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Resistors with same spec, but different size. Same?
Resistors with same spec, but different size. Same?
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Old 7th May 2017, 08:17 PM   #1
avanc is offline avanc
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Default Resistors with same spec, but different size. Same?

Didnt know where to put this, but I have ordered resistors from different vendors for my diy amp. I noticed that some resistors are about half the size of others, but they have the same values (R, W, %).

They are the same type. Axial. Film.

Are they interchangeable? Whatever fits?

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Old 7th May 2017, 08:34 PM   #2
scottjoplin is offline scottjoplin  Wales
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Yeah, should be, size variation usually indicates wattage, maybe sign of the times....... fake (new{s}) resistors haha
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Old 7th May 2017, 09:26 PM   #3
Dan Thomas is offline Dan Thomas  Canada
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Quote:
Originally Posted by avanc View Post
Didnt know where to put this, but I have ordered resistors from different vendors for my diy amp. I noticed that some resistors are about half the size of others, but they have the same values (R, W, %).

They are the same type. Axial. Film.

Are they interchangeable? Whatever fits?

Sent fra min EVA-L09 via Tapatalk
Quite likely the spec on the max voltage, voltage dependency and/or temperature coefficients differ.
For the most part they should be interchangeable though it can make a difference in some situations. In an audio amp the feedback resistor connecting the output to the input stage is critical and should be of high quality. (The voltage across the resistor causes it heat up changing the resistance.)

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Old 7th May 2017, 09:45 PM   #4
Conrad Hoffman is offline Conrad Hoffman  United States
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There are newer series of resistors that have high power ratings in smaller packages. They have to run hotter as a result. In many situations it won't matter, but I tend to stick with the tried and true, and then derate that. +1 on feedback networks. Whatever imperfections your feedback divider has, those will get impressed on the amp. Not only the series resistor, but the resistor (and cap, if present) to ground.
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Old 7th May 2017, 10:20 PM   #5
rayma is offline rayma  United States
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Originally Posted by Conrad Hoffman View Post
Whatever imperfections your feedback divider has, those will get impressed on the amp.
Not only the series resistor, but the resistor (and cap, if present) to ground.
As I think NP has mentioned, the NFB network is best made up of several identical series resistors,
each equal to the value of the R to ground. This gives the least thermally induced distortion, since all
behave the same and drop identical voltages. That is, if you use a 10k feedback, and a 1k to ground,
then the 10k should be made of ten series 1k resistors. All eleven resistors should be identical,
and all should have the same power rating. The unity gain capacitor is a real can of worms, though.
It's best to avoid that and use a servo instead.

Last edited by rayma; 7th May 2017 at 10:27 PM.
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Old 10th May 2017, 11:36 AM   #6
davidsrsb is offline davidsrsb  Malaysia
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Quote:
Originally Posted by avanc View Post
I noticed that some resistors are about half the size of others, but they have the same values (R, W, %).
Is that Wattage at the same ambient temperature?
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Old 10th May 2017, 03:20 PM   #7
avanc is offline avanc
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I ordered just by looking at the w, r, % specs. Don't know about the other parameters, but I guess they can't possibly measure the same in all situations.
What i'm wondering is if it matters. If so, are there any other spec than w, r, % that should be taken a look at?

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Old 10th May 2017, 05:01 PM   #8
myhrrhleine is offline myhrrhleine  Belize
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Quote:
Originally Posted by avanc View Post
I ordered just by looking at the w, r, % specs. Don't know about the other parameters, but I guess they can't possibly measure the same in all situations.
What i'm wondering is if it matters. If so, are there any other spec than w, r, % that should be taken a look at?

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It really is dependent on exactly how the resistor is used.
In some places it wont matter but in other places it can be critical.
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Old 10th May 2017, 05:07 PM   #9
avanc is offline avanc
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I see. Looks like I have overlooked the obvious; resistors too shape the output.
Well, the BOM of the amplifier just specify w, r, %. So I dont know which other values to compare or look for better qualities.

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Old 10th May 2017, 05:19 PM   #10
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by avanc View Post
If so, are there any other spec than w, r, % that should be taken a look at?
The temperature coefficient as has already been mentioned. If in doubt use the larger resistors
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