Listening tests of high end capacitors...

[fyl]

Would putting in a dummy switch test scenario, one with nothing connected to it, aid in offsetting any bias?

I did some tests a while ago with a dummy switch. Subjects were told that one position was straight wire, the other a "subjective signal enhancer". Non blind tests - where subjects knew that A was straight wire and B the DUT - led to 90% of the subjects finding a huge difference between the two positions and describing it lyrically (some loved the DUT, others didn't - only two subjects didn't find any difference). Proper blind tests showed no statistical difference/preference between the two positions.

[Rick Turner]

Unfortunately, not surprising...

There are many mirrors and much smoke in our little field of musical audio...

[David Schwab]

Would putting in a dummy switch test scenario, one with nothing connected to it, aid in offsetting any bias?

Bassist Anthony Jackson had something he called a "producer switch" on his bass. When the producer of the recording session asked if he could get a different tone, he would flick the switch, which was not wired to anything, and then the producer would say he liked that tone better!

A dummy would be good for "tone pot on 10" tests, but obviously wouldn't work for the tone rolled off. And with the pot on 10, the cap really doesn't do anything.

[Ronsonic]

I'm very interested to see what a careful test from an open-minded test administrator turns up.

I'm following this one.

[CRU JONES]

Ha ha! Good stories!
The treble bleed circuit is not very sensitive I think. I mean, I can tell my tone is different if my tone is rolled off a bit, I just can't tell how much. Unlike if my treble control on my amp was moved a small amount, I can definitely tell my tone has changed. The standard instrument tone control is just...mediocre! Maybe expensive capacitors could make it... really, really mediocre!

[RoadToNever]

I'm very interested to see what a careful test from an open-minded test administrator turns up.

I'm following this one.

+1

[JGundry]

If you are going to test them only do it if they are different types of capacitors. Such as polyester, polypropylene, PIO, styrene, ceramic. Ceramic does have a little more clarity in the treble response than the rest and they can be microphonic enough that at very high volumes it does begin to have an impact on the tone. Caps of the same type no matter what the cost are nearly impossible to tell apart IMO if they are the same value and voltage rating.

[jason lollar]

well thats part of the deal - if those caps i tested were in an amplifier you would hear a difference for sure depending on where they were in the signal path but on a guitar we found no difference.

[JGundry]

Personally I can hear the difference in a guitar tone circuit between POI, polyester and ceramic. It is extremely subtle though and really seems to affect the treble attack when you pick a note. Personally I prefer polyester for Les Pauls. Higher cost does not necessarily mean better tone when it comes to caps though.

One thing I would add is the difference seems to be more evident when you add a little bit of gain.

[Ronsonic]

Personally I prefer polyester for Les Pauls. Higher cost does not necessarily mean better tone when it comes to caps though.

This.

In the pedals I'm building there is a place for those cheap little chiclet caps. Here we're talking flavoring to taste, not better or worse, just different flavors.

[Bill M]

Personally I can hear the difference in a guitar tone circuit between POI, polyester and ceramic. It is extremely subtle though and really seems to affect the treble attack when you pick a note. Personally I prefer polyester for Les Pauls. Higher cost does not necessarily mean better tone when it comes to caps though.

One thing I would add is the difference seems to be more evident when you add a little bit of gain.

I totally agree. I've done a test with an external rotary selector switch with different compositions of capacitors that were matched for value. You can definately hear a difference. My favorite cap is a difilm polyester/paper dry cap such as the sprague PS series, which i don't think is made anymore. Same internal construction as the old bumblebees/ black beauties. I know everyone thinks that they are pio, but they are not. Just cut black beauty open and you will clearly see the construction is difilm and not pio. I've been in the vintage amp restoration business for a long time and have bought out many old radio and tv repair shops to have stocks of vintage caps for my clients. I've disected just about every cap made and have documented their construction. A lot of people also think that when your tone pot is on 10 that the cap is inaudible, well hook a switch up in series with the cap to be able to remove it from the circuit and tell me you don't hear it when the tone control is on 10. Granted, it is more pronounced with 250k pots vs. 500k pots.

