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A/B Testing Capacitors Help

Discussion in 'Amp Tech Center' started by _Steve, Oct 23, 2020.

  1. _Steve

    _Steve TDPRI Member

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    Hi, and apologies for another capacitor thread.

    I sit on the skeptic side of the debate but open to being convinced otherwise so I want to do some A/B testing for myself. I have a very flexible prototyping amp chassis that is currently a PP 6V6 with 2 standard-ish gain stages and an LTPI. At the moment its fitted with the cheapest film and electrolytic caps available on AES. No ceramics.

    So my question is, which one or two capacitor locations in an amp do you believe will have the biggest impact on tone with particular high-end capacitors?

    I want to install some on switches, do some testing and report back. I have a pair of ears, a cap tester, a scope and a basic spectrum analyzer. I'd like to keep my comparison to just film and electrolytic types.
     
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  2. Wound_Up

    Wound_Up TDPRI Member

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    Dylan Talks Tone on YouTube has a vid showing how to set up a test station in your guitar, to easily swap, caps to compare one to the next.

    Edit: sorry. Didn't read the whole thing first. This doesn't apply since I didn't realize it was in Amp Tech. Please ignore this post!
     
  3. tubelectron

    tubelectron Tele-Afflicted

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    IMHO @_Steve, on a tube guitar amp, you won't be able to find a significant difference - the value being exactly the same, and supposing that the caps in test are in good condition in term of leaks and losses.

    I made the test several times and never come to a indisputably conclusive result...

    For me, the most important influence is the value of the capacitor (for the tone) and AC and DC insulation voltage (for the lifespan)

    But it's me, OK ? :D
     
    Last edited: Oct 23, 2020
  4. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    I'm on the skeptic side too -- I doubt I'd be able to hear the difference between healthy capacitors of the same value -- but I'm interested in this experiment nonetheless. To make it truly scientific, you should enlist a buddy to assist you in blind testing. :cool:
     
  5. jvin248

    jvin248 Poster Extraordinaire

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    .

    Make sure you measure the actual capacitance of any parts you are testing.

    Looper or tone generator to give the same input every time.

    Have a repeatable output measurement system. Pitch shift, overlay traces, perhaps something like pluck a guitar string and measure time to fade below a certain db. Whatever it is you need to have a way to measure accurately. Your output measurement system could be an oddball measurement like how many fruit flies die every time you strike a power chord -- but it needs to be consistent so that cap A kills ten flies and cap B kills three flies and putting cap A back in kills either nine or eleven flies not two, three, or four. If you are rating 'tone' on a scale of 1-10, and you mix in repeats of cap A three times (randomly) are you giving that cap the same 'tone' rating number every time or is it as scattered as results from B and C? Having an accurate output measurement system will be the most important factor in proving if your theory is true or false.

    Blind testing -- so you don't know what sound sample you are doing something in.

    Random order testing -- use a random number generator and test "C/A/D/B" order that the generator gives you. This protects you from equipment issues like a tube amp chassis and speaker warming up from cold to hot during the test.

    One of the things I've learned from a lot of testing ... a change is only useful if it is blatantly obvious to a casual observer. If there are subtleties and nuances or a trained ear is required and especially if it takes statistics to prove with a certain % confidence that the results show a difference -- then making that change in the real world is too insignificant to be marketable. Only if you find an obvious change in feel like the difference between a feather falling on your foot or a bowling ball falling on your foot have you found an important lever. If you are trying to decide if a chicken or a duck feather fell on your foot then it's not important, no one cares unless there is a whole duck attached to the feather.

    Last is how can someone else set up their experiment to reproduce your test, do they get the same result?

    Only then can you publish your detailed paper "How to kill dozens of fruit flies with power chords by changing just this one capacitor".

    .
     
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  6. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Given the value of the caps are identical...
    Possibly the tone stack treble and mid caps could be noticeable followed by the first coupling caps. I am skeptical of caps made of the same materials but think there might be a duck feather when comparing polyester to polyethylene to silver mica etc.

    I doubt you could hear a difference in smoothing caps but it would be interesting if an audible ripple could be heard.
     
