Evolution of the tonal/midrange voicing in Mesa/Boogie amps-

[petejt]

(I posted this at HarmonyCentral, but would like input from here as well, please.)


I'd like to discuss the tonal/midrange voicing of Mesa/Boogie's amplifiers, in particular the Mark series amps and the Rectifier series amps.

How do you reckon the midrange voicing has evolved? It's obviously become lower throughout the years.

• But, how much has the midrange voicing changed between each amp?
• What is the frequency of the midrange knob on each amp?
• And how much does the midrange knob affect the tone of the amp? Is it a spiked/notched (high Q) midrange, or very wide (low Q) midrange frequency band?
• Why does the 5-band graphic EQ have the 750Hz band? Why not 800Hz?
• How narrow/wide are the frequency bands on the 5-band graphic EQ?
• Why did Mesa/Boogie choose to have the 5-band graphic EQ on their Mark series amps?
• And, why is the 5-band graphic EQ NOT included on the Rectifier series amps?
• How would a Rectifier amp sound with the "Classic V" set 5-band graphic EQ in its effects loop? Both with the midrange tone knob cranked and set low?
• Should the 5-band EQ be upgraded to 8 bands?

 

[shredi knight]

How narrow/wide are the frequency bands on the 5-band graphic EQ?


I asked this same question (along with wanting to know the dB range of the bands) almost 2 months ago and never got an answer, so I'd be interested in knowing as well.


http://forum.grailtone.com/viewtopic.php?p=109542&highlight=#109542

 

[Boogiebabies]

From Randall Aiken.

Have fun.

Tone Control Scaling
General

Scaling is the process of shifting an electronic parameter up or down. Frequency scaling refers to shifting the frequency breakpoints of a circuit up or down, such as moving the corner frequency of a low pass filter up from 1kHz to 2kHz, or down from 1kHz to 500Hz. Impedance scaling refers to shifting the impedance breakpoints of a circuit up or down, such as changing a tone control circuit that uses 1Meg pots to one that uses 500k pots, or changing a 75 ohm filter to a 50 ohm filter. Any tone control network or passive filter network can be frequency or impedance scaled very easily, by following a few simple steps.
Impedance Scaling
Impedance scaling is accomplished by first calculating an impedance scaling factor, ZSF, as follows:
ZSF = Znew/Zold
The impedance-scaled values are then calculated using the following formulas:
R' = R*ZSF
L' = L*ZSF
C' = C/ZSF
where
R', L', and C' are the resistance, inductance, and capacitance values after impedance scaling
Frequency Scaling
Frequency scaling is accomplished by first calculating a frequency scaling factor, FSF as follows:
FSF = desired frequency/existing frequency
The frequency-scaled values are calculated as follows:
R' = R
L' = L/FSF
C' = C/FSF
Frequency and Impedance Scaling
Both frequency and impedance scaling can be accomplished in one step with the following equations:
R' = R*ZSF
L' = (L*ZSF)/FSF
C' = C/(ZSF*FSF)
Examples
For example, if you have a tone control that has two 250K pots, and a 10K pot, and 250pF, 0.1uF, and 0.047uF caps, and a 100K "slope" resistor (standard Fender values), and you would like to impedance-scale the network to use 500K pots, you would use the following values:

ZSF = 500K/250K = 2
Pot1 and Pot2 =250K*2 = 500K
Pot3 = 10K*2 = 20K
R1 = 100K*2 =200K
Cap1 = 250pF/2 = 125pF
Cap2 = 0.1uF/2 = 0.05uF
Cap3 = 0.047uF/2 = 0.0235uF

(Of course, you have to round the values to the closest available 5% or 10% available components)
If you desired to shift the center frequency of the tone controls from 300Hz to 600Hz, you would calculate a frequency scaling factor as follows:

