Opinions.....outside foil

[Malcolm Irving]

I'm pretty sure we (that is, the whole human race) has not yet proved that there isn't a rain god, but that question doesn't get a lot of play. We have not proved that the color of the tolex doesn't make a difference to sound quality either.

Then there's the whole issue of it being logically impossible to prove a negative - no one is every going to prove that it doesn't.

Totally agree, but we are in a rather different situation here. We have a well established scientific theory (electro-magnetic theory) which tells us that there is an effect. I am just wondering if that effect is audible or not - surely susceptible to a scientific test (if anyone has the time / inclination / skill / equipment)!

[Enzo]

yep, there is the effect. More important though, any phenomenon occurs within a context. So does that effect have a significant influence on the sound in the context of an amp? Not unlike dose make the poison. Botulism is one of the worlds most deadly poisons, but only in lethal doses. tiny amounts are injected in people every day for cosmetic reasons. Belladonna alkaloids are a powerful poison, but they were nonetheless the active ingredient in Contac Time Pills cold medicine for years.

[Jazz P Bass]

[R.G.]

Totally agree, but we are in a rather different situation here. We have a well established scientific theory (electro-magnetic theory) which tells us that there is an effect. I am just wondering if that effect is audible or not - surely susceptible to a scientific test (if anyone has the time / inclination / skill / equipment)!

Yes, it is susceptible to scientific test, but there is a fundamental problem here: "audible" is not a binary quantity. It's not audible or not, it's audible by how much in comparison to everything else, and in relation to the human auditory threshold.

The human auditory threshold varies from human to human and also within the same human with age and loud sound exposure, and with auditory masking phenomena. But even sounds below the auditory threshold can be amplified up to be plainly audible. And we are assuming an amplifier is involved here, so the question again turns on "how much amplification". As Enzo notes:

More important though, any phenomenon occurs within a context. So does that effect have a significant influence on the sound in the context of an amp?

And I'd add to that - which amp, and how much amp?

It definitely is possible to answer the question of whether outside foil orientation noise pickup is above or below the noise threshold in a specific amplifier, with specific tubes, control settings and speakers. And any one boutique amp maker could do that test, find a result, the pepper the internet with what they now personally have experienced, assuming that their personal experience is universal and that anyone that doesn't share that experience is defective, malicious, or naive. But the qualifications of which amp, which conditions, which listeners, etc. get lost in the process.

Not all questions are susceptible of a general answer. Some have to be qualified so much that you can't make sweeping statements.

[cyclone]

It might be superstition but I will always succumb to superstition relating to noise I can see on on an oscilloscope rather than that relating to "tone" Noise is a quantifiable and measurable component of an sudio signal. Thanks a pantload RG for writing an article that convinced the world that CC resistors are magical. I know that was not the intent!! but people use it as "mojo justification" I will accept that my superstition about cap orientation is just that

[R.G.]

It might be superstition but I will always succumb to superstition relating to noise I can see on on an oscilloscope rather than that relating to "tone" Noise is a quantifiable and measurable component of an sudio signal.

As we say here in Texas, it ain't braggin' if it's true.
If it's repeatably measurable by third parties, it's not superstition.

Thanks a pantload RG for writing an article that convinced the world that CC resistors are magical.

Magic may loosely be defined as a technology you don't understand. The guitar world held that CC resistors were tone magic and an unparalleled good before I wrote that. What I did was to find the residue of truth under the layers of foo-foo dust and describe where it's useful and where it's not. It's not useful in input stages where the excess noise is prominent. It is useful where there are BIG signal swings. And if you can measure and reproduce it, it's no longer magic mojo. It's just a technology.

I know that was not the intent!! but people use it as "mojo justification"

That's OK. They were using nothing-at-all as a mojo justification before I wrote it. At least now there is a place to find the grain of truth.

I will accept that my superstition about cap orientation is just that

But it's not - there is an underlying physical effect there - but what is real is the relationship of the cap orientation to the rest of the circuit in a schematic sense AND the rest of the circuit in a physical layout sense. Simple rules of thumb like "make them all point the same way" are going to miss the boat (in a technical sense).

As Pope said:
"A little learning is a dang'rous thing;
Drink deep, or taste not the Pierian spring:
There shallow draughts intoxicate the brain,
And drinking largely sobers us again."

And someone's (can't remember who at the moment) sig says"
Some drink at the fountain of knowledge. Others just gargle.

