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Resistors
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Resistors
LektroiD
After reading a BoM that specifically calls for Carbon resistors, I thought I'd ask the question; Carbon Composite, Carbon Film, Metal Film, which is best in an audio path?

I wanted a simple answer to a simple question, but after reading a lot of discussion regarding this, I seemed to open a can of worms for myself. I found a lot of posts on various audiophile forums regarding resistor types. This is my findings...

Carbon Composite (don't bother)

Carbon Film:
Pros: Warm sound
Cons: Noisy, temporary resistance change due to heat, irreversible resistance change due to moisture, wider tolerance, fire risk under stress.

Metal Film:
Pros: Stable, tight tolerance, low noise
Cons: Colder sound (less coloured).

Could this be what makes those classic synths of the '70s and early '80s have that magical warmth compared to modern remakes? I've used metal film throughout all of my modular systems. I'm wondering how different things might sound if I'd gone down the Carbon Film route.
Bodo1967
Hmm. Just a thought...

This might be worth a try:

Build two not too complex/expensive identical modules, perhaps VCOs. Build one with 1 % metal film resistors and the other one with 5 % carbon film ones. Calibrate them as required.

Then compare both with an oscilloscope and with your ears. Preferably build them into a case so other people can't see which is which, and let them play around with it and ask if they prefer one over the other, or can tell which one sounds "better" to their ears.
tarandfeathers
Warm and cold are meaningless terms that convey nothing, except that people describing something as warm usually means they like it, and cold usually means they don't. I have done comparative listening tests with people where my perception of what was warm and cold was opposite to other participants. You need to quantify what you mean by these terms to have a realistic discussion about the relative benefits.
ashleym
Coming from the audio world, I see you’re using the right amount of caution!!

One answer is the best resistor (on any other component) is the most appropriate. Manufacturers back in the day might have picked up the cheapest, the best, the bulk lot they had hanging around etc. The synths sound good because they were designed by good engineers or because we’ve been told that’s the classic sound for several decades.

Drive yourself mad and get some exotic metal film and carbon resistors and do the test below!! The results could be interesting. As long as the resistors are used within their limits, as they should be in a module. Then repeat with SMD.......

I care about sound and I’ve always been happy with metal film but branded (I understand the likes of Vishay have endless ranges and manufacturing plants).
ixtern
LektroiD wrote:
After reading a BoM that specifically calls for Carbon resistors, I thought I'd ask the question; Carbon Composite, Carbon Film, Metal Film, which is best in an audio path?

I wanted a simple answer to a simple question, but after reading a lot of discussion regarding this, I seemed to open a can of worms for myself. I found a lot of posts on various audiophile forums regarding resistor types. This is my findings...

Carbon Composite (don't bother)

Carbon Film:
Pros: Warm sound
Cons: Noisy, temporary resistance change due to heat, irreversible resistance change due to moisture, wider tolerance, fire risk under stress.

Metal Film:
Pros: Stable, tight tolerance, low noise
Cons: Colder sound (less coloured).

Could this be what makes those classic synths of the '70s and early '80s have that magical warmth compared to modern remakes? I've used metal film throughout all of my modular systems. I'm wondering how different things might sound if I'd gone down the Carbon Film route.


There is no such thing as "warm/colder sound" regarding resistors. I think by "warm" you mean sound with lover level of high harmonics than "cold" sound. Resistor type doesn't matter when you are talking about frequency characteristics.
Due to a noise generated by some old, carbon, high-ohm resistors placed in a sensitive points sound perception may change but it is due to noise only.
Low-frequency noise may mask some higher harmonics, for example but then noise should be audible also.

Stability is another issue. When I need good, stable resistors, I always buy it from the vendor providing product chart from manufacturer stating temperature stability. Also resistor heating may be an issue with an ohm stability. As a rule I am using maximum power of resistor at least four times greater than power lost in it - but not for value-sensitive points. For stable conditions it should be at least ten-to-one.
fuzzbass
ixtern wrote:
There is no such thing as "warm/colder sound" regarding resistors.


I have experienced a "warm smell" coming from resistors.
papz
Resistors with golden leads have a richer sound.
NV
Resistance introduces thermal noise into the signal path. Carbon resistors are noisier than metal film, and metal thin film are an improvement over thick film. All that is dependent on how much resistance the path is going through to begin with, you'll run into different noise levels with a 1M than a 10 ohm. This is a big deal in some circuits - in astronomy many circuits have cryogenic cooling to reduce thermal noise, which can add light years of observational range. Maybe less dramatic in a synth making bongo whatevers, but still part of the equation.

Whether that noise is interpreted as "warmth" is subjective, but personally I would say any uncontrolled source of noise isn't necessarily a good thing. Design a circuit to reduce noise as much as possible, then if you want it add it manually with one of any variety of simple noise circuits. Filter it into pink/brown/blue/violet noise before injecting it even. Adding noise is vastly easier than taking it away.
mskala
There's no solid evidence that anyone can really hear a difference between the types of resistors in an ordinary audio application. Even the differences in noise level that NV talked about, which are real and objectively measurable, are pretty unlikely to break through the noise floor imposed by other components to become audible in a real circuit.

