Determining optimum solder temperature

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markiteight
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Determining optimum solder temperature

Post by markiteight » 2019-04-15 00:12

I have almost everything I need to make a set of optimum K400/2:
  • Raw K400 cable
  • Linn Knekt bananas (old style)
  • Lejonklou recommended solder
  • Weller WSD80 with broad tip, and
  • A modicum of soldering skill.
What I don't have is the ideal soldering temperature for my specific iron. Here's what I'm thinking might be an efficient way of determining what that might be:

I have a length of K400 that is too short to be useful and enough BFAs and Knekts to make 3 pairs of speaker cables. What I propose is to make 3 pairs of identical length but very short (no more than 15-20cm) "jumpers" with BFAs at the amp end and Knekt at the other end (my Klout is a late production model that unfortunately requires BFAs). The only variable (at least as far as I can control) will be the iron's temperature. One will be soldered at the temperature Thomas has found ideal on his iron, one at two degrees Fahrenheit cooler, and one two degrees hotter. I can then insert the chosen pair of jumpers in-line with my existing speaker cable, quickly and easily switch between the three, determine the loser, desolder/clean the connectors from that pair and resolder onto a fresh length of cable at a new temperature. Wash. Rinse. Repeat. This method will almost certainly perform worse than a single run of optimum length cable in absolute terms, but I should still be able to determine musical performance strictly from a better-or-worse perspective.

I have a few questions about my proposed method.
1) Can anyone see a flaw in my logic?

2) What is the dependant variable in determining the optimum solder temperature? Is it the
materials being joined? The type of solder being used? The temperature itself? Or a
combination of all the above? In other words...

3) Is the optimum temperature tied to a specific solder type or can I use any ol' solder for the test?
If the optimum temperature is always the optimum temperature regardless of materials being
joined and solder being used I can save what little Lejonklou recommended solder I have on
hand for applications that will actually be used and enjoyed long term.

4) Does the optimum temperature apply only to speaker cable terminations or will it also be ideal
for other applications (circuit boards, interconnects, etc.)? For that matter, is the ideal solder for
speaker cable also the ideal for these other applications?

5) Is there an optimum quantity of solder that should be used? Is this another variable I should control?

I have another amp with proper banana terminals arriving tomorrow so it's time to line up the ducks and get a proper set of cables made! Thanks in advance for any insight you can provide.

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Re: Determining optimum solder temperature

Post by lejonklou » 2019-04-16 21:48

Hi markiteight and apologies for the late reply!

1. No, it sounds just right. If your system is well installed and you can judge better from worse even when the differences are small, you jumpers will work. I would advise arranging so that you can swap quickly and then listen repeatedly to A versus B versus C before you make a final judgement.

The "too low" temperatures sound a bit bright, forward and tend to chop off the notes, almost as if something is "too cool". This can trick you into thinking they're agile while they're actually a bit too stiff.

The "too high" temperatures sound fat and thick, which may sound fuller but in reality has less information than when notes decay naturally and in balance with each other.

You can make these judgements pretty well when the joints are brand new. If you wait a day or two after soldering, they can change a bit unpredictably, which will make the judgement more difficult and more prone to errors. Most reliable is to wait around four months and also have them connected and playing some music. But immediately after soldering is reasonably accurate as well.

2. The solder metals, the flux, the chosen tip (the larger the better for these high mass jobs), the station's and pen's power and the mass of the joint will determine the optimal tip temperature.

3. It's tied partly to the solder metals used, but more importantly to the flux in the solder wire. A different solder wire could therefore have an optimal temperature that is 10-20 degrees higher or lower.

4. The mass of the joint has some influence. If you are using the same tip and solder wire on a low mass detail on for instance a circuit board, you will likely need to lower the temperature by 1-2 degrees. If you change the tip from a fat and wide to a thin and pointy, you will likely need to increase the temperature by 10-20 degrees. Therefore the best thing to do is to evaluate each tip and mass of joint combination independently. Time consuming, I know.

5. No, this is not critical. Don't use too little and you'll be fine. The longer you heat up a cable like K400, the more solder it will suck from the joint, as it travels further into the cable. Therefore don't heat for too long. And don't heat too little, as the joint will then not reach optimal temperature. When you've done a couple of hundred joints, you'll get the hang of it. :)

Best of luck!

