Posts Tagged ‘Modern’

The idea was to take Vintage on Channel 2 and make it sound very similar to Modern on Channel 3.  The results ended up being very close, but I didn’t have the time to completely match the EQ (for the most anal of comparisons).  The overall response was what I was going for and that is achieved.  (more…)

EQ Schematic

Schematic of tone stacks for Channel 2 and 3.  Note the Presence control circuit and the value differences for its resistors

When Modern Mode is selected on Channel 3 of a Dual Rectifier, an additional capacitor is added to the circuit.  This changes the capacitance value from 500 pf to 680 pf.  By doing this, it moves the frequency from which the treble swings on axis from 1.27 kHz down to 936 Hz.

The effect of this change is twofold: 1) The upper mids receive a greater emphasis in the sound; 2) The overlap of range between the Mid control and the Treble control forces the Mid frequencies to move up in dB, effectively giving a mid-boost throughout the range of the Mid control.  The change also prevents the Mid control from being as scooped at the minimum setting by about a maximum of 2 dB between 600 Hz and 800 Hz.

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June 2016- I realize the flow of this article could use some work.  I have plans to reorganize it at another time.  

We’ve looked at the input and Clean, the Mode voicing and Gain control, V2 and V3EQ and modes and Presence.  I am going to bring it all together and take a less detailed, wider, view of the system as a whole.  I’m concentrating on Channels 2 and 3, since they are the primary identity; the “Recto” sound.

Additionally, I’m going to cover a little bit about the power amp, even though I have not concentrated on it in my writing this year.  I think the intention of Mesa when designing it is misunderstood.

I’m going to be making certain assumptions based on the overall design and historical precedents in guitar amplifiers and Mesa designs.  I could be wrong, but I am presenting it the way I best understand it, based on how everything interacts, and considering the differences between this amp and others much like it.  Mesa tends to tune their amps by ear, so some of the effects from changes may be unintentional or accidental.  That doesn’t negate the actual effects from being valid points innovation on the design.

For filter analysis, I’m using the Okawa website.

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I already covered the input stage and clean channel.  I’m not going to repeat the information about the input, except for applications to the dirty tones.

The input stage is followed by a coupling cap and a 2.2 M load resistor.  Most amps made prior to the Recto place the grid resistor between the coupling cap and the load.  The load is usually a potentiometer to control gain.  Mesa eschewed this and it’s one of the innovative ideas that distinguishes the amp from others like it.  I can only speculate the exact reason they made this change, but I suspect stability is the main one.  The resistor to ground also gives a path for stray electrons to prevent popping when changing mode relays. (more…)

This is in regards to the Presence circuits for a 3 Channel Dual/Triple Rectifier and the Roadster/Road King.  I do not have information on the Reborn or miniature versions, though I suspect they kept it pretty much the same.

Mesa came up with a clever Presence circuit for the 2001 3 Channel Rectos, which carried over to the Road King and Roadster on their relative channels.  For the sake of flexibility, the Presence pot is flanked by relays to swap the function between modes.  The modes are used to determine power amp response due to negative feedback and the amount of distortion it is capable of producing.  From most to least: Modern, Vintage, and then Raw.

Using Modern, the negative feedback is disconnected and treble frequencies are being attenuated by an RC filter connected between the the Presence pot and the wiper of the Treble pot.  Using Vintage, negative feedback is being fed from the transformer to the PI.  The amount of feedback is controlled by the Presence pot, which also sets the frequency cutoff; it has dual functions as a resistor divider and a filter.   Raw is a special case and is discussed on its own below.  I will be using Channel 2 for the examples, but I will contrast the circuit differences with channel 3. (more…)