If anyone has a Peavey Rage 158 and knows any good metal settings for it to sounds maybe a bit like Slayer or Lamb of God...? I have a pedal but im wondering if my amp can sound good without it.
I have that amp, and the sounds I can make with it are clean, and sludge. I'm getting a new one pretty soon.

Anyways, you should put the post gain at about 1-2, and the pre gain at about 9 for a really distorted metal tone. Make the bass high, and you might get a decent Slayerish sound.
i had that amp for over a year

if you want metal settings on the amp you would need a dist pedal or a multieffects
ibanez rg370dx (Crunchlab/Area 58/Liquifire)
ibanez rgr320ex (EMG 81/85)
ibanez grx20 (Super 3/PAF PRO)
ibanez gsr205 bass
randall rh150 head
avatar 2x12 contemporary cab (GK-100's)
boss GT8
ibanez weeping demon wah
line 6 ux1
theres no bass setting on it, just high low medium, and a modern/vintage switch and a lead/something else switch, and pre gain and gain
well i got that amp and its kinda impossible to get a good overdriven sound on it, the cleans are good but switch it to overdrive and u get mud basically, id say get a pedal