What are some of the mistakes, failures or bad purchases of your audio history?

Kind of the opposite of "best of".  I, like most, have made some mistakes or purchases that were poor choices. 

The worst were some speakers "I built".  Anything I owned that was "quadrophonic", Lamp cord for speaker wire, BSR turntables...yes they were in my "poor just home from Vietnam" days...but still.., early Japanese receivers that were not much better than appliances, ...and even though I got into some of the best in later years, some of my beginnings were more bad than humble,...but my taste in food, friends, mates and many other "things" went through what can kindly be called a "learning curve". 


Sometimes there's value in the journey, but with hindsight being 20/20 I could have skipped the detour on my way to owning my Pathos Classic One MkIII.  I saw the Pathos in a local shop used and while it was a great price, it was more than I was in the market for at that time.  Instead, I decided to scratch an itch purchased a Cambridge Audio 840A with the hope that the home theater bypass would give me the best of both worlds with my home theater receiver and stereo.  It always made noise when connected as a power amplifier and I simply did not enjoy its sound.  The silver lining was that while trying to determine if it had an incompatibility or an actual problem I picked up a Cambridge Audio receiver cheap that I was able to eventually sell to a friend and he's still using it.  I ended up trading the 840A in on the Pathos once its price dropped even more with my net cash investment being the first price that I saw it at.

The second round of disappointment was scratching another itch and purchasing a Krell S-300i.  It also had a home theater bypass, but once I rolled some tubes in the Pathos there was simply no comparison, so I ended up selling it as well.

Ironically, the Pathos Classic One, Cambridge Audio 840A, and Krell S-300i were all options when I purchased my Integra 50.1 receiver that I still have.  I almost purchased the 840A then and considered the Krell and Pathos to be out of reach.  Now I've had them all and still have the two that I enjoy most.

Going back aways here,… the Terk Pi amplified FM antenna. I got better reception with manufacturer included “T” wires tacked on the wall.

B&W Matrix 803, Classe CA-200, Clearaudio Delta -S, what really hurts is that i bought them brand new. Fortunately sold them quick with min loss.

Buying expensive speaker stands before I knew -- for sure -- I'd not be upgrading the speakers. I think it was a way of affirming my speaker purchase, but it was short-sighted and I regret it.