# Resistors, Carbon and Noise. What is the deal?



## keeperofthegood (Apr 30, 2008)

Hey oh

OK

I have read a few break downs on this topic. Carbon = noisy seems to be a pretty solid feeling across the board.

What I am wondering is

1) What?
1) why?
2) where?
3) how much?

1) Just what do people mean by "noise" in regards to carbon resistors?

2) Why is it that people WANT the noise of carbon resistors?

3) Where is the most effective use of carbon resistors for the noise?

4) will a 1 ohm 1 watt carbon resistor be every bit as noisy as a 1 meg-ohm 1/4 watt? or is there a relation between value/wattage for noise?

If I were to put a 1 ohm carbon in series with a 220K metal oxide resistor, would that give me the same noise benefit as using a 220K carbon resistor?

Noisy or not, if I did a 1 ohm carbon in series with anything else .... is it still good for measuring voltage drops across for a current reading or does the noise value make that inaccurate?


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## Emohawk (Feb 3, 2006)

People like CC resistors because they claim there's more "mojo" there. I can't comment on if that's real or not. I'll leave that to others to assess. I've heard clips of a 2204 build that used all metal oxide (mil spec in fact) and it sounded killer (and quiet).

CC resistors tend to be noisier with higher values & "hot" signals. It's not a bad idea to use metal oxide with values of 100k+ if noise is an issue. You might want to try CC's in the lower values in the pre-amp to see if you can hear a difference.


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## Wild Bill (May 3, 2006)

keeperofthegood said:


> Hey oh
> 
> OK
> 
> ...


In the beginning they invented the carbon composition resistor. Basically, you press grains of carbon together within a ceramic shell. The amount and density of the grains determines the resistance.

This never did work that great! First off, if they had to pass any real current they would heat up. This would often burn the grains, changing the resistance value. Also, a voltage surge could cause an arc inside the resistor, making the connection between the grains rather "sooty". This could cause a hissing noise like frying eggs in audio circuits, as the current arced through all the carbon grains.

Worst of all, when they burned out they often burst into flame!

In the early 60's new manufacturing techiques appeared. Carbon film resistors were much quieter and much more stable. A bit of heat wouldn't change their resistance value. They also tended to char instead of bursting into flame if they burned out. They were actually advertised as "New Improved FlameProof Resistors!"

Metal films are the quietest but even carbon films are more than quiet enough for guitar amps.

Why do some folks prefer carbon comps? First off, rarely are any of these people techs. They simply believe that if you use the same parts as Muddy Waters had in his amp then you will somehow sound like him. Easier than practicing, I guess!:smile:

The idea of using them in a guitar amp always makes me smile. Why would you want to make a guitar amp more hifi?

Using them in an audiophile amp makes me laugh! Why would you think that a tire for a 1930's Ford would give you better mileage than a modern one? Carbon comps are an old, antique techology! We IMPROVE as the years go along, not the other way around!

Can you hear a difference? There is a guy named R G Keen who has a FAQ about this at his website http://www.geofex.com

RG is FAR smarter than I am! Much better educated and I suspect he actually invented the volt! Anyhow, he performed many tests in his lab with REAL test equipment and came to the conclusion that yes, there is a difference but it is extremely small! 

You can get a bit of vintage compression on the signal, but ONLY when the carbon comp resistor is in a position in the circuit where it is both in the signal path AND is passing a reasonable amount of current. That eliminates almost ALL the resistors in your amp! The only ones that he could find a difference were the two plate resistors in the long tailed phase inverter used in most amps.

Even then you had to be cranking the amp and have extremely good ears. Not the sort of thing that everybody in a bar would notice and be impressed about when you played.

Most times when there is excessive hiss in an old amp it is coming from antique carbon comp resistors. Replacing them with carbon or metal film will quiet them down by an incredible level! You will always have at least a faint hiss. That's from electrons boiling off the cathode of the tubes. Still, you should have to put your ear right up to the speaker to hear it.

There is no relationship between resistance value and noise. High current in ANY carbon comp resistor can cause noise! If you used them for bias test points as 1 ohm cathode resistors for your output tubes there is almost zilch heat built up in a 1 ohm resistor. You'd need a NASA level bias meter to be able to see any noise on the bias reading!

Putting carbon comp and carbon/metal film in series will do nothing! The idea is not to have noise at all. Since the value is not a factor, the only thing that could happen is that the carbon comp could ADD noise! Nothing is going to make noise go away! 

One point that is not often understood is that resistors are totally PASSIVE devices! THEY DON'T AFFECT TONE! Except in a negative way, by adding noise. 

