Resistors: 1% vs 5% ?

[GGBB]

Purely speculation, but I would think that 1% is a better choice - possibly audible - in circuits where sections need to be 'matched.' So the input and output stages of a chorus for example, phasers too I suppose. Of course, 1% doesn't automatically give you perfect matching, that would have to be done manually. And you can match 5% resistors if you have enough of a sample size. So 'matched' 1% has no advantage over 'matched' 5%, but if you don't want to bother matching manually, you might achieve better results on average in that circuit with 1%. Otherwise, as already stated, in most pedals circuits it won't matter.

[anotherjim]

Don't write off low value resistors.

Dealing with hum loop issues, a 4R7 in series with a 0v feed can be enough to stop the noise going in the signal return path (it takes the path of least resistance) without significantly reducing supply voltage. or signal level.

RC inductive drive compensation networks (as on output of most power amps) known as Zobel networks, frequently require 10R or lower.

A 1R or 10R in series with a  supply feed makes a handy current test point - read the volts (it'll be millivolts) across it. I=V/R. With 1R, it's a direct read of mV as mA. Much easier than swapping the meter leads to current reading and clipping it in series with the feed. Besides, you probably already blew the little fuse in the meter current jack anyway
Don't forget to check power rating W=I*R. A 1R with 1A through it will have 1W in it.

Low wattage low value R can be sacrificial fuses. I blew a midi input once (power plug using same 5pin DIN!) and found a little smd 100R burnt out. Did it's job and protected the opto-couple LED.

[duck_arse]

a question - what's the tolerance on 0R resistors?

an answer - say a company was making memory boards pack in the 72 pin days. there were many different computers with many different specs for memory, but only "a few" memory chip types. so, design THOUSANDS of different PCB's, one to suit each PC, or design one or two PCB's, and use links to select the end porpoise?

so now you have your three PCB's, in the pick and place machine, and you want XYZ memories coming out the end. how well do you think the pick and place machine is going to go having to pick up wire links, how good is its aim at sticking them through the holes? here's an idea; make a resistor shaped link, the machine won't know the difference, the board-rework section will have no trouble correcting/modding, and we'll all get filthy rich from the increased throughput.

and, imagine if you were assembling computer motherboards with all their options, and could just use smd links to configure them .....

[PRR]

>> I actually have some 0-ohm resistors too (seriously, it's a thing).  How much current can you safely pass through a 1/4-watt 0-ohm resistor?
> If it's actual 0 ohms, there's no voltage drop, no power dissipated

Correct in theory.

Wrong in a real world.

Obviously it has leads (this "1/4W" type). If they are not infinitely fat, they will melt. I was cranking a cold Diesel just now, warming half-inch battry cables. I'm sure I coulda melted any puny "1/4W size" part.

Read The Fine Datasheet!!
Metal Film Resistors, Zero Ohm Jumper, Industrial
http://www.vishay.com/docs/31016/frj.pdf

"Zero Ohms" is really 10 milli-Ohms max (0.010r).

AND they tell you the maximum current! 25 Amps at 25 deg C, zero Amps at 150 deg C.

To my eye, 25A in a 0.020" lead is dubious. For longer wires in cable, NEC wants a 0.081" (#12) wire, 16 times the area! As the short lead cools better, and no plastic jacket to melt, I'm sure the "25A" rating is correct in some sense. However a "DSCC" spec gives 5A for a part like this. At 5A I would not worry, at 25A I would really look at the job and see if I were making trouble.
______________

> They are useless

Every electronics factory has a robot to insert resistors. A "zero ohm" is same-as a resistor as far as the robot needs to know.

Yes, in hand assembly it is about as easy to handle scraps of bare wire. Apparently robots don't do that well. Or, since they do do resistors, it was expedient to make "resistors" with zero Ohms so the robot didn't need an add-on.

[ashcat_lt]

If you're pulling 5A in a (solid state) pedal, you've got much bigger problems. 

[greaser_au]

why do 0 ohm resistors even exist?

these are basically jumper wires, but in standard resistor package to make board design and automated population easier.

I still do not see the point in using those. They are useless

In present day smd circuit design where size is critical, a zero ohm resistor is a jumper over a very small trace where a through hole jumper just won't fit or work. Think about multi layer boards. They are anywhere between 2 and probably a dozen layers possible in multilayer pcbs. Through hole components aren't always possible in these layouts. We used 0ohm resistors a lot when I was at Harman. They can be used in our pedals too. handmade jumpers are just easier and more cost effective. 0 ohm through hole resistors might be easier for radial/axial machines to dispense onto boards too.

Zero-ohm resistors are an excellent solution to a mass manufacturing problem for a number of reasons (you probably wouldn't use them in a one-off DIY project, but as I still do a little service work I keep some in the box!) 

Another factory anecdote: where there is an exposed top layer, especially where there is no solder mask* some method is required to ensure a link does not short to tracks underneath. During building boards like these in the factory, we used to have to slip an appropriately-sized bit of sleeving over the jumper wire, or, if specified, use some sort of standoff support.  Zero-ohm resistors would have been a godsend, as they have a similar voltage rating to the family of resistors they are part of... 

* note that while adding an insulating solder mask (or using 0Rs) in manufacture would have been a great idea, older 'approved' designs would likey not allow for changes like this as it would have made them non-compliant with the documentation (making changes to the doco in many environments would cost far more than the manual labour required - this is especially true with things like government contracts)...

david

[antonis]

Besides, you probably already blew the little fuse in the meter current jack anyway

True and Correct...!!! 

Personally, I use 1% 400mW metal film resistors if there is a need for "tight" PCB population - they can be used in horizontal position mounting in two adjacent rows (or pads).
(even the 600mW are slightly smaller than the 250mW carbon resistors..)

[GibsonGM]

If you're pulling 5A in a (solid state) pedal, you've got much bigger problems. 

If you're pulling 5A in (ANY) pedal, you have VERY, VERY much bigger problems, ha ha ha!!! 

100W head in a box, LOL....