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BOM question on resistors specs
Posted: Jun 17th, '21, 23:25
by tumes
Hey all. Excited to start my build!
I noticed the Mouser cart contains a bunch of varying resistor wattage requirements, but that's not really discussed in the actual BOM or docs as far as I can tell (please let me know if I missed it though!). Is there any reason I can't just do 1/4 watt 1% across the board? Kind of hard to tell if the mouser cart choices were for a particular reason or if that's just what was in stock/economical at the time of its creation.
Re: BOM question on resistors specs
Posted: Jul 28th, '21, 13:22
by metro_electro
Hi!
I can't weigh in on what the schematic and design demands but I went with 1/4W all the way around. I've built everything but the Ride/Crash and it seems to be holding up just fine. I think it's a stock-related decision but if you want to be 100% sure, check what the original TR-909 service manual and parts list shows. that would tell you if 1/2W is necessary by design.
Re: BOM question on resistors specs
Posted: Jul 29th, '21, 11:13
by gihaume
You're probably very much more interested in size than wattage. For more "fidelity" choose carbon resistors, but of course metal ones work fine too.
Re: BOM question on resistors specs
Posted: Jul 29th, '21, 15:52
by metro_electro
gihaume wrote:You're probably very much more interested in size than wattage. For more "fidelity" choose carbon resistors, but of course metal ones work fine too.
He's specifically asking about wattage.
If you look at the BOM these parts relate to the 5K/20K/40K/80K/160K values needed for the HH/Ride/Crash. It looks like that decision in the BOM is based on the accuracy of the resistor. Those more expensive 1/2W resistors have a .1% variant so no, in this instance you may not be looking for color. You're looking for more accurate resistor values to create the array. I note that some show 1/6W and 1/10W so higher wattage isn't necessarily what's driving the BOM item.
These are all available in 1/4W so it's just matter of adjusting the BOM or choosing another source. I note that the PCB is snug in these sections so an array of 1/2W resistors would be pretty tight. You may have to stuff them vertically.
As I mentioned though, I stuck with 1/4W 1% metal film all around. The build sounds fantastic (mine includes the Extra9 mod too).