Using all metal film vs carbon film resistors in a pedal

[wsaraceni]

Looking at a klon pedal. Or overdrive pedal in general. I see some places saying use metal film for everything and some saying to mix them for the klon like the original. Is there a difference in sound/feel/etc if you were to build a klon using all metal film resistors?

[TUBEDUDE]

It'll be quieter.

[Stevem]

Other then the noise floor being better with metal film resistors the pedal would have to be tube based to take advantage of the tone factor of having carbon type resistors, and even then the B+ voltage has to be high enough.

[WhopperPlate]

One of my favorite pedals of all time has the Analog brown mod . Carbon comps in select Positions . Every pedal I have tried using all Metal film hurts my ears and , might sound alright in the store , but eventually gets returned to the guitar shop after a day of testing at loud volumes .

On the other hand , my favorite EP3 Echoplex has all carbon film , and every unit I owned that had all carbon comp was meh to me in comparison. To emboldened my previous claimed experience , my least favorite Echoplex was a Mike battle modified ep3 into the plex circuit, all metal film tube driven , nails on a chalkboard .

[drewspriggs]

Looking at a klon pedal. Or overdrive pedal in general. I see some places saying use metal film for everything and some saying to mix them for the klon like the original. Is there a difference in sound/feel/etc if you were to build a klon using all metal film resistors?

There is no benefit whatsoever to carbon film resistors, especially in pedals.

Anybody who claims there is is just cork sniffing.

[nuke]

Save a few bucks buying carbon film where they're not critical. Metal film if you want lowest noise and greatest precision.

If you're buying qty 5000 of something, the costs differences add up. Metal film are about twice as much carbon films.

Curiously, if you're buying 1 of each, they're usually about the same. It costs way more for Digikey or Mouser to snip you one off the tape reel than the part actually costs.

Looking over the Klon circuit breakdown, there's a couple of places I'd want a metal-film resistor. One of the less obvious places is the voltage divider in the power supply that derives the +4.5v. If I'm reading the circuit right, there might be some benefit in having that nice and tight, since it is used as the floating reference in several places. If you were mass-building these, 1% metal film would be a good idea. If you're just building one of these, then simply going through your stash of 27k resistors and getting two that matched really closely would work very nicely too.


There are a few other places where it might help to have MF, for lowest noise. Just roll through the circuit and in your head, imagine the resistor has a tiny little noise generator inside of it, and whether that will get amplified in that stage.

Using the resistor thermal noise formula (simplified):

E =2.718 7.43 * SQRT( R * T * bw)

Where R is ohms in k-ohms, T is temperature in degrees K, and bw is the bandwidth in khz, E is the noise in nanovolts.

The important take-away is that the higher the resistance, temperature and bandwidth are, the greater the thermal noise. Since a guitar pedal is most likely room temperature and the bandwidth is kind of limited to 60hz to maybe 10khz, the thing we want to think about are high resistance values in critical places early in the gain structure.

So, that 1M resistor that biases the input of the first opamp input to the divided 4.5v source, is probably the most influential source of noise on the board.

The other noise from resistors is "current noise" aka Johnson Noise and that is influenced by the type of material the resistor is made of and how much current is passing through it. In order of lowest-to-greatest noise: Wirewound, metal foil, thin-film (metal film), carbon film, thick film, and noisiest of all being carbon composition.

In the Klon circuit, there's about 3 or 4 resistors I'd pick metal film for a reasonable purpose, especially if I was making hundreds or thousands of them.

Guitar signals are already noisy as all heck, and most people are plugging noisy guitars into multiple noisy pedals into noisy tube guitar amps, to play in noisy dive bars with noisy bandmates right next to the inevitable neon beer sign. So, does it really matter?

So if you wanted to build just one for yourself, I think it would be perfectly fine to use whatever you have under your work bench in your parts stash. Can always swap a few parts around for grins as you go.

[mwelch55]

I only use metal film in the signal chain for pedals and amps. I can't stand the hiss that carbon resistors create.

[wsaraceni]

so essentially this is the same as what ive read elsewhere. most saying metal film is better tolerance but insignificant tonal differences with others saying metal film sounds bad and some saying carbon too noisy.


ill find out soon enough. im building 2 Klon clones. one with the standard mix of carbon and metal film. one with all metal film. and the metal film I went with are high precision (.1%) and like $1.50 each.

[wsaraceni]

One I even tried to go with more expensive caps but the wima caps aren’t available in every value needed

[drewspriggs]

One I even tried to go with more expensive caps but the wima caps aren’t available in every value needed

Are you using Mouser for WIMA caps? Never encountered a value they haven't had. Those are some sweet PCB's btw.

Also did the wanky thing with PRP 9372's for a meme a while back. Made absolutely no difference to sound except for lightening up my wallet (being literally 50x the price of Tayda resistors)

[wsaraceni]

One I even tried to go with more expensive caps but the wima caps aren’t available in every value needed

Are you using Mouser for WIMA caps? Never encountered a value they haven't had. Those are some sweet PCB's btw.

Also did the wanky thing with PRP 9372's for a meme a while back. Made absolutely no difference to sound except for lightening up my wallet (being literally 50x the price of Tayda resistors)

WIMA doesnt even make the capacitors in some of the Klon's values. and others they are only in a different footprint than this board was designed for. I am finishing it off with some TDK blue capacitors so unfortunately a mix of blue and red and green and gold and black


as for your build. thats what im talking about. all red everything. that definitely sounded better. what exactly is it?


I've had my first experience with tayda UV printing. came out well. just wish I made the font a little bigger. I wanted my mini klone to look somewhat more professional than sharpie written text.

[WhopperPlate]

so essentially this is the same as what ive read elsewhere. most saying metal film is better tolerance but insignificant tonal differences with others saying metal film sounds bad and some saying carbon too noisy.

Surprise surprise

ill find out soon enough. im building 2 Klon clones. one with the standard mix of carbon and metal film. one with all metal film. and the metal film I went with are high precision (.1%) and like $1.50 each.

Far more productive than trusting opinions… I would be happy to read your experience .

[drewspriggs]

WIMA doesnt even make the capacitors in some of the Klon's values. and others they are only in a different footprint than this board was designed for. I am finishing it off with some TDK blue capacitors so unfortunately a mix of blue and red and green and gold and black

as for your build. thats what im talking about. all red everything. that definitely sounded better. what exactly is it?

I've had my first experience with tayda UV printing. came out well. just wish I made the font a little bigger. I wanted my mini klone to look somewhat more professional than sharpie written text.

Revv G4