Where to put the outer wrap of caps in a Tone control circuit?

[pompeiisneaks]

For me, any whisk(e)y is nifty, but I prefer Islay scotches like Lagavulin or Laphroiag as my favorites, but they're not cheap so I don't get them often

~Phil

[R.G.]

Used to drink Laphroiag, got too sensitive to the phenols, so it's over to the Speysides for me.

You want something truly eye opening for dessert? Pour some Speyside over high quality vanilla ice cream. Blasphemous, I know, but seriously, try it.

And do try the Hibiki. None of the stores in central Texas had it, but my complaining about not finding it got one local store to buy a few bottles. When I went in for more, they were out. They told me I bought the first of their shipment, a clerk there took home the second, and then a slew of customers wiped out the rest. They're thinking of making it a staple, even if it's more expensive than the Islays, and a blend to boot.

I can't afford it often, so I meter myself down to the milliliter.

[pjd3]

Well. Now we all know what we all have to do.

Place two caps at half the value in parallel to equal the desired capacitance in each and every position, with each pairs foils facing opposite direction.

Now we have a 50/50 chance of getting it both right and wrong 50% of the time.

Whew. Glad I figured that out before the next build. I'm 25 years sober so I can't share in the same spirits as some of you. But, I can play with capacitor outer foil voodoo majic.

pjd3

[JD0x0]

I'm still back at "how the devil can outer foil make an audible difference in sound or noise out of a guitar amp?"

I can't/won't argue for sound/tone differences, but the noise theory is pretty solid.. Have you ever used shielded coax on your grid wires? What benefits do you notice when you use it? Lower noise and more stability, less chances for oscillations?

Okay, so I think it's safe to say we've established shields work... Now, we have a cap with this 'outer foil' (hey foil is conductive, maybe we can use it as a shield, eh?) So, let's connect that shield to the lowest impedance to ground.. We now effectively have shielded caps, yes? So is it terribly far fetched to believe that this could potentially reduce noise potential just as shielded grid wires do?

The only way I can see it really affecting tone is due to 'talk' between components add positive and/or negative feedback in places, which would affect amp performance and tone, to a degree. In the same way bad/good lead dress can affect tone and performance, caps 'talking' to other parts of the circuit can also affect tone and stability too.

[R.G.]

I'm still back at "how the devil can outer foil make an audible difference in sound or noise out of a guitar amp?"

I can't/won't argue for sound/tone differences, but the noise theory is pretty solid.. Have you ever used shielded coax on your grid wires? What benefits do you notice when you use it? Lower noise and more stability, less chances for oscillations?

Okay, so I think it's safe to say we've established shields work...

Theories are proposals which are stated for the purpose of verifying them. One quip I like about theory comes from the Atomic Rockets website (highly recommended, by the way):

Theories are for testing. As I mentioned, I have a couple of hard-print textbooks that spend chapters on things like shields, and how to make them effective. As you may guess from that, there are many ways to make shields INeffective. So a general "shields = good" has been proven to be a poor theory. More complex theories about how shields work are needed.

Yes, I have used shielded coax on grids, and many other things. Oddly, it was problems with getting the right results from such a setup that first drove me to the textbooks on EMI and noise. Here's a tidbit for you: a simple grounded shield is effective in many (but not all) cases shielding things like grid wires. The penalty for that is that the parasitic capacitance of the shielding sucks high frequencies disproportionately from the grid wire, the impedance of the grid being so high. But shielding theory (!) predicts you can have your cake and eat it too by not grounding the shield, but instead driving the shield from a low impedance point that has the same, or nearly the same, signal as the grid. Now the capacitance of the shield doesn't matter so much because there is little voltage difference to inject signal current into the grid wire. Low impedance, relatively even, trumps grounded if you have signal bandwidth issues. Oddly, lumped element circuit theory predicts the performance well, by including the source impedance of the signal, the impedance of the shield drive and the capacitance/resistance of the grid and wiring, you can predict the grid voltage and the performance pretty darn well. If you think about it, this is a form of positive feedback, as a common technique is to drive the grid/base/gate shield from the cathode/emitter/source. That being the case, it's good to know the theory so you can predict what the circuit actually does, not what "shields = good" says. A really common situation is to drive a "guard ring" around the sensitive inputs in high impedance opamp circuits, but this being a theory, it can be adapted to other circuits.

