From: Winfield Hill
Subject: Re: Output Impedence
Date: 31 Oct 2002 14:27:33 -0800
Organization: Rowland Institute
References: <email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
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email@example.com Tom Bruhns wrote...
> Winfield Hill wrote ...
>> Tom Bruhns* wrote...
>>> I thought it would be interesting to remind myself of what a real
>>> transformer's frequency response does as a function of output load,
>>> so I dredged out an old 600:600 "bridging transformer". What I see
>>> is that the low end isn't terribly affected by load (-0.1dB at 0.6Hz,
>>> yeow!), but the high end is quite sensitive to load. ...
>> Conversely, the low end is quite sensitive to source resistance,
>> especially if it's higher than the "spec" resistance.
> :-) Actually, you caught me in a slight indiscretion here, Win.
> When I measured that, I was doing it from a 50 ohm source impedance,
> but in a manner which tested only the transformer, not the system.
> That is, I was measuring the transformer output voltage/input voltage.
> I should (do) know better than to pass that off as a reasonable
> characterization, ('specially since I'm in the midst of coming up with
> a DC-6GHz three-way power splitter specifically so we can make just
> such a measurement correctly!) and have re-tested with a 600 ohm
> resistance between the reference channel and the transformer; now I
> see a 14.0Hz -0.1dB point, still not too shabby. Also, putting in
> that resistance damped the resonance with the unloaded secondary,
> though only partially. ...
Right, especially since a typical computer codec Z-out is, hmm,
well at least the AD1885 output impedance spec is 800 ohms max.