  7. Nickfl

    Nickfl Friend of Leo's

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    I think the suggestion of using a looper for your input is a good one. I would also suggest you look up something called the "triangle test". It is a method used in sensory analysis of non quantifiable data like taste testing food and it could be applied effectively here.

    Basically you provide three unmarked samples, two of which are the same. The tester is asked to identify which is different from the other two and which they like better. If people can't reliably tell you which is different, then you know there is no discernible difference and you ignore the preference data, if they can tell the difference then you have a meaningful difference and you look at the preference data and find out which option is better.

    You need to get a large sample size, but you can probably manage that on the internet and it would be a good way to try to actually prove that it does or does not make a difference.
     
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  8. elpico

    elpico Tele-Afflicted

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    If you're going to find any difference at all in signal caps you'd expect it to be in positions where they're actually changing the sound in some way. The usual 20n - 100n coupling caps are large enough to pass all frequencies untouched. I wouldn't waste a lot of time with those. On the other hand something like the small first coupling cap in a vox, the 250pf cap in a fender tone stack, volume switch bright caps etc. are small enough that they form AC filters. Those ones have a better chance of doing something detectable/measurable to the signal.
     
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  9. _Steve

    _Steve TDPRI Member

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    Thanks for the replies.

    Tone stack will be super easy for me to put on a switch, coupling caps a little less but not undoable.

    What about bypass caps? Do people think they benefit posh caps?

    I'm not going to get mega scientific. If I can or can't hear anything or see something on the spectrum analyzer thats good enough for me. If i can ill post a blind a/b test here and see if anyone can hear any differences. The looper was a great idea thanks!!

    Also what are the must have uber-mojo expensive caps i should use?
     
  10. tubelectron

    tubelectron Tele-Afflicted

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    Yes : a looper as a guitar tone generator... It's so simple that I never thought about it ! :oops: Thanks for the tip ! ;)

    -tbln.
     
  11. tubelectron

    tubelectron Tele-Afflicted

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    I have some sealed military NOS Silver Mica caps from the Golden Era of the vacuum tubes : 50nF and 0.1µF / 2000VDC. I also have 10nF 500V. I use them soemtimes in my Audio circuits... Mainly because I have them !

    Below in a pair of Full-Range BSC / Bandwitdth correctors :

    [​IMG]

    Otherwise, for modern production caps, I use Mundorf "M-Cap Classic" capacitors.

    Below there are 10µF/630V/3% used as coupling caps (the sole ones) to the grids of the output stage of my OTL mono blocks amp (the 2 big white cylinders in each chassis) :

    [​IMG]

    [​IMG]

    The M-Cap Classic serie is the less expensive of the range, but nonetheless fine quality and flawless : I paid them 10.50 Euro per unit for the 10µF.

    Taht said, Mundorf offers very costy ones : the M-CAP Supreme Silver Gold Oil serie which, still for 10µF, show a price tag at 249 Euro per unit... :eek: Would I hear a significant difference ? Not sure... o_O

    But it's me, OK ? :D

    -tbln.
     
  12. King Fan

    King Fan Poster Extraordinaire

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    Cool thread. At least one builder here did two identical 5E3s except for having all red Jupiters in one and all yellow in the other (IIRC). Given the materials difference in *that* case (I believe the reds are made with papyrus and sealing wax from Egyptian tombs) I was willing to believe him that it made a difference (again IIRC.) :D

    Given what @elpico noted about smaller caps actually shaping sound, and what @Lowerleftcoast pointed out about different materials, I'd be interested in testing some common (but possibly fairy dust) wisdom, like polystyrene is smoother than silver mica as a treble cap, or *NOS* CD can have a 'comb filter' effect (???), or polypropylene is more suitable for very small (pF) caps than polyester (I forget why, but I've read this is actually logical). Good luck getting all your small caps to test exactly the same capacitance, though. :)

    I like that you're testing just for your ears and your amps. If someone was gonna go all objective with blind listening and randomization and the 'triangle' method / sample size by @Nickfl , it'd actually be massively *useful* to test say 'all polyethylene' vs. 'all polyester' on the board, and things like that... tests at the "macro" (eg, Ford v. Chevy) level and not just the "micro" (eg, Champion v. Delco spark-plug) scale. But even if you could do it, I'm sure you couldn't get most of us stubborn builders to believe the results....

