1uF NP, whats NP?

[kvb]

Looking at the Tonepad Callate Gate II pdf. there is a cap listed as 1uFNP.
What does NP mean?

[mojotron]

Non-polarized. These are pretty common use for coupling caps as they don't really influence the frequency responce of the circuit. In this case - Callate Gate - the 1uF cap allows a low impedance path around a DC path that has an extra 100kOhms. I would think that a polarized cap would be just fine in this application. Basically, it's an electrolytic cap that is not polarity specific - Mouser and others sells them.

[kvb]

thanks.

[Eb7+9]

... as they don't really influence the frequency responce of the circuit.

actually, they dominate the Bode responses

NP caps are made by sticking two polarised caps in series ... + 2 +

yes, you can actually "make" your own ... just use two caps of twice the intended value

[zpyder]

actually, they dominate the Bode responses

can you explain what you mean by this?  Bode?  dominate?

cheers
zpyder

[R.G.]

actually, they dominate the Bode responses
NP caps are made by sticking two polarised caps in series ... + 2 +
yes, you can actually "make" your own ... just use two caps of twice the intended value

Just out of curiousity, is there a shortage of capitalization and punctuation up there? They always yelled at me for using elipses (...) instead of real punctuation. A single period and a capital letter actually use the same number of key presses as an elipsis, and it's a lot easier to read. We were always taught that an elipsis represented either a breathless pause in speech or a place where you left out parts of something you were quoting.

'Course, old Mrs. Williams in 7th grade could have been wrong on that too. Maybe it's a different English. Or maybe punctuation means only whatever the writer means it to mean, too.

But anyway:
No, in this case, the NP cap does not dominate the "Bode response" unless, like our dearly departed president William Jefferson Clinton, it means whatever you mean it to mean. For the Bode response I was always taught, the 0.047uF/22K immediately preceding the 100K/1uFNP dominates the Bode response. The 0.047/22K is a highpass with a rolloff at 154Hz, and the 100K/1uFNP is a high pass at 1.59Hz. I'd say the 47nF and 22K dominate the Bode response - unless you had in mind some OTHER Bode response. The 47nF and 22K control what happens.

Nota bene: the "Bode response" I was taught about was the frequency response in terms of where the frequency response went up or down, or remained flat, and what the phase response did while the frequency response was doing its thing.

Could be, I guess.

There are a couple of ways that NP caps are actually manufactured, but none of them consist of putting two polarized caps in series. There are a couple of ways, but the more common is to oxidize BOTH plates with aluminum oxide. That way, no matter which way the polarity goes, one plate is correctly polarized.

You can FAKE an NP cap by sticking two polarized electros + to + or  - to -. This is not the same as a real NP cap, but it works in a pinch.

You do not use twice the intended value. Well, you might, but I would not.

When a polarized electro is reverse polarized by X volts, it conducts ohmically like a diode. In the region right around 0V, both caps appear to be in series and so the caps-in-series formula holds, but after X volts, one conducts ohmically, so it's no longer in series with the cap which blocks the applied voltage, and the capacitance jumps to the value of just the cap doing the blocking. As one might guess, it gets hard to say exactly what the rolloff frequency of such a combination is, and so it's wise (well, OK, wise if you want to make it do what you want, not what it wants) to not use such a combination to set frequency rolloffs, especially since the tolerance on electro caps is so bad compared to other parts.

In fact, this 1X-2X capacitance response makes it a bad idea to use polarized caps to control frequency response. The conservative approach to making circuits do what you want is to use electros only when you can make the actual value not matter much by putting the response poles 'way outside the frequency response of interest, then controlling the actual response with tighter initial-tolerance parts that don't vary in capacitance as they age like electros do and don't do the 1X-2X series capacitance dance for NPs.

But that's just my opinion. Your mileage may vary.

[kvb]

OK, so apart from worrying about frequency cutoffs and Bode responses (one more thing to look up)
would it work just as well to try some different combinations and measure the capacitance with a meter?

