Hi-Fi Tunig Fuses & Parasound A21

The idea that fuses and power supply components are not part of the signal chain is not entirely correct. Anything coming in from the A/C, power cables, fuses, rectifiers, regulators, or power supplies can all become part of the output signal.

An operational amplifier circuit (whether discrete or monolithic op amp) will only pass through the actual signal if the signal is coming in on the inverting input of the op amp AND the negative feedback gain is unity gain (0 gain) or less than unity gain (i.e. it’s forcing op amp to de-amplify the signal). In this case, the waveform signal will actually route itself around the op amp using the negative feedback line as a pathway.  That being said, even with unity gain, the type of op amp or power supply elements will still influence the character or sonic signature of the audio.

If the negative feedback circuit is set to create a "gain" (or amplify), it increases the voltage of the waveform by using voltage from the positive/negative rails from the power supply (i.e. +/-15V). This additional voltage is sent through the output pin of the op amp. It this case, the fuse, power cord, A/C elements will contribute to the character of the waveform (in the sense of affecting how the op amp slews in relating to the input waveform, how far/fast it slews, character of the DC noise, etc.).

In a power amp circuit, the output transistors have to create massive gain (turning a 1V input into something like 15-100 watts or more). It has to use the A/C power coming in to create this voltage, so your signal is actually something like 98% A/C voltage.

https://www.youtube.com/watch?v=7FYHt5XviKc

I’ve posted that link before, but it’s an excellent lecture on how op amps actually work.

relating to this quote:

"Otherwise, do what actual music and sound professionals and amp designers do…ignore the nonsense of silly and fraudulently marketed psuedo tweaks."

I would like to say that amp designers have a completely different set of requirements to work against. They are working against limitations on cost and manufacturing processes. They need to weigh the availability of individual components when the equipment is actually manufactured or assembled. The idea that a Hi-Fi Tuning fuse can actually improve the sound is valid, but when it comes time to have these amps/equipment built on time and on demand so that they can ship to their distributors/retailers, the available of individual components becomes critical. What happens when a set of fuses are not available for weeks? A company like Bryston/Classe is not going to be able to wait to ship 20-50 units.  Also, cost of every single component adds up and the company's goal is always to use the cheapest components that allow them to meet a certain threshold (difference between a $4 Littlefuse and a $60 Hi-Fi Tuning becomes significant).

However, we also have companies like Audio Note or Audio Research who do focus on actual individual components (even down to what kind of carbon resistors are used or the type of solder). However, their manufacturing output is a lot less and item cost is a lot higher.

Music and sound professionals have an entirely different set of responsibilities and don’t have time to be critical about every single piece of equipment. I’m sure recording studios have something like 2-5 million dollars of equipment (tons of devices - racks and racks of equipment) and need all their time to focus on recording/mixing/effects/etc. They need equipment that is good enough to meet the bottom line, but they are not going to spend another 1-2 million and hours of time when "off the shelf" equipment is going to be decent enough to produce their product. In their industry, time is money. Unless your Cookie Morenco, who has tremendous focus on how individual components and wiring affect the sound. However, that is a very small niche market.