Phil

Phil Allison
Guest

Sat Jan 12, 2019 12:45 am   



whit3rd wrote:

Quote:
The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).



** Where does this utter drivel come from ???


..... Phil

whit3rd
Guest

Sat Jan 12, 2019 12:45 am   



On Friday, January 11, 2019 at 3:36:18 PM UTC-8, Phil Allison wrote:
Quote:
whit3rd wrote:

The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).



** Where does this utter drivel come from ???


From a guy with a Ph.D who did a bunch of magnetism studies.
When unloaded, power transformers have lots of undesirable signal-handling
features.

Phil Allison
Guest

Sat Jan 12, 2019 1:45 am   



On Saturday, January 12, 2019 at 10:41:18 AM UTC+11, whit3rd wrote:
Quote:
On Friday, January 11, 2019 at 3:36:18 PM UTC-8, Phil Allison wrote:
whit3rd wrote:

The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).



** Where does this utter drivel come from ???

From a guy with a Ph.D who did a bunch of magnetism studies.


** Really ??

Has he got a web site - I could do with a good laugh.


Quote:
When unloaded, power transformers have lots of undesirable signal-handling
features.



** More and worse drivel than the last lot.

Give up - you have NO clue about audio or mains transformers.



.... Phil


Guest

Sat Jan 12, 2019 1:45 am   



On Fri, 11 Jan 2019 15:07:21 -0800 (PST), whit3rd <whit3rd_at_gmail.com>
wrote:

Quote:
On Friday, January 11, 2019 at 9:07:33 AM UTC-8, et...@whidbey.com wrote:

Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted.

That can happen because of saturation and remanence: the addition of a load on
the low voltage side (like, a light bulb) will help greatly. The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).

I had no idea! But I should have. So if I had loaded the xmfr down
some the wave form would have more closely resembled a pure sine wave.
Because of the tube amp I bought I have got the bug a little to learn
about audio stuff in general and tube stuff in particular. I ordered a
B&K Precision 4100 function generator last night and when it gets here
in a week or so I'll be hooking up the TEK 465B to an audio xmfr, and
some others, to see how the waveform gets distorted with frequency,
voltage, and waveform.
Thanks,
Eric


Guest

Thu Jan 17, 2019 8:45 pm   



On Friday, January 11, 2019 at 7:31:12 PM UTC-5, et...@whidbey.com wrote:
Quote:
On Fri, 11 Jan 2019 15:07:21 -0800 (PST), whit3rd <whit3rd_at_gmail.com
wrote:

On Friday, January 11, 2019 at 9:07:33 AM UTC-8, et...@whidbey.com wrote:

Some time back I wanted to use the mains power as a frequency standard
when adjusting a generator. I was worried about connecting my 'scope
directly to 125 volts so I used a 12 volt out step down xmfr. The
wave form was really distorted.

That can happen because of saturation and remanence: the addition of a load on
the low voltage side (like, a light bulb) will help greatly. The best small-signal
audio transformers are potted in protective shells, in order to prevent
strain on the magnetic laminations (which makes the magnetic core
do those nonlinear things).
I had no idea! But I should have. So if I had loaded the xmfr down
some the wave form would have more closely resembled a pure sine wave.
Because of the tube amp I bought I have got the bug a little to learn
about audio stuff in general and tube stuff in particular. I ordered a
B&K Precision 4100 function generator last night and when it gets here
in a week or so I'll be hooking up the TEK 465B to an audio xmfr, and
some others, to see how the waveform gets distorted with frequency,
voltage, and waveform.
Thanks,
Eric


Core saturation is not a function of load "TO A FIRST ORDER APPROXIMATION".

Only the primary voltage matters.

But to a second order, if the transformer core is near saturation unloaded, when you load the secondary, the primary current and the primary resistance will in effect LOWER the primary voltage and reduce the core saturation.

So considering the second order effect of primary winding resistance, yeah, loading a transformer _may_ reduce the distortion a little.

mark

Phil Allison
Guest

Thu Jan 17, 2019 10:45 pm   



mako...@yahoo.com wrote:

Quote:



Core saturation is not a function of load "TO A FIRST ORDER APPROXIMATION".

Only the primary voltage matters.


** And of course the input frequency - the two operate in reverse proportion.

Quote:

But to a second order, if the transformer core is near saturation
unloaded, when you load the secondary, the primary current and the
primary resistance will in effect LOWER the primary voltage and
reduce the core saturation.


** True even when the applied primary voltage has no changed one tiny bit cos it is coming form the mains supply.


Quote:
So considering the second order effect of primary winding resistance,
yeah, loading a transformer _may_ reduce the distortion a little.


** With a tube amplifier, the effect can be very marked - since the voltage applied to the primary drops when a load is applied to the secondary.

The source impedance of a pentode or beam tube output stage is pretty high, triodes are somewhat better.

Only those amplifiers with large NFB ratios avoid the issue.


...... Phil

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