Confused About Which Resistors I Need

[dreadlocks1221]

Not only are there Metal film and Carbon film, but there are 1/4W, 1/2 W, 1W, and even 5W! I'm building my first pedal, a simple boost, and the schematic only denotes the OHM rating. I don't want to just know which one to buy for this schematic but why one would buy one type at a certain wattage over another at a different etc etc.

Thanks for every one's help!

[rutabaga bob]

Congrats on the first build!  Be warned: it's addicting!  As to the resistors, 1/4 watt carbon film is fine for these boxes.  You can use metal film ones, but they are more expensive.  I have found that anthing special is (usually) called out on the schematic.  1/2 watt and above are found in amplifiers, generally 1/2 watt for most uses, and larger ratings for power supply resistors.   Cheers!  Larry S.

[Pollinator95]

I'd recommend metal resistors because they tend to have 1% tolerance, and there's not that much cost difference (in fact, they cost the same in Tayda). I might be missing something, though.

[dreadlocks1221]

Thanks for all the info! What does the tolerance mean?

[slacker]

Tolerance is how close the actual value of the resistor will be to it's quoted value.
So a 1% 10K Ohm resistor will be within 1% of 10K, so somewhere between 9.9K Ohms and 10.1K Ohms
5% would be somewhere between 9.5K and 10.5K etc

For what we do 5% is fine.

[petey twofinger]

you can check the " tolerance " by using your multimeter :

http://www.youtube.com/watch?v=AwUhuJZvdfM

i find that they are usually all very close to the same number , in a batch , and yes , you dont need the metal ones . in somecase , like for biasing it may be good to have a slightly off value to nail the sweet spot , but ....

[LucifersTrip]

as long as they are reasonably close to the value on the schematic and as long as they will fit on your board, it really doesn't matter....

I think most non-mojo-part-builders consider the cost and the physical size first

[PRR]

Resistors are not sexy.

Yet they are the most common part (you use more resistors than anything else).

The basic rule is to use the cheapest resistors you can find.

Back in the 1960s, when most pedals originated, this was 1/2W 10% carbon composition. Carbon-comp is coal-dust and clay. It is a sloppy process. If you try to make "10K", you get everything from 2K to 50K. So the makers tested and sorted. First to 20%, where "10K" could be 8K to 12K. That's plenty close-enough for radio and such. Later 10% became cheap, and that's what most pedals use.

Miniaturization was a fad, so 1/4W and 1/8W resistors became common.

Carbon-Film used to be exotic, expensive, only for microwave work. But when simplified and expanded, carbon-film became cheaper than carbon-comp. No more coal/clay, they heat little rods very hot in a vacuum furnace and inject a little propane (even street-gas). The hydrocarbon gas breaks down, hydrogen blows off, carbon deposits on the rods. Control is so good that 5% is eazy and 2% isn't expensive.

If there's any need for better than 5% tolerance, the plan should say so. Many-many circuits will be fine with 20% tolerance.

Some golden-ears "must" use exotic metals and plastics and oils in their parts, or conversely very old technology, especially jaded hi-fi fanatics who never hear live music. But basic resistors are very excellent, and *entirely* suitable for most audio, especially getting-started. The cheapest resistors you get today are much better than ever before.

HOWEVER: for the specific purpose of StompBoxes, I strongly suggest you start with one of the StompBox parts specialists. DIYstompboxes (our host), Small Bear, etc. They know what you want. They specialize in small quantities. If OTOH you go to Mouser or DigiKey (or eBay!!) you get WAY too many choices of parts which are NOT what you want, but as a beginner you don't know how to narrow it down.

> and even 5W!

10W 20W and 50W are standard items. 225W too. Larger sizes can be multiples, or custom-made out to 10,000W or more. Older electric trains all had 70,000 watt resistors on their roofs. But the total power in most pedals is under 1/4W, spread out over several parts, so 1/4W or 1/8W parts are plenty big enough.

[Mark Hammer]

To add to Paul's already sensible and informative post, people tend to forget how many build errors stem from the builder misreading the color coding on resistors.  Case in point.  I was making something the other night and was certain I didn't have any more 27k resistors (red-purple-orange), but did have these 20k ones in the drawer (red-black-orange).  Don't know what would have possessed me to buy a bunch of 20k when I knew how many circuits used 27k.  Just for the hell of it, I measured the 20k units.  They were actually 27k; the purple band was dark enough that it looked black in the lighting I was using.

These were 1/4w units, so clearly larger size won't completely prevent such errors.  But the nice thing about 1/4w resistors is that they are more easily and accurately recognized/read than 1/8w units.  So, even IF the circuit doesn't really require anything more than 1/8w, do yourself a favour and make it a habit to get 1/4w so you can read them reliably and avoid at least one source of beginner's project failure; particularly since it will be a while yet until you have separate drawers for each resistor value and will likely be sifting through drawers/bags makred "Less than 50k" and "50k to 500k", or something like that.

