Thanks Granger. I read on headfonia that polarity of headphone amps is very important. I attached the FAQ section. After reading this I really want to hear the difference. I want to test before I commit to any permanent changes. The XLR solution that PB suggested is the least expensive, however I will have to cut the plug off my Teslas and convert them to stereo XLR. The matching transformer solution leaves everything else unchanged, and allows other headphones to be used. The real problem with the input transformer solution is that there is not much room in the Crack for the extra matching transformers. I am now on a search for the most elegant solution to flip the polarity of the Crack and still allow all headphones to be used, not just my modified Tesla T1s. I wonder if anyone else has listened to the crack with positive polarity so I would know if this is worth pursuing.
from
http://www.headfonia.com/faq/20. How do I know if my headphones are wired with a reverse polarity?
First, a reversed polarity is not when you switch out the left and right channels (that’s reversed channels). A reversed polarity is when you wired the + and – incorrectly, like swapping the red and black wires on a speaker set up.
The most obvious effect of a reversed polarity wiring is on the soundstage image. Things that are supposed to play in the center of the soundstage image (that’s right in front of your forehead) instead is like split into two and now playing on the left and right edges of the soundstage image.
Do this for illustration purposes: take both of your hands and put it in front of your forehead. With a correct polarity (and a good heapdhone and a good recording), a certain singer or instrument would be projected there right in front of your forehead.
Now, spread your two hands apart to the left and right. This is how an incorrect polarity would sound. The instrument or the singer is no longer in the center, but rather split and is now playing on the left and right edge of the soundstage image.
Other effects of a reversed polarity may include a shift in the frequency balance. You may get more treble, less midrange and such. Of course this may be give the impression that the headphone is now better (i.e with more treble comes more apparent detail), but the fact is that the soundstage image is plain wrong.
The best recording to evaluate this phenomenon would be a good live recording. A one instrument live recording like live piano solos would be even better since you have no distraction from the other instruments.
Some headphones like the Grado HP1000 comes with the polarity switch (so you can reverse the signal at will) but I personally have never encountered a recording with an erroneous polarity so I don’t see what the need is for such switches (Although I don’t doubt its cool factor). Likewise some DACs like the Cambridge Dacmagic also comes with a polarity reverse button. If you happen to have the Dacmagic you can play around with the button to see the effect of a reversed polarity.
