The suggestions to verify cable connections and integrity are good ones. You have to troubleshoot this type of issue systematically or you will drive yourself crazy. It is highly suspect that all of your amps have the issue on the left channel only. Swap only one set of cables or components at a time.
One last thought, have you completely ruled out the left speaker as the issue? Will it play music at all? If the cable swaps do not solve the issue, hook the left speaker to the right channel using all of the cables that were hooked up to the working channel. It would be highly unusual, but not impossible for the speaker to be the culprit (I.E. a broken connection internal to the speaker), since the issue seems to be coming from one side only. This would be something that I would try only after ruling out cable and connection problems. Good luck
One last thought, have you completely ruled out the left speaker as the issue? Will it play music at all? If the cable swaps do not solve the issue, hook the left speaker to the right channel using all of the cables that were hooked up to the working channel. It would be highly unusual, but not impossible for the speaker to be the culprit (I.E. a broken connection internal to the speaker), since the issue seems to be coming from one side only. This would be something that I would try only after ruling out cable and connection problems. Good luck