How to connect resistors in parallel?

headrott

I need som ehelp in how to physically connect 2 resistors in parallel. I need a 1.3 ohm resistor replacement. Mills does not make a 1.3 ohm, so Jeff at Sonic Craft suggested I parallel a 2.5 ohm and a 2.7 ohm. I understand the math fine how that equals 1.3 ohms. 1/R=1/R1 + 1/R2. So, 1/R= 1/2.5 + 1/2.7

You take the inverse of each value which gives: .4000 + .3704= .7704
Then you take the inverse of that to get: 1/.7704= 1.298 or basically 1.3 ohms. Fine...... What I need help with is how you solder the 2 resistors to the circuit board. I have never ran 2 resisters in parallel (or series for that matter). If someone could post pictures of 2 resistors paralleled and soldered to the circuit board I'd appreciate it. Do both ends of the resistors have to be soldered together and then one set of the leads soldered to the 2 holes in the board? Thanks for your help.

kcoc321

Sorry IDK how exactly to do that. I remember it is different way between Caps and resors.
Madisound has the Mundorf 1.5's....someone more expert can chime if that was ok..
since they are +/- 10% that's 1.35...see I can do math too...hehe

http://www.madisound.com/catalog/product_info.php?cPath=356_86_415&products_id=8412
Update: I just looked and SC has the 1.5's too... so maybe if you must/want the values closer, he can test a couple and find some that are even closer..

Jed Leland

Hello,
One approach is to take one of the resistors and bend its leads at right angles so it fits into the holes in the circuit board. Then turn the circuit board over and solder the leads to the circuit board traces. Leave the leads that are coming through the board untrimmed. Take the second resistor and trim the two leads just enough so the leads can be formed into small loops. The goal is to have the second resistor's leads wrap around the leads from the first resistor. You can roughly estimate how much of the second resistor's leads would be trimmed off to allow you to use a pair of needle nose pliers to wrap the shortened leads into a small loop that will slide over the first resistor's leads on the bottom of the circuit board. One resistor above and one below connected in parallel.
Then trim off the excess leads, from the first resistor, once everything's soldered.
Cheers, Ken

Wardsweb

Resistors in parallel half their resistance while doubling their current capability. Here is a quick calculator to determine your resistance.

http://www.1728.com/resistrs.htm

As for hooking them together, there can be many possibilities; mounted one on top of the other where ones leads are bent at a right angle to the other, the leads parallel and twisted together, both leads soldered at a terminal or hole, etc... The end result will be the same, as long as the circuit sees them together.

hearingimpared

When bending the leads make sure you place your neednose pliers on the lead against the body of the resistor as a brace before bending the leads. This will keep the lead from breaking inside the resistor.

NJPOLKER

Thanks Joe,
Thats a good reminder for everyone working with leads coming off resistors and capacitors.

quadzilla

Jed Leland wrote: »

Hello,
One approach is to take one of the resistors and bend its leads at right angles so it fits into the holes in the circuit board. Then turn the circuit board over and solder the leads to the circuit board traces. Leave the leads that are coming through the board untrimmed. Take the second resistor and trim the two leads just enough so the leads can be formed into small loops. The goal is to have the second resistor's leads wrap around the leads from the first resistor. You can roughly estimate how much of the second resistor's leads would be trimmed off to allow you to use a pair of needle nose pliers to wrap the shortened leads into a small loop that will slide over the first resistor's leads on the bottom of the circuit board. One resistor above and one below connected in parallel.
Then trim off the excess leads, from the first resistor, once everything's soldered.
Cheers, Ken

I've always done something very similar, but most of the projects I've worked on have not had clearance to mount a resistor below the circuit board. So, what I've always done is basically the same, but I solder the first resistor so it has enough clearance to mount the second resistor below it, with both mounted on the same side. Then I just loop the leads as per Ken's directions.

headrott

Thanks for everyones replys. Now my next question is if I needed to get some Mills resistors from parts express, how close does the final value have to be to "be OK"? If I get a 2 and a 4 ohm resistor it would be 1.3333 ohms, but is this value to far out of whack for the crossovers? Also, would this affect the sound quality even if this is close enough to "be OK"? Can anyone recommend where I can quickly get some mills 12W resistors and would have the 2.5 ohm AND a 2.7 ohm (as Sonic Craft is closed for maintenance). Thnaks again for you help.

kcoc321

I did a search and found these guys who carry the 12w Mills resistors.
They do list those sizes ^^ as well as a 1.2 and a 1.5 as well....
I can't vouch for them though....as I have never used them, maybe someone else has.

What speakers are you upgrading, BTW? (sorry if I missed it)

ALso they are in your neck of the woods.

kcoc321

opps forgot the link:
http://speaker.rosaryshop.com/index.php/r/components#resistors

headrott

I am upgrading some SDA SRS 3.1TLs. They require a 1.3 ohm resistor on each crossboard.

I looked at the web site you posted the link for, but I did not see a 2.7 ohm or a 2.5 ohm resistor listed (in 12W, or any other). Did I miss it? Thanks again.

kcoc321

I give up..I thought you wanted a 1.3, I found you a 1.2..

headrott

Wardsweb wrote: »

Resistors in parallel half their resistance while doubling their current capability. Here is a quick calculator to determine your resistance.

http://www.1728.com/resistrs.htm

As for hooking them together, there can be many possibilities; mounted one on top of the other where ones leads are bent at a right angle to the other, the leads parallel and twisted together, both leads soldered at a terminal or hole, etc... The end result will be the same, as long as the circuit sees them together.

So would this be paralled or series? It seems that both leads would have to be connected before going through the board holes, correct? Or would this work?



Thanks to Ricardo for the image. I hope he doesn't mind me using it. Sorry if it's a problem....

megasat16

^^^ Those two resistors are in series ^^^.

Here is how you parallel the resistors. You solder both legs of one resistor (let's say 2.7ohms) as you normally would but solder it high above the circuit board to allow room for another resistor to solder on top of this one.

You need to cut a few mm from each leg of another resistor (this one would be 2.5ohms) and solder on top of another one. I'll post a picture of how you solder parallel resistors tomorrow.

WilliamM2

Here's a crude 1 minute drawing to show parallel connection of resistors:

headrott

Thank you very much for your help! It made sense that that's the way they should be..... I think the wording and the pictures on Ricardo's 1.2TL mod page played with my mind about it. Anyway, thanks for the picture. That makes it ultra clear.:)

megasat16

WilliamM2 wrote: »

Here's a crude 1 minute drawing to show parallel connection of resistors:

I was going to solder a few resistors but you make the point far easier than soldering.

But that 1 minute, is that in Martian Time?

WilliamM2

megasat16 wrote: »

I was going to solder a few resistors but you make the point far easier than soldering.

But that 1 minute, is that in Martian Time?

Earth time, but it shouldn't take you any longer on mars. Three shapes, and four lines in Corel Draw, doesn't take long.

TECHNOKID

megasat16 wrote: »

I was going to solder a few resistors but you make the point far easier than soldering.

But that 1 minute, is that in Martian Time?

He must have been talking your time to solder a few

TECHNOKID

megasat16 wrote: »

I was going to solder a few resistors but you make the point far easier than soldering.

But that 1 minute, is that in Martian Time?

He must have been taliking your time to solder a few (I would hope it takes shorter time to draw then actually solder resistors)