Solid State Guitar Amp Forum | DIY Guitar Amplifiers

If I cut some 4 in. holes in my Mustang II v2 amp
in the back panel what effect can I expect on the sound?Anyone have any experience with this?

It will alter the sonic outcome a bit but it won't turn a mini minor into a Rolls Royce. 8|
In My Observation (over the last 45 years of playing guitars).
Open back fender style amps are more effected by the room you play in,, whereas with closed cabs the sound is less effected by room acoustics so the tone/sound remains much the same.

As for *ported cabs* it's anyone's guess as to what will happen as the port size is dependent on the speaker used.

If you are wanting more bass response then consider a Graphic EQ pedal in the FX loop that will help a lot.
If you are still not happy then you need to upgrade to a better amplifier.

BTW be careful as that amp has mains wiring on the back panel so don't just drill holes willy-nilly as you could damage the amp. :trouble
Phil.

  In my experience, closed back means more bass.  So if you put holes in the back you will lose bottom end and get more mids.

Short answer and backing what was said above: do not touch it.

I thought it was a little 1x8" 15W job or something equivalent, but it´s a mid sized single 12" 40W amp.

be certain that Fender Engineers whoare no fools, already milked that cow to the last drop, neither you or any of us won´t casually "improve" it.
If a hole in the back could improve sound they would have done it themselves, after all it costs nothing.

You want to *really* improve sound, make it sound louder/better, with more projection*

Replace the cheesy (but adequate) Chinese speaker it has now with a Celestion Vintage 30 and stand back.

Or add an extension jack and whenever possible plug it into a Marshall 4x12" cabinet or equivalent ... and stand back.
You´ll get something like *this*:
https://www.youtube.com/watch?v=eNHdJmsfdMM