Johnson IA-423 is the best sounding solder I have experience with. Lead free with a high silver content, 6.4%. Much perfer it to the WBT and Cardas solder.
If you really want to find out what different solders sound like, make a run with it as speaker wire, thats about the only way to A:B test it.
Part of the question should also be the best way to solder. If you just place a wire in a loop or tag strip and solder it then the solder is a bridge between the 2 parts, and very much in the path. The better way is to put the wire through the loop then wrap it tightly, so much so that the solder almost becomes redundant to the connection.
I would be careful with some of the "audiophile" solders. Some have pretty corrosive flux in them. IF you dont clean it all off, will eventually attack the joint.
In one of our audio club meetings, we had one demo where we tried different solders. They do make a very big difference, bigger than I would have thought. The other thing is you need to have a good mechanical connection over time.
we ended up picking Kester 63/37 with a 285 flux as the preferred choice. 63/37 is also eutectic, which most others are not.
This thread reminds me of something that happened in my senior year of engineering school. My room mate's brother was an audiophile. He was having trouble with one of his speakers and asked if I would have a look. He had purchased these speakers 2nd hand and I pulled out the crossover board on the offending speaker and plainly seen that someone had been inside the speaker before and modified the crossover. The modification was a real hack job and I found many cold solder joints. I simply broke out an iron and some trusty Kester lead free and reflowed the bad joints. I reassembled the speaker and gave the speaker back to my room mate to give back to his brother telling him I just had to resolder some joints. I recieved a note from his brother thanking me for the repair and using that special solder. He continued by saying it was a marked improvement over the working speaker and asked if I could use the special solder and resolder the joints on the second speaker for him. I just shook my head, kept my mouth shut and laughed.
Jeff at Sonic Craft (who knows a lot about this stuff) advised me to use Cardas Eutectic solder. He gave me reasons why it was better than the Mundorf and others, but I can't remember what they were. I think it had something to do with the amount of silver content and also long term corrosion. Call him.
I had My Rogue 99 Super Magnum -Se preamp built completely with the Mundorf Supreme solder which I found out is 9% pure silver 1%gold and 3%Copper and then the standard tin mix.It is the best solder on the market and complement my Mundorf silver gold oil capacitors,even the Hifi tuning Supreme fuses which are superb and the new rave were designed with this exact Supreme Solder.
For me it's WBT.I have a lifetime of experience with soldering in High-End Audio. The Quality of sound shows up big-time on interconnect terminations RCA and XLR. UnGodly exspensive and
worth every penny.I have not yet tried Mundorf Supreme.
I found out the hard way one time when I ran out of WBT and used Kester Silver solder. Not the same, in any Audio application.