There is one area where carbon comp resistors are a better choice and that's in some positions in radio circuits. Carbon comps have zero self-inductance. Carbon and metal films have a slight bit. Some self-proclaimed audiophile gurus cite this point as proof that carbon comps will thus make a difference in audiophile amps (please send a cheque for $10 per carbon comp resistor!). What they don't mention (or don't know, since they've never actually read the WHOLE book on resistors, or any electronics book, for that matter) is that the self-inductance is so minute that it only becomes important with ultra high frequencies. For a radar set in an F-14 Tomcat it might matter. For an audiophile amp I don't believe it would be even possible to measure it, let alone actually hear it.

Hope this makes things clearer, Keeps!

:food-smiley-004:


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## keeperofthegood (Apr 30, 2008)

kqoct So that hiss is from the resistors eh! Never had that in mind before... that I can remember, though I bet at some point I did.

Ok, 1 ohm metal oxides it is then


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## nonreverb (Sep 19, 2006)

keeperofthegood said:


> kqoct So that hiss is from the resistors eh! Never had that in mind before... that I can remember, though I bet at some point I did.
> 
> Ok, 1 ohm metal oxides it is then


Work on a few old Fender (insert model here) amps from the '60's or '70's...sooner or later you'll hear plenty of carbon comp. hiss:smile:


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## keeperofthegood (Apr 30, 2008)

nonreverb said:


> Work on a few old Fender (insert model here) amps from the '60's or '70's...sooner or later you'll hear plenty of carbon comp. hiss:smile:



:bow: I have heard it on old radios a lot 'off station', and other old equipment. I just never really put that "hiss" together with the resistors it was made of that I know of. Never really followed the "now where is that coming from" chain.


Using 1 ohm resistors for voltage measurements in the milli-volts or even micro-volts, is the resistor tolerance more critical. Should I be looking for 1% or 0.5% or 0.1% tolerances? >.< What I should do is chart the error % in EXCEL really >.<


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## Fader (Mar 10, 2009)

Didn't they use carbon to make microphone elements a long time ago?


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## keeperofthegood (Apr 30, 2008)

Fader said:


> Didn't they use carbon to make microphone elements a long time ago?



I believe they still do. They suffer compaction issues though. Since the demise of the rotary phone, I am not sure what or who would still use them ... hmm ... wiki time!



http://en.wikipedia.org/wiki/Carbon_microphone

http://www.shure.com/stellent/group..._UG/documents/web_resource/us_pro_104c_ug.pdf

AH! There ya has it 

But other than Convoy, I am not sure who else would use it or when to record with @[email protected]

[YOUTUBE]<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/JuyLTDAC7fE&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/JuyLTDAC7fE&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>[/YOUTUBE]


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## Shiny_Beast (Apr 16, 2009)

It's the same as the caps argument, you think different components sound different or you don't. The scientific community is confident in it's mature belief that if you can't measure it, it isn't there, and scoff at anyone else who believes different. Many amp builders have their preferences for different positions, although they may just be knowingly getting in on the mojo, who knows.

Something else to consider is resistor quality, those Alan Bradley CCs are nice resistors, carbon comp or not. There's other properties of resistors worth noting, like inductence and whether they are magnetic or not.


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## p_wats (Nov 11, 2009)

This thread is great! Thanks guys.

...That said, I have nothing to offer but my humble and knowledge-seeking ears. I think I'll try updating the resistors in my old tube amp and see what happens!


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## keeperofthegood (Apr 30, 2008)

p_wats said:


> This thread is great! Thanks guys.
> 
> ...That said, I have nothing to offer but my humble and knowledge-seeking ears. I think I'll try updating the resistors in my old tube amp and see what happens!


:wave: that sounds ambitious!! BUT it could be an interesting project if you take some time. If you record 10 seconds of the amp at each replacement then you will have a tone record of what changes led to what outcomes. Even pluck through your strings just open once each. See and hear what noise breaks through when and hear how it may sound different as you go through it!!


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## keeperofthegood (Apr 30, 2008)

p_wats said:


> This thread is great! Thanks guys.
> 
> ...That said, I have nothing to offer but my humble and knowledge-seeking ears. I think I'll try updating the resistors in my old tube amp and see what happens!


OH AND

I read that a good source of carbon noise (google ftw) can also be the pot's and that conductive plastic are far quieter!!

kqoct I have had pots still perfect from 1935, I don't know if in 70 years conductive plastic will be the same.


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## dtsaudio (Apr 15, 2009)

Having been in the repair business for years, I occasionally get the asked about carbon comp resistors. Some guys think it will give them the "vintage" sound. If by vintage they mean hiss, crackles and pops then that's what they will get. Carbon comps have no place in any modern audio or music equipment gear. As Wild Bill has stated, they do tend to drift when stressed, they will burn, and are noisy.
I use primarily metal films. However wire wound resistors have their specific uses as well. Particularily in power supplies. 
There are other types as well - thick film, tantalum, carbon film, and a few other specialized types.
One other aspect that hasn't been touched on is the wattage rating. Run a resistor to close to it's max rating and it will tend to get noisy. Even metal films will do this. The larger the wattage rating the quieter it will tend to be.


