The bulk of what we enjoy as distortion is from the design, not the components. The operating point of the tube determined by the load line creates distortion due to uneven distance between grid lines. The contribution to distortion by the parts is small. The contribution to NOISE can be significant. The sterility argument as a function of parts is flawed. I will bet you, in the most gentlemanly fashion, a six pack of your favorite beer right now that your all metal film build will be just as glorious and warm as an all carbon comp build, and very probably even better because of the low Shot and Johnson noise of a good metal film resistor. Metal films get a bad rap likely because the guy shooting off his mouth on the internet came to the conclusion that all metal films result in cold and lifeless amps, because he used some garbage part with steel leads and not-insignificant inductance as well as other undesirable characteristics. All parts are not created equal nor are the builders using them. As you say, lead dress and transformers make a massive difference in how an amp sounds.JMPGuitars wrote: ↑Fri 08/16/19 1:12 pmYou're missing an important detail/part of the argument here. HiFi amps want to be clean and distortion free. Even a guitar amp's clean sound has some level of distortion, if it doesn't, it sounds terrible. If every component used in an amp is designed to reduce distortion, then you're potentially negatively affecting desired tone.
Your study was still very good and I thought perfectly valid. You can split hairs ad infinitum with the setup. Guys will talk you to death about the minutiae. The point is, what difference do you hear, if any? I watched that video as well, long time ago. To my ear, in some amps, with Polypropylene you don't get so much of the midrange smear you do with polyester. But the construction of the capacitor will also make a difference in its performance and sound.Regarding your MF amp build, the only way to determine that being the best build (for that reason), is to double-blind A/B test the same amp with both MF and other resistors. The difference in all the other components, and your skill level at the time of each build, all come in to play. You know all this though.
This is an old (not-very-scientific) demo I did comparing capacitors: https://www.youtube.com/watch?v=kUDhBnMSuG0
I built all 3 amps at the same time, with all the same components, except for the tone/coupling caps. For that demo to be closer to scientific, I should have used the same amp build, and swapped the caps. I should have also used a prerecorded track on my looper pedal to make sure that the playing and levels were the same for each test. Obviously there are other factors too. But still, there's distinct characteristics that are more likely the caps, than the variance between transformer sets. To me, and most of the comments I received, the polyester caps were preferred. That doesn't mean that PP caps don't also sound great. A couple people did like the OD PP caps, but they were the least popular. Still sounded good, but not the best.
Also, just to pour gasoline on the fire...I hear quite a bit of difference between say a Vishay Dale RN65 (metal film) and other metal films.
There is some internet lore that says a guy goes into a music store and asks to try out a Custom Shop guitar. He plays it and then plays the Not Custom Shop version. He then says to the proprietor, "huh, I don't hear a difference so how come that guitar is so much more than the other one?" The shop keep says, "well, if you don't hear a difference, then there must not be one".