However, there may be meaningful differences in temperature coefficient. Metal film resistors tend to be the most temperature-stable and are sometimes specified for stuff like VCO control circuits; they also often have better tolerances on basic resistance value than other types. Both those points depend on the ratings of the specific resistors in question, though - it's not just instantly determined by what they're made out of.

At one time, carbon film resistors were the only ones that were cheaply available to hobbyists, and metal-film were considered better but were much more expensive. (Carbon composition resistors were only cheap a LONG time ago.) So you'll see BOMs saying "carbon" when all it really means is "It's okay to use the cheaper ones, you don't need to pay extra for metal film." Some of the old classic synth schematics have a few resistors marked with stars or the letters "MF" to indicate that those ones need to be metal film for stability, while it's implicitly okay to use the cheaper carbon film resistors for all others. Nowadays, the price gap is a lot smaller and for many people it makes sense to just use metal film everywhere whether it's really needed or not, and have one less thing to think about.
BugBrand
Good tech-y detail (amongst lots of other great stuff) in Doug Self's 'Small Signal Audio Design' book - highly recommended if you want to go waaaay deeper!
synthpriest
Bugbrand thanks for the tip, just ordered a copy of this book. Miley Cyrus
cornutt
Back in the day, 10% bulk carbon resistors were standard issue. A whole bunch of consumer and semi-pro and even some pro stuff used them all over the place. Anything else (other than low-ohms, high-wattage wirewounds) was really expensive. Some gonzo people like EML plunked down for mil-spec, which had better specs but were still mostly carbon.
Grumble
carbon film resistors have a higher inductance and capacitance level as the metal film resistor types, so that will have an effect on the frequency responce of the cirquit where these resistors are used.
So maybe that explains the ‘warm’ sound seriously, i just don't get it
mskala
Grumble wrote:
carbon film resistors have a higher inductance and capacitance level as the metal film resistor types, so that will have an effect on the frequency responce of the cirquit where these resistors are used.


Yes, at frequencies higher than audio by a factor of thousands.
ashleym
synthpriest wrote:
Bugbrand thanks for the tip, just ordered a copy of this book. Miley Cyrus


Mr Self is very much in the objectivists camp rather then subjectivist. Remember this when you read his, useful and good, books.
home_listening
I'm not really aware of any synth manufacturer that used anything much better than the cheapest stuff around when they were building... except for a few key locations such as expo converters etc.

That said I did actually build up a pair of Arp Odyssey oscillators, one with carbon the other with metal film. Other than the carbon one maybe being more difficult to calibrate than the metal there was no difference. Just use what is convenient to you, in the grand stack of electronics synths are closer to novelty farting toys than aerospace - they aren't really precision instruments.
EATyourGUITAR
I know some synth technicians that are well respected for servicing an original minimoog model D. they would be no talent hacks if they did not install carbon comp resistors when replacing old components. carbon comp resistors are not ideal for every application but there are clients and use cases that require them. to elaborate a bit more, carbon comps are better at being carbon comps than a metal film resistor. people have tried to build vintage synthesizers with all 0.1% resistors and the result was something so perfectly tuned, stable, and linear that it was completely unrecognizable from the thing that it was a clone of.

in the modular world, MOTM was one that had really good versions of vintage designs. you would need a noise source and a mixer to introduce noise. you would need the wave warper to add non-linearity to your pitch cv. buying a real model D would be a more direct route to get a model D.

ironically, the majority of people that like out of tune synths do not know that they like out of tune synths. resistors are not your problem. the problem is audiophile forums spreading useless or incorrect information.
UltraViolet
synthpriest wrote:
Bugbrand thanks for the tip, just ordered a copy of this book. Miley Cyrus


Thanks for the tip. That is a least two copies you just sold.
joem
EATyourGUITAR wrote:
I know some synth technicians that are well respected for servicing an original minimoog model D. they would be no talent hacks if they did not install carbon comp resistors when replacing old components. carbon comp resistors are not ideal for every application but there are clients and use cases that require them. to elaborate a bit more, carbon comps are better at being carbon comps than a metal film resistor. people have tried to build vintage synthesizers with all 0.1% resistors and the result was something so perfectly tuned, stable, and linear that it was completely unrecognizable from the thing that it was a clone of.

in the modular world, MOTM was one that had really good versions of vintage designs. you would need a noise source and a mixer to introduce noise. you would need the wave warper to add non-linearity to your pitch cv. buying a real model D would be a more direct route to get a model D.

ironically, the majority of people that like out of tune synths do not know that they like out of tune synths. resistors are not your problem. the problem is audiophile forums spreading useless or incorrect information.


applause
speakeron
Clearly the answer is to socket them, so you can swap out as your heart desires...
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