# lost with different values for resistors you can substitute for others

Discussion in 'General Electronics Chat' started by phantom trigger, Aug 14, 2013.

1. ### phantom trigger Thread Starter New Member

Aug 14, 2013
2
0
I'm trying to do a bulk order off the jaycar website, but some resistors aren't on the website. I know there are sometimes different values for resistors you can substitute for others, if you don't have the exact value the schematic specifies.
in particular, my fuzz pedal needs:
Resistor 1/4 Watt 5% 1M
Resistor 1/4 Watt 5% 200K

I reckon they must have an equivalent or sibstitute for these on their website, but not sure how it works exactly! Any help on this would be greatly appreciated...thanks

2. ### #12 Expert

Nov 30, 2010
16,679
7,322
Two 100k resistors in series will make 200k.
A 1.8 meg in parallel with a 3.3 meg will make 1.16 meg.
I guess you don't have the formulas. Two resistors in series just add. Two (or more) resistors in parallel will add like this:
1/R1 + 1/R2 +1/R3 = 1/Rtotal
If you aren't using 3 resistors, just don't write the third one into the formula.

3. ### vk6zgo Active Member

Jul 21, 2012
677
85
You will probably get away with 820k or 1.2M for the first case,and
180k or 220k for the second.

In many cases,(not always),you can go up or down one standard value,before you have to start messing around with series & parallel combinations.
In modern usage there is another level of standard values between the historical "preferred values",so you may be able to get even closer.

4. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
It depends on the circuit and how the resistors are being used. Some circuits can work with a resistor three times as big or one-third the size. Others are not gonna like it if you vary them much at all. And many circuits have some resistors that can be loose and others that need to be tight, so it is hard to say.

The fact that these are 5% resistors means that getting the value exactly right isn't that important. In fact, today these are pretty much the sloppiest resistors you can buy (used to be that 20% resistors were the norm). You can probably go 10% and maybe even 20% and not notice a difference.

The fact that these are 1/4 W resistors probably means that they aren't dissipating much power at all. Depending on how old the unit is, it wasn't that long ago that 1/4 W resistors were the norm and that's what you bought if you didn't need anything beefier. Now, for through hole, it's 1/8W. But my guess is that the design for you unit is old enough that it just used 1/4 W. So, if at all possible, get resistors that are 1/4 W or more, but if you HAVE to put in 1/8W, my GUESS is that you are PROBABLY okay (and there is no warranty, expressed or implied, in that guess!).

There are also different types of resistors -- carbon film, carbon composition, metal film, wirewound, etc -- and each has applications that it is good for (if for no other reason than being cheap) and applications that it is bad for (if for no other reason than being expensive). I'm guessing that it is unlikely that this is an issue in your unit, so don't stress over this point.

Nov 9, 2007
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515
6. ### WBahn Moderator

Mar 31, 2012
18,087
4,917

Apr 30, 2011
1,426
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200k & 1M are standard values and ¼W is the most common size so I'd consider another supplier.

8. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
I visited their website and I pity anyone having to deal with it to find something.

1M is certainly a standard value, but 200k is only a standard value for the E24 series (5%) and up and I've run across a number of places that only stock E12 values (10%) even though, of course, they are all now 5% or better. This is also very common in resistor kits.

9. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
Thank you WBahn, but I did link to the correct page, which includes post#1 and several subsequent posts about substituting resistors. sgt Wookie did post a good resistor table on the page you linked to.

(Modestly) I did start the thread after all.

10. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
I'm confused (but that's not new and it's somewhat irrelevant at this point). Are you saying that you meant to link to page 5? Your link goes to page 5 and has the screenshot of SgtWookie's calculator program. The page you linked starts with post #41 (at least with the default options of 10 posts per page) and does NOT have the first several posts in the thread on it. I linked to page #1, which does. All I did was copy your link and change the page number from 5 to 1.

11. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
I think we are both referring to the same thread which is the

I started a few years ago.

It is thread number 6 permanently pinned to the top of this general electronics chat forum.

I kicked off with a variation of the parallel resistor formula to achieve non standard resistor values.
Various other contributors added other ideas.

I have my AAC set to show the latest posts first when linking to a thread. Maybe this has caused the difference.

12. ### WBahn Moderator

Mar 31, 2012
18,087
4,917
That may be. So when you follow your link, is Post #1 at the very bottom of the page?

I guess it's a bit disconcerting that you don't get the same content when given the same link as someone else. But I guess that's all-but-inevitable if you are going to give users very much in the way of being able to custome their settings.

That's good to know. Because it means that I need to be more careful when I include links to threads. Although I think I am okay out of sheer luck because I usually either link to the thread only (no page number) or link to the specific post. But I have assumed that people always see the first post in the thread at the top of the page when I link to a thread. Need to be sure I don't make that assumption in the future.