It is its own thing for sure. The normal channel should sound somewhat normal, it doesn't have too much bass cut, but many believe it almost too dark. It doesn't have any EQ controls other than the cut control which is actually part of the power amp section. The brilliant channel ( the one everyone buys the amp for ) is ungodly bright to my ears. It has a TON of bass cut and goes through a significant amount of circuitry before it gets to the power amp. The Tremolo channel is also pretty bright and has a different topology than most tremolo channels. It is the least used channel in the amp. The brilliant channel is where all the AC30 gain comes from. It drives a cathode follower circuit where it makes a little bit of grit and then when at a considerable volume, the PI and power amp distort into that classic AC30 grind. The phase inverter and the power section are probably the most important part of the AC30 distortion sound. Aside from the bass cut ( by way of a TINY coupling capacitor ), the brilliant channel is pretty much like a Marshall JTM45 ( a single triode going right into a cathode follower circuit followed by a tone stack ). The Normal channel is more or less normal. The tremolo is just weird, but whatever... The PI and power amp are different from most other amps though.
The AC30 is probably what gave EL84 amps such a bad taste in people's mouths. Everyone thinks that EL84's = glassy, brittle, low bass, and gritty distortion; not exactly true. EL84 tubes are actually VERY linear and will gladly amplify full-range sound amazingly. The problem is all the copying that goes on. Most amp makers would take the AC30 format and graft in their ideas and tweaks and then resell it. Well, it started as an AC30 and pretty much still ended up being an AC30. Before long all amps that are EL84 powered are placed into " That " type of sound category. The AC30 thing is an acquired taste and some can make it work, and others like me can't deal with it.
Getting back in line about how the PI and power amp are the core of the AC30 sound, let's compare it to a Marshall 18-watt ( AKA Watkins Dominator ). The amps have similar attributes with the exception that the 18-watt doesn't neuter all the bass and the original versions didn't have a cathode follower circuit. The PI and power amp sections are the same, but different... How is that you ask? Well, the PI in each are nearly identical in most regards. The majority of resistor values are different, but the topology is the same. Where they really veer off is the resistor values after the PI. The 18-Watt uses 470K while the AC30 uses 220K grid leak resistors. The Marshall has a LOT more gain going to the power tubes. The AC30 cuts a bit of level going to the power tubes. What this means is that the 18-Watt is spanking the power tubes pretty hard making them distort before the PI does, whereas the AC30's PI is distorting before the power tubes do. Another big difference between the two is the grid stopper resistors for the power tubes. The 18-Watt uses 8.2K's and the AC30 uses 1.5K's. The lower the resistance the brighter the sound. So while the topology between the two's output sections are identical ( aside from the number of power tubes and a cut control ), the AC30 has more grit coming from the PI and the power tubes are brighter sounding with the relatively small grid stoppers.
I recently designed an amp using EL84's and have the same power section topology as the 18-Watt and AC30. I of course used my own resistor and cap values and have what you could say is a hybrid of three different types of power sections. What I can say is that my amp is not lacking in bass and can give you the chime if you desire. My amp is designed to get PI breakup well before the power tubes do and I can say that PI distortion has a gritty kind of grind to it. It is smooth and sweet, but it has that edge and grit that makes designs like the 5E3 and other Fender amps famous.
I have a Strymon Iridium pedal, which has an AC30 emulation in it. I cannot for the life of me make it work. It is too bright, or too dark, and there just seems to be no way to get an even sound that is not trying to clear my sinuses out with an ice pick or sound like an amp with a mattress over it. With the Round and Punch channels, I can do what I need. In having actually used an AC30, it was so shrill and bright, I just couldn't stand to be near it. Having mic'd dozens up as a live sound engineer, I can say that it was hit or miss if they were just bright as ever-living shit, or somewhat decent sounding. Some say brightness is next to godliness, but the AC30 may have found God's mother then!!! The speakers it comes with do kind of contribute to that sound as well. Rhett Shull recently released a video going on about how much he loves the AC30. I will say that of all his intro songs and demos, the AC30 was my least favorite sounding. The chirp, brashness, and grit is just too much for me. Brian May has an arsenal of AC30's and they are HEAVILY modified. He runs his amps dimed and to me, they sound muddy and undefined, leaving me with the feeling that they were modified to cut LOTS of HF content; perhaps too much.
I say if you are gassing for one, pay the extra doh for a vintage model and look for a 1966 model. This is a darker sounding variant that uses the speakers that are synonymous with the AC30's sound. Certainly, try them out first, I think if you are not used to bright amps, the AC30 will definitely show you the meaning of it.
