How come the "Super Hard-On" crackles?

[zachary vex]

do conductive plastic pots wear out faster than carbon pots, in a DC situation?

[puretube]

way way less fast mechanical wear
(as long as you don`t have too much current running through them at those last degrees of rotation, and burning them in that area).

It`s all in the datasheets;
You can get c.p. pots with guaranteed 1 mio cycles
with less than 5% deviation from their initial parameters.

[R.G.]

Dead right Ton - as long as you don't let the current through the wiper get high. That softens and degrades the element fast. But with low signals, they're great. You have to get the sealed ones, though, or dirt and dust will do its thing on them just like on carbon elements

I don't know how people get through life without datasheets.

[Hiwatt25]

What a livley little discussion has been started.  I'm surprised Mr Vex hasn't chimed in.

[markm]

He's obviously "okay" with crackle 

[bwanasonic]

Would the noisy pot rotation in the Tripple Fuzz be cured with a conductive plastic pot?

Kerry M

[zachary vex]

i am okay with the crackle, and i did chime in up there.

if conductive plastic pots were available in the packaging i use for the rest of my pots, i might consider using them.  as it is, i see very few failures in the pots i use because i use custom tapers for all dc-carrying pots. 

as far as reading data sheets, i subscribe more to the Edison empirical approach (with some modifications, of course):

"At the time I experimented on the incandescent lamp I did not understand Ohm's law."

On another occasion he said, "I do not depend on figures at all. I try an experiment and reason out the result, somehow, by methods which I could not explain."

if i did things "by the book" i'd never get anything done, nor would anything i make fit in such small spaces.  i find shortcuts by using my imagination and not being limited by pre-established design...

here's an example.  i needed a switching power supply to provide my nano head with 230VDC from the 12VDC input (i decided to use DC so it could run off a gel cell for busking in the subway, or deep-woods woodshedding using your car lighter).  i looked around for switching circuits and everything was far too big... nothing would fit in the "two postage stamp" area i had reserved for the power supply, so i decided to build one from scratch using the negistor as the oscillator (never used in a commercial product before, just a laboratory curiosity).  i had a lot of experience with negistors and recognized the pulse-width v frequency possibilities.  the oscillator was three components... a negistor (2N2222A), one resistor (adjustable to set the operating frequency), and one ceramic oscillator cap.  to this, add a blocking cap and diode to direct the pulses, and we have 5 components.

negistors can provide a "pure" sawtooth when left nearly unloaded, but with loading, they change their waveshape significantly, almost to a pulse.  i needed to square up and strengthen this pulse, so i loaded the negistor with a high-gain transistor in clipping mode... excess loading and maximum gain are easy if you leave out unneeded resistors.  8^)  one transistor and one resistor.  now we're up to 7 components.

by changing the bias on the buffer transistor following the negistor using feedback directly from the output at the HV capacitor, i could change the pulse width and regulate the voltage...  so as the output voltage climbed, the pulses were pinched off to limit the time spent charging the coil.  so i created a little feedback/protection circuit using 4 high-voltage zeners and a resistor to feed d.c. bias back into the buffer/loading transistor following the negistor.  4 zeners, one resistor, and one trimmer to control how much bias was making it back for regulation, to set the output voltage.  6 components here for a total of 13.

another thing i had to prepare for was when the battery input voltage began to fall, say from a peak of 15 VDC to a low point of 9VDC (as you will often see in gel cells).  over this range the negistor oscillator's frequency would naturally drop (because it's a VCO) which would increase the "on" time spent charging the coil, boosting the output voltage.  because this happened automatically, zero extra components.

of course, there were two complimentary transistors needed to provide high-current/high speed drive to a power mosfet feeding a coil, resulting in 4 more components, and then a high-speed rectifier to take the power pulses off the coil and store them in the power caps, for a total of 5 components. now we're up to 18.

between these two types of regulation, the feedback network and the negistor VCO, i could control the output voltage within 5% with a 50% change in input voltage over a range of 0mA to 17mA output draw on the high voltage side.  i did all of this with 18 components, all discrete, in the space of 2 postage stamps, using zero data sheets.

i could have used chips and done a more practical mathematical modern approach to the thing, by reading datasheets and trusting modern methods, but i would have been forced to create a daughter board and even then it might not have fit and would have upped my costs per unit significantly.  i figure there's always a solution to doing things more simply and smaller out there, more often than not, in forgotten/obsolete/"lab curiosity" and maverick approaches.  often, data sheets slow me down and distract me from simpler possibilities.  8^)

[gez]

if conductive plastic pots were available in the packaging i use for the rest of my pots, i might consider using them. 

Omeg do custom orders, or so it says on their website. 

I've been using their plastic pots for a few years and love them, they have a very pro feel to them when you turn them (think knob on a hi-fi system).  No failures to date.  The other thing I like about them is the shafts are plastic and can take a fair bit of vibration/bending without damaging them, plus grub screws have something to dig into.

PS  Data sheets have saved me a lot of money over the years! 

[puretube]

http://www.vishay.com/resistors-variable/motion-transducers/rotational-sensors/


they may be higher priced than the carbons, but sometimes it`s worth it.

(I had some custom triple-ganged-pots made ~12 years ago by sfernice with 2 identical logarithmic high synchronicity elements, and a 3rd anti-log element of a different value;
12mm, sealed, 1/4"" metal shaft,
for 30$ each for 12+ pcs).

of course, mono pots of stock value and taper are a lot cheaper...

