There is one "slight" problem with making "prevission" resistors out of carbon resistors: They drift all over the place, not only with temperature, but also with age, so after you trim them, after a short while they are off again. So no, it does not make sense at all. By the way they were trimmed already at the factory to pretty much the exact value. Any difference you see is just how they drifted over the time since manufacture, and they will continue to drift. So you won't get any real accuracy.
Thx for sharing. Not many know about this technique now they do. I used to work at a company and that is the exact method that we used to make precision valued resistors. However, it was found later on that they can fail. by not knowing exactly where the resistive element is you may be narrowing the conductor to the point that the resistor is compromised causing them to fail. So, what to do? If you accept this as a temporary stopgap measure then sure use this method, but replace the resistor with a 1% or better resistor. For DC applications make a resistor outta wire. Wind wire around some form of bobbin. I have seen this technique used in fluke instruments where a hyper precision DC applied resistor was needed. Again, thx for sharing. That's all I have.
Yes, one reason you might use this method is for when you want a value right now, especially a matched pair. The carbon composition resistors work much better with this method, as long as you can tolerate their shortcomings.
"Carbon" and "precision" are mutually exclusive. Just buy actual 1% resistors, they cost next to nothing in any case and will make your life that much easier.
If you're in the middle of a project and need a specific value then this method is one option to solve a problem. Once the project is proven, then order the parts as needed. I mention at 6:56 that the viewer should understand the shortcomings of carbon composition resistors, but they're the easiest to adjust.
The method I show here is just one more option among many. I mention the series/parallel option at 5:38 and if that gets you close enough then use that method. Filing a carbon resistor can be pretty quick. Use a trim pot if you have the space etc.
Glad to help fill that bag. I have a project coming up that will need two custom resistors in the op-amp gain loop. DIY resistors will be good enough to prove it works.
I think it should be fine. The resistor surface is rough from the grinding so I think it should provide good adhesion. I've used nail polish with success for decades inside of radios to hold trimmer capacitors and the slugs of adjustable RF transformers. These modified resistors are mainly for use in op-amp gain loops, DAC ladders and similar low power applications.
This is the first of your videos where I actually knew exactly what you were talking about most of the time. I'm usually playing catch up. Thanks!
There is one "slight" problem with making "prevission" resistors out of carbon resistors: They drift all over the place, not only with temperature, but also with age, so after you trim them, after a short while they are off again. So no, it does not make sense at all. By the way they were trimmed already at the factory to pretty much the exact value. Any difference you see is just how they drifted over the time since manufacture, and they will continue to drift. So you won't get any real accuracy.
Thx for the drifting insight. I knew how temp sensitive Carbon resistors are but not about aging.
Again thx for the insight.
Thx for sharing. Not many know about this technique now they do.
I used to work at a company and that is the exact method that we used to make precision valued resistors. However, it was found later on that they can fail. by not knowing exactly where the resistive element is you may be narrowing the conductor to the point that the resistor is compromised causing them to fail.
So, what to do? If you accept this as a temporary stopgap measure then sure use this method, but replace the resistor with a 1% or better resistor. For DC applications make a resistor outta wire. Wind wire around some form of bobbin. I have seen this technique used in fluke instruments where a hyper precision DC applied resistor was needed.
Again, thx for sharing.
That's all I have.
Yes, one reason you might use this method is for when you want a value right now, especially a matched pair. The carbon composition resistors work much better with this method, as long as you can tolerate their shortcomings.
"Carbon" and "precision" are mutually exclusive.
Just buy actual 1% resistors, they cost next to nothing in any case and will make your life that much easier.
If you're in the middle of a project and need a specific value then this method is one option to solve a problem. Once the project is proven, then order the parts as needed.
I mention at 6:56 that the viewer should understand the shortcomings of carbon composition resistors, but they're the easiest to adjust.
@@MoreThanElectronics whatever happened to series/parallel connecting values you *do* have on hand?
The method I show here is just one more option among many. I mention the series/parallel option at 5:38 and if that gets you close enough then use that method. Filing a carbon resistor can be pretty quick. Use a trim pot if you have the space etc.
Never done this before but I LOVE IT. Maybe I should go back to using thru hole parts places
Or you could put your surface mount resistors in to a laser engraver and make your own laser trimmed resistors. At least it sounds easy.....
A clever technique that I did not know. Thanks for adding to my bag of tricks!
Glad to help fill that bag. I have a project coming up that will need two custom resistors in the op-amp gain loop. DIY resistors will be good enough to prove it works.
You can get more precision carbon film resister by rotating it a bit when the values start jumping so you can shoot for the .1% tolerance.
And a much finer file than I had at hand.
Discovered your channel. Seems very interresting. You got a new sub.
Thanks for the comment.
how is the nail polish holding up with repeated heating/cooling over time ? wont stick too long on human nails. how is it on heating carbon traces?
I think it should be fine. The resistor surface is rough from the grinding so I think it should provide good adhesion. I've used nail polish with success for decades inside of radios to hold trimmer capacitors and the slugs of adjustable RF transformers. These modified resistors are mainly for use in op-amp gain loops, DAC ladders and similar low power applications.
I would use conformal coating vice nail polish.
same price I think.
Agreed. Conformal coating is preferred over nail polish if you have it.
Good tip. Thanks.
Thanks for the comment.