Mixing wattage

Mixing resistor wattages wont have any effect upon your output level, resistor wattages refer to how much power they can withstand flowing through them (how much heat they can dissipate) , i.e. a 1W resistor can handle and amount of power up to a watt flowing through it. BUT the danger is when overloading a resistor, or using a resistor with too low a power rating will almost certainly result in failure possibly even a fire.

Whenever I do an electronics project I tend to use resistors that are twice the required power rating, this is just a fail safe. If you have knowledge about electronic circuits and understand power equations then go ahead and check your resistors are up to the job, else I'd use 1 watt resistors as a minimum.

 

Lewis B is spot on. I would (if you know the maths) calculate out how much wattage each resistor would be seeing and get one that handles more for peaks.

For most instrument-level effects, it's not a major concern as there usually isn't a major amount of wattage flowing through the circuit. In most cases of course. Preamps and high gain boosters would require higher spec'd parts.

While it may seem like a good idea to grab some 10-watt parts so you don't have to worry, they take up a lot more size.

This holds true for most components.

 

Most common pedals use 1/4 or 1/2 watt resistors