Noise in Resistors

  • Hi All,

    First of all thanks all for the support received here. I know sometime some excessively lighted up discussions occurred but overall so far I have accepted all the advises, suggestions, your proposed even if sometimes those were given a very direct harsh way. I think I understand now how it works on this forum.

    The direct approaches overall has pushed on squeezing brain thinking logical rather than copying a DIY build out of step by step instructions and pictures.

    For example I understand now a lot more about capacitors, resistors their purposes and the utilization at specific places but also how really dangerous can be if something isn't done correctly like caps explosion and so on so forth.

    Now the question:

    I am reading the Design tube Preamps for Bass and Guitar.

    I am to the point about Resistor Noise

    I was aware already about Resistors Carbon Composition to produce noise, therefore on modern design, this something I was told on a different Forum, to avoid as much as possible Carbon composition.

    reading the advised book now, the same is mentioned at page 62

    It says: Specifically that Carbon Composition should be avoided in the input stage.

    I have looked at original circuit such 18 Watts or even Fender Simple Circuit 5F1 and I see basically Carbon Composition being used as the only resistors type except for a couple of Metal Oxide but those are not at the input stage.

    Therefore I would assume that turning on an Amp like that would produce all kind of cracking noise and hum?

    There are today a lots of American Kits such the one from Stewmac or Mojotone that still uses Carbon Composition.

    At this point I bet that utilization of Metal Film is simply the easiest way to avoid such issue?

    So back in the 60s those amps had a lot of hum noise? I have an Amp in Italy that is an Original Fender Champ 5FE it was refurbished since it is from the 70s or around that period not sure exactly and in fact it makes a lot of noise when turned on.

    So can we really say that Carbon Composition resistors should be avoided?


  • Hiss&Hum is Vintage,Vintage is cool :D ,

    But build in Amp with modern Components to avoid Hiss&Hum,is much better,than build a new Amp with Vintage Components and get annoyed afterwards,cause it hisses and hum´s ;)

    In Some cases,Carbon Comp resistors make Sense,but not in Signalway.

    But it make Sense,to restore a Old Amp,with same Component´s for Example those R´s,as them did have it in Original state.

    " Du willst keine sarkastischen Antworten ? :huh: ,dann stell keine blöden Fragen ! :D "

  • Make sense indeed

  • Hi Davide,

    It really depends on the circuit. It is true that those vintage parts Like carbon resistors produce more hum than modern one but that's just one aspect. The circuit design and the values chosen as well as the build quality also play a huge part. And moreover, it all comes down to how much gain your amp has. As hum is amplified along with the signal, low gain amp circuits (like basically all vintage amps) will tolerate more hum than some modern high gain beasts as the hum is not amplified as much in the low gain circuits.



  • carbon resistors don't produce more hum. Hum is referred to mains AC voltages/currents.

    They produce more noise (or hiss if you like the word) because the micro structure of carbon composits is more irregluar than that of metal oxides.

    And to end that damn rumor about carbon composite resistors: Because they are more nonlinear in respect to their resistance depending on the (dc) voltage applied to them they will add more harmonics to the signal resulting from this nonlinearity.

    But this is only a weak effekt which will be noticed only at high voltages and so the only use of this kind of resistors would be that of anode resistors in tube amps. Other use is only done by "specially talented" people without a sturdy base of knowledge.


  • Thanks I actually intended more noise rather than hum. That is what I read on the book indeed and depends on the voltage applied to them.

    Would you say that Carbon Resistor may be used on modern amp build if you don't use them on input stage? I think Carbon Comp Resistor may produce more warmth ?

  • Let me explain the reason of the question

    I am going to purchase 2 more kits, one is going to be entirely built out of a schematic and layout no step by step instructions or pictures.

    That will be the simplest circuit on earth, well there might be other simple out there not sure lol :) , that is the 5F1 Champ

    I am sourcing all parts very few components, cheap and nice sound from this little amp, it seems that Eric Clapton used it to record Layla, I am obsessed by Eric music and B B king and Blues so... that is the reason.

    The other one I'd like to try out is Kit Madamp G3 Blues both should help more understanding and they are easier to build I should have started with something like that but anyway never too late

  • Would you say that Carbon Resistor may be used on modern amp build if you don't use them on input stage? I think Carbon Comp Resistor may produce more warmth ?

    Well, you can use whatever components you want as long as the ratings are fine for the application. I think everything has been already said regarding carbon resistors. Of course you can use them. Will they actually sound different? I suppose not, although others swear the difference is massive. Will the additional noise be a problem or even audible? Depends on the circuit, probably not in these low gain circuits.

    Me, personally, wouldn't even bother with these outdated voodoo-components as there are superior options and much more important factors influencing the sound. But that's just my opinion.

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