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Re: Diff amps spec at 500ohms plus, why?

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On 2017-12-25 09:53, krw@notreal.com wrote:
> On Mon, 25 Dec 2017 07:51:38 -0800, Joerg <news@analogconsultants.com>
> wrote:
>
>> On 2017-12-25 07:46, krw@notreal.com wrote:
>>> On Mon, 25 Dec 2017 07:26:55 -0800, Joerg <news@analogconsultants.com>
>>> wrote:
>>>
>>>> On 2017-12-25 05:51, krw@notreal.com wrote:
>>>>> On Mon, 25 Dec 2017 00:56:23 -0800 (PST), Klaus Kragelund
>>>>> <klauskvik@hotmail.com> wrote:
>>>>>
>>>>>> Add a transformer to get low output impedance and wrap the feedback loop around that?
>>>>>
>>>>
>>>> We need this to work down to DC.
>>>>
>>>>
>>>>> He already stated that he needs to drive several volts, for some
>>>>> strange reason.  A transformer just means he has to drive even higher
>>>>> levels out of the amp.  Seems counterproductive.  I'd look at the
>>>>> assumptions.  High line levels are the problem.  See if something can
>>>>> be done about that.  If you don't like the answer, change the
>>>>> question.  ;-)
>>>>>
>>>>
>>>> High line levels are customary in industrial environments. You also have
>>>> those with DSL and such and there are nice chips for it. They are
>>>> single-supply though (can be hacked if needed) and have huge power
>>>> dissipation which would be a serious problem in this case. Those are
>>>> meant to drive at >10Vpp.
>>>
>>> If it's so easy, what's your problem?
>>>
>>
>> As I have described, heat. Plus space. This thing also has to be very tiny.
>
> So you want power but no heat.  That is an interesting problem.  Ya
> think it's time to change the question, yet?
>

No, I want linearity with a modest quiescent current. Power during 
signal peaks is not a problem because they will be short burst 
transmissions.


>>>> Anyhow, it's the customer's wish and the customer is always king.
>>>
>>> The customer is always the customer but you're the one he's hired to
>>> be the expert.
>>>
>>
>> If the customer wants something they usually have good reason why and I
>> am the guy that needs to make it happen. If it was easy they wouldn't
>> need me. Consultants tend to only get the difficult projects which is
>> something I thoroughly enjoy.
>
> Usually <> always.  Without understanding the complete problem, you
> (and we) can't know.
>

Well, I know :-)


>> In essence I have a solution which is brute force. If needed two regular
>> diff-amps get paralleled. The main reason for this thread is my
>> curiosity why most diff drivers are spec'd at unrealistically high Z.
>
> The answer to that is pretty obvious.
>

Looks like a marketing decision on the part of the mfgs to me. IMO there 
would be nothing wrong with stating "Here, this would be the max swing 
and distortion specs if you run it at 100ohms like almost anyone who 
wants to drive a line does".

-- 
Regards, Joerg

http://www.analogconsultants.com/

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Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-21 15:48 -0800
  Re: Diff amps spec at 500ohms plus, why? George Herold <gherold@teachspin.com> - 2017-12-21 18:53 -0800
    Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 09:31 -0800
  Re: Diff amps spec at 500ohms plus, why? Winfield Hill <hill@rowland.harvard.edu> - 2017-12-21 19:48 -0800
    Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 09:34 -0800
    Re: Diff amps spec at 500ohms plus, why? bloggs.fredbloggs.fred@gmail.com - 2017-12-24 09:37 -0800
  Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-21 19:55 -0800
  Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-21 19:59 -0800
    Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 09:39 -0800
  Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 12:07 -0800
    Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highland_snip_technology.com> - 2017-12-22 12:54 -0800
      Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 13:29 -0800
        Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highland_snip_technology.com> - 2017-12-22 14:06 -0800
          Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 14:19 -0800
            Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highland_snip_technology.com> - 2017-12-22 14:40 -0800
              Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 15:16 -0800
                Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-22 16:30 -0800
                Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-22 16:57 -0800
                Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-22 20:33 -0800
                Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 08:21 -0800
                Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-23 10:20 -0800
                Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 11:33 -0800
                Re: Diff amps spec at 500ohms plus, why? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-12-23 13:56 -0500
                Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-23 11:08 -0800
                Re: Diff amps spec at 500ohms plus, why? Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> - 2017-12-23 14:11 -0500
                Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 11:42 -0800
  Re: Diff amps spec at 500ohms plus, why? LM <sala.nimi@mail.com> - 2017-12-23 21:36 +0200
    Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-23 12:18 -0800
  Diff amps spec at 500ohms plus, why? Klaus Kragelund <klauskvik@hotmail.com> - 2017-12-25 00:56 -0800
    Re: Diff amps spec at 500ohms plus, why? krw@notreal.com - 2017-12-25 08:51 -0500
      Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-25 07:26 -0800
        Re: Diff amps spec at 500ohms plus, why? krw@notreal.com - 2017-12-25 10:46 -0500
          Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-25 07:51 -0800
            Re: Diff amps spec at 500ohms plus, why? krw@notreal.com - 2017-12-25 12:53 -0500
              Re: Diff amps spec at 500ohms plus, why? John Larkin <jjlarkin@highlandtechnology.com> - 2017-12-25 09:58 -0800
              Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-25 11:39 -0800
                Re: Diff amps spec at 500ohms plus, why? whit3rd <whit3rd@gmail.com> - 2017-12-25 17:16 -0800
                Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-27 16:17 -0800
                Re: Diff amps spec at 500ohms plus, why? Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-12-27 19:06 -0800
                Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-28 00:47 -0800
                Re: Diff amps spec at 500ohms plus, why? Lasse Langwadt Christensen <langwadt@fonz.dk> - 2017-12-27 16:38 -0800
        Re: Diff amps spec at 500ohms plus, why? George Herold <gherold@teachspin.com> - 2017-12-27 18:03 -0800
          Re: Diff amps spec at 500ohms plus, why? Joerg <news@analogconsultants.com> - 2017-12-28 00:50 -0800

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