On Friday, 26 February 2021 at 15:45:36 UTC, Scott Dorsey wrote:
gray_wolf wrote:
kludge wrote:
Catastrophic ringing: http://www.panix.com/~kludge/xformers/DSC00258.JPG
Any idea what the catastrophic ringing harmonics would look like on a spectrum
analyzer.
They aren't harmonics!
They are the result of parasitic LC networks caused by the series inductance
of the transformer winding and the capacitance between turns. In the case
of simply-wound transformers (like the one in that picture), the result is
one big narrowband resonance somewhere. Any signal anywhere near that
resonance excites it, even the harmonics of the 1kc. And once it gets excited,
it will continue bouncing back and forth at its resonant frequency until
the energy is gone and that capacitor is discharged.
So on a spectrum analyzer that would likely be one single narrow spike.
Now... there are better ways to wind transformers in order to distribute
that across a wider area, so that you get more smaller resonances instead
of one big one. Those can result in multiple smaller spikes.
If the transformer is designed well, the spike is well above the audible
region where it can be eaten by a zobel network.
That severely ringing transformer was designed for communications applications
where having a very high ratio was more important than bandwidth or low
distortion, so that resonance is much more extreme and much lower than anyone
would tolerate for a pro audio transformer. But, this is a 200:80k ohm
transformer.... the fact that it works at all is a miracle.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
So it might be possible that the company's mod advice of 100 ohms in parallel with 0.1uF should really be 100 ohms in series with 0.01uF?
Gareth.