Mesa/Boogie graphic equalizer
The Mark Series Graphic EQ
One very well known and important feature of the Mark series is the on board graphic EQ. Analysis of a Mesa/Boogie Mark IV schematic revealed the following settings for recreating the famous amp's eq controls:
Frequencies:
- 87.61 Hz
- 371.74 Hz
- 723.43 Hz
- 1575.87 Hz
- 4822.88 Hz
Q:
- 1.414 (ideal for octave equalizer)
- 1.3 (actual, due to component values used)
There's about 18dB of cut and 17dB of boost. This is in the ideal world, so +/- 15dB was probably the design goal. The pot response is logarithmic – i.e. most of the cut/boost is near the end of the pot travel. Also, this is not a constant Q design, so the Q decreases (or bandwidth increases) with less boost or cut. I don't know if Cliff's graphic is constant Q, but the parametric should be constant Q, given you have a Q setting.
One of the most common uses of the on board EQ in the "Classic V" curve:
Shredi Knight had a great post on recreating this using the Parametric EQ after the amp sim...
The supposed real frequencies and Q's can be found [above], but I never liked how they sounded. I just use the actual frequencies as they appear on the front of the Mesa amps (like in the above pic) with the Parametric's default Q's (with a couple of exceptions) and it sounds pretty close to me (I can give you the exact settings I use if you want).
Here's the settings I use for the Parametric EQ on my Mark IV patch. It goes directly after the Amp block:
Parametric EQ:
F1 Freq. 80.8 Hz Q. 0.812 Gain. 8.79 dB Type. Shelving
F2 Freq. 238.8 Hz Q. 0.707 Gain. (minus) -0.47 dB
F3 Freq. 748.2 Hz Q. 0.718 Gain. (minus) -7.46 dB
F4 Freq. 2181 Hz Q. 0.707 Gain. 2.36 dB
F5 Freq. 6618 Hz Q. 0.707 Gain. 0.00 dB Type. Shelving
One very important thing is to use the Amp blocks Depth control. I use this instead of boosting the 238.8 Hz frequency in the Parametric EQ. Experiment with turning it up until you get the desired amount of "Thump". On my Mark IV patch the Depth is at 6.69, and is set to Active on the advanced amp page.
