Resistor rating??

[Adamo]

This is a very noob question but is there a standard wattage rating for resistors for pedal building? I see alot of materials lists and they show the ohm ratings of the resistors but not the ratings (ie 1/8W, 1/4 W, etc). I see that at the madbeanpedals site he lists all the resistors for his fuzz face clone as 1/8W.

Thx
Adam

[mth5044]

1/4 and 1/8 are very common and can be used in practically every pedal you build unless the schematic or layout specifies a higher wattage. If you get into amps, power supplies or higher voltage things, watts may become more important, but for our generally @#$%ery 1/4 or 1/8 are common and fine.

[Adamo]

Many thx!

[armdnrdy]

What Matt said plus...

It is extremely common to see notes on a schematic that give details as to the wattage of resistors and the voltage of capacitors.

Typical notes read: All resistors 1/4 watt unless noted.
                           

[GibsonGM]

What Matt said plus...

It is extremely common to see notes on a schematic that give details as to the wattage of resistors and the voltage of capacitors.

Typical notes read: All resistors 1/4 watt unless noted.
                           

+1     1/4W seem to me, at least, to be the most versatile. If I were getting a set of them, that is what I'd get.

And I did....4 or 5, ha ha, many years ago.  Plus a lot of extra 1, 10, 100K's.  Still using them up

[guitarpedalparts]

Yes, 1/4W are standard due to their availability, price and size. 1/8W are a bit more difficult to work with and anything larger could take up more space than needed.  1/4W 1% metal film is certainly the "standard".

[PRR]

Once upon a time, pedals were powered by 9V Batteries.

A 9V can supply about 10mA (0.01A) and have "acceptable" life; more, it goes flat too fast.

Therefor the maximum power for the WHOLE pedal is about 0.09 Watts.

This is usually split among two or more parts. (Usually a resistor fights a transistor near-fair.) So the max in any one part is likely to be 0.05 or 1/20 Watts.

You might find 0.05W resistors in a catalog, but if you drop it you'll never find it under the bench. Also super-small parts cost more. 1/4W parts are currently cheapest, though 1/8W parts are also very cheap. OTOH my fat fingers prefer 1/2W parts (if I can make them fit the layout).

[Liquitone]

Lately I have been using mostly 0.6W metal film resistors, mainly because they where available for 1,90euro per 100 pieces a 5 mins bikeride from here, have 4-band color codes which I prefer to 5-band, but also for lower noise. I'm not a schooled engineer, so I'm not sure if this lower noise the higher the wattage is a correct assumption. Can anyone confirm this for me? Also is it correct to assume noise in resistors only has effect in resistors in series with the signal chain and from power to signal, and have no effect from signal to ground? My latest germanium treblebooster has the 0,6W's in it  and it does seem extremely quiet, noise-wise, but that could also be because of careful layout and short wiring.

[DrAlx]

Lately I have been using mostly 0.6W metal film resistors, mainly because they where available for 1,90euro per 100 pieces a 5 mins bikeride from here, have 4-band color codes which I prefer to 5-band, but also for lower noise. I'm not a schooled engineer, so I'm not sure if this lower noise the higher the wattage is a correct assumption. Can anyone confirm this for me? Also is it correct to assume noise in resistors only has effect in resistors in series with the signal chain and from power to signal, and have no effect from signal to ground? My latest germanium treblebooster has the 0,6W's in it  and it does seem extremely quiet, noise-wise, but that could also be because of careful layout and short wiring.

The resistor power rating should have no effect on noise whatsoever.  Thermal noise in a resistor is determined purely by its resistance. It will be there regardless of whether you place the resistor in series or parallel with the signal chain. Google Johnson-Nyquist noise. 

[PRR]

Resistor bulk (power rating) can have effect in some very low hiss systems, but not for guitar work.

For low hiss, series resistors should be much smaller than the source impedance, shunt resistors should be much larger than source impedance. If 10X difference, that's about as good as it gets (unless you are doing radio-astronomy).

Guitar has around 100K impedance in upper-midrange where our ear is sensitive to hiss. That's why we keep the series resistor down around 34K and the grid resistor up around 1Meg. (34K is a bit high for lowest hiss, but may be necessary to snub strong radio signals, which can be far more annoying and unexpected than the trace of hiss.)

Carbon Composition hisses. It is old-school. It finds favor in some guitar amplifiers in higher-level stages for "authentic noise", but is otherwise bad mojo. Metal and carbon films are both much better than carbon composition.

Big enough resistors with stripes you can READ are good. Wrong-value is probably the #3 most-popular mistake.

[Liquitone]

Thanks guys! That cleared a few things up for me.

[Seljer]

There's also a difference at high frequencies (radio stuff that runs at many tens/hundreds of megahertz) where the physically larger resistors will have enough parasitic inductance/capacitance to stop being resistors!