How do I get Zacky Vengeance's sound on my SG Special electric guitar? The sound I would like to get is from Avenged Sevenfold's "Hail to the King".
Here is an article and a video where the technicians for Avenged Sevenfold display and explain all of the equipment used by Zacky Vengeance and the other guitarist and bass player in Avenged Sevenfold.
Rig Rundown: Avenged Sevenfold at Premier Guitar Magazine
I had a listen to his/their music, here is my opinion on tips for getting a similar sound:
What amp are you using? Their music is heavy, but there is still a lot of crunch to the rhythm guitar by the sounds of things. Dial in a modern med to high gain sound, not too much bass or treble, lots of mids.
Now, for the options that cost, cheapest to most expensive: That guy ZV is using a .10 string gauge, the easiest thing you can change is your strings, this may have little effect though, not everyone notices a string gauge difference in sound. Less than $10
Next, to get a good modern gain sound you may want to look at a distortion pedal to push or shape your sound before it hits the amp. ZV's sound has a lot of punch so a Boss SD 1 (used is fine) or Joyo Ultimate Drive (very cheap) could help you with a high gain crunch without giving the fizz that a lot of distortion pedals give. This all depends on your amp though, so unfortunately no short or simple answer. Less than $50
A fair amount of the rhythm guitar tone seems to come from the pickups. If your guitar is a stock Epi Special, the pickups probably have a more vintage voicing, and if you really want to nail it you may need to look at getting a Seymour Duncan JB installed. Used is fine, as long as it still works. This may really be worth it, its a great pickup used by many rock and metal players. About $100, you can save if you do the installation yourself or know someone who can solder and get their help.
On modern metal recordings there's a pretty involved process to get the sound that you are hearing. There are likely many layers of guitar tracks and a lot of studio tricks are applied. In many cases a traditional guitar amp and cabinet setup isn't used, but rather some modeling technology like Axe Fx or Kemper is used. With that in mind, it will be hard to get a sound like that from a single guitar with an amplifier.
Most metal guitar players are using active guitar pickups these days. These pickups need a battery, so to install them in your SG might need some modifications. There are passive pickups that try to emulate the active ones, and then no modifications are needed. The pickups is one important aspect of the sound, but the amplifier (or emulation of it) is more important.
Since the sound you are looking for isn't coming from a single guitar connected to a single amplifier, and I'm guessing you're not playing in a band situation, my advise would be to try out some modelling solution, like Guitar rig for your computer. There should be quite a lot of sounds created by users on the internet. There should be free trial versions so you can try it out and see if it works for you. You will need to be able to connect your guitar to the computer via an interface.