Sorry, this will be a long one but when I've finished I'll try to stick to answering any questions which may arise and not continue with another "tome".
I also try to keep myself from getting too serious by applying my childish sense of humour, this is not an attempt to mock in any way!
When we are in the great Cap type debate it's important to differentiate at outset between the facts that make caps genuinely different and those which do not. The capacitance value and tolerance is not a factor in this debate in any way, as the starting point of any comparison has to be to find cap examples of each type which are of exactly the same value so as to remove any differences caused purely by the amount of capacitance. We are comparing differences in sound due to materials and construction here, not value. I agree there are people who can hear the difference caused by having a different value in some applications. But you can select any specific value you want by simply applying a meter and selecting your choice from batches of any type. If it sounds wrong because to you of that then you could just get a different value of the same type.
Let's face it, if a 0.022uF made by monks on a particular Greek island out of medieval parchment and sun kissed olive oil from a tree on the side of Mount Olympus which measures at 0.02uF is compared to a 0.022uF bog standard ceramic as used by Gibson, (booh hiss!
), which measures at 0.024uF, you have a 4nF difference to account for anything you may hear. That will swamp any other effects and no reliable conclusions could be drawn from that comparison on either side.
As to resonances, do you mean the natural resonances in the characteristics of the types themselves or the resonances set up between the pup inductance and the cap? If it's the former, they are well above any frequencies we are working with and their effects do not translate down into the audio band in any way. Those cheap ceramics Gibson got slammed for using in its guitars have natural resonance at above 10MHz and that's pretty much the ballpark. As we know, they become inductive above that but who cares? I can't see a mechanism whereby that can make a difference below 10kHz, can you? This isn't radar technology, it's guitar amps with a bandwidth of 8kHz on a good day with the wind behind them! If it's the pup inductance resonance you mean, yes of course that is audible. However it's only created by the value of the capacitance at that frequency, (and associated damping resistances), the pup inductance more than swamps anything any cap would show.
Yes, the longevity of caps is a factor in choosing them but not because of overall tone. Electrolytics are nowadays criticised to the point of almost hatred, totally unfairly, despite the fact that at their rated temperature, voltage and ripple current they will offer 1000s of hours of reliable working. Yes they can be improved by paralleling with higher frequency types, but once again, the effects are high frequency and will not be game breaking. Their fault modes are well documented now and the way they work is well explained elsewhere, yet still we see people swapping out every capacitor in their amps on a regular basis as "necessary maintenance". That's like changing every bolt on your car at a service because one might strip or snap.
What can be heard can ultimately be measured! You cannot hear a difference that would remain invisible to measuring technique for ever. It is of course possible that it may be a newly identified phenomenon and the measuring technique needs to catch up but I would respectfully suggest we aren't at the cutting edge of technology here. These issues have been done dusted and laid to rest decades ago very publicly in the hifi industry, a much more revealing, (not demanding), arena than the guitar and its amp. The results of their findings are that it has noticeable but limited effect in a few specific places at the most demanding level. As I said before, 0.005% is a lot more transparent to these things than 2%. And nowadays the heavyweights like Seymour Duncan are now becoming vocal in their support of the view that cap type makes no difference to sound.
Over the years I've set up a number of very simple blind listening tests with adamant believers in this phenomenon in the driving seat and, while everyone can hear differences when they klnow which is which, no one has ever been able to identify any repeatable differences when they don't know which is being applied. As I said, hifi is another thing. Differences of 0.05% distortion can be appreciated consistently but not in terms of tone which is the only criterion for our guitar amps which do not have to deal with 3D soundstage presentation.
If I may, I'll put in a trite little anecdote to make a point here. Early in my working life I was able to mix with a lot of classical musicians. The talk often turned to hifi equipment they used. I thought that they would have demanded the most accurate and transparent kit they could afford. It turned out that most of them used gear which was very average at best, yet they still insisted it was incredibly revealing of the music they played on it. The answer turned out to be very simple, they are the worst ones to review hifi equipment! They know most of that music so intimately their brains were able to inject any minor nuances which were missing and to hear an almost live performance. Even in comparison with ultra top flight kit most of them could hear virtually no differences. The power of their imagination really was strong in that case, and that's potentially in all of us, in both directions!
I can't see us easily agreeing on this one
, the debate lines are drawn as strongly as the trenches in the Somme.
I am really not just "an acolyte of the negative way", I argue over issues like from a flexible position looking to have it changed by exposure to different viewpoints which may educate my own further. That way I understand more and become wiser!
So, I've put forward a few ideas which I hope are worth at least considering and will do the same with anything in return, but I really don't want to start an ongoing war here, just a swapping of technical points for and against the idea.
EDIT: Oh and I should have added. My own systems includes my late 1960s Marshall Super Lead 100 and Marshall 4 x 12 that I bought in 1970 and still have and love today. I'm of that era too and have experience of "real amps" to draw on. They're great, but not all they're made out to be when other factors are taken into account.