Unbelievable, the only thing I hadn't changed was the jack adapter!
I didn't have my HP's with me as I lent them to a friend and was using the amp with some cheap HP's. The amp didn't work and I panicked!
After a two days worry, it came to my mind that one the one thing I didn't try was the 3.5mm to 6.35mm jack plug adapter!
Oh well...lesson learned...
Thanks everyone for your help!
Should have mentioned you were using an adapter.
You need to use a good 1/8" to 1/4" adapter…a lot of them are junk.
Good to hear that you resolved the issue and it was a simple fix.