I recently ordered a Peavey 6505+ 112 and after what seemed like forever (three days) it came in today! I have to say, the gain on this amp is unbelievable, there's no wanting more. The only issue I have is it just seems to be "thin sounding" and higher notes don't have much sustain at all, I didn't expect creamy solos but I expected it to sound better than this. How do I warm up the gain? Would getting an OD pedal and using it as a volume boost solve both the warmth issue and the sustain issue?

Also the reverb is just horrible, it seems be almost no difference between half reverb and max reverb. Are there any cheap reverb pedals that would pass for spring reverb?
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The Legion
Yes, an OD pedal is usually my first suggestion with that amp, followed by an EQ pedal in the effects loop. A tubescreamer will definitely put more edge on your rhythm tones and bring out more "singing" leads. Hit a pinch harmonic and it will squeal for days. I'm a little concerned about your lack of sustain though. Does your guitar sustain through other amps? My 6505+ 112 has endless sustain.

Running an EQ pedal in the loop can really enhance your tone as well. I like to cut the highest highs quite a bit to get rid of fizz. I also put a spike on my low and upper mids. That brings in more punch but also more clarity on high notes.

Lastly, I don't think the reverb sounds horrible, it just doesn't do a whole lot. I like a much bigger, longer decay on my reverb. There are lots of pedals to choose from. I bought a TC Electronic Hall of Fame and am very happy with it. It can sound downright cavernous and also has several modes that add a slight chorus effect. I've found that mild chorus can also enhance the warmth/sweetness of your leads as well.
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My guitar hasn't had that issue before, which is why it stood out so much to me... I'm going to really sit with it tomorrow and try and figure it all out. At one point it even cut out on me a couple times but it was once, and it never happened after that. I'm hoping this is all due to the break in period
"Any statement beginning with the words 'In truth' is almost always a lie."

The Legion