FSF = 600Hz/300Hz = 2
The frequency-scaled values would be calculated as follows:
Pot1 and Pot2 = 250K (no change)
Pot3 = 10K (no change)
R1 = 100K (no change)
Cap1 = 250pF/2 = 125pF
Cap2 = 0.1uF/2 = 0.05uF
Cap3 = 0.047uF/2 = 0.0235uF
If you desired to both frequency- and impedance-scale the circuit, you would calculate both a frequency scaling factor and an impedance scaling factor as follows:
ZSF = 500K/250K = 2
FSF = 600Hz/300Hz = 2
The new component values would be as follows:
Pot1 and Pot2 = 250K*2 = 500K
Pot3 = 10K*2 = 20K
R1 = 100K*2 = 200K
Cap1 = 250pF/(2*2) = 62.5pF
Cap2 = 0.1uF/(2*2) = 0.025uF
Cap3 = 0.047uF/(2*2) = 0.01175uF
One more thing to take into consideration is the driving source impedance. A typical Marshall tone stack is driven from a cathode follower, which has a very low output impedance (a few K) in relation to the tone stack impedance. A typical Fender tone stack is driven from the plate of a 12AX7, which has a 100K plate resistor, so the driving source impedance is around 38.5K (the 100K plate resistor in parallel with the 62.5K internal plate resistance of the tube). This source impedance can skew the center frequency and attenuation levels if it is significant in comparison to the tone stack impedance. This is not a problem with a cathode follower drive, unless the impedance of the tone stack is very low in comparison with the cathode follower output impedance.
These scaling techniques work on any passive RLC circuit, including tone controls, lowpass, bandpass, and highpass filters, crossover networks, etc.

 

[Restless Rocks]

(I posted this at HarmonyCentral, but would like input from here as well, please.)


I'd like to discuss the tonal/midrange voicing of Mesa/Boogie's amplifiers, in particular the Mark series amps and the Rectifier series amps.

How do you reckon the midrange voicing has evolved? It's obviously become lower throughout the years.

I hope Boogiebabies' most eloquent post has offered info you can use, however here's a simpler explanation from a guitarist.
I read somewhere that one of Randall's goals was to create a guitar voice with which the lead guitarist could replace the saxophone as the main solo instrument. The focused mid gain sound accomplished this quite well ala: the Carlos Santana sound. Although the scooped mid sound became popular with many as a chunk rhythm sound, it makes for a not so good solo sound. The single notes tend to get lost in the mix of drums, cymbals and bass. You could look at it this way; Many (not all, and no offense to differing opinions) really great lead/solo guitarists prefer the Mark sound and many (not all) into heavier, louder chordal rhythm like the Recto sound.

 

[Boogiebabies]

(I posted this at HarmonyCentral, but would like input from here as well, please.)


I'd like to discuss the tonal/midrange voicing of Mesa/Boogie's amplifiers, in particular the Mark series amps and the Rectifier series amps.

How do you reckon the midrange voicing has evolved? It's obviously become lower throughout the years.

I hope Boogiebabies' most eloquent post has offered info you can use, however here's a simpler explanation from a guitarist.
I read somewhere that one of Randall's goals was to create a guitar voice with which the lead guitarist could replace the saxophone as the main solo instrument. The focused mid gain sound accomplished this quite well ala: the Carlos Santana sound. Although the scooped mid sound became popular with many as a chunk rhythm sound, it makes for a not so good solo sound. The single notes tend to get lost in the mix of drums, cymbals and bass. You could look at it this way; Many (not all, and no offense to differing opinions) really great lead/solo guitarists prefer the Mark sound and many (not all) into heavier, louder chordal rhythm like the Recto sound.

So, basically you are not going to do the math either.

 

[Restless Rocks]

MMMM No! Leo Fender had the smarts to design the Bassman circuit, then Randall and Mike tweaked it to perfection! 8) I guess I'm really BiPolar when it comes to Boogies; in the day when I'm doing techy stuff I'm surrounded by text and computers, parts and numbers. When I plug my guitar in all I want to be surrounded by is the glorious sound of me, my Ibanez and my Boogie and I'm really glad these guys did all the wet work :wink:

 

[pmb]

[*]Why did Mesa/Boogie choose to have the 5-band graphic EQ on their Mark series amps?
[*]And, why is the 5-band graphic EQ NOT included on the Rectifier series amps?

The markseries have their normal EQ after the first gainstage.
The graphic EQ has a little bit the same function as the normal EQ in marshall type amps, where the normal EQ is more at the end of the preamp. Just like a rectifier.

 

[petejt]

Cool, thanks everyone so far for getting this discussion started.



But, does anyone actually know how much the midrange voicing has dropped between each amp?

Eg., what frequency is the midrange voice of the MarkIIC+? Of the MarkIV? Of the Dual Rectifier tremoverb?



Get an oscilloscope if ya have to

 

[darkbluemurder]

Looking at the schematics (I haven't played all M-B models) I would guess that the Mark I, II, IIa, IIb, IIc, III and IV have approximately the same midrange in the overdrive, the Mark I probably a bit less than the others, and the Mark IV probably the most. This is because both bass and treble frequencies are cut in the overdrive stages (caps to ground, plate resistor bypass caps) leaving the mids fully amplified. The Mark I circuit has less of these things.