    For myself, I think it's perfectly likely it doesn't make much difference, but I love harmless tweaks that make my amps my own, and give me a chance to enjoy my confirmation bias for a few extra bucks.
     
    Last edited: Oct 24, 2020
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  13. _Steve

    _Steve TDPRI Member

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    After giving some thought to the recommendations posted here i've decided I'll test using a TMB substitution box that I built recently as it has 3 caps in the tone circuit as well as the outbound coupling cap.

    20201024_090744.jpg 20201024_092453.jpg

    I can put all 4 caps on a 4-pole switch and switch back-and-fourth between them while the guitar signal is running through my looper pedal.

    Surely if these high-end caps are worth the hype and cost then I should be able to hear a noticeable difference with these 4 cap locations right??

    I was thinking I could even record/video it and post a blind A/B poll on the main amp forum. Could be fun and not much effort.
     
    Last edited: Oct 24, 2020
  14. _Steve

    _Steve TDPRI Member

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    I like the idea of testing the different composition types. First however I want to test like-for-like composition and values between cheap and expensive/boutique caps. If I do it as planned with the substitution box (above post) it should be easy to do another test afterwards with the different compositions. I suspect the different compositions will likely yield more noticeable results, and this would be a good learning exercise.
     
  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I would like to remind all of us that in the early gain stages additional wire and/or the positioning of wire may act as an antenna which could be detrimental and misconstrued as a cap not audibly performing well.

    Carry on.:)
     
  16. _Steve

    _Steve TDPRI Member

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    Yep understood and thanks for the advice. I do have the tools to perform noise analysis if it becomes an issue but I don't expect it would as the input/output cables are shielded and keeping these caps away from the noisier parts of the amp could make for a healthier comparison too. Mainly though I'm just lazy and it makes it a simple job :)

    Which caps should I buy? SoZo?
     
  17. printer2

    printer2 Poster Extraordinaire

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    Before you stick in the capacitors wrap them in paper (a little capacitor box with leads sticking out?) and install them so you do not know which capacitor is in which switch position eliminating subconscious bias. Also don't have the leads too long coming out.
     
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  18. Digital Larry

    Digital Larry Friend of Leo's Gold Supporter

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    If you live switch caps like this be prepared for a giant POP when you do so. This could be mitigated by placing a 22 Meg resistor across each cap, which will Heisenberg your results, but I'd prefer that to Hindenberg.

    btw I've made my feelings about capacitors known elsewhere, but to add to all that, I consider capacitors analogous to screws, or maybe washers. You're building a table. If you use really crappy screws, you might notice a difference. But... what about these silver plated screws that cost 100x? Why would they make those if they weren't better?
     
    Last edited: Oct 25, 2020
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  19. King Fan

    King Fan Poster Extraordinaire

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    Heisenberg, or Hindenburg. Love it!!!

    Which boutique cap? Oh no! :):):) *Whose* fairy dust do I believe in?

    I might try the boutique cap *you’d* be most tempted to use. No reason to test Jupiter reds if you aren’t interested in their materials or supposed ‘era.'

    The other question is what you’ll use for a *cheap* cap. Are Mallories too good? Etc.

    Agree with @printer2 also. I love this kind of experiment, but unless we take some real steps to make it blind and in random order, we gotta know we’re testing our confirmation bias more than the caps. Maybe put the covered box out of sight behind you, with a dummy switch and an A/B labeled real switch, and have a friend switch one or the other a few times before you start testing? Have him keep score of how often you like A or B? Even just see if you can tell when the real switch is flipped instead of the dummy?
     
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  20. printer2

    printer2 Poster Extraordinaire

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    I found the thread on your amp, I have some TV tubes I would like to make a 1-2W OTL amp with. Why? Just because.
     
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