Posts Tagged ‘Vintage’

I don’t have time to type right now, but here are the images from the analysis for a 2 Channel Orange, 3 Channel Vintage on ch 2, and 3 Channel Vintage on ch 3.  The responses of the 2 Channel Orange and 3 Channel Vintage on ch 2 are very close.  Other factors could influence the differences between them.

2ch voicingandpresencevintageorange

2 Ch Orange

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I very quickly drew the negative feedback filter controlled by the presence control when using Vintage mode on a 2001 3 Channel Dual Rectifier.  The red line represents the -3 dB half boost mark from the point of the most filtering.  I tried drawing the entire phase inverter, but it didn’t make a difference on the plots, so I removed it and kept it simple.

R2 is being instructed to act as a variable resistor with 11 points to represent each 30 degrees of travel from 0 -10 on the control.  Anytime a part of the plot goes below the red line, the feedback is lessened by quite a bit and those frequencies pass the phase inverter more easily.  The maroon line on each picture is representing the control being at maximum and a massive amount of the frequency band is passing easily. (more…)

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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We’ve looked at the input and Clean, the voicing and Gain control, and V2.  Now, it is time to examine V3, the coupled cathode follower.  I urge you to read about cathode followers if you do not understand how they work and wish to learn more.

The biggest things for a novice to know are:

  • A cathode follower is usually used to lower impedance to drive a tone stack or an effects loop.
  •  The cathode of the second tube follows the voltage on its grid closely (hence “cathode follower”).
  • The first tube provides amplification of the signal and stability to the cathode follower.
  • When coupled (wired together), the two tubes act like one (mostly). (more…)

Here’s an example of the way I’m setting my amp lately.  It utilizes what I’ve learned about the Clean circuit, FX Send, Solo, and other things.   (more…)

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…)

ACDCPlexi VintageCleanThese settings are for an approach to getting some vintage tones from a Mesa Boogie Dual Rectifier.  The Clean uses the ideas I’ve been developing about a higher gain setting against a lower Volume setting.  It also has less Bass dialed in.  This made the moderate use of Mid and Treble possible to control sizzle and distortion.  The Presence is just an extra treble control, because Channel 1 has no negative feedback in the power amp.  This setting is very full through the mids and has enough bass and treble to sound good, without either dominating.

The Dirty setting is copping a nice late-70s AC/DC tone.  It sounded really good for many Classic Rock tunes that aren’t fuzzed up.  Raw has a lot of top and bottom rolled off.  It only needs a little nudge to move into Plexi territory, though it could take some more Mid if a person wished to do so.  The Solo is engaged and dialed-in just enough to change the top frequency response.   (more…)