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Re: Ever heard of this...

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On 2017-02-10 06:59, jrwalliker@gmail.com wrote:
> On Friday, 10 February 2017 14:49:26 UTC, Chris Jones  wrote:
>> On 09/02/2017 09:19, Jim Thompson wrote:
>>> On Wed, 8 Feb 2017 17:04:41 -0500, Phil Hobbs
>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>
>>>> On 02/08/2017 04:58 PM, Jim Thompson wrote:
>>>>> Ever heard of this...
>>>>>
>>>>> Client has issues with audio transformers... at low signal levels they
>>>>> exhibit roll-off in coupling at low frequencies, like -10dB at 50Hz
>>>>>
>>>>> But high signal _levels_ do not.
>>>>>
>>>>> Strange?  Or a known phenomenon?
>>>>> 		
>>>>>                                          ...Jim Thompson
>>>>>
>>>>
>>>> Sure.  Lots of core materials have lower permeability at low flux
>>>> levels--it's the magnetic version of traps in semiconductors.
>>>>
>>>> Cheers
>>>>
>>>> Phil Hobbs
>>>
>>> So there's no cure?  I was pondering current drive, but it doesn't
>>> sound like that would help?
>>> 		
>>>                                          ...Jim Thompson
>>>
>>
>> Maybe add another secondary winding, and use it for negative feedback in
>> the circuit that drives the primary, a bit like old valve audio power
>> amplifiers did.
>>
>> You would want the feedback secondary and the real secondary to have
>> similar coupling to the primary.
>
> Why would this only affect low frequencies?
>

At higher frequencies less inductance is needed and the impedance of the 
transformer will still be sufficient despite the reduced permeability. 
Not so at low frequencies. It's the same with RF transformers such as 
baluns. There it is more extreme in that at really high frequencies the 
core wouldn't even have to be there.

-- 
Regards, Joerg

http://www.analogconsultants.com/

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Ever heard of this... Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-08 14:58 -0700
  Re: Ever heard of this... Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 17:04 -0500
    Re: Ever heard of this... Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-08 15:19 -0700
      Re: Ever heard of this... Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-08 17:27 -0500
        Re: Ever heard of this... Tim Wescott <seemywebsite@myfooter.really> - 2017-02-08 17:35 -0600
          Re: Ever heard of this... pcdhobbs@gmail.com - 2017-02-08 15:52 -0800
          Re: Ever heard of this... bitrex <bitrex@de.lete.earthlink.net> - 2017-02-08 19:04 -0500
      Re: Ever heard of this... John Larkin <jjlarkinxyxy@highlandtechnology.com> - 2017-02-08 17:15 -0800
      Re: Ever heard of this... George Herold <gherold@teachspin.com> - 2017-02-08 17:56 -0800
        Re: Ever heard of this... Pimpom <Pimpom@invalid.com> - 2017-02-09 13:05 +0530
      Re: Ever heard of this... Chris Jones <lugnut808@spam.yahoo.com> - 2017-02-11 01:49 +1100
        Re: Ever heard of this... jrwalliker@gmail.com - 2017-02-10 06:59 -0800
          Re: Ever heard of this... Joerg <news@analogconsultants.com> - 2017-02-10 07:29 -0800
        Re: Ever heard of this... Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> - 2017-02-10 08:35 -0700
          Re: Ever heard of this... Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-02-10 11:20 -0500
          Re: Ever heard of this... John Larkin <jjlarkin@highlandtechnology.com> - 2017-02-10 08:37 -0800
            Re: Ever heard of this... makolber@yahoo.com - 2017-02-10 08:48 -0800

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