A couple of technical questions about the Mark IV graphic EQ

[shredi knight]

I need to know a couple of specific things about the on board graphic EQ on the Mark IV (the Mark series amps in general I guess):


1. What is the + and - decibel range of the faders?

2. What is the Q range of the frequencies (80hz, 240, 7550, 2200, 6600)?



Thanks.

 

[shredi knight]

(Bump)


Anyone know?

 

[Blueracer]

Ok I did some rough calculations on this. This is what I got for the equalization. The frequency ranges will have a low, high and resonate number with the low and high numbers being the 3 dB points. The dB ranges will be +/- and corresponds to the middle of the filter (resonance). I did this analysis fairly fast and made some assumptions that I would need to go back and verify. Also this is from the Mark iv equalization unit. I don't know if the eq units are all the same for various types of amps. Anyway here is what I got.

Band 1
Low : 61 Hz
High : 132 Hz
Res : 87 Hz
Gain Range : +/- 18 dB at res

Band 2
Low : 288 Hz
High : 480 Hz
Res : 371 Hz
Gain Range : +/- 18 dB at res

Band 3
Low : 574 Hz
High : 913 Hz
Res : 723 Hz
Gain Range : +/- 18 dB at res

Band 4
Low : 794 Hz
High : 3127 Hz
Res : 1576 Hz
Gain Range : +/- 13 dB at res

Band 5
Low : 2984 Hz
High : 7793 Hz
Res : 4823 Hz
Gain Range : +/- 13 dB at res

Note the resonate numbers should be the same as marked on the amps. They are not. Band 1 and 3 are close at 87 verses 80 and 723 verses 750 but the rest of them deviate quite a bit more. This could be my bad math or it could be Mesa's less than accurate schematics. If I get motivated I will go back and do a more careful analysis but for now this is it. Hope it helps.

 

[richt]

Ok I did some rough calculations on this. This is what I got for the equalization. The frequency ranges will have a low, high and resonate number with the low and high numbers being the 3 dB points. The dB ranges will be +/- and corresponds to the middle of the filter (resonance). I did this analysis fairly fast and made some assumptions that I would need to go back and verify. Also this is from the Mark iv equalization unit. I don't know if the eq units are all the same for various types of amps. Anyway here is what I got.

Band 1
Low : 61 Hz
High : 132 Hz
Res : 87 Hz
Gain Range : +/- 18 dB at res

Band 2
Low : 288 Hz
High : 480 Hz
Res : 371 Hz
Gain Range : +/- 18 dB at res

Band 3
Low : 574 Hz
High : 913 Hz
Res : 723 Hz
Gain Range : +/- 18 dB at res

Band 4
Low : 794 Hz
High : 3127 Hz
Res : 1576 Hz
Gain Range : +/- 13 dB at res

Band 5
Low : 2984 Hz
High : 7793 Hz
Res : 4823 Hz
Gain Range : +/- 13 dB at res

Note the resonate numbers should be the same as marked on the amps. They are not. Band 1 and 3 are close at 87 verses 80 and 723 verses 750 but the rest of them deviate quite a bit more. This could be my bad math or it could be Mesa's less than accurate schematics. If I get motivated I will go back and do a more careful analysis but for now this is it. Hope it helps.

Blueracer -You are a true devotee to help out our friend like that! I was going to say the frequency bandwidth (Q) was 1/3 of an octave like most graphic Eq's...maybe that's what your numbers say, but I'm not going to dig that deep! Enjoy this weekend and play those Boogies!

Cheers,

Richt

 

[shredi knight]

Well it took almost 2 months, but I finally got a reply. Thanks a lot for doing that Blueracer.

I originally wanted this information because I was trying to be as accurate as possible with the parametric eq on my Fractal Audio Axe FX. It has a Mark IV amp sim and I was using the parametric like it was the on-board graphic eq on the Mark series amps. So I wanted to know the dB range and the correct Q of the frequencies so I could accurately create the "Classic V' with the parametric. Even without the info, I got an absolutely killer tone with the amp sim that really sounds amazing.

