Ralph...
I do not consider loading of the secondary of a transformer an acceptable way to control transformer behavior. Of course there will always be some minimal load and with a known source impedance the transformer can be designed to work into that minimal load. From a purely subjective viewpoint I have always found that reasonably well behaved unloaded transformers have sounded better than transformers forced into submission by loading. If you start with a couple of unknowns loading suddenly becomes the only thing left in your toolbox to get acceptable results and that is the way the industry has gone.
From a measurement perspective it is interesting to look at the HF phase response of an unloaded transformer that rings and the same transformer loaded down for critically damped response. The link below is for the sweeps of the peerless 4722 driven from a 4Ω source with varying secondary loads.
http://www.intactaudio.com/images/SUT%20white%20paper/4722%20load.png
It is interesting to note that as the frequency response approaches flat at 20kHz the phase shift increases further down into the audio band. In this case it becomes the choice of the lesser of two evils. Since no two people hear the same, it is no wonder loading of cartridges is such a hotly contested subject when it comes to transformers. It is my belief that often times when you adjust cartridge loading via the secondary of a SUT, the sound (and measured response) of the transformer is what is heard. This change in sound is then falsely attributed to the cartridge seeing a different load.
dave
Loading the transformer is well-known to control issues in the high end- the 'underdamped' part to which you refer.
I do not consider loading of the secondary of a transformer an acceptable way to control transformer behavior. Of course there will always be some minimal load and with a known source impedance the transformer can be designed to work into that minimal load. From a purely subjective viewpoint I have always found that reasonably well behaved unloaded transformers have sounded better than transformers forced into submission by loading. If you start with a couple of unknowns loading suddenly becomes the only thing left in your toolbox to get acceptable results and that is the way the industry has gone.
From a measurement perspective it is interesting to look at the HF phase response of an unloaded transformer that rings and the same transformer loaded down for critically damped response. The link below is for the sweeps of the peerless 4722 driven from a 4Ω source with varying secondary loads.
http://www.intactaudio.com/images/SUT%20white%20paper/4722%20load.png
It is interesting to note that as the frequency response approaches flat at 20kHz the phase shift increases further down into the audio band. In this case it becomes the choice of the lesser of two evils. Since no two people hear the same, it is no wonder loading of cartridges is such a hotly contested subject when it comes to transformers. It is my belief that often times when you adjust cartridge loading via the secondary of a SUT, the sound (and measured response) of the transformer is what is heard. This change in sound is then falsely attributed to the cartridge seeing a different load.
dave
