Sorry if this is an overly generic question but I built a dual version of the adsr module and the 10r resistor next to the power header (I didn’t have ferrite beads) occasionally burns out randomly. I just assumed after trying to fix this that I had built something wrong. I then built a mixer (not lmnc) but used the same 10r resistor arrangement for the power. This also burned out randomly.
Being the cowboy that I am I just replaced the resistor with a resistor leg and now it works.
My question is:
Is there a reason other than a short or Rev polarity that would cause this to burn out?
Also whats the ohms law logic here. If its 12v and 10r then that give 1.2a. Is that relevant? Would be good to understand that.
Also whats the ohms law logic here. If its 12v and 10r then that give 1.2a. Is that relevant?
That’s if you short the supply to ground through a 10 ohm resistor without anything else in the way, which you’re not supposed to do If everything works as expected, you want 12 V on one side of the resistor and close to 12 V on the other side, with the voltage drop determined by the amount of current that goes through the resistor.
E.g. if your module uses 20 mA, the drop over a 10 ohm resistor will be 20 mA × 10 ohm = 0.2 V which corresponds to 4 mW.
(the max current for a 1/4 W resistor would be sqrt(0.25/10) = 158 mA so if you keep frying your resistors your modules use a lot more current than they should)
You can try measuring the voltage across the resistor to get an idea of what’s going on here.
(Or you can measure the current to the module with your multimeter, but be careful so you don’t blow the multimeter fuses instead; they’re more expensive than resistors.)
Related: beads are probably pointless, 10R series resistors may be, see here for an overview of different supply filtering approaches:
(I was about to say that they weren’t pointless in your case, but on the other hand you did replace them with a wire when they burned out, so the net effect is the same )
This info is very helpful. I’m going to run more tests on the adsr as I did have it in a state where it worked but if I turned the sustain to 0 then the resister started to smoke. I turned it back and it stopped.
Maybe if I do more fiddling I can find the exact situation that it does it
Not necessarily if you don’t count in the resistor itself. If the resistor is of a low wattage, then it will heat up and cool down and it will wear / age quickly because of this. You might not notice that since the modules seem to do their work. Eventually the resistor may break at an unexpected moment.
This is similar to an old fashioned non automatic circuit breaker. Those used to contain a silver wire. When a current got too high they would melt. With allowable high currents or short peak currents (e.g. at startup of a major appliance) however this could heat up but not melt, but some of the material could evaporate ( I’m talking years of usage here ). Until that final day when the material is too thin to withstand the ‘standard’ current and it would break.
That’s definitely not normal. Agree with @fredrik, measure the voltage across the resistor. Maybe not while it’s smoking but close to that state? If it’s much more than a few tenths of a volt that indicates a problem in the circuit. Otherwise… are all these 10Rs from the same batch? I guess I could just barely imagine a bad batch of resistors.
Agree with above post, and fredrik. If youre referring to the 1157 adsr, just make sure that if you subbed an op amp that your impedance isnt off, and check your current draw. Especially try and monitor what it is thats specifically burning out the res, i.e., turning one or more of the pots all the way CW or CCW, or incoming signal. If you made it yourself on strip board, double chck that something isnt causing a short. I had the same prob on one of my homebrew modules, and i also had same issue w bartons arp module before he fixed it. In my experience my 10rs smoked because of a short or reversed polarity. Keep us posted, id like to know the poss culprit.
Ok so for anyone who cares I think I may have found what my issue was. I spent ages checking my stripboard layout etc and cleaning up my soldering but was still occasionally burning out. I noticed that one of the pots felt a bit “scapey” so I started twisting the hell out of it and it burnt out again. I replaced it and noticed that there was a bit of metal loose inside. So hopefully it was just that shorting occasionally when fiddling with the knob. Im still half expecting it to explode but its ok so far.
If everything works as expected, you want 12 V on one side of the resistor and close to 12 V on the other side, with the voltage drop determined by the amount of current that goes through the resistor.
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