Now, we have a cap with this 'outer foil' (hey foil is conductive, maybe we can use it as a shield, eh?)

Maybe. As I pointed out, that 'conductive outer foil' is inextricably linked to that other 'conductive not-outer foil' by the intended capacitance of the capacitor. This complicates matters because (1) not all of the 'conductive outer foil' is in a place where it can be connected to an otherwise isolated ground, and (2) that 'conductive outer foil' is being driven by the signal on the 'conductive non-outer foil' by whatever signal source/sink impedance is connected to the other end. At least one degree of freedom in using the outer foil as a shield has been taken away by that well designed capacitor linking it to what you're trying to shield. It raises the issue that "shield=good" may not provide all the notional goodie we'd like. What is required is some actual thinking about the circuits, the impedances, the required bandwidth, the source impedance, the sink impedance, and probably, sadly, the capacitor's parasitics.

So, let's connect that shield to the lowest impedance to ground.. We now effectively have shielded caps, yes?

In that one instance, you do get some shielding ... IF the actual terminal lead is connected to that section of the "outer foil". It turns out that there is likely to be some portion of the internal ESR and (worse) ESL from winding the foils/insulators into a cylinder. The actual lead may be connected to the actual foil at one or several "tabs", each/any of which may or may not right at the wire that goes outside the cap. So some portion of the ESR and ESL may be between the lead and the distributed capacitance that makes up the actual capacitor. It turns out that you have to quantify "effectively" by reference to the rest of the circuit.

So is it terribly far fetched to believe that this could potentially reduce noise potential just as shielded grid wires do?

No. But neither is it close fetched enough to always presume that it's a universal good. Circuits matter. Fortunately we have a century-plus of circuit THEORY telling us how to estimate what a given resistor/capacitor/inductor will do to circuit performance. If you'll do a re-read of my post, you'll find that I was trying to do that next step forward, from "shields = good" toward estimating what an outer foil really might do. I'm not arrogant enough to think that my analyses are always perfect, but I do make an effort to understand what circuits might do. And more importantly, I'm always willing to learn.

If there was some part of what I posted that you don't agree with, please point it out and let's discuss it. It is possible that >I< didn't understand deeply enough, and I'm always ready to learn.

[Charlie Wilson]

It would take less time to swap a few caps and see if you hear a difference than it would to read through all the tech reasons why you shouldn't. If you don't hear a difference, then the orientation wont matter to you. If you do hear a difference, then all of the reasons why you shouldn't hear a difference don't matter.
CW

[R.G.]

It would take less time to swap a few caps and see if you hear a difference than it would to read through all the tech reasons why you shouldn't. If you don't hear a difference, then the orientation wont matter to you. If you do hear a difference, then all of the reason why you shouldn't hear a difference don't matter.
CW

You're right. The problem is that people (1) can convince themselves they hear >anything< and (2) the ones with the least supportive reasoning are at the same time the least capable of supporting the idea, the least capable of doing repeatable tests, and the most likely to present the idea as the purest truth. There are some people who want to know whether and why.

But you are right - the analytical types will and should just try it, and move on. The ones who either really hear a difference or think they should cannot be convinced by logic. Then there's that whole which and how many caps have to be oriented to magnetic north... er, flipped to outer foil out.

It's the humans that are the problems, I tell you.

[Mark]

Not wishing to resurrect this topic, but more of a point of reference where the idea entered my mind. I think Gerald Weber first mentioned this sort of thing and Aiken then put forward his ideas.

https://www.aikenamps.com/index.php/whe ... capacitors