I am on my second VT40+ as my first one died after 8 months. Thank you Vox Warranty!!! I got a free replacement with new warranty but had to pay for shipping.
On to more important issues. The dreaded HISS. I never noticed the hiss that has plagued so many VT+ models...until now. Granted, I don't usually play it very loud and it is normal for me to have the Master knob around the 10 o'clock position and the Power knob around 9 o'clock.
Recently I started noticing an annoying hiss that trailed off after playing notes. It was especially noticeable if I lightly struck my low E string. Seems like the lower the note, the worse the hiss was. Brushing my high e produced only a mild barely noticeable trailing hiss. This being my 4th Valvetronix and having just purchased the Joe Webb's effects loop mod kit (not installed yet), I was really ticked off to say the least.
I started doing some experimenting. I changed power outlets, cords, etc.. I played a lot with the Master and Power knobs. What I found is this:
More Gain = worse hiss (which seems obvious)
More Master = worse hiss
More Power = worse hiss
Master vs. Power (high Master with low Power vs. low Master with high Power = no difference
Overall Volume as a result of the combination of Master and Power: higher overall volume = worse hiss
Presets vs. Hiss: Some built-in presets are worse than others.
Noise Reduction: BINGO! This seems to have a HUGE effect on the problem
I never messed with the noise reduction settings before. It's possible my son messed with it recently but it's such an obscure process to access it, I didn't think much of it. Per the manual, noise reduction is set individually for each program or manual mode. What I noticed about the hiss was that it was very artificial sounding the way it trailed off. When I started messing with it, I found that all the way on to the right was terrible sounding (NR on maximum). All the way to the left (NR off) and the hiss was bad. If you turn the knob up just barely, you will hear an audible change when the NR system engages.
It's very similar to when you use one of the Pedal effect and turn the "Value" knob up slightly from the left (off) position. You hear an audible change as soon as the effect is ON.
What I found was that the hiss seemed to be minimized with the NR in this "barely on" state. The audio quality is preserved but the hiss is minimal. When the NR was in the fully off position, the hiss was horrible. Eventually I was able to get it fairly clean with the AC30TB model in manual, dials all at the 12 o'clock position, and the Master and Power knobs also at the 12 o'clock position. Some slight hiss like any other cranked amp, but the trailing hiss seemed minimal at best. Certainly livable if you're outside your return period.
Since I never noticed this problem before, I am considering doing a factory reset since that wipes both user presets AND resets the factory NR settings. I'll post how it goes. Let me know if anyone else can duplicate my results, either good or bad.