Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old January 12th 19, 12:41 AM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

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

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Old January 12th 19, 01:21 AM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

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
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Old January 12th 19, 01:37 AM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

On Fri, 11 Jan 2019 15:07:21 -0800 (PST), whit3rd
wrote:

On Friday, January 11, 2019 at 9:07:33 AM UTC-8, 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
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Old January 17th 19, 07:58 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

On Friday, January 11, 2019 at 7:31:12 PM UTC-5, wrote:
On Fri, 11 Jan 2019 15:07:21 -0800 (PST), whit3rd
wrote:

On Friday, January 11, 2019 at 9:07:33 AM UTC-8, 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
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Old January 17th 19, 10:19 PM posted to sci.electronics.repair
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Default What differentiates good audio xmfrs from bad ones?

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




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Old January 19th 19, 12:42 AM posted to sci.electronics.repair
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First recorded activity by DIYBanter: Jun 2012
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Default What differentiates good audio xmfrs from bad ones?

"
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.


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