Newb Resistor Question...

[Evad Nomenclature]

Hey guys.

I was just wondering, (didn't see it in the wiki or anything) Is there any sort of noticeable difference between using carbon or metal film resistors?
Also, I had ordered 1/8 watt resistors from ppp a while ago, but I noticed in the wiki it said that generally 1/4 or 1/2 are used in pedals...
Anything wrong with using the 1/8?
Thanks

[Auke Haarsma]

long answer: check all the mojo discussions
short answer: metal film is technically better: it keeps the signal more intact. Carbon tends to drop some highs... some perceive this as 'warm'.
shorter answer: if the resistor is not in the signal path, than why even bother? Just take the metal films.

[asfastasdark]

Regarding the watts:
P=IV

So, if you're running the effect off a nine-volt battery:
1/8=9I

I=.0138 amps.

[petemoore]

I was just wondering, (didn't see it in the wiki or anything) Is there any sort of noticeable difference between using carbon or metal film resistors?
  Dare I say not in Fuzzes at least ? ok, maybe...any sort ? really depends on how much heat they generate, how much current is going through them, and...what are they actually doing in the circuit.
  ok maybe yes and it still depends on...buncha other stuff, where any 'noticable differences'd be actually noticable compared to say all the carbon types used to exactly replicate vintage gear or like, what I always use for getting resistances set up. Metal can be fun, expensive, I can't imagine just plunkin' on a buncha expensive metal because I didn't read where to look for any samll differences.
Also, I had ordered 1/8 watt resistors from ppp a while ago, but I noticed in the wiki it said that generally 1/4 or 1/2 are used in pedals...
Anything wrong with using the 1/8?
  That is in the DIY FAQ.
  1/2 vs 1/4 watt resistors which ones???
  For most if not all of our stompbox effects, 1/4 watt resistors are used. You can use 1/2 watt resistors but they take up more space and do not provide any benefits. Yes, you can mix and match 1/2 and 1/4 watt resistors in a circuit.    
  Let's see first how this gets filtered by some of the more knowledgable members before applying underwatted resistors to circuit boards...
  put two where one was and about double the heat dissipation.
  2x 2k parallel = 1k  [halves resistance
  2x  100k series = 200k [doubles it
  Let someone have time to chime in, I thought I'd throw that in there, also there are places in circuits where current draw is low and 1/8w resistors could do the work.

[kurtlives]

Regarding the watts:
P=IV

So, if you're running the effect off a nine-volt battery:
1/8=9I

I=.0138 amps.

What are you trying to say?

[asfastasdark]

That he can use 1/8W resistors for approximately 0.0138 amps or less. In his OP he asked, and I quote: "Anything wrong with using the 1/8?"

[kurtlives]

I think it would be more beneficial if he he was worried about the voltage drop across the resistor instead.

Its easier to find and easier to related to the power rating of a resistor.

[asfastasdark]

Argh!!! Even when I know for sure that I have it right, I'm wrong!  Congrats on your soon-to-be 1000th post by the way. Buy yourself a birthday cake  .

[kurtlives]

You were right....

I was just saying its a lot easier to measure the voltage drop across a resistor than measuring the current.

[R.G.]

I was just wondering, (didn't see it in the wiki or anything) Is there any sort of noticeable difference between using carbon or metal film resistors?

In a stomp box, no. You will see people claiming great advantages for carbon comp. This is done much like medicine shows used to sell snake oil. The fact is, carbon comp can have a slightly beneficial effect on tone in a highly specific circumstance in the high voltages of a tube amp. There's a whole article on this at GEO, http://www.geofex.com. If you're asking newbie questions, go read everything at GEOFEX. It's where most of the boutique pedal makers went to learn to make pedals, years ago. There are answers there for questions you haven't thought of yet, but will.  

Also, I had ordered 1/8 watt resistors from ppp a while ago, but I noticed in the wiki it said that generally 1/4 or 1/2 are used in pedals...
Anything wrong with using the 1/8?

Pedals are a low power environment. You're often safe with 1/8W, except perhaps as a limiting resistor for an LED.

As a newb, you simply must learn the following:

V = IR, and the algebraic corrolaries, R = V/I  and I = V/R. These are the three most common statements of Ohm's law, saying that the voltage across a resistor is always equal to the current through it times the resistance; perhaps more aptly, an "ohm" is one volt per ampere, or 1k ohm is one volt per milliampere. All statements of the same thing. You need to know this just as certainly and as unconsciously as you know where to put a spoon when you're eating your morning corn flakes.

Power is always P = I *V (power equals volts times current). For a resistor, that equates to P = I²*R  and P = V²/R. You need to know these as instinctively as you need to know Ohm's law.

Once you know that, you know all the answers to "Is it OK to use 1/8W resistors in pedals?".  In a pedal with 5V across a 1K resistor, the power is
P = 5*5/1000 = 0.025, or 25 milliwatts. 1/8 watt is 125 mW, so you have a 5X safety factor there. the same 5V across a 220R resistor is
P = 5*5/220 = 113.6mW, and the resistor will be quite hot to the touch, but will function OK. A 180R resistor would dissipate 139mW, and a 1/8W rated resistor would have a short lifetime under those conditions.

So - is 1/8W safe in pedals?
Yeah, mostly. But the details matter. No way to say yes or not without computing the power used.

[Evad Nomenclature]

Wow,
I went away all day and had a whole big thing to read when I got home!   
Thanks for all the input.  I'll do some more reading and experimenting.