[cyclone]

But can you measure the change in resistance (or distortion of an ac signal) with applied voltage assuming temperature is stable? I know that CC's change value when being installed in the circuit, by 3% or so in my tests, my feeling was that your article seeked to justify a perceived phenomenon. I don't use a lot of carbon comps but I have piles of nos ones, I have variable HV power supplies, I have not been able to measure a change in resistance with an increase or decrease in applied voltage.

I am more than willing to run more tests, I think data is beautiful I just got my new shop set up and restored an Eico 1030 HV supply. I have a nice Tektronics 200mhz scope so i can interface with a pc etc. If there is a relevant test (hv ac square wave test?) please let me know, glad to contribute.

i still use a stereo univibe and fuzz face I built 20 yrs ago from the awesome info you posted back in the mid 90's. I truly appreciate all that you have done to dispell myths and internet BS and douchebaggery and push us all forward.

[R.G.]

But can you measure the change in resistance (or distortion of an ac signal) with applied voltage assuming temperature is stable?

Yes. The key information is even specified on the resistor data sheet: the voltage coefficient of resistance. The *resistance* of the resistor changes with voltage. It's measurable, and the the makers specify it as "the resistors won't be any worse than this...".

I know that CC's change value when being installed in the circuit, by 3% or so in my tests,

If you're measuring with no voltage, it may be drift caused by heating. If you're measuring with voltage on them, you *may* be seeing the VCR effect in action.

my feeling was that your article seeked to justify a perceived phenomenon.

Actually, it was written to clarify the real facts underneath a superstition.

For years, I considered the idea that CC resistors were tone magic to be the purest crap. I can't even remember what made me notice the voltage coefficient of resistance, but when I noticed it I did some calculations. It turns out that if you have a big signal - nearly 100V or even more - the signal itself is big enough to cause a change in the effective resistance. When you feed that signal through the resistor as a current, the resistor's VCR causes an effective distortion. It's measurable. But the signal has to be big - like in tube amps just before the power tubes.

So in addition to showing how the "CC sound better" could have a grain of truth, I showed where NOT to do it (anywhere but the PI in standard tube amps) and that the idea that all CCRs is best really is a myth, and only adds noise and drift. So people can build amps that are both quieter and retain a sound that is audible.

Just the facts.

I went off to find a suitable datasheet. Most of the manufacturers' data sheets have been updated since I found the one I worked from, but here's an example that still does quote the value:
Sharma Carbon Composition Resistors
Check on page 4.

I don't use a lot of carbon comps but I have piles of nos ones, I have variable HV power supplies, I have not been able to measure a change in resistance with an increase or decrease in applied voltage.

It's not an easy measurement to make. I would try this setup: (1) feed a test resistor enough *current* from a high impedance source to put 100Vdc across the resistor (2) feed it a high-purity sine wave *current* in an amount to make the voltage across the resistor swing between 0V and 200V (3) measure the distortion in the sine wave *voltage*. This is not how Sharma specifies it, and may not produce a "datasheet" quality answer, but it should sure cause measurable distortion if the resistance changes with voltage.

I am more than willing to run more tests, I think data is beautiful

Super! Go for it. I'd love to see the results.

[Steve A.]

Not that I am qualified to comment, but...that has been my understanding as well. That is why we shield the "open side" of a chassis against a piece of metal (I buy big aluminum cook pans from the dollar store), so that any RF from the outside world does not mingle with the amp circuit.

Yes, the disposable aluminum foil pans and oven liners, right? Great idea! Much better than using thick aluminum foil which can tear or shred, or dealing with sheet metal from the hardware store.

Thanks for the idea!

Steve A.

P.S. As for how to tell which lead goes to the outer foil, I just posted this in another thread...

>>> I had first tested Orange Drop caps for the outer foil lead using a 1/4" cable with two alligator clips plugged into a guitar amp. I would clip the test clips first one way and then the other to see which hummed more while holding the cap in my hand. Sure enough the bulge in the cap indicated the outer foil lead every time.

I have not bought any OD caps for many years so perhaps they have changed. (I usually use Mallory 150's instead of orange drops since they cost less and take up a lot less space.)<<<

At least on the old 630vdc Orange Drops you could see and feel the lead going to the outer foil (kinda like you can tell which leads go to the start and finish windings of a strat pickup.)