HXDA & Dallas custom mods and related information
Thought I'd post this here...FWIW, it's the official description of how the HXDA "3 mini-toggles" that shift between the HX and the DA work. Also provides a description of how the Dallas' "tone stack lift" works...which mirrors Mark's (EM7) description from about a week ago. And, a bit of insight into how the "Kitchen Sink" mod on the HXDA functions.
From PRS and Matt King:
I talked with Doug and he given me the following description of functions for the two amps.
The switches on the back of the HXDA amp take the amp from a “bass” (DA) amp to a “lead” (HX) amp in incremental stages.
The first one changes a bypass cap value from brighter to fatter.
The second one adds a bypass cap to the cathode follower circuit—with the cap is “lead” gain-wise without is “bass”.
The third switch adjusts negative feedback. More negative feedback lowers gain and keeps the amp under control. Less adds harmonics and gain.
The series/parallel switch on back takes the two channels normally running parallel with each other (additive gain) and places them in series (multiplicative gain). It would be (circuit wise) similar to going from a plexi topology to a JCM 800 topology.
The tone stack lift on the Dallas adds back in what gain is normally thrown away in the tone stack circuit. The tone stack bleeds various frequencies to ground through the midrange pot. The switch just breaks the midrange pot connection to ground.
The gain boost adjusts the resistor that blends the dry signal with the wet reverb signal. Since the dry signal is so much hotter than the reverb signal, it is knocked down quite a bit with a relatively large resistor. The switch adjusts this big resistor down to a smaller value to add the gain back in to the circuit.
Just thought others might find this information interesting and potentialy useful.