kruz
Well-known member
oh well.. i know i'm dumb but..
what's the difference between these two kind of resistors?
:roll:
what's the difference between these two kind of resistors?
:roll:
"carbon composition" and "carbon film"
- Thread starter kruz
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Guest
Guest
Thanks Gus! I was just wondering about this exact thing. Now all I need is to build a tube mic. :twisted:
kruz
Well-known member
Thank you guys, that article is very interesting..
but still.. let's say that i want some of that "mojo" in a box i'm building..
i can't find any CC resistor, just Carbon Film.. so i'm wondering if those CF (?) will have the same sweetening effect that's measurable on the CC ones.
Well.. when back home i'll read some datasheets to check for "voltage coefficient of resistance" values.
but still.. let's say that i want some of that "mojo" in a box i'm building..
i can't find any CC resistor, just Carbon Film.. so i'm wondering if those CF (?) will have the same sweetening effect that's measurable on the CC ones.
Well.. when back home i'll read some datasheets to check for "voltage coefficient of resistance" values.
> i can't find any CC resistor, just Carbon Film..
Try antique radio dealers, and guitar-amp part suppliers.
http://www.angela.com/catalog/resistors/Resistors.html
> i'm wondering if those CF (?) will have the same sweetening effect that's measurable on the CC ones.
Measurable?
Anyway: carbon composition is lamp-soot, coal-dust, pencil-dust mixed with clay and pressed into a lump, wires shoved in the end, and more clay over that. Or at least it used to be like that. Even if they use highly-refined carbon now, it is still a funky mechanical-contact thing: grains of carbon touching but not really bonded.
Metal Film is high-resistance metals vaporized and condensed on a ceramic rod. The metals are fully bonded, no mechanical contact between grains (no grains).
I'm not sure how they make carbon film. I think the carbon is graphite and far better bonded than in composition resistors, but you don't have the full molecular contact of metal-film or the forging of wire-wound. Ah, here's some poop:
From http://www.mcekdi-resistor.com/pdfiles/APPNOTE5.pdf
"Carbon film resistors. Carbon film was one of the earliest materials employed for microwave resistors. This film is used primarily for coaxial element devices, because it is difficult to process into flat stripline and microstrip. The carbon film is in the graphitic crystalline structure. Although not a metal, the nature of electronic conductivity in graphite does approach that of metallic conduction.
"The film is prepared by high-temperature pyrolysis. Heating methane or propane gas in the absence of oxygen causes a complicated series of reactions that eventually result in graphite. The overall reaction is CH4 → C + H2. The film is quite pure when compared to evaporated films, is robust and reacts well to high-power pulsing. In situ, masking is not feasible because of the high temperatures involved in the process.
"Since there are no practical etchants for carbon, machining techniques are the only way to pattern carbon resistors. Some of the various limitations of carbon resistors are:
"The high-reaction temperatures necessitate high-temperature materials such as stable ceramic.
"The graphite does not chemically wet or react with a ceramic surface but must be mechanically ?locked? to it. To do this, the substrate must be roughened. A typical ceramic substrate will have a fired finish of 30/40 microinch RMS, and then be etched to several times that value. Since heavy, low-resistance carbon film is only four microinches thick on this rough substrate, this film is no longer a ?two-dimensional? device. Carbon resistors do not generally perform well at very high frequencies."
Some of those comments do not apply to audio.
Try antique radio dealers, and guitar-amp part suppliers.
http://www.angela.com/catalog/resistors/Resistors.html
> i'm wondering if those CF (?) will have the same sweetening effect that's measurable on the CC ones.
Measurable?
Anyway: carbon composition is lamp-soot, coal-dust, pencil-dust mixed with clay and pressed into a lump, wires shoved in the end, and more clay over that. Or at least it used to be like that. Even if they use highly-refined carbon now, it is still a funky mechanical-contact thing: grains of carbon touching but not really bonded.
Metal Film is high-resistance metals vaporized and condensed on a ceramic rod. The metals are fully bonded, no mechanical contact between grains (no grains).
I'm not sure how they make carbon film. I think the carbon is graphite and far better bonded than in composition resistors, but you don't have the full molecular contact of metal-film or the forging of wire-wound. Ah, here's some poop:
From http://www.mcekdi-resistor.com/pdfiles/APPNOTE5.pdf
"Carbon film resistors. Carbon film was one of the earliest materials employed for microwave resistors. This film is used primarily for coaxial element devices, because it is difficult to process into flat stripline and microstrip. The carbon film is in the graphitic crystalline structure. Although not a metal, the nature of electronic conductivity in graphite does approach that of metallic conduction.
"The film is prepared by high-temperature pyrolysis. Heating methane or propane gas in the absence of oxygen causes a complicated series of reactions that eventually result in graphite. The overall reaction is CH4 → C + H2. The film is quite pure when compared to evaporated films, is robust and reacts well to high-power pulsing. In situ, masking is not feasible because of the high temperatures involved in the process.
"Since there are no practical etchants for carbon, machining techniques are the only way to pattern carbon resistors. Some of the various limitations of carbon resistors are:
"The high-reaction temperatures necessitate high-temperature materials such as stable ceramic.
"The graphite does not chemically wet or react with a ceramic surface but must be mechanically ?locked? to it. To do this, the substrate must be roughened. A typical ceramic substrate will have a fired finish of 30/40 microinch RMS, and then be etched to several times that value. Since heavy, low-resistance carbon film is only four microinches thick on this rough substrate, this film is no longer a ?two-dimensional? device. Carbon resistors do not generally perform well at very high frequencies."
Some of those comments do not apply to audio.
kruz
Well-known member
Thank you PRR for this in depth information..
> Measurable?
well.. reading this: http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm
it seems that the "voltage coefficient of resistance" is measurable..
i could easily be wrong
> Measurable?
well.. reading this: http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm
it seems that the "voltage coefficient of resistance" is measurable..
i could easily be wrong
nacho459
Well-known member
I am kind of a Carbom Comp junkie, I build guitar amps and the CC resistors are part of the tone. Besides all the great old gear we build (1176, LA2A, Pultecs) were built with CC resistors.
A local electronics store closed a few weeks ago and had tons of CC resistors in the back and they would sell them for about 5¢ each. I knew once they closed I would be screwed and would have to pay $.75-$1 each resistor from MOJO or some other parts place. So I bought about two-thousand resistors, enough to fill a grocery bag, and they charged me $15 +tax.
A local electronics store closed a few weeks ago and had tons of CC resistors in the back and they would sell them for about 5¢ each. I knew once they closed I would be screwed and would have to pay $.75-$1 each resistor from MOJO or some other parts place. So I bought about two-thousand resistors, enough to fill a grocery bag, and they charged me $15 +tax.
I have to admit that my (cloth?) ears can't detect a difference in sound in the circuits I've built, apart from the bacon-frying, that is.
The carbon-film vs carbon-comp debate has been done to death in the guitar amp based forums, with some people claiming almost magical tonal properties for the comps.
-Steve
The carbon-film vs carbon-comp debate has been done to death in the guitar amp based forums, with some people claiming almost magical tonal properties for the comps.
-Steve
SSLtech
Well-known member
It's subtle, I went with carbon comp (Clay and soot) for thepower ones, but the low-signal-level resistors at the front end were metal film... low noise, no "mojo" to be gained at such small signal levels anyhow... The thing sounds great and reads super-low residual noise and THD at nominal level... I vote for that combo!
Keith
Keith
