A Few Changes To Recto Articles

Posted: June 20, 2016 in Mesa Boogie Dual Rectifier, Tube Amps
Tags: , , , , , , , ,

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).

Additionally, the bias point is set to prevent clipping.  This type of clipping is referred to as bias excursion.  The screen becomes positive and draws electrons, clipping the signal and lowering the power output.  A Recto has significant sag and reacts more slowly to bias excursion than, say, any 100W Marshall.  Looking at estimates of load lines, I believe the power amp operates in Class A more often, because of an imbalance caused by the bias point.  This is also the cause of the non-linearity.

I also realized a mistake regarding the impedance load of V1 for channels 2 and 3.  The 2.2M resistor is in parallel to the voicing circuit and gain pot.  This makes the characteristic curves change and slightly reduces gain for Modern or Vintage.

I’ve been very ill and I can’t really go back through all the articles right now.  Just keep the new information in mind as you read through other posts.

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