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## keeperofthegood (Apr 30, 2008)

dtsaudio said:


> Having been in the repair business for years, I occasionally get the asked about carbon comp resistors. Some guys think it will give them the "vintage" sound. If by vintage they mean hiss, crackles and pops then that's what they will get. Carbon comps have no place in any modern audio or music equipment gear. As Wild Bill has stated, they do tend to drift when stressed, they will burn, and are noisy.
> I use primarily metal films. However wire wound resistors have their specific uses as well. Particularily in power supplies.
> There are other types as well - thick film, tantalum, carbon film, and a few other specialized types.
> One other aspect that hasn't been touched on is the wattage rating. Run a resistor to close to it's max rating and it will tend to get noisy. Even metal films will do this. The larger the wattage rating the quieter it will tend to be.


Another aspect that I have encountered too is; if I compare them by cost, the less noise, the lower the price :O

Carbon Comp 1K 10% 1Watt *$2.45* (no 5% available)
http://ca.mouser.com/ProductDetail/Ohmite/OA102KE/?qs=sGAEpiMZZMuDPtTs5Gda25kxdIMr9q4Ho2aFEd0Gso0=

Carbon Film 1K 5% 1Watt *$0.204*
http://ca.mouser.com/ProductDetail/Xicon/294-1K-RC/?qs=sGAEpiMZZMsCQIGbZVRXMAbiv8drm45/HjQunp9I5Zo=

Metal Film 1K 5% 1Watt *$0.181*
http://ca.mouser.com/ProductDetail/...=sGAEpiMZZMtMTfExsNintc56s6GDee8Tt4Lo55V2bAc= 

Metal Oxide 1K 5% 1Watt *$0.079*
http://ca.mouser.com/ProductDetail/Vishay-BC-Components/PR01000101001JR500/?qs=sGAEpiMZZMtMTfExsNintc56s6GDee8Tt4Lo55V2bAc%3d 

I also have tended to see that many companies are making mostly the same physical size of part but that the price difference between 1/2 and 1 watt are not ... huge (usually a cent or two), so, going all 1 watt MOX makes economic and booboo-proof sense.


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## Wild Bill (May 3, 2006)

keeperofthegood said:


> Another aspect that I have encountered too is; if I compare them by cost, the less noise, the lower the price :O
> 
> I also have tended to see that many companies are making mostly the same physical size of part but that the price difference between 1/2 and 1 watt are not ... huge (usually a cent or two), so, going all 1 watt MOX makes economic and booboo-proof sense.


Price is driven by volume, Keeps. If your market volume for a part is small then the price will be higher, even if the specs are better on the cheaper part. In the late 90's I was working for TTI Electronics, a big American disti. We were exclusive for the brand Allen Bradley carbon comp resistors. AB were the last manufacturer in the world for those kind of resistors. They would have stopped years earlier as well except for one thing - the military market!

There is a natural tendency to believe that mil-spec means better quality. That might be true of a cog-wheel in the tread assembly of a tank but in much electronics it sure wasn't when I was selling to them! They cared far more about their paper work and their specs than moving with the times. They had written their specs on resistors back in WWII and they absolutely did not want to change them to use modern resistors! As long as the old mil-spec carbon comp resistors were available then that was what they would buy, NO MATTER WHAT THE PRICE!

At the end of the 90's even the military could not buy enough resistors to make it worth AB's while to keep making them. We were selling them at over $1 each, no matter the quantity! This was for half watts, which are cheaper than the 1 watt prices for modern resistors that you posted. So we took orders for "Last chance - lifetime buy!" from all our military customers who wanted to take advantage of the offer and that was that - no more AB carbon comp resistors were made.

Of course, even though we had told our customers what was gonna happen many of them still didn't pay attention. A year or two later they were frantically begging us to supply more and we kept telling them it was too late. So the military finally started updating it's specs to use modern resistors.

Meanwhile, there was a cowboy's market for surplus carbon comps, supplying those who had to have the old resistors, at incredible prices! Some far east folks started making carbon comps. Lotta quality problems at first. I saw some where the leads had actually fallen off in the package!

Along with the new technologies came the ability to make resistors smaller for the same wattage rating. This trend is true for pretty well all electronic parts. Everybody wants smaller parts so you can stuff more on the same size of printed circuit board.

There may come a day when we can't get leaded resistors of any kind! Surface mount devices are the modern way to go. That's where all the volume sales happen. Resistors are a mass production part. When you are selling zillions of surface mount units it just isn't worth your while to set up a factory to supply a few repairmen and hobbyists. Luckily, we seem to be good for a few decades yet!

