1/2watt Metal Film vs 2watt Carbon Comp -Hiss
Moderators: pompeiisneaks, Colossal
1/2watt Metal Film vs 2watt Carbon Comp -Hiss
Which plate resistor generates more hiss in a typical preamp?
If it says "Vintage" on it, -it isn't.
Re: 1/2watt Metal Film vs 2watt Carbon Comp -Hiss
Per Randall Aiken (paraphrased):
The are three kinds of resistor noise: thermal noise, contact noise and shot noise. In any given circuit, thermal noise is dependent only on resistance value, so there is no difference among resistor types. Contact noise is a function of DC current, the resistor material and the resistor size. Generally, a metal film resistor will be quieter than a carbon comp in this regard and the larger the resistor (wattage), the quieter it will be. 2-watt carbons are supposedly three times quieter than 1/2-watt carbons, so the quietest resistor would be a 2-watt metal film. (Actually, the QUIETEST resistor would be a wirewound of any wattage since they have no contact noise at all, but probably impractical.) Shot noise is a function of DC current and resistor type so metal film (or wirewound) will likely be quieter.
In terms of your specific comparison, I'll bet that 1/2-watt metals would be marginally quieter than 2-watt carbons, but the difference may be small.
BTW, in some amps, the dropping resistors in the B+ rail also contribute a significant amount of noise, so these should be optimized for quietest performance, too.
In later stages, where resistors are operated at high voltages and the signal is larger, the distortion characteristics of carbon comps come into play, so you may want to keep CCs in these stages (PI, maybe third gain stage).
The are three kinds of resistor noise: thermal noise, contact noise and shot noise. In any given circuit, thermal noise is dependent only on resistance value, so there is no difference among resistor types. Contact noise is a function of DC current, the resistor material and the resistor size. Generally, a metal film resistor will be quieter than a carbon comp in this regard and the larger the resistor (wattage), the quieter it will be. 2-watt carbons are supposedly three times quieter than 1/2-watt carbons, so the quietest resistor would be a 2-watt metal film. (Actually, the QUIETEST resistor would be a wirewound of any wattage since they have no contact noise at all, but probably impractical.) Shot noise is a function of DC current and resistor type so metal film (or wirewound) will likely be quieter.
In terms of your specific comparison, I'll bet that 1/2-watt metals would be marginally quieter than 2-watt carbons, but the difference may be small.
BTW, in some amps, the dropping resistors in the B+ rail also contribute a significant amount of noise, so these should be optimized for quietest performance, too.
In later stages, where resistors are operated at high voltages and the signal is larger, the distortion characteristics of carbon comps come into play, so you may want to keep CCs in these stages (PI, maybe third gain stage).