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Aug 27 2014

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Tin and Rosin for Audio – which one ?

Recently I have received a question about those silver wires that I often use within my various signal paths.   Since it is “silver” as opposed to “copper”, and since I make the vague suggestion that it does make a difference, then we obviously come down to the question of the type of Tin and Rosin that could / should / would be used to bind it with all the various electrical elements.

So, plain, bluntly and shortly: What is the “best” tin / rosin combination to use for Audio ?

I do not know.

But I *DO* know what works best for me, for my ears, and what is my favorite preference.

Since I am such a “silver-biased” freak, for reasons which are outside of the scope of this short blog entry, it could be anticipated that I shall go for the brand name, Pb-free, high silver content types of tin solder.

Guess what: you guessed wrong. Well, partially wrong (50%).

The reasoning is basically sound:  Take a Tin that has a relatively high silver content, of say 3,5% to 4,5% would be reasonable.  But there is one caveat thereto. This type of tin, taken “on it’s own, has it’s pro’s, but also it’s con’s.

The con’s, as are see them, are the following:

a). These tins are obviously Pb-free. Apart from that, they contain a certain amount of silver, which happens to be a metal with a fairly high melting point temperature. The result is that the aggregate melting temperature of such tin is also fairly high. Significantly higher than that of “normal” tin.   I do not like to use tin that melts at such excessively high temperatures, because under such conditions it is much easier to destroy (by temperature increase) many of the fine and delicate elements that need to be affixed. This especially applies to elements that need to be attached to a thick ground-bar or a ground-plane, which possesses a fairly thermal inertia.  By the time you heat up the ground-bar or the ground-plane to the point of tin melting temperature, you have a good chance of thermally destroying the very element that you are soldering. Even if you bind the cold element to the pre-heated ground-bar or ground-pane, the heat “stored” in that bar or pane is sufficient enough to weaken or destroy the fragile element that is being affixed.

b). The process of conversion from “liquid” state to “solid” state of such tin is very short and rapid. For me, this tends to make the soldering task somewhat more difficult, as to the unpredictability of the “moment” when it “grips”.

Taking into consideration the former, I tend to use a special mix of two different kinds of tin;

I take 50% of the Pb-Free tin with the 3.5 to 4.5% silver content.

But then, I add to that another 50% of a very traditional, old-style 60%/40% Sn / Pb type of tin.

Yes, the NON Pb-free tin of the times long gone and past.  I am fortunate enough that in our country it is still possible to purchase such Pb holding tin.

Now, you may be wondering why am I reverting back to such a 60% / 40% Pb bearing tin ?

My reasons are quite simple and tested in praxis:  The fairly high Pb content of that 50% of other tin shall result in quite a significant overall decrease of the melting / binding temperature of the resulting mix.  Yes, it is fair to say that by introducing such a mix I effectively halve the share of silver in the resultant mixture. But from my practical observations it seems to be a non-issue.

The resulting mixture has the following characteristics:

+ A significantly lower temperature operating point.

+ Very good “wettability”

+ Very good “cooling” and “binding” characteristics.   The bond is less mate, dull, it has a higher gloss, so it is easy to assess the quality of the bond and hence it is visually much easier to spot and eliminate / correct “cold solder joints”.

+ Soldering fragile elements to thick bus-bars is much more relaxed and easier.

+ Less risk of destroying an electrolytic cap or other temperature sensitive element.

+ Better visual control of the “state” of the solder.  Is it still liquid, is it solid, or is it something “in-between” ?   The “something in-between” holds for a slightly longer period of time. Generally, that makes life easier in certain cases.

+ Last but not least: it sounds good, too.  It bonds very well both to copper, as well as to silver.

Ok. So that would be the tin. But what about the rosin ?

kalafonia

Maybe I am a bit of an old-style type of guy.

I use plain and simple pine resin. Sort of like straight from the tree … Well, they actually do sell this stuff by the kilograms on the Polish auction services. You can also try to ask about it in musical instrument shops, especially those with violins and stuff.

Here is an example of an auction where you can by the stuff dirt cheap and by the kilograms:

http://allegro.pl/listing/listing.php?order=dd&string=kalafonia+%281kg%2C+0%2C5kg%29+-cyna+-100g&search_scope=wszystkie+dzia%C5%82y&bmatch=seng-v6-3-default-0827

Ok, so this stuff I use directly in the case of thread-through-hole type of elements.

But what about small, tiny little IC’s, with multiple legs and very dense pin formats ?

Fret not. For such purposes, you simply need to buy additionally a bottle of plain rectified spirit (98%, such as from a pharmacy or something).  Then, simply toss in a few stones of the pine resin into a jar with the rectified spirit and allow it to dissolve.  Once you get a uniform liquid, you can simply apply it with a fine painting brush onto the suface that needs to be surface-soldered.

With an additional eye-glass and the “third-hand” tool for affixing your work bit, you can achieve true wonders. Providing that you have an ultra-sharp solder-bit at the end of your solder-iron.

Actually, I have made very special, needle style solder tips for this very purpose. I recently managed to solder a tiny Wolfson DAC chip in this way. Magnifying glass x10.  The x3 was not strong enough. A very stressful operation indeed. But possible to accomplish on your kitchen table.

Cheers,

Ziggy.

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