[R.G.]

Actually, you can just connect two 1uF caps plus to plus or minus to minus and not worry about the specific value.

The frequency of the nominally 1uF cap and the 100K resistor is a highpass of 1.59Hz, way below audio. The real frequency response is controlled by the 0.047 and 22K. If the "1uF"  was as much as 10uF, or as little as 0.1uF, it would still be no higher than 15.9Hz or as low as 0.159Hz. So the 0.047uF and the 22K would still make all the difference.

Just make up your own NP cap and put it in. You don't need to measure.

[343 Salty Beans]

I'm not sure if RG mentioned this in his bloody long (and quite informative) post...

But they make 1uf mylar caps (which of course are NP) too...they're just really damn big. as in the size of half your thumb big.

[RedHouse]

Wow. having a bad day RG? that reply to JC seems overloaded with Angst.
(not that it's any of my business)

[Mark Hammer]

Just out of curiousity, is there a shortage of capitalization and punctuation up there? They always yelled at me for using elipses (...) instead of real punctuation. A single period and a capital letter actually use the same number of key presses as an elipsis, and it's a lot easier to read. We were always taught that an elipsis represented either a breathless pause in speech or a place where you left out parts of something you were quoting.

JC lives on an island.  They GET punctuation but the shipments have to come in by ferry.  Given that the island has a disproportionate number of aging hippies, poets and arteests, if you're not fast enough getting down to the docks when it comes in, all the punctuation gets used up and bought out by others, and you're stuck with the leftovers.  You're lucky.  In landlocked Austin, all your punctuation comes in by truck.

[R.G.]

JC sometimes has a decidedly nonstandard view of the way things work. That's fine for him to use if it works for him. No problems with that, and he may have found his own strange and beautiful way of describing nature that not only works but is completely outside the mainstream of conventional technical thought. And that's not only OK, it's great - for him.

But it's not the way the professional technical world sees things, and it can be a decided impediment to a beginner trying to understand. This is going to sound patronizing, but I feel a certain responsibility to beginners to let them see the real technical way things work, and a description that is portable - i.e., I'm not the only one who would explain things that way.

Let's illustrate.
Here's a discussion of the Bode response as it relates to circuits: http://www.engin.umich.edu/group/ctm/freq/freq.html
That's the same thing I was taught over 30 years ago, and it doesn't seem to have changed. Bode response is the gain and phase response of a circuit shown under certain graphical conventions. The advice about the NP dominating the Bode response was flatly wrong as any pro in the EE field would understand it.

Angst? Maybe. I don't have much tolerance for nonstandard semi-technical explanations that appear to be technically correct but mislead beginners, just as I don't have much tolerance for advertising that uses techie sounding mumbo jumbo to sell things.

Beginners have a hard enough time learning how things work without dealing with things that are either misleading or wrong. Alternate explanations are fine, but they should not be wrong.

They GET punctuation but the shipments have to come in by ferry. ...  You're lucky.  In landlocked Austin, all your punctuation comes in by truck.

ROTFLMAO!!!
Of course, it's fair to mention that until recently, Texas didn't write enough to need much. 

[mojotron]

...
Of course, it's fair to mention that until recently, Texas didn't write enough to need much. 

Always wanted to get me one-of-them-there 'talkin' Texan' CDs from the "County Line BBQ" But, once the brisket showed up I quickly forgot about it.

Actually, for the time I lived in Texas, I loved the fact that the schools were generally very, very good at educating kids. I grew up on the west coast where we import our punctuation from Asia in fragments to be assembled later.

Getting back to this topic. Thanks everyone for the notes on ways to make a fake NP cap; ya learn something new every day!

I think we always have to keep in mind that, for the signal path in Guitar effects, we are always talking about effective audio 20-20kHz ranges - which for some effects is really more like 100-10kHz. Generally, if you want to couple a signal between 2 sub-circuits and don't want to influence the signal in a significant way (nor do the math to figure out how small of a cap you could use) it is generally safe to use a 1uF NP cap for audio signal coupling in effects where you're goal is to block - or route around - DC voltages.

