What differentiates good audio xmfrs from bad ones?

[et...@whidbey.com]

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]

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

Greg

[peterw...@gmail.com]

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]

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

[whit3rd]

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.

[Look165]

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

[et...@whidbey.com]

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

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]

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).

[Phil Allison]

et...@whidbey.com wrote:
>
>
> >
> >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.

> 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]

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 ???


.... Phil

[whit3rd]

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]

On Saturday, January 12, 2019 at 10:41:18 AM UTC+11, whit3rd wrote:
> 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.

> 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

[et...@whidbey.com]

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

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

[mako...@yahoo.com]

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]

mako...@yahoo.com wrote:

>
>
>
> 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.

>
> 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.

> 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

[jurb...@gmail.com]

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


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


** More and worse drivel than the last lot.

Maybe he has a minor in AP. AudioPhoolery.

[mako...@yahoo.com]

yep good point...

so it is very possible for a tube amp to have a bit less transformer saturation distortion when loaded compared to unloaded.

i.e. the distortion can go DOWN when loaded.


m

[Look165]

NO !

Saturation is a value coming from the magnetic core, yes.

But H (magnetic strength) is directly proportional to the current, not
to the voltage, at constant frequency.
The load is very important.
This leeds the core to the satruration point if too high.

A free transformer (without load) rarely comes to saturation.

Eddy's current (we call it Foucault's current in France) are
proportional to I^^2, like copper losses.

[Phil Allison]

Look165 wrote:

> NO !
>
> Saturation is a value coming from the magnetic core, yes.
>
> But H (magnetic strength) is directly proportional to the current, not
> to the voltage, at constant frequency.

** WRONG !!!

The applied AC voltage and frequency are what matter.

> The load is very important.
> This leeds the core to the satruration point if too high.
>

** TOTAL BOLLOCKS !!!

> A free transformer (without load) rarely comes to saturation.
>

** Try using an unloaded 120V supply transformer on 240V and see what happens.

Others here have it right cos they know that they are talking about - you don't.

Piss off you bloody idiot.



.... Phil

[Fox's Mercantile]

Or, you know, you COULD just look this shit up and learn
how it works.
<https://www.ieee.li/pdf/introduction_to_power_electronics/chapter_12.pdf>

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

[mako...@yahoo.com]

it is about current,

the so called magnetizing current that flows even with no load.

the additional current that flows in the primary when the secondary is loaded IS CANCELED by the current in the secondary.

So it is all about the current that flows only due to the primary inductance and not due to the load current.

Yours is a common mis-conception. I'm glad to help you learn.

m

[whit3rd]

On Tuesday, January 22, 2019 at 10:13:17 AM UTC-8, Look165 wrote:

> Saturation is a value coming from the magnetic core, yes.
>

> But H (magnetic strength) is directly proportional to the current...

> A free transformer (without load) rarely comes to saturation.

NO, that's exactly backwards: a 'free' transformer with negligible secondary current
DOES near-saturate. The primary current and secondary current are in
the opposite direction, so load (secondary) current CANCELS
the magnetization caused by the drive (primary) current.

A lot of secondary current (high load current) removes the
risk of saturation.

[Phil Allison]

whit3rd wrote:

>
>
> NO, that's exactly backwards: a 'free' transformer with negligible
> secondary current DOES near-saturate.
> The primary current and secondary current are in
> the opposite direction, so load (secondary) current CANCELS
> the magnetization caused by the drive (primary) current.
>
> A lot of secondary current (high load current) removes the
> risk of saturation.
>
>

** While adding load current does not directly alter the magnetising current in the primary, it does reduce the effective AC supply voltage seen by the primary.

This is due simply to the resistance of the primary winding - current flow produces a voltage drop which must be subtracted from the external supply voltage to accurately model what is going on.

Eg, say the primary current due to load is 1 amp and the winding has 5 ohms resistance - then the effective voltage is 5 volts LESS than the AC supply.


.... Phil

.... Phil