Originally Posted by goodvibes
Normal solder has 11.5% the conductivity of copper but modern lead free solders can contain 3% silver even if not noted and be higher. Typical 4% silver solder has 11.9% the conductivity of copper. That resistance is part of why you always want the best mechanical connections before soldering even if solder flows the joint. In the grand scale, silver to standard solder is a subtle difference in conductivity. 3% of something far off copper to begin with. When you consider the amount used on a pad or to surround a wire the effective differences become even smaller. That doesn't mean it will sound the same but why I question the amount of 'better' in this use. Not to say that I may not prefer the J version when available but it could be the other way as well. One also needs to remember that all the circuit work and voicing was done with the current solder.
The differences in resistivity and conductivity are not major. But of course these are not the only factors. Does the trace amounts of silver change the signal flow in a major way? Many materials are "doped" with trace elements to make major changes in the characteristics. I don't know enough of how silver could affect the conductivity to say anything meaningful, but I do postulate that there may be more going on than just the ratio of silver, how much tin and lead, etc. We are more like the alchemists of the middle ages, looking for the secrets to turn lead to gold. Trial and error is what we have, to see if there is a meaningful impact on SQ.
Regarding Jamato's comment about solder connections needing to be redone periodically, I believe in that. I worked with industrial soldering/reliability, with telephone switches, and had a chance to see connections that had been in use for many years. And while it takes a lot before the connectivity is lost, you can see how the solder joint looks different, and the joint is not as strong, after many years. There is no doubt that solder oxidizes. Just look at old copper water pipes..