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
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…)
Update: This is the final version of the DR Booster:
The R10 is actually a pot, not a resistor. With R10 at 10k, the boost is 19.1 dB; At 0 it is 3.5 dB. The frequency band is 33 Hz – 2.9 kHz, with 330 Hz as the center. (more…)
In some of the articles, I made statements regarding a possibility of mild power amp drive, because I had not had time to really dig into the power amp to confirm or deny it, and due to the sound of Modern mode. The power amp does not overdrive. If you come across anything relating to this, any descriptions should be discarded if they contradict the following paragraphs.
Modern has some distortion present, but it isn’t clipping distortion; It’s regular ol’ harmonic distortion, which is otherwise known as “the tube sound”. I don’t have time or energy to get into it, but the power amp is designed to stay as clean as possible, but tubes do not always amplify in a “linear” way. This adds curvature to the sound waves, distorting them by bending (coloring the sound). (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…)
The purpose of the article about changing the anode resistor value was to improve the clean channel and smooth the dirty channels. That is exactly what it will do, but I wanted to talk about conceptual ideas regarding this change. I’m going to use pedals for illustration and then translate that over to tube amplifiers.
I used to build guitar pedals and I’ve spent a lot of time cascading circuits into each other. While transistors and op amps react differently than tubes, the overall result on dynamics is similar from one component to another. (more…)
I had just a few thoughts come to mind regarding modifying amps, modifying EQ, or creating your own.
It’s a fact that Mesa Engineering uses two modified forms of the Marshall tone stack for their Dual Rectifier series. Compared to a classic Marshall tone stack, the Vintage/Raw tone stack moves the center of the “Mid” control down in frequency and has more attenuation. This carves out some of the meatier part of the guitar frequency to make room for the massive lows and a high-mid emphasis. The tone stack enabled for Channel 3 Modern has boosted upper-mids, but has a very similar, low-to-low-mid frequency response. (more…)
(Note: During the initial 5 year period of warranty, using tubes other than those branded by Mesa will void the warranty of your amp. This article is meant for people who have amps which are not under warranty.)
Mesa’s 6L6GC STR tubes are manufactured in China for Ruby Tubes. It is a reproduction of the classic Sylvania 6L6GC STR. Mesa buys a big batch from Ruby, tests them, keeps the tubes that meet their requirements, and sends back the tubes which fall out of range. Ruby’s matched version of this same tube is the 6L6GCMSTR. It costs considerably less than Mesa’s tubes. (more…)
(Edit: I confused some 6L6 sub-types in the original article, which I don’t think is hard to do).
I ran across this article about Sovteks and how the rating charts for several tube brands compare. I am needing tube replacements and this seems pretty handy for finding tubes that fall into Mesa’s bias range for their 6L6GC.
I’ve been using Ruby 6L6GCMSTR, which is an excellent tube, and I will likely stick with it, but these others have piqued my interest in differences between the sub-types. (more…)
