Author Topic: Noobing hard... resistor power ratings - does it matter?  (Read 3574 times)

antosaurus

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Noobing hard... resistor power ratings - does it matter?
« on: July 27, 2017, 01:08:34 AM »
Ello,

I've just started getting into pedal building - like I've built one - the 10min Boost/Dirt from DIYGuitarPedals.com.au - now I'm hooked.

I'm looking at making the Mudbunny and just had a question re resistor power ratings. Does it matter?

I note that some pedal parts stores seem to stock .25w resistors, but my local parts store only stocks .5w in the values I need- does it matter for the use in pedals?

Cheers team.

Ant



somnif

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Re: Noobing hard... resistor power ratings - does it matter?
« Reply #1 on: July 27, 2017, 01:22:22 AM »
The difference for 99% of pedal purposes will be of size. Half watt resistors are bigger than quarter watt, and will be awkward to fit onto layouts. There are 1/8W resistors as well that will often see use on 1590A sized layouts, or extremely tight builds.

The one exceptions where wattage might actually matter is if you have a current limiter on the 9V supply. Madbean used to, ages ago, have a 10 ohm resistor between the power jack and the circuit on many of his boards. On a few, high current drain circuits a 1/4W resistor wouldn't handle this and would fry itself (This feature was removed from most of his modern builds). You will also see higher wattage resistors used in things like amplifiers, where the power flying around is a lot higher than in a tiny effect circuit.

So short version: Yes, half watt resistors will work, but are big fat things that will crowd each other on the board. While in town electronic stores are awesome I love my local) they cannot come close to matching online suppliers. Checkout Tayda (http://www.taydaelectronics.com/) for dirt cheap components (resistors are 1 cent each) or Small Bear (http://smallbear-electronics.mybigcommerce.com/) or Mouser (http://www.mouser.com/) for higher end components.
« Last Edit: July 27, 2017, 03:08:43 AM by somnif »

somnif

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Re: Noobing hard... resistor power ratings - does it matter?
« Reply #2 on: July 27, 2017, 01:30:28 AM »


Found a picture comparing them. 1/8W on the far right, then 1/4W, 1/2W, 1W, etc going right to left.

antosaurus

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Re: Noobing hard... resistor power ratings - does it matter?
« Reply #3 on: July 27, 2017, 02:54:37 AM »
Legends. Thanks heaps everyone!

Sent from my SM-G900I using Tapatalk


gtr2

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Re: Noobing hard... resistor power ratings - does it matter?
« Reply #4 on: July 27, 2017, 06:49:37 AM »
ohms law is your friend for choosing but for "most" guitar effects the standard is 1/4watt

Josh
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oip

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Re: Noobing hard... resistor power ratings - does it matter?
« Reply #5 on: July 27, 2017, 06:17:41 PM »
was reading up on this last night... due to accidentally ordering 5 builds' worth of 1/8 watt instead of 1/4 watt resistors in the last tayda order.  i'm sure they would all be fine to use but decided calculating safety for each one was too much brainwork compared to the $5 to go buy replacements from the local electronics place.

on topic, as others have said tayda is amazing for passive components and hardware.  if you're in australia the shipping is stupid fast, got last order in 2 days.  can heartily recommend.

kgull

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Re: Noobing hard... resistor power ratings - does it matter?
« Reply #6 on: July 28, 2017, 03:20:38 PM »
was reading up on this last night... due to accidentally ordering 5 builds' worth of 1/8 watt instead of 1/4 watt resistors in the last tayda order.  i'm sure they would all be fine to use but decided calculating safety for each one was too much brainwork compared to the $5 to go buy replacements from the local electronics place.

on topic, as others have said tayda is amazing for passive components and hardware.  if you're in australia the shipping is stupid fast, got last order in 2 days.  can heartily recommend.
Ohm's Law for this is:

Minimum Resistance = Max Voltage^2 / Wattage Rating

So for a 9V circuit, you are good with 1/8W resistors down to 648ohms (9^2/0.125). Anything below that, you want to use a higher wattage resistor.
« Last Edit: July 28, 2017, 03:22:55 PM by kgull »

davent

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"If you always do what you always did- you always get what you always got." - Unknown

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oip

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Re: Noobing hard... resistor power ratings - does it matter?
« Reply #8 on: July 28, 2017, 09:07:59 PM »
Ohm's Law for this is:

Minimum Resistance = Max Voltage^2 / Wattage Rating

So for a 9V circuit, you are good with 1/8W resistors down to 648ohms (9^2/0.125). Anything below that, you want to use a higher wattage resistor.

thanks - makes sense, i ended up just buying a batch of 1/2W anyway as they are cheap locally and still small sized.  but i still have a lot of the 1/8W left so will use them at some point.