Lets Talk Measurements!
DISCLAIMER #1: These were taken in a less than scientific manner using an old USB SoundBlaster I almost forgot I had. The characteristics of the measuring device are less than ideal, particularly in the manner in which I had to take the tests (see below). So, take them for what they are worth. These will mainly serve as a RELATIVE comparison.
DISCLAIMER #2: The output on the transformer-based boxes is down ~15db from the input. Because of this, I was unable to use the Line Out/Line In method to capture the data (not enough gain to register a clean measurement). So, these were taken using Line Out/Mic In, which, has a bit more gain to work with, but, is far less accurate (and is mono of course). So, do not be surprised when you see the SoundBlaster loopback results used for reference. Again, please remember the point is a RELATIVE comparison.
DISCLAIMER #3: The attenuation of the transformer boxes is the entire point of this little exercise. The sample levels for those devices were 100% output with the Mic input at ~43%. In contrast, that amount of signal completely swamps a standard loopback measurement made with a cable from Line Out to Mic In. The loopback reference had about 20% output with the Mic input at ~20%. So, a lot of signal was thrown away on the loopback reference vice the transformer-based measurements that enjoyed a completely unattenuated signal.
Nevertheless, here are the results. Again, the reference comparison is a loopback cable through the SoundBlaster card, the second is the original nikongod version of the circuit and the third is the jcx variation of the circuit:
Frequency Response (swept):
IMD + Noise
So, as you can see, the extra signal coming through is put to good use by the transformers. On the jcx Variation, dynamic range is up almost 6db and noise is down almost 6db. Distortion is held in check and the frequency response, save for a bump in the low end matches the loopback reference. Not too shabby. Good stuff.
Let the debate continue....