1/4w units take up a little more room on the board, but if you are cramped for space, they can be easily mounted vertically.

[Perrow]

To counter Marks statement, do your self a favor and buy a pack of plastic CD sleeves, use a good (permanent) marker and label them for resistor values, I still have them sorted based on just the two first digits (10, 12, 15, 18, ...), but I'll make the transition to individual values soon. It'll make it that much easier to see what I have/don't have.

You can use this system for capacities too until you start buying bulk volumes.

[Mark Hammer]

Good idea.

[dreadlocks1221]

Thanks for all the tips, I've already made the first beginner mistake: I bought some 390K 1/4W resistors when I only needed 390 (read the schematic wrong). I like the CD sleeve idea, I know with computer parts you need to keep things in an anti-static bag do I need to worry about that with these components?

I bought my components from taydaelectronics.com, as recommended in my previous post. The difference in price for the carbon film vs metal film resistors was  $0.002 per resistor, I guess maybe if you're buying them by the 1000s the price makes a difference? Does it matter where the components are made/shipped from? I noticed these are coming from Thailand and I'm wondering if buying from different websites/countries would make a significant difference? When it comes to purchasing things I'm really more about the quality to price ratio rather than whats the cheapest.

[Perrow]

Thanks for all the tips, I've already made the first beginner mistake: I bought some 390K 1/4W resistors when I only needed 390 (read the schematic wrong). I like the CD sleeve idea, I know with computer parts you need to keep things in an anti-static bag do I need to worry about that with these components?

I bought my components from taydaelectronics.com, as recommended in my previous post. The difference in price for the carbon film vs metal film resistors was  $0.002 per resistor, I guess maybe if you're buying them by the 1000s the price makes a difference? Does it matter where the components are made/shipped from? I noticed these are coming from Thailand and I'm wondering if buying from different websites/countries would make a significant difference? When it comes to purchasing things I'm really more about the quality to price ratio rather than whats the cheapest.

Antistatic? No, resistors and capacitors shouldn't really matter, though capacitors could theoretically get hurt by static.

Tayda balances the cost/quality quite well. It was a while since I last bought toggle switches from them, and they were a bit on the cheap side. Other than that I've only had good experiences with Tayda.

[rutabaga bob]

I store mine in what are termed 'coin envelopes', approx. 3" x 5".  Since I have neither paypal nor credit cards, I can't buy from Tayda.  At the semi-local store where I shop, metal film resistors are quite a bit more than the carbon film.  Larry

[Mark Hammer]

It's a small pet peeve, and maybe only unique to me, but I HATE the sticky crap on the leads of resistors (and caps where applicable) when you take them out of the paper that holds them in rolls.  I understand why it has to be there, but that doesn't make me like it any more.

[LucifersTrip]

Thanks for all the tips, I've already made the first beginner mistake

I still think the best advice is to measure each component one final time with a meter before you solder to the board

Does it matter where the components are made/shipped from? I noticed these are coming from Thailand and I'm wondering if buying from different websites/countries would make a significant difference?

I doubt it...the only difference will be price. for our purposes, if you use a component close enough to what is called for, that's cool enough.  Btw...don't know what country (I'm US) you're in, but Tayda ships all my orders from the US now. I get em in 7-10 days

[snap]

It's a small pet peeve, and maybe only unique to me, but I HATE the sticky crap on the leads of resistors (and caps where applicable) when you take them out of the paper that holds them in rolls.  I understand why it has to be there, but that doesn't make me like it any more.

Just cut them off right next to the paper rails. The leads of resistors at least will still be long enough in most cases. No more sticky fingers!

[amptramp]

Thanks for all the tips, I've already made the first beginner mistake

I still think the best advice is to measure each component one final time with a meter before you solder to the board

+1

Some manufacturers have a funny idea what red is.  Some of the red bands look orange.  Not too bad in the second significant digit but not good in the multiplier band.

[defaced]

And when you measure them, measure them properly.  Don't hole the probes and resistors with your fingers, because you are a resistor and are now in parallel with the resistor you're trying to measure which can effect the readings.

I use these to avoid this and other (consistency mainly) problems.  They push on over your pointed DMM leads.  http://www.radioshack.com/product/index.jsp?productId=2062221&znt_campaign=Category_CMS&znt_source=CAT&znt_medium=RSCOM&znt_content=CT2032235

[Mark Hammer]

It's a small pet peeve, and maybe only unique to me, but I HATE the sticky crap on the leads of resistors (and caps where applicable) when you take them out of the paper that holds them in rolls.  I understand why it has to be there, but that doesn't make me like it any more.

Just cut them off right next to the paper rails. The leads of resistors at least will still be long enough in most cases. No more sticky fingers!

If I were only installing them on PCBs or veroboard, that would be one thing, and certainly a good idea.  But I often use perfboard, and frequently make use of every bit of the lead to interconnect components.  It's having to remove the adhesive from that last 3/8" that drives me batty.