Weird little pedal. It was my first effects pedal; it sounded terrible through my Peavy solid state practice amp as a kid. It was really cheap then, too, like 30 bucks. That said, I was probably cranking the gain to max and then using the cut/boost high/low knobs to either try to get a scooped sound or cutting out all the bass and treble entirely. The Peavy was terrible and by virtue of my inexperience, probably EQ'd wrong too.
This pedal doesn't really sound like any kind of metal to my eyes, hair metal or otherwise.
Today while organizing old pedals, I put it in front of some fuzzes to see what it sounded like. In the process I turned the gain way down and realized that the stereo output's "soft" mode isn't just for doing a line-level output to something that needs a lower volume level, like I always assumed. Nope, putting your cable in Out2 and switching to "soft" gives you slightly smoother distortion. I can actually match the lowest gain setting on the Metal Master with the max gain setting on my Sparkle Drive fairly closely. I was intrigued, so I opened it up, which I've never done.
Inside was the typical zillion components for a soft switching / buffer, but also 3 JRC4558 opamps. So it's related to the Tubescreamer, in a way. No schematics online. (I was actually kind of hoping it would be related to the Marshall Shredmaster, but alas, I've never gotten the amazing lead tones out of this pedal.)
The cut/boost knobs are interesting. For example, if you wanted to filter out most of the high frequencies for some really heavy BRUTALZ riffing / power chords, you can cut out most of the treble, keep the gain low, and put it into an Algal Bloom or other bass-friendly fuzz (like the pharoah, but I don't have one of those to confirm.)
Final verdict: You can get these things for $10 on eBay, if you want something that is as black as your heart while secretly being a high-gain tubescreamer, this is it. That said, it is a plastic buffered pedal that is over a decade old at this point, and will probably break on you at an inoppurtune moment. Snatch it up for free if you can, and use it to stack