Like richt was saying, I still don't understand what the Q range of the frequencies are from those specs.

 

[Blueracer]

The Q of the circuit is freq @ resonance divided by the 3 dB bandwidth of the circuit. Therefore for the 5 bands the Q is as follows.

Band 1 : Q = 1.225 Resonant Freq = 87 Should be = 80
Band 2 : Q = 1.932 Resonant Freq = 371 Should be = 240
Band 3 : Q = 2.133 Resonant Freq = 723 Should be = 750
Band 4 : Q = 0.676 Resonant Freq = 1576 Should be = 2200
Band 5 : Q = 1.003 Resonant Freq = 4823 Should be = 6600

Again note that the resonant frequency of the bands are not lining up with what is on the amp front panel. Bands 1 and 3 are pretty close but the others are significantly different. I believe this is because the scematics are suspect as the resonant frequency of these circuits is pretty easy to determine. The bandwidths I have calculated are for the LCR portion of the circuits. When I think about this it may not actually translate into the circuit quite like that so I will look into this more when I have some time. I am reasonably confident of the gain ranges at resonance for these bands though. Again all this needs to be double checked but I thought the community might like a first shot at this. Note it was the other thread about mid range response from a historical perspective that got me going on this. Again this is at least a start and I hope in some way helpful.

 

[shredi knight]

The Q of the circuit is freq @ resonance divided by the 3 dB bandwidth of the circuit. Therefore for the 5 bands the Q is as follows.

Band 1 : Q = 1.225 Resonant Freq = 87 Should be = 80
Band 2 : Q = 1.932 Resonant Freq = 371 Should be = 240
Band 3 : Q = 2.133 Resonant Freq = 723 Should be = 750
Band 4 : Q = 0.676 Resonant Freq = 1576 Should be = 2200
Band 5 : Q = 1.003 Resonant Freq = 4823 Should be = 6600

Again note that the resonant frequency of the bands are not lining up with what is on the amp front panel. Bands 1 and 3 are pretty close but the others are significantly different. I believe this is because the scematics are suspect as the resonant frequency of these circuits is pretty easy to determine. The bandwidths I have calculated are for the LCR portion of the circuits. When I think about this it may not actually translate into the circuit quite like that so I will look into this more when I have some time. I am reasonably confident of the gain ranges at resonance for these bands though. Again all this needs to be double checked but I thought the community might like a first shot at this. Note it was the other thread about mid range response from a historical perspective that got me going on this. Again this is at least a start and I hope in some way helpful.

Thanks a lot for that. I dialed those Qs in (as close as I could get to them anyway) with the parametric eq on my Mark IV patch and I'll see how it sounds tomorrow. I play pretty loud and it's a little too late for that right now. The tone at low volume was promising though. Gave a different character to it.

 

[Boogiebabies]

The Q of the circuit is freq @ resonance divided by the 3 dB bandwidth of the circuit. Therefore for the 5 bands the Q is as follows.

Band 1 : Q = 1.225 Resonant Freq = 87 Should be = 80
Band 2 : Q = 1.932 Resonant Freq = 371 Should be = 240
Band 3 : Q = 2.133 Resonant Freq = 723 Should be = 750
Band 4 : Q = 0.676 Resonant Freq = 1576 Should be = 2200
Band 5 : Q = 1.003 Resonant Freq = 4823 Should be = 6600

Again note that the resonant frequency of the bands are not lining up with what is on the amp front panel. Bands 1 and 3 are pretty close but the others are significantly different. I believe this is because the scematics are suspect as the resonant frequency of these circuits is pretty easy to determine. The bandwidths I have calculated are for the LCR portion of the circuits. When I think about this it may not actually translate into the circuit quite like that so I will look into this more when I have some time. I am reasonably confident of the gain ranges at resonance for these bands though. Again all this needs to be double checked but I thought the community might like a first shot at this. Note it was the other thread about mid range response from a historical perspective that got me going on this. Again this is at least a start and I hope in some way helpful.

There used to be a better online calculator. I used the same one the other day and it is way off.