[RedHouse]

...the advice about the NP dominating the Bode response was flatly wrong as any pro in the EE field would understand it....

Wow, there is clearly some underlying thing going on here, a page of response to a 3-sentence post, but oh well, sorry to stir the pot, it's a shame you and JC don't see eye-2-eye, as (most) of the rest of us here like (both) your posts on subjects of interest.

a'hem...cough...(UNIVIBE)...cough!

Ach well. There were clearly two questions on the table:

1.) can you make (sub) one?
2.) does it sound different?
(does it influence the frequency responce of the circuit.)

Yes one can, and, I think it would ...but....

Dunno why, but I'm reminded of something I learned years ago (I'm not an EE but only a lowly bench-tech...and musician) when servicing a NEAVE mixer board, I noticed the 47uF/63v (Electrolytic) coupling caps were bypassed by .1uF film caps (100k impedance level).

Electrically (and scholastically) there is no benefit to this parallel combination as it's only the sum of the two values, but to the musicians ear there IS a real difference, and it seems the film caps bring a brightnes and phase-correctness to the coupling.
(noticable enough NEAVE got the big bucks)

Sometimes the "ear of the beholder" hears more than the pencil of the mathmatician.
(...and sometimes not)

How that applies to this thread, well I do not know, but it reminded me of this anyway.

(ok, Ill be over here if anybody needs me)

[Joe Kramer]

Dunno why, but I'm reminded of something I learned years ago (I'm not an EE but only a lowly bench-tech...and musician) when servicing a NEAVE mixer board, I noticed the 47uF/63v (Electrolytic) coupling caps were bypassed by .1uF film caps (100k impedance level).

Electrically (and scholastically) there is no benefit to this parallel combination as it's only the sum of the two values, but to the musicians ear there IS a real difference, and it seems the film caps bring a brightnes and phase-correctness to the coupling.
(noticable enough NEAVE got the big bucks)

Sometimes the "ear of the beholder" hears more than the pencil of the mathmatician.
(...and sometimes not)

Hold on a sec, let me get out my punctuation (fumbling in back pocket.). . . .   Okay.  Bypassing an electrolytic with a film cap is electrically, scholastically AND musically valid.  In laymans terms (the only terms I can confidently claim for myself), electrolytics suffer from ESR which rises as frequency increases.  In other words, higher frequencies see steadily higher and higher impedance.  Film caps do not suffer much, if at all, from this.  Bypassing the electrolytic is sort of like providing a short-cut or safety valve for the higher frequencies.  Make sense? 

[davebungo]

Yes, it makes sense.  This is also why you will see 100nF caps in parallel with electrolytics in many power supply designs.  The Neve example was probably a case of trying to achieve some "air" as they say in the sound (not wanting to start a debate here).

[R.G.]

1.) can you make (sub) one?

I agree, that is one of the questions.
And the answer is, clearly, yes.

2.) does it sound different? (does it influence the frequency responce of the circuit.)

While I don't think that was one of the original poster's questions, but it did come up peripherially.

As to whether a real NP and a fake NP sound different, the answer is no, they don't, because the same micro-operation is happening in each one as voltages and currents change.
As to whether the NP cap has any effect on the frequency response of the circuit in question, the answer is no, it doesn't, for reasons having nothing to do with whether it is an NP, electrolytic, or anything else. As mojotron accurately stated, the NP cap is a low impedance path around a 100K resistor. The time constant of the 1uF NP and the 100K is such that the 100K may be neglected as insignificant to the frequency response starting at the rolloff of the 1uF and 100K, which is very much sub-audio at 1.59Hz if I did the math right.

There is another cap in series with the 1uF NP for AC purposes. That's that 0.047uF just upstream. That cap is only 1/20th of the value of the 1uF, is effectively in series with it to AC signals. The 0.047uF cap is the one which determines the audio response of this circuit, along with that 22K resistor. Their rolloff point is up at 154Hz, well into audio.