[Paul Marossy]

i did all of this with 18 components, all discrete, in the space of 2 postage stamps, using zero data sheets.

And that is why Z. Vex ain't your average Joe! 
Very interesting, thanks for sharing that design process Z.V. 

[Meanderthal]

 You know, this plastic pot thing has me looking at zvex effects with a whole new eye! If that's all it takes to fix That One Big Problem...

And I can totally respect the mad scientist approach! Any really profound advancements always seem to come from thinking outside the box. While the established Powers That Be proclaim things impossible, bicycle mechanics just go right ahead and build flying machines in spite of all the snickering... and they DO fly, don't they?

[stm]

Datasheet v/s datasheetless design... that's the question.

Both have strenghts and weaknesses, as already mentioned.  Of course it is always good to be able to do some "lateral thinking" in order to find a novel/simpler/cheaper/better solution to a problem, thus this may favor a datasheetless approach in a sense.  On the other hand, it is equally important doing at least a simple datasheet verification AFTER the design is ready, as you don't want a design that may be using or abusing a component beyond its design limits, as this poses a risk for failure in the short term with its associated costs.

Thus, I'm in favor of using both of them, as it appears to me if properly used some sinergy might come out of the process, like for example, identifying a component could that could be safely pushed further, thus increasing the efficiency or output power from a given design.

I always try to apply the philosophy that most things are not black or white, but rather many different shades of gray...

[Meanderthal]

 Yeah, reading my last post it seems to imply that I was advocating avoiding datasheets entirely.... ummm... I wouldnt do THAT. Next thing you know I'll unintentionally inspire someone to try and build a Bajak Flux Capacitor or something insane like that....
Yeah, outta the box is one thing, but datasheets are very much a good thing...
Can't just go around trying to circumvent the laws of thermodynamics or ohm's law and such...
Sorry 'bout that...

[zachary vex]

hey, i'm not saying "don't use datasheets."  i'm saying that some problems are best solved by wit, folly, chance, and intuition, combined with a few things you're absolutely sure about.  8^)  datasheets are absolutely necessary for things like finding out how many rotations you can safely expect from a conductive pot, or which pins on a Winbond voicecorder are used for what, and how much voltage they can safely take.  datasheets are absolutely necessary for knowledge about more complex electronic devices.

but sometimes the answer is to go simpler and design something using knowledge you already have and taking some stabs in the dark.  here's another man's version of my view:

..."reality, or the world we all know, is only a description.
      For the sake of validating this premise I will concentrate the best of my efforts into leading you into a genuine conviction that what you hold in mind as the world at hand is merely a description of the world; a description that has been pounded into you from the moment you were born.
      Everyone who comes into contact with a child is a teacher who incessantly describes the world to him, until the moment when the child is capable of perceiving the world as it is described. We have no memory of that portentous moment, simply because none of us could possibly have had any point of reference to compare it to anything else. From that moment on, however, the child is a member . He knows the description of the world; and his membership becomes full-fledged, perhaps, when he is capable of making all the proper perceptual interpretations which, by conforming to that description, validate it.
      The reality of our day-to-day life, then, consists of an endless flow of perceptual interpretations which we, the individuals who share a specific membership, have learned to make in common.
      The idea that the perceptual interpretations that make up the world have a flow is congruous with the fact that they run uninterruptedly and are rarely, if ever, open to question. "

the point being... question everything, and try your own methods, and you may drag some new truth in out of the dark.  8^D

[R.G.]

Here's another man's version of my views:

Everything should be made as simple as possible, but not one bit simpler.

Albert Einstein

[markm]

Here's a good one;
"never drink downstream from the herd"
----Will Rogers.

[The Tone God]

but sometimes the answer is to go simpler and design something using knowledge you already have and taking some stabs in the dark.

I have mixed feelings about this statement. I understand that one might get bogged down with read through information even to the end of not solving the problem. An example would be the Vanishing Points. I couldn't find anything equivalent or much theory on how to do it so I just designed on what I already knew and it turned fairly good IMHO.

Sometimes though a key piece of information might be buried somewhere unexpected that could change everything. An example of this is I have dabbled a bit with switching supplies and while I did not like some of the texts on the topic nor the part solutions sold by various manufactures the datasheets for some products provided information that was very often was much better then the texts even though I did not use any of those products. So now because I have read those datasheets, and some texts, I can look at your description and design a supply that uses 12-13 parts, eliminates the trimpots, takes less space, has no need for the fan, has no need for the fuse, has several safety features, more efficient, use a smaller size inductor, and a few other things.

I guess the point I am making is that while doing some research it may seem like you are wasting time you may sometimes find something toward a better solution that you would have not known if you designed purely off what you knew before hand.

Andrew

[zachary vex]

yeah, but try doing it without a space-hogging chip.  8^P

the fan and fuse are for the tubes as well... good luck keeping the tubes cool without a fan while running them at 50% over maximum rated plate voltage.  removing a fuse from the "mains" on any high-powered circuit is always a terrible idea.  what if there's a direct short of the +12VDC supply to ground inside the nano head?  can you imagine the current levels a gel-cell can achieve under direct short conditions?  i wouldn't trust your fuse-free design any further than i could throw it.

[The Tone God]

yeah, but try doing it without a space-hogging chip.  8^P

...takes less space...

Besides by eliminating some of those now un-need parts I could stick in a DIP IC with little trouble.

Andrew

[zachary vex]

talk is cheap, kid.  8^)