Contrasts of Filter Response For Dual Rec 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.

2 Ch Orange

Advertisements

Mesa Engineering Dual Rectifier Presence Pot Frequency Plots

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.

Visualizing Graphic EQ Curves and Level

I put together a rudimentary representation of the effect on filter curves when setting a graphic EQ.  It isn’t exact.  Use it to get a general idea for the way a graphic EQ shapes the signal.

Boss GE-7 For Boost or Tone Shaping

Blank Settings Form For Boss GE-7

Using an equalizer to boost the guitar’s input signal makes a lot of sense.  It provides a clean gain and a lot of headroom.  Aside from boosting the signal, it can, of course, be used to carve out specific frequencies.  Unlike most overdrive pedals, an equalizer has the ability to be very precise with multiple frequency bands and can create special effects.

The downside to this specific pedal is noise.  It uses cheap tantalum capacitors in the signal path.  This creates a hissing sound when the sliders are moved away from the zero mark.  The MXR 10 Band EQ is reputedly better, but I don’t own it and can’t comment about it further.

Cathode Mods: Mesa Dual Rectifier 3 Channel

In any tube amplifier, the cathode resistor can be bypassed with a capacitor to increase the gain.  Aside from the benefit of wringing extra gain from each stage, a shelving filter is created by this RC combination.  Since the resistor sets the bias of the stage and would normally need to remain at a particular value, the capacitor can be be chosen, or changed, to set the cut off of the filter.

In most modern guitar amps, the cut off is set to voice the stage for a particular bass response.  While there are many filtering options in an amp, the cathode cap is  powerful.  The frequencies below cut off are amplified much less, which means that frequency also gets driven less during overdrive or clipping.  For low frequencies, this is important.

RC Filter Spreadsheet Chart

I decided to have one hanging up and figured someone else may want the same.  Some values are rounded, but with tolerances, it’s all ballpark anyway.

RC Filter Chart