As somebody mentioned the Recto is different as it stems from the Soldano SLO which in turn is a high gain Marshall with a Mesa Boogie Mark II flavor thrown in (= more mids than a typical Marshall). The Rectos definitely have less mids than any of the Mark Boogies.

I doubt you can measure the midrange frequencies unless you use a signal generator and a scope. The guitar and speaker have an influence, too.

Hope that helps.

 

[petejt]

Looking at the schematics (I haven't played all M-B models) I would guess that the Mark I, II, IIa, IIb, IIc, III and IV have approximately the same midrange in the overdrive, the Mark I probably a bit less than the others, and the Mark IV probably the most. This is because both bass and treble frequencies are cut in the overdrive stages (caps to ground, plate resistor bypass caps) leaving the mids fully amplified. The Mark I circuit has less of these things.

As somebody mentioned the Recto is different as it stems from the Soldano SLO which in turn is a high gain Marshall with a Mesa Boogie Mark II flavor thrown in (= more mids than a typical Marshall). The Rectos definitely have less mids than any of the Mark Boogies.

I doubt you can measure the midrange frequencies unless you use a signal generator and a scope. The guitar and speaker have an influence, too.

Hope that helps.

That does help. Thank you. 8)





I have another question though- why is it that on the Mark series amps as well as the Rectos, is the bass so excessive? People (including myself) often blame the Recto amps for sounding rumbly and flubby when the bass is cranked, especially with high gain settings, but apparently the Mark series amps also have this issue.

Why did/do Mesa/Boogie design/ed those amps with so much boomy bass?

 

[ToneAddictJon]

I think the extreme amounts of bass available are so that it's available if you need it
Some guitars and speakers (and f/x and cables and blah blah blah) lower the bass or don't put out as much bass (single coils vs humbuckers, different woods, different speakers) and this way you can dial in as much as needed, it's better to have more than enough available than having to push it to the max and not getting the response you want.

 

[Elpelotero]

would you rather want to run out of bass or have enough so you can turn it down?

 

[petejt]

would you rather want to run out of bass or have enough so you can turn it down?

It just seems that most of the bass available, is unusable.



Does anyone know why the 5-band EQ is not on the Recto amps?

 

[yettoblaster]

Wouldn't the frequency ranges reflect the sound of the era?

The cabinets are going to skew the ranges too.

I remember the 3/4 backs being evolved as tastes changed in combos and smaller cabinets (Thiel small cabinet design, et al) tried to sound deeper.

My early Mesa 4 X 12 was compact, and had a removable top back section for the Black Shadows (C90's), but the bottom EV's stayed in an infinite baffle section. Great outdoors and the drummer still got some splashed around sound for finding the "1" beat.

Marshall used infinite baffle (sealed 4 X 12) I think to limit speaker excursion because Jim Marshall was replacing a lot of blown speakers.

That became the sound (and look) of Marshalls. Never mind a Mark I was advertised as "...sending other amps running for their mammas..." or words to that effect, during that era.

As speaker adhesives evolved and P.A's got huge a full stack wasn't as necessary anymore, except it looked like Hendrix and everybody just played louder and louder, and mic'd those up too! 'Course by now stadium concerts were more common for more successful bands (and us garage bands didn't want to look wimpy down at the local club).

Marshall stacks had a "thump."

Naturally Mesa wanted to out-thump them, even if they were a different beast circuit-wise.

So the Recto (a much bigger 4 X 12 than mine) was introduced, and the thump wars began.
I mean, why should a bass player with an SVT have all the fun?

Naturally this is just the rambling memories and remembrances of a doddering old geezer who can't fit into my Spandex anymore, and is deaf from using big Ampeg 4 X 12's and V-4's with 1/8" "breather holes" in the back so the speakers COULD have more excursion (now that adhesives had improved) for more bass. :wink:

Anyhow as music became "heavier" sounding, bass was emphasized more I think.

Randall Smith used Fender tone stacks as a point of departure, and it seems to me he has always been interested in lower and upper midrange areas. Why else have graphic EQ's? But dusty sliders are problem prone.

 

[petejt]

^^ thanks for that, yettoblaster. 8)

 

[yettoblaster]

Welks.

And NOW everybody seems to be TUNING lower and lower.

How low can it go before bass rigs and guitar amps are the same? :wink: