Better resistors from a pencil

Many of us here in the office (myself included) can’t tell the difference, but the audiophiles out there who want the best sound from their resistors should check out [Troel's] write-up for making your own non-inductive graphite resistors. Graphite resistors have the traits for being non-inductive, have a negative temperature coefficient, and supposedly sound better. We liked the detail of his tutorial and how he gives many examples for making your own graphite resistor.

[Thanks Maxime]

Comments

  1. Almost_There says:

    Graphite is one of the few materials that have a negative temperature coefficient (resistance goes DOWN as it gets hotter)… what I used to LOVE to do back in High School is sharpen both ends of a pencil, wrap a stripped extension cord around both ends, and plug it in to 120 VAC.

    It goes in to Thermal Runaway; the hotter it gets the lower the resistance, the lower the resistance the more current it draws, the more current it draws…

    Great fun! Try it! (Just don’t try it at school ’cause you might get expelled – don’t ask.)

  2. Grazz256 says:

    Seems to me that buying graphite refills would be much easier then buying pencils and removing the wood. Drafting pencil refills are about the same diameter as regular pencil graphite possibly not as long tho.

  3. Tachikoma says:

    Ah man, those wires and contacts better be gold plated!!!

  4. cmcdugan says:

    I don’t know about solid carbon rods, but I do know that standard carbon composition resistors (which I would imagine would be very similar in construction) are measurably noisier than thin- or metal-film resistors. Vishay’s bulk metal foil devices are non inductive as well.

    I can appreciate the sense of satisfaction to be had by building your own components, but don’t pretend they are better than what can be had commercially.

  5. Inventorjack says:

    @Almost_There: I know what you mean about getting in trouble with school.

    As a kid I was curious, if naive, about electricity and electronics. My first solo electronics experiment was to take a chain of paperclips, plug them into a socket adapter, and plug this into the electrical outlet… of my third grade classroom. Thankfully I was clever enough not to plug the paperclips directly into the socket so I didn’t get shocked. Unfortunately, the blinding flash of light at the back of the classroom, and flickering lights in adjacent rooms sort of gave me away.

  6. Uri Geller says:

    For the best natural undisturbed sound quality you need to use japanese char coal. You can buy them for $10 or so for a small stick to put into water to purify it and rectify the water crystals. A little expensive but the sound is worth every penny!

  7. xrazorwirex says:

    LOL!

  8. Monica says:

    I think this is BS. Electronics superstition. Save your creative energies for something really helpful, not kludging together absurd resistors.

  9. sean says:

    @cmcdugan

    Funny how us old enough to have worked with tubes know this and appreciate the new technology. Tube repairs usually had the following order: replace rotten tubes, replace rotten capacitors, replace rotten composition resistors. It’s a joy to put together a modern tube amp and the only thing you’ll ever have to replace are the tubes, and eventually, the electrolytic power supply caps.

  10. medix says:

    @Monica: I think not. The structure of graphite has all sorts of amazing properties, which is why nanotechnology is so infatuated with graphite (ie. graphene sheets, nanotubes, etc). Isn’t ‘kludging’ what *real* design is (and always has been) all about?

    The issue of ‘sound quality’ is most surely debatable, however unless you yourself have spent long hours listening to the minute differences in sound coming from a ‘good’ stereo system (before and after ‘burn in’ etc.. ), you have no basis on which to judge.

    Give it a shot. You’d be amazed at what little difference it can make..

  11. medix says:

    Good post btw.. ;)

  12. anon says:

    Oh whoopee, audiophile snake oil.

  13. Ivan says:

    @Uri Geller
    This is what I’ve ben using in my cars plasma-hyperdrive system. It’s really great! I don’t rectify the crystals though, I uni-polarize them with voodoo.

  14. xmd says:

    @Uri Geller & @Ivan – I concur, but I am still working on a way to remove that oxygen… I am thinking of running the whole system in a vacuum. I should get the most detailed silence ever!
    @medix – ever heard of the emperors new clothes?

  15. asdf says:

    I smell bullshit. While using graphite pencils as emergency resistors is a valuable hack known for almost a century, the first feature resistors used in professional audio must have is low noise. Carbon and chemical resistors were replaced by metal film ones for that reason, and graphite is a type of carbon.
    Anyway, a good rule of thumb is to always assume bullshit wherever the word “audiophile” is detected.

  16. xmd says:

    The original artical written by Troel is actually a very good write up. He doesn’t make any absurd claims about the sonic performance of the resistors he is making, but details the work nicely including some sensible suggestions and analysis on quality. Excellent work.

  17. John Bokma says:

    @asdf: diamond is also a type of carbon…

  18. medix says:

    Eh.. whatever.

    Perhaps that was not worded properly.. I could care less if this makes a difference in performance (along the same lines as oxygen-free copper and all the other BS)

    Could be interesting to try though, especially if a real noise analysis was done for comparison (ie. thermal and shot noise)..

    For example: http://www.aikenamps.com/ResistorNoise.htm

  19. xmd says:

    That aikenamps article on resistor noise is interesting. I have never heard of shot noise being an issue in resistors… His statement about shot noise being a greater problem with larger currents seems to be pretty much the opposite of the scenarios I have come across. I thought shot noise was a problem when you are dealing with currents small enough that you notice current fluctuations from the random movements of individual electrons. This is much more pronounced in PN junctions – resistors though..?..interesting

  20. octel says:

    @medix
    stereo system “burn-in”? what?

  21. Tachikoma says:

    In defence of the website featuring the carbon resistor, the author does make it clear that benefits using graphite resistors is questionable at best.

    That said, I do find its negative temperature coefficient properties quite interesting.

  22. medix says:

    @xmd: I first learned about it in a class called “Off the shelf design with integrated electronic components” taught by a 60’s era (deaf) prof who spent his career working in / designing components for the power industry. I was familiar with PN junction noise, and have seen many white noise generators based on this phenomenon, but resistor shot noise was a new one.

    @octel: cp.literature.agilent.com/litweb/pdf/5989-5560EN.pdf

    “Accelerated life tests that subject
    units to higher-than-usual levels of
    stress such as voltage, temperature,
    humidity, pressure, and loading are
    used to speed up the deterioration of
    materials or electronics components.”

    i.e. It ain’t perfect off the shelf. The above link is for electronic component failure testing, but the same can be said for changes in device properties from extended use / over stress.

  23. Matt says:

    It’s a lot of fun to play with .7mm mechanical pencil lead connected to the 5V rail of a PC power supply. Connect alligator clip leads, with a penny connected to the ground lead and about a 1cm length of graphite in the other. Touch them together, and the graphite should glow white hot and start to melt the penny.

  24. Frogz says:

    these will never beat my amplifier built on a lm555 and a resistor based on the contact between an old flashlight’s on “switch” with reverse inductance capacitors
    it even has monster cables!(i made sure to cut them in half and solder directly to the braid so as to keep high quality connections)

    hm, i found a old ass record player, wonder if the tubes are any good… it was sitting in a leaky basement under a metal chest that was rusting away
    think i should try to restore it or just make it into a amp?

  25. Richard says:

    Listening to your hair grow is all very well for those of you who still have any… ;-)

  26. Roly says:

    @Almost_There

    Glass can also be made to go into thermal runaway by heating the inch or so between mains connections (limited by a lamp) to dull red heat with a bunsen burner. Apply heat until the lamp starts to light, then it should go into thermal runaway, melt the glass, and break the circuit.

    Small carbon rods can be used to create arcs (and UV not good for eyes or skin), and current-oriented as a spot welder for very light jobs.

    Worth repeating;
    @cmcdugan
    “I can appreciate the sense of satisfaction to be had by building your own components, but don’t pretend they are better than what can be had commercially.”

    @sean.

    Amen.

    Where is this *non-linearity* that changes the sound? Show me.

    Over 50 years in electronics, a lot of it working on all manner of audio gear, I have yet to encounter distortion originating in a resistor. Noise certainly, but never distortion.

    @medix

    My problem with subjective evaluations is that as a soundie I know too well how unreliable ears and memory can be. In some repects such as pitch the sensitivity can be exquisit, but in others such as loudness it is worse than useless. If the same programme sounds different, was it distorted before, or is it distorted now?

  27. medix says:

    @Roly: That’s exactly why I try not to sound like a lunatic when I talk about it. I’ve noticed that these things change from day to day even. I’ve noticed it in my car as well as my Grado SR80 headphones. It’s a funny thing really. I remember seeing a study somewhere on the THD of oxygenated ‘studio quality’ speaker cables and plain old lamp cord (the DIYer’s staple speaker cable for years) and the results were negligible, much less anything you’d be able to pick up without expensive test equipment.

  28. ben says:

    I am not interested in making this to test it, but what are the inductive characteristics of the coil of copper wire wrapped around each end of this resistor?

    I understand that it will be a very poor inductor because the wire is not coated and there is a lot of conductivity between the coils where they touch the graphite and each other. Still, the resistors you would be comparing these to would be very low inductance. Is this negligible inductance more or less than the negligible inductance of a normal resistor? My gut says more, but not enough to matter.

    All that said, I still want to make some of these, but not because I am an audiophile.

  29. Jeeves Stobbs says:

    But is it danceable?

  30. Axaj says:

    Come on, you people are such complainers. It’s a resistor. Made out a pencil. Does that not scream “hack”?

  31. Almost_There says:

    >But is it danceable?

    What the “hack” do you mean?

  32. ldopa says:

    @Roly

    Carbon comp resistor *are* noted for distorting signals:

    http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm

    According to this, amongst other sources, there is “measureable second harmonic distortion.”

    Furthermore, real resistors are nonlinear devices. It can be shown that inductive and capacitive effects of real world resistors are detectable in audio bandwidth signals.

  33. Sharky says:

    It’s so strange, we all had a supervaluable material in our hands for centuries. And know ,some, people know what it is capable of.

    It’s like the caveman using a gun to scratch his groin instead of hunting.

  34. Th3_uN1Qu3 says:

    This has been around for ages. One cool application of pencil lead is wiring it to your car battery. Offers good light for about 15 minutes – enough to carry an emergency repair.

  35. kristian says:

    @Th3_uN1Qu3: you’d better have another battery too tho lol

    i was going to mention this earlier (i.e., when it posted) that you wouldn’t need a “low-ohm meter” like the writeup said, just a constant current source and a volt meter. then again, perhaps everyone here knew that already…

  36. Seth says:

    New money-making idea: Paint a stick with black paint and sel it to audiophiles as a new, high resistance component which improves the audio when connected between speaker leads.

    What’s the difference between an audiophile and god?
    God doesn’t think he’s an audiophile.

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