I just bought a DT50 112. I am noticing some serious fizz when using the amp with Helix (I am using L6 Link).
Right now, I have the PV Panama preamp running into the DT.... fizz city. I would have thought a guitar speaker would remove most of the unwanted high end, but it doesn't. If I place a Hi/Low cut EQ block and set the Hi cut to even as high as 15k, it still makes a big difference in eliminating the fizz. That's a pretty high setting, so there is a lot of very high frequency information coming from the amp. Similar issue with most of the preamps and even full amp models I have tried.
At first, I thought the stock L6/Celestion speaker was the issue, but if I use the built-in DT preamps, there is no fizz... the amp sounds as expected.
I don't mind including a high cut in my Helix chain, but this doesn't seem like normal operation for a combo amp with a guitar speaker. Anyone else notice this? I tried a Google search, but I am not coming up with much.