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Re: Determining optimum solder temperature

Post by markiteight » 2019-04-18 01:09

lejonklou wrote:
2019-04-16 21:48
Hi markiteight and apologies for the late reply!
No apologies necessary! Considering the hectic weekend you just had I appreciate such a quick response. Thank you so much for all the brilliant info. That will provide very useful.
lejonklou wrote:
2019-04-16 21:48

5. No, this is not critical. Don't use too little and you'll be fine. The longer you heat up a cable like K400, the more solder it will suck from the joint, as it travels further into the cable. Therefore don't heat for too long. And don't heat too little, as the joint will then not reach optimal temperature. When you've done a couple of hundred joints, you'll get the hang of it. :)

Best of luck!
I've noticed that as the iron approaches the preset temperature it seems to "ease off the throttle," as it were, in order to reduce the chance of overshooting the target temp. If I set the iron to the target temp it takes an excessively long time to reach it, sitting one degree below target for quite a while. I've taken to setting the iron a few degrees above the target temp and just watching the display. When it reaches the desired temp I pull the iron, but it seems like this still takes an eternity (but is probably more like 10-15 seconds) and sometimes so much heat has been absorbed into the materials that the solder remains molten for several seconds (as long as ~10 seconds in some cases) after the iron is removed. Is this right or is there a flaw in my technique?

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Re: Determining optimum solder temperature

Post by lejonklou » 2019-04-18 12:00

markiteight wrote: I've noticed that as the iron approaches the preset temperature it seems to "ease off the throttle," as it were, in order to reduce the chance of overshooting the target temp. If I set the iron to the target temp it takes an excessively long time to reach it, sitting one degree below target for quite a while. I've taken to setting the iron a few degrees above the target temp and just watching the display. When it reaches the desired temp I pull the iron, but it seems like this still takes an eternity (but is probably more like 10-15 seconds) and sometimes so much heat has been absorbed into the materials that the solder remains molten for several seconds (as long as ~10 seconds in some cases) after the iron is removed. Is this right or is there a flaw in my technique?
This is not good. Don't try to outsmart the soldering station. The figure you see on the display is not accurate. It's constantly lagging behind what's happening at the joint, where the heat is drained.

Set the temperature.
Wait until the temperature is stable.
Ignore the display while you solder.

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Re: Determining optimum solder temperature

Post by markiteight » 2019-04-19 01:19

lejonklou wrote:
2019-04-18 12:00
This is not good. Don't try to outsmart the soldering station. The figure you see on the display is not accurate. It's constantly lagging behind what's happening at the joint, where the heat is drained.

Set the temperature.
Wait until the temperature is stable.
Ignore the display while you solder.
Thank you Fredrik. That makes a lot more sense. It just didn't feel right! I just finished making up another batch of cables, this time heeding your advice. I set the temperature to the desired setting and pulled the iron 4-5 seconds after I stopped adding solder. Here's the result:

Image

How's that look?

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Re: Determining optimum solder temperature

Post by lejonklou » 2019-04-19 09:55

Looks like Knekt soldered to K400. Difficult to say much more.

How do they sound?

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Re: Determining optimum solder temperature

Post by hcl » 2019-04-19 18:53

It looks quite ok, but a bit low on solder. Add some (maybe) 30% more than you done to the joints in the pictures. When applying solder and heating after, pay attention to what happens to the solder. There will be a point when the solder suddenly breaks into more free floating. That is when to stop applying more heat.

- Apply heat (by putting the tip to the cable and connector, touching both parts)
- Add solder to the junction between the tip and the cable/connector so that it is released into the cable and joins with the connector
- After a couple of seconds the solder will suddenly become more free floating
- Stop applying heat
- Done
Last edited by hcl on 2019-04-20 08:43, edited 1 time in total.

markiteight
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Re: Determining optimum solder temperature

Post by markiteight » 2019-04-20 06:04

lejonklou wrote:
2019-04-19 09:55
Looks like Knekt soldered to K400. Difficult to say much more.

How do they sound?
Hehe...I guess that's a good sign I'm not completely mucking it up.

With all the changes to my system lately it's impossible to isolate the speaker cables' performance, but it's sounding better than it ever has.

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