What differentiates good audio xmfrs from bad ones?

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   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

Re: What differentiates good audio xmfrs from bad ones?
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Frequency response delivering full power is what I think. Some trick
winding process is likely to cost more.

Greg

Re: What differentiates good audio xmfrs from bad ones?
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

Re: What differentiates good audio xmfrs from bad ones?
On 1/9/2019 9:38 AM, snipped-for-privacy@whidbey.com wrote:
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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

Re: What differentiates good audio xmfrs from bad ones?
On Wednesday, January 9, 2019 at 9:32:20 AM UTC-8, snipped-for-privacy@whidbey.com wrote:
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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.

Re: What differentiates good audio xmfrs from bad ones?
wrote:

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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

Re: What differentiates good audio xmfrs from bad ones?
On Friday, January 11, 2019 at 9:07:33 AM UTC-8, snipped-for-privacy@whidbey.com wrote:

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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).

Re: What differentiates good audio xmfrs from bad ones?
whit3rd wrote:

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


....   Phil  

Re: What differentiates good audio xmfrs from bad ones?
On Friday, January 11, 2019 at 3:36:18 PM UTC-8, Phil Allison wrote:
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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.

Re: What differentiates good audio xmfrs from bad ones?
On Saturday, January 12, 2019 at 10:41:18 AM UTC+11, whit3rd wrote:
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 **  Really ??  

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


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** More and worse drivel than the last lot.  

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



...   Phil

Re: What differentiates good audio xmfrs from bad ones?
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  Has he got a web site - I could do with a good laugh.


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** More and worse drivel than the last lot.

Maybe he has a minor in AP. AudioPhoolery.

Re: What differentiates good audio xmfrs from bad ones?
wrote:

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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

Re: What differentiates good audio xmfrs from bad ones?
On Friday, January 11, 2019 at 7:31:12 PM UTC-5, snipped-for-privacy@whidbey.com wrote:
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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

Re: What differentiates good audio xmfrs from bad ones?
snipped-for-privacy@yahoo.com wrote:

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

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


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** 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



Re: What differentiates good audio xmfrs from bad ones?
On Thursday, January 17, 2019 at 4:19:56 PM UTC-5, Phil Allison wrote:
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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




Re: What differentiates good audio xmfrs from bad ones?
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.


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Re: What differentiates good audio xmfrs from bad ones?
Look165 wrote:

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**  WRONG !!!  

 The applied AC voltage and frequency are what matter.


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** TOTAL  BOLLOCKS !!!


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** 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  

Re: What differentiates good audio xmfrs from bad ones?
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
We've slightly trimmed the long signature. Click to see the full one.
Re: What differentiates good audio xmfrs from bad ones?
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 load
ed IS CANCELED by the current in the secondary.

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

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

m


  
On Tuesday, January 22, 2019 at 1:13:17 PM UTC-5, Look165 wrote:
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TION".
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oportion.
bit cos it is coming form the mains supply.
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ltage applied to the primary drops when a load is applied to the secondary.
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high, triodes are somewhat better.
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turation distortion when loaded compared to unloaded.
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Re: What differentiates good audio xmfrs from bad ones?
On Tuesday, January 22, 2019 at 10:13:17 AM UTC-8, Look165 wrote:

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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.

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