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Manual DIY Resistor Trimming

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dsp_

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diy resistor

I used this a few times, with success 8)
A Resistor could by trimmed to almost every required value simply by reducing the cross-sectional area through filing out a bit of the resistor.
After that the resistor gets sealed with nail polish.

Pro:
realization of non-standard values possible

Contra:
Power Handling get lower since the current density gets higher
Noise gets higher :?: (assumption)

Neutra:
Resistor value gets higher :roll:

Detailed Instructions:
http://www.physicsenterprises.andrews.edu/diy_archive/references/res_trim.html

:?: Is there anyone who uses this method?
Are there "better" methodes? (for example: parallel/series combination)

BTW: I think the "hobby electronics circuits" section should be widened to "hobby electronics"

HTH
dsp_
 

flatulent

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diy resistors

It all depends upon the construction of the resistor. Bulk carbon ones can be easily trimmed down by this method but they then absorb moisture from the air (beause you filed away the outer protective covering) and drift in value. You are much better off starting with a larger value and paralleling it with another.
The 1/x function on a pocket calculator is very handy for calculating the second resistor because conductances in parallel add. The stack on RPN calcuators are even handier in storing the values during the calculations.

1. Calculate the conductance of the total you want from 1/R
2. Measure the resistance you have and calculate the conductance 1/r
3. Calculate 1/R minus 1/r to get the conductance of the paralleling resistor and 1/x the value to get the resistance.
 

dsp_

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build active resistor

i meant all excepte the parallel/series combination =)
pls look @ the link i just wrote an excerpt.

by this method but they then absorb moisture from the air
thats y they r coated with nail polish.

3. Calculate 1/R minus 1/r to get the conductance of the paralleling resistor and 1/x the value to get the resistance.
the problem with the paralelling method is that this x is non standard most of time :cry:

but with this brute force calc its not that bad ;)
kewl thingy
http://www.hippy.freeserve.co.uk/e12calc.htm


HTH
dsp_
 

E-design

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resistor diy

I downloaded a very handy program for my HP49 calc that will give you all the possible values and the tolerance from the required value. The explanation is in French but the program is easy to understand.
 

flatulent

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lower resistor trimming

The real problem is temperature coefficients. Unless you use 1% resistors, the temperature effects will make your resistors be over 1% off anyway. If you use the method I described you will usually get within 1% with the combination even if the second resistor is rounded off to the next standard value. The cracks induced by mechanical stress will propigate with temperature cycling and raise the resistance of your tuned resistor.
 

GrandAlf

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resistor trimming

Has anyone condidered that most resistors these days are carbon or metal film. These are coated onto a ceramic substrate, and the spiral cut by automatic machinery to get thr final value. Very difficult to alter I would have thought.

I suggest sticking to parallel/serial combinations, or use a pot.

Anyway always better to design using standard comps, if at all possible.
 

abc123

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detailed diy turntable manual

dsp_ said:
I used this a few times, with success 8)
A Resistor could by trimmed to almost every required value simply by reducing the cross-sectional area through filing out a bit of the resistor.
After that the resistor gets sealed with nail polish.

:?: Is there anyone who uses this method?
Are there "better" methodes? (for example: parallel/series combination)

dsp_
It has been used a lot for RF circuit in the old days, (on the carbon composit resistors) it is not good to use parallel resistors since the capcitance and inductance will be a problem.

Laser trimming is used today for chip resistors.

abc123-
 

S

sick_man

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diy power resistor

the best resistor is made from carbon and these are easy to trim

the kind of tube resistors used for tv.s

but these also drift

best to use an active resisistor if your going to go to the hastle of tunining a resistor you may as well build a small r2r pll
 

dsp_

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manual computation of resistor value

hey gandalf these mehod is thaught for carbon /metal film resistors -- =)
these is just thought as an alternative to the parallel series combinatiopn method
since i knwo this calculator posted in the 2nd post which doess all work for me i'll think about this method twice *g*

but i still think filing for fine tuning isstill a good hobby alternative =)

dont take this post to serios cause im too serios :drinking:
ey sleep well sim

----------
i fly so high............. then fall so low

one of these mornings
wont be very long
you'll look for me
and i'll be gone :((
 

Jayson

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diy parallel resistors lower inductance

How do you make an active resistor? Does it work like a normal resistor? Do you control its power rating somehow?

- Jayson
 

jinny

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diy measure resistor

This method wouldn't guaranty stability of resistance. Some time ago
I was working with 1/3 octave audio equalizer. And as soon as we
couldn't get 1% resistors in time, we tried this kind of adjustment
for prototyping. At the time of measurements we found out that
the frequency response was changing from time to time. As soon as
we changed resistors – this effect gone away.
If you need 1% tol. Resistors and you are not able to get them, the
Better way is to use good multimeter to try to choose from 5% or
10% val. Or you can use parallel or successive connection of 2
resistors. Stability of 5% or 10% resistors is worse than of 1%
but much better, than in the way, you’ve asking about.
 

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