Has anybody tried using single solid core cables?

i second nonoise on mapleshade helix/double helix

outstanding cable

I used to manufacture audiophile cables in the 90s. Music Music Audio Cables. all my cable were multi strand solid core cables. I tried single wire and it either rolled the high end or bottom end depending on diameter. Had to use multiples of various gauge to have it sound right. The only single wire conductor that worked was a rectangular silver plated wire for digital. That said, I think some folk might use silver plated single wire cable. Pick the diameter that gives good base then use silver plate to bring in the highs. That said, Silver plated copper always sounded wrong to me. Exaggerated highs and discontinuity in the sound. As I recall, my interconnects were using something like six 29 gauge oFC copper wire per side and multiple 20 gauge solid core wires for speaker wire. 
I got started making cables after talking to Stan Warren (PS audio) about single core. I used to develop cable by laying multiple bare wire on a piece of masking tape, then placing another piece of masking tape over the top to make a flat "Flypaper" cable. I attached plugs and just played around until it sounded right.
Good connectors are mandatory. I liked connectors without ferrous metal. Silver on brass or Brass with Silver then gold, no nickel. plate to bind the gold. Cardas SLVR and Vampire locking RCA are excellent as well as the ones with a hollow center pin. I also used to favor Wonder Solder for connections. 
So find someone who sells OFC bare wire and have some fun. Don't use these on digital sources or phonos you will just get garbage. Good for CD player to Amp and Pre to amp.
I recently got hold of some cable I made in the 90s and they stand up to some newer model quite well. Obviously technology has improved in 30 year. 
The nice thing about these fly paper interconnects is the dielectric, the paper is as close to an air dielectric as you can get. No Teflon coating or PVC to alter the sound of the wire. 

Best solid core I ever tried is from Acoustic Revive. Sold my Nordost Valhalla and Audioquest and never looked back. Using bare wire, and short lenght. Very analog and organic sound. Still loads of details. Pure music bliss

I’ve tried some VERY cheap solid core telephone wire (0,5mm) for high tones, solid core electric cable (not sure, maybe 2mm) for low tones. OMG the sound was freakin awesome! But of course it’s not a pretty sight all those loose cables. Maybe I’ll try to wind em all together this weekend or something.

I have been wrestling with cable connectivity for many years now. Recently purchased several MORROW cables after reading all of the reports. Their design approach was different than other cable manufacturers I have tried, and been and been left with that "lack luster" feeling, just shy of dissapointment ! Anyhow, MORROW'S cables sounded at least as good as the best I have tried, right out of the box with minimal break in. I was set back a bit, by their claim that the cables had to be broken for 400-500 hours to reach their peak performance. Basically, after several hunderd hours, I did some very detailed A/B tests with the MORROW cables against my other three top performing cables. The results were somewhat mixed. Bottom line; - -  the MORROW cables sounded as good as my other three test cables, in most areas, but I honestly can't say that I found any significant increase in audible performance by comparison, as their advertisments promote.  So, on to the next step.!!

Several years ago I purchased some solid core cables that proved to be very difficult to install in my large audio console, due ti their extreme stiffness. At the time, I didn't pay much for them so I gave it up, and set them aside. A couple of years later I purchased a pair of solid core interconnects from an individual associated with the Chicago Audio Engineering Society. Very strong performance testimonies ! Again they proved to be very difficuly to route and install. I asked for a specific length, which the individual accomodated me with. Anyhow after installation and break in, I felt that the cables did sound different than others, in a good way. Without going into detail, I liked the cables enough to leave them in my system and purchased another pair. Again, as time went on, I ended up retiring them, and were replaced  with some very expensive interconnects that I managed to obtain two pair from a dealer who I had an association with, at a very large discount.  The cables impressed me in several areas and resulted in my leaving them installed as my reference cables. 

That brings me up to a couple of weeks ago.  I had some time on my hands, so I decided to do some experimentation after reading blogs pertaining to solid core versus stranded cables. 

I happened to have (lying around) A  solid core power cable that I used on and off, plus the old solid core interconnects and speaker cables. I thought, "what the hell", I'm going to try ALL solid core wiring from my power outlet; - -  the interconnect between my CD player to the amp, and then (with a great deal of wrestling) managed to route the very stiff speaker cables to my reference speakers. Anyhow, after system warm up, I thought that I would try a listening test with a couple of CD's that always had a slightly distorted, grainy sound, especialy during very dynamic higher frequencies. Well, surprise, surprise !! All the grain, strain and distortion disappeared. At first I was set back a bit, having some difficulty understanding what was going on here, and beliving what I was hearing. So I dug out several other CD's that I felt had always proven to be problematic sounding, in different areas.  "SAME RESULTS" They all sounded as though they had been "re-mastered", so to speak.  All the "grunge" was gone.  Anyhow, after this revelation,I thought I'd share this with anyone who wants to read my ramblings. It seems, at this point, that the "trick" here was using solid core wiring connections from the power outlet all the way to the loudspeakers.  When I have more time, I intend to do more A/B tests to determine, in my mind, if the premise here is valid. All I can say at this point is that the experience here was a real eye opener, and a strong accolade for the use of solid core OCC high purity copper cableing throughout an audio system. That seems to be the answer as to why using solid core, just here and there during listening tests, never yielded these astounding results.  So be it !!