Electrically (and scholastically) there is no benefit to this parallel combination as it's only the sum of the two values,

From Alexander Pope (1688-1744) - An Essay on Criticism, 1709:

"A little learning is a dangerous thing; drink deep, or taste not the Pierian spring: there shallow draughts intoxicate the brain, and drinking largely sobers us again."

Electrically and scholastically, there is no benefit to the parallel combination - if all you know is basic circuits and assume that the capacitance value printed on the capacitor tells the whole story. However, if you also remember that there is a string of second and third order effects, imperfections in every part, that you have to take into account, then electrically and scholastically, the parallel combination makes sense.

The construction of an electro cap involves winding the aluminum foils into a radial package. The contact to the insulated foil is not through a metal contact, but throught the electrolyte. Removing water from the electrolyte was very important to achieving long life, so they removed all they could and still kept whatever conductance possible. The winding leads to self inductance. This is neglegible for small caps, but builds up in bigger caps.

A perfect cap would have an impedance that declined with increasing freqeuncy forever. A real cap has these unavoidable inductive and resistive components. The resistive part puts a floor on the impedance  of a real cap. The cap's impedance will NEVER be less than the Equivalent Series Resistance. Worse yet, that Equivalent Series Inductance has a rising impedance versus frequency. At some point, however small the ESL is, its impedance will get not only bigger than the caps, but bigger than the ESR, and the cap will act like an inductor for all higher frequencies. The real impedance versus frequency plot of a cap is a bathtub shaped thing. The low freqeuncy response is dominated by the capacitance, sloping downwards with increasing frequency. This hits a bottom when the cap impedance equals the ESR, and starts rising again when the ESL takes over.

To lower the high frequency impedance of the cap, using a bigger cap doesn't help. But paralleling another cap does. Smaller caps have lower ESL (usually!) and putting more ESR in parallel lowers the total resistance. Simply splitting a 100uF cap into ten 10uF caps produces a superior cap (if you watch the ESR and ESL on the replacements) because the ten have their ESRs and ESLs in parallel and that's usually lower.

But if you didn't have all the space in the world, and wanted to reduce the impedance of a large cap at high audio and RF, you might only put in a smaller cap that was film or ceramic. This will have the same ESR and ESL problems, but they will happen at a higher frequency, maybe high enough to do you some good.

Apparently Neve though so.

[RedHouse]

I guess I should have said, in the past, higher learning types have dismissed the effect in conversations I've had regarding audio gear.

I just can't count how many times I've discussed this sort of thing over the years.

[R.G.]

It's a sad fact that EE "higher learning" has had to yield to the pressures of the digital age. To get an EE degree, the logic and chip specalities that you must have to earn a living have crowded out a lot of the component level stuff that used to be taught to undergrads. If a higher learning type is never taught second order effects, never taught to critically read a datasheet, never put into a situation where imperfections dominate the response, then they never learn either.

"Higher learning" has become ever more specialized. The more specialized your knowledge, the less time you have had for broad knowledge, and the more disposed you are to being ignorant in areas outside of your specialty.

This also leads to the re-mystifying of science - people can't or don't understand the basics, so they start accepting things on faith that they don't understand. From there, it's a short step to Tice clocks and pyramids sharpening razor blades.

A good rule of thumb is if you can repeatably measure the effect it's real, even if you don't understand the reason for it. Things that are not measurable may be real or they may not.

All components include imperfections of series and parallel resistance, series inductance, shunt capacitance, nonlinear conduction, and many others. Whether the imperfections can be ignored or not depends on the numbers: how big is the base effect compared to the parasitic imperfections at what frequencies? If you know the numbers and have an accurate model, you can make predictions that are close, if not right on. That's what design is about - proposing combinations which you predict will produce the desired result.

If you don't know the numbers, you can't make accurate predictions of how components will act.  And you may easter-egg, but you can't design.

[aron]

NP is in the FAQ too