Hello gas hed,
The answer depends on how you’re amplifying the signal on your guitar, whether it’s with a built-in mic, piezo, or bridge pickup, and whether or not your guitar has a quality built-in preamp, like a Fishman or equivalent. With a built-in preamp you may connect it directly to the H90’s input and take the H90’s output straight to the input of your mixer/PA. If you only have a piezo pickup attached to your guitar, you may want to have that signal connected to a dedicated preamp/DI box made for acoustic guitars to tone shape your sound before you connect to the H90. You always want to ensure the H90 is receiving a strong signal, but more importantly, that your guitar sounds natural and balanced before connecting it to any piece of gear. A good acoustic preamp helps tremendously. My recommendation would be, if your guitar already sounds wonderful going straight to the PA, then you may put the H90 in between without issue. Find out if the signal coming from your preamp is line level or instrument level and adjust the I/O of the H90 accordingly in the System menu.