Someone mentioned carbon pots. Good point! They weren't inherently more noisy than modern conductive plastic and the like but they did wear out a lot faster, needing more and more cleaning until finally they wore out.

Carbon microphones were the first microphones ever invented. They worked but were never a hifi device. They were good enough for telephones, though! Ma Bell used them for decades, right up until the late 70's. You don't need a wide frequency response for just speech frequencies. 

You mentioned "off-station" radio noise, Keeps. That's atmospheric noise. You get that on any receiver. Different from internal noise coming from resistors. Think Jodie Foster in the movie "Contact"!:smile:

Anyhow, I'm off for my morning coffee! Have fun!

:food-smiley-004:


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## keeperofthegood (Apr 30, 2008)

HAHA!! Thank you Wild Bill!!

Hmm, atmosphere makes sounds that speak to me on TV @[email protected] think they made a movie about that too 

Just had my morning coffee, but I am coughing too much, and going back to bed 

OH... plastic pots, your take on them is positive over the long term? I'm cool with them if they last at least as long as the traditional 

Yes, reading the pdf on the carbon mic, the bandwidth is stated 300hz to 4000hz @[email protected] not a very large range at all. There is a guy that is making stage mic's as altered art (Calls them "Bing Carbon Microphone CIRCUIT BENT TELEPHONE MIC" on eBay) with the telephone ones. His "you tube sample" video is ... really bad LOL or I would take the time to post it saying "see, you can use it, it is just very limited"


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## Emohawk (Feb 3, 2006)

I love threads that debunk these types of myths!  I figured someone would chime in & provide some solid technical duscussion about the true merits (or lack thereof) of using carbon comp. I guess if you want to be "authentic" in a restoration or build project, go ahead. Personally I don't see the point. If there's no appreciable negative impact on tone from using CF or MO instead - other than making the amp run with a lower noise floor (can't see how that could be a bad thing) - then I see no reason to use CF at all.

The capacitor argument is a whole other issue.


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## keeperofthegood (Apr 30, 2008)

Emohawk said:


> I love threads that debunk these types of myths!  I figured someone would chime in & provide some solid technical duscussion about the true merits (or lack thereof) of using carbon comp. I guess if you want to be "authentic" in a restoration or build project, go ahead. Personally I don't see the point. If there's no appreciable negative impact on tone from using CF or MO instead - other than making the amp run with a lower noise floor (can't see how that could be a bad thing) - then I see no reason to use CF at all.
> 
> The capacitor argument is a whole other issue.


For sure, when I get to restoring my Marconi TV, anything "visible" will be as vintage original as possible. I want to have something that looks "as it was when new".

Capacitors now  I really think there is a physics that hasn't been documented with them to the degree needed. As I mentioned before, there is a "knee" where the different dielectric materials change in how they respond to signal frequency. Only by the historical time people really began to study that behavior, new materials had come along that simply had far better stability. Also, because there was a "frequency ceiling" all the work and research really done was on that goal, pushing the ceiling higher and higher, and the concern for low frequency was not there, _parts simply worked so why spend time studying the minutia of them_. That I think is the rub, and continues to be the rub. The argument should be "ok, paper works, and ceramic works, but why are some people able to say they can hear a difference between them?". Human hearing can hear distortion even at very low amounts apparently so I dunno, worthy of looking into by some over eager university guys in the labs at night on a Friday XD


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## Wild Bill (May 3, 2006)

keeperofthegood said:


> Human hearing can hear distortion even at very low amounts apparently so I dunno, worthy of looking into by some over eager university guys in the labs at night on a Friday XD


"very low amounts"? News to me, Keeps!

I was taught that the human ear cannot detect less than 3% distortion. Even a 'scope can't directly show less than that!

As for capacitors, I think it's more a case of inherent ESR. Films and oil-filled have a much better ESR figure than ceramics or micas. However, once you have a device that gives good results it doesn't make sense to go crazy with overkill. I truly don't believe there's an improvement you can hear between an Orange Drop and a $40 audiophile coupling cap. In a guitar amp those yellow metallized film caps everybody sells are more than good enough.

:food-smiley-004:


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## keeperofthegood (Apr 30, 2008)

Wild Bill said:


> "very low amounts"? News to me, Keeps!
> 
> I was taught that the human ear cannot detect less than 3% distortion. Even a 'scope can't directly show less than that!
> 
> ...



 I was under the impression it was 1%


LOL I agree really I do. I do think there is investigative merit in looking because of the number of claims and because from all that reading I did a few weeks back it doesn't appear anyone has looked in this manner, but I also really do suspect it is a Snark. Hehe but hunting a Snark on a late night can still be fun if you expect nothing more than a good hunt and that the Snark you hunt is not a Boojum.

LOL and having said that, I now have the desire to give that a read again, its been a few years XD


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