[Rick Turner]

With those of you who hear a difference, what I'm not seeing is whether or not you actually measured the capacitance of each device to match them all within + or - 2%, and I'm not seeing if you're testing caps of the same voltage rating. If you haven't done this, what you heard is not of any scientific validity; it's basing and opinion on faulty research.

[dcoyle]

I have two observations.

Rick Turner said:

"given that they are treble bleed and are literally not in the signal path"

Here's another way to think about it. While the signal that is passed by the cap goes to ground, to say that the cap is not in the signal path is not accurate. It is in the signal path, it removes a perceptible amount of the signal and what frequencies it removes or doesn't is what the discussion is about. What isn't in the signal path are any distortions the cap may add.

and Rick said:

"With those of you who hear a difference, what I'm not seeing is whether or not you actually measured the capacitance of each device to match them all within + or - 2%, and I'm not seeing if you're testing caps of the same voltage rating. If you haven't done this, what you heard is not of any scientific validity; it's basing and opinion on faulty research."

If you stipulate that differences of voltage rating affects the sound of caps and that slight variations of value affect the cap sound, doesn't this indicate that there are sound differences between caps, desirable or not in that application?

It seems to me the real question that a constructor needs to answer is not if a $7 cap sounds different from a $1 one in a given use, but what is the better sound for that application.

I am very interested in what you find out and appreciate you're writing it up.

Thanks

Dan

[David Schwab]

What isn't in the signal path are any distortions the cap may add.

Explain that. It doesn't make sense.

The cap removes the high frequencies because of a low impedance path. What distortion would there be?

Personally I have not heard a difference in different style caps of the same rating. More expensive doesn't make the cap better, and they are only more expensive in the guitar and audio market.

[Rick Turner]

Dan, in audio engineering, "in the signal path" means exactly that...that the signal that we hear literally goes through whatever device it is that you're talking about. Capacitors are used "in the signal path" in a lot of preamps, sound modifiers like EQs, and power amps as one means of passing AC (which is what audio signals are) while blocking DC. Treble bleed capacitors are NOT "in the signal path", they are exactly as David describes. They drain high frequencies off to ground leaving the lows to go onto the next stage (usually in our case the front end of a guitar amp). You do not hear the signal that goes through the capacitor.

And just because someone changes a capacitor in a guitar from one brand or build type of a supposedly given value over to another does not mean that the quality or style of the cap is the reason it may sound different used in that circuit. The range of tolerance for parts is pretty wide, and in electronics, one of the things you do pay for is tighter specs. A .047 cap of garden variety could be a .0423 or it could be a .0517 if it's sold as being .o47 + or - 10%. That's plenty enough value swing to change the sound quite dramatically.

I have no idea whether voltage rating means anything at all in the case of passive treble cut capacitors, but the only way to be fair in a test such as I am proposing would be to attempt to use the same rating for every cap and test the caps so they are within + or - 2% or better.

Capacitors used to couple active stages definitely color tone in different ways depending on what they're made of and the overall quality of build. And that's where people get confused...by not understanding the different roles that capacitors play in electronic circuits and thinking that the same "rules" apply wherever you use a capacitor. You have to get away from guitar amp-think, or "re-cap the console"-think to understand the role of capacitors as passive tone control filters.

As a side note...some of the very best audio circuits do not use coupling capacitors in their design; they run "DC" coupled with servo controlled voltage regulation which automatically correct plus and minus power rails for any DC offsets. These circuits cost more to build; it's much cheaper to just throw in a coupling cap to get rid of DC trying to get from one stage of amplification to another. But...the signal path in DC coupled circuits is more direct and it does not go through coupling/blocking capacitors. I have had the opportunity to play through some completely DC coupled systems...guitar or bass straight on through to the speaker cabinets, and it is...well, revealing would be the right word. Coupling caps always introduce phase shifts, and DC coupling helps avoid them.

My inclination is to believe as do David, Jason, and some others here do...that given truly equal capacitance and voltage rating, you will not hear a difference among the various styles and "quality levels" of capacitors. However, when I do this experiment, I intend to do it double/triple blind to take my own prejudices out of the picture.