I was trying to mod my Audio Research LS2B following a few treads that recommend replacing MIT Multicaps caps with Dynamicaps. Decided to mod the left channel first. As suggested, I turned the Dynamicap in the opposite direction (positive lead towards RCAs) and turned the preamp on: what a surprise! After a strong puff sound there was black smoke coming out of the Dynamicap. Didn't know polypropylene capacitors have polarity, but after close inspection realized that one side does have a longer lead, which I assume was indicating the positive side (???). I then turned it around, and also subsequently replaced the cap in the right channel following the original direction of the MIT Multicaps, and the right channel works great. However, there is now only a strong hissing noise coming out of the left channel. Would anyone know what did I blow in the process? A MOSFET, the Sovtek tube? The sound of the right channel has a significant improvement over the Multicaps, but now I don't have the left channel. Can anyone help? 
Thanks in advance.
Thanks in advance.