Resistors: metal film vs carbon...

[DamnYankee]

I apologize if this was discussed earlier - I didn't find a specific thread dedicated to this topic.

Metal film is lower noise - but what would be disadvantages of using metal film over carbon in effects boxes and other gear (carbon seems to be very common...)???

As always, I'm greatly appreciate to everyone's expertise as I'm continuously reading/learning...

Steve

[Fredrik]

Originally Posted by DamnYankee

I apologize if this was discussed earlier - I didn't find a specific thread dedicated to this topic.

Metal film is lower noise - but what would be disadvantages of using metal film over carbon in effects boxes and other gear (carbon seems to be very common...)???

As always, I'm greatly appreciate to everyone's expertise as I'm continuously reading/learning...

Steve

There are no disadvantages that I know of, metal film are available in more exact values with tolerances down to 0,1% I believe. They will hold their value with heat increase better than carbon as well AFAIK.

[JohnRoberts]

cost.

JR

PS: Noise benefits are perhaps over stated but if cost is no object use them.

[Jim Williams]

There are 2 types of carbon resistors, carbon film and carbon composition. The film one's are very common for low end audio, they are a penny or less a piece and have decent noise specs. The carbon comps are what's found in older Fender amps and outboard. These pick up hum fields pretty good, are noisy and add some aural excitment or spit to the sound. Some would call this an agressive tone.

Both have drift problems with heat cycling. The metal films are more controlled and have much better HF specs. Some are 50 ppm or less temp co's. That means they hold their values under stressful operating conditions.

Then you have your bulk foils, the best resistors in the world are bulk foils, rarely found in audio gear as they start at $1.30 each and go over $10 each for the tightest specs.

Jim Williams
Audio Upgrades

[mikeg]

RN60, RN65 from Newark. Film Rs. .1% tolerance and hold their value well after being soldered.

Carbon comps also change value over time, a lot.

[DamnYankee]

Originally Posted by Jim Williams

There are 2 types of carbon resistors, carbon film and carbon composition. The film one's are very common for low end audio, they are a penny or less a piece and have decent noise specs. The carbon comps are what's found in older Fender amps and outboard. These pick up hum fields pretty good, are noisy and add some aural excitment or spit to the sound. Some would call this an agressive tone.

Both have drift problems with heat cycling. The metal films are more controlled and have much better HF specs. Some are 50 ppm or less temp co's. That means they hold their values under stressful operating conditions.

Then you have your bulk foils, the best resistors in the world are bulk foils, rarely found in audio gear as they start at $1.30 each and go over $10 each for the tightest specs.

Jim Williams
Audio Upgrades

Thanks All for your response!

So...if I'm designing an EQ, would it be advantageous to use one of the carbon resistors for lows to mid frequencies and metal films for higher frequencies to help keep some of the aural excitement/spit, clearer/air-ier highs and cut down on the overall noise?

And one last question: a week ago or so I asked about the carbon caps that looked like resistors but with 5 color bands. I've seen several different references and they all contradict. If I have a Blue-Red-Orange-Gold-White, what is its value and how do I read it (to replace it)?

I apologize for what's probably dumb questions to many of you...I'm still learning.

Thanks - and Happy Thanksgiving to you and your families,

Steve

[JohnRoberts]

Originally Posted by Jim Williams

There are 2 types of carbon resistors, carbon film and carbon composition. The film one's are very common for low end audio, they are a penny or less a piece and have decent noise specs. The carbon comps are what's found in older Fender amps and outboard. These pick up hum fields pretty good, are noisy and add some aural excitment or spit to the sound. Some would call this an agressive tone.

Both have drift problems with heat cycling. The metal films are more controlled and have much better HF specs. Some are 50 ppm or less temp co's. That means they hold their values under stressful operating conditions.

Then you have your bulk foils, the best resistors in the world are bulk foils, rarely found in audio gear as they start at $1.30 each and go over $10 each for the tightest specs.

Jim Williams
Audio Upgrades

Not to contradict, but to expand on this, there can also be exceptions between vendors. I had very good experience with ROHM carbon films and experienced little value drift even from some so overloaded they burned off their paint.. Note: don't try to use them as cheap fuses because they don't open easily.

Also not all carbon comps are created equal. Some carbon comps were better than carbon film for excess noise, or noise caused by current flowing in resistor (useful when a high value resistor is acting as a biasing string in say a tube circuit). The closest solid state app is the phantom power build out resistors in front of mic preamps, but at 6.8K the excess noise is minimal. These are usually MF anyhow to get 1% or better matching for good CMR.

In general the noise in resistors is dominated by the value, not the type. Johnson or thermal noise is caused by heat at room temperature causing random electron movement. This "current" is converted to a voltage by the resistance, since the heat looks like a constant power input, higher resistance means more thermal noise, no matter what kind of resistor.

So don't blow all your money on expensive resistors unless everything else is tight already. If everything else is already optimized and you still have money burning a hole in your pocket, it won't hurt to use decent MF, and the precision is always nice.

JR

[Wavebourn]

I bought a lot of Russian MLT resistors on ePay. People don't know yet a real value of them so they go very cheap.