Those with Ralph's amp can do a quick test.....just remove the covers and remove all the hardware on the toroidal transformer.....lift it off the chassis and place a quarter inch thick piece of wood underneath.....put the transformer back down and listen. This CANNOT be measured.....but it can be heard....by YOU!
Actually this one is easily measured (you don't even need test equipment, you can do it with your hand for Pete's sake) and it is audible for a simple reason.
All toroidal transformers are supposed to have a very compact radiated magnetic field, but in practice they are a bit sloppy. Transformer manufacturers supply a mounting bolt with the transformer, but that bolt is always been a regular steel bolt and is magnetic. If you use it to install the transformer, it will be a magnetic short to the transformer. So you'll find that it heats up more than the transformer itself (you can feel this with your hand... you can see how laughable the idea is that this can't be measured 🤣). So its easy to show the difference in temperature and output voltage of the transformer when the magnetic steel bolt is replaced by a nonmagnetic stainless part.
We've been doing that for at least 30 years.
Fun fact: the bolts holding EI core (conventional) transformers together are also magnetic. They are usually insulated from the metal of the transformer and this does mitigate a lot of the magnetic load they place on the transformer core. But not all of it. You can reduce the temperature of a conventional power transformer by using non-magnetic stainless bolts (don't forget to keep the insulators!) and you can increase output power in tube amps slightly by changing out these bolts in output transformers for the same reason.
You can see here that someone claiming this can't be measured hasn't even bothered!
The issue with measurement is often figuring out what to measure, and then sorting how. For example, if you want to measure the effect a fuse or power cord has on an amplifier, you don't measure that fuse or power cord- you measure the effect on the amplifier.
Similarly if you think that a certain tweak has improved the bass in your system you demonstrate this by doing a frequency sweep in the room, install the tweak and measure it again. A customer of ours used this technique to show that a certain filter capacitor he had installed in a power supply was not only improving the bass but also reducing distortion. He was able to show a correlation between the perceived improvement in bass and clarity of the system and his part replacement in this fashion; that the perceived benefit was more than just expectation bias.
I can go on with other examples but you get the point. If you hear a difference, and especially if others report the same difference, then if you think about it you can probably figure out why that's happening and measure it. But you do have to think...
I remember very clearly the first time I heard a power cord make a difference- I was at CES in 1990 and heard a set of Magnaplanar MG3s that had been modified with a wood frame made by George Cardas. It was an impressive frame and did wonders for the speakers. I asked him if I could play our MA-1s on them after hours, he agreed and we made it happen. The amps seems to have a prodigious ploddy bass on the speakers; George suggested a pair of his power cords, which we installed. The bass was instantly improved! Switching back and forth the difference in the power cords was not subtle. I bought the pair of power cords on the spot.
It really bothered me that I could hear this but there was no clear cut explanation why, other than the mysterious claims that so many cable producers make. Turns out it was something simple: voltage drop across the power cord, easily measured. I sorted this out by measuring the output power, output impedance and distortion of the amp, which led me to measuring the input AC voltage at the IEC connector. Voila!
Power cords are one of those tweaky things that a lot of people over on ASR will deny has any effect on a system's performance. Power cords are subject to Ohm's Law like anything else. When I see that kind of denial, I like to ask if they caused their hand to move and make the measurements they laud so often, rather than just blindly making a pronouncement. If there's no measurement they are no better than the subjectivists they denigrate.
