metal film resistors: any fact against?

[barret77]

Hello all

I'm wondering if there's any application or recommendation to do NOT use metal film resistors;

I've been using carbon film, but I need to buy a new batch of resistors; metal film is fairly cheap, and there's the promise of lower noise levels...

I know that there's a lot of mojo on the "cold tone" of metal film, but I'm not sure what is fantasy or reality - at least for pedals, not amps.

[MarshallPlexi]

In the guitar amplifier world, carbon comp resistors are prized for the warmer sound specifically when used as plate resistors. Since the gain is developed across these resistors and they are connected to high voltage, they will produce an audible effect on the tone (including hiss) of the amplifier.

Since we are dealing with 9V here, I'm not sure if carbon comps will really be of any special use, aside from the fact that they look dead cool and are noisy. I'm sure I'll try this out on a Fuzz Face or something, but I'm leaning toward using Metal Films to keep the noise to an absolute minimum.

Remember any noise you feed into the front of an amplifier will be multiplied thousands of times. I can understand using noisy parts within an amplifiers after the first gain stage or so, but injecting noise into the FRONT of an amplifier seems like a really bad idea.

FMMV

[aron]

Check out geofex.com

http://geofex.com/tubeampfaq/TUBEFAQ.htm

" Are Carbon Comps really magic tone mojo?"

Interesting.

[R.G.]

Is there any reason not to use metal films? (presumably in pedals)

No. They tend to be a little lower power rated than carbon films, 1/10 W in the same size as 1/4W carbon films, but that's usually not a consideration. Most pedals don't use anywhere near 1/10W in any resistor.

Carbon films are the standard. They're good, cheap, not very noisy, although slightly noiser on a everything-else-equal basis than metal film. You'd probably never hear it except some highly specific circumstances.

Carbon comp is the old standard; that's because they were cheap. They're noisier than either carbon film or metal, their value drifted with temperature, soldering, mechanical abuse and just life. They do have a higher voltage coefficient of resistance than any other commonly available resistor. This is responsible for that "carbon comp is god" nonsense you hear in the tube amp world.

Carbon comps actually have a **better** high frequency response than either CF or MF. This is a difference up in the 100s of MHz, not audio. The do NOT make audio sound "brown" or "warm". In highly specific uses (go read the article) they have slight second harmonic distortion, and amp listeners go for slight second harmonic like a chicken goes for a June bug.

Using carbon comp will NOT make your pedal sound warmer, more vintage-ey, like Eric Clapton,  or like anything in particular, except it might make some things noisier, especially high gain distortion pedals.

Metal film is NOT colder, except by comparison to our second-harmonic-making friends, the CC. Even at that, there are only about two places in a typical amp where CC can step up and do its distortion thing. The rest of the places, especially at the first stage input resistors and plate, are much better served by metal film to keep noise down.

Boy - you'd almost think that there's nothing I hate more than mojo-fluff and nonsense.  

[aron]

Boy - you'd almost think that there's nothing I hate more than mojo-fluff and nonsense.

But... didn't you say somewhere they smelled better? (I'm not kidding.... I thought I read that!) :shock:

[barret77]

Great

Thanks for all replies. I've read RG article, brilliant as always.

This kind of explanation is what I love in this forum. I feel really grateful on all patience you guys have to explain stuff to less experienced diyers.

That's what I thought about metal film. I'll try the Vishay Metal Films from Mouser (any better suggestion for low quantity, varied values?).

[KORGULL]

Check out //www.goldmine-elec.com item#G14232 & G14233 - metal film resistor assortments - 10 each of 24 values in each box - 1/8W type.
Radio Shack has a decent metal-film asst. also.