Understanding the Signal Path through the Circuit

[Decko]

Hi All,

I am trying to understand the schematic.
Is there a summary describing the signal path and how it is amplified through V1 though the tone stack to the PI, etc? I would like to understand how this circuit differs from let's say a Marshal JMP. How is Ken's layout and use of cap and resistor values through the circuit create the touch and tone of the circuit? What is the mojo or magic of this circuit?

Thanks!
Danny

[gearhead]

As far as I know, there is no summary. Would love to se it. Many observations spread around.

One BIG thing is that the first point of distortion is the power tubes, by design. It's a distortion with different characteristics than preamp distortion, besides being dang loud. That also effects the way the volume knob works.

There is an effective increase in volume only for the first quarter turn of the volume knob. After that the distortion kicks in at the PTs, then PI, and finally the preamp. Most folks set the volume knob at 1 oclock and use the guitars volume knob for volume/distortion control. That works -extremely- well. If you've seen Glen K's vids, that's what he's doing.

Another is the .0022uf cap before the third triode. That and the 150k resistor function as a high pass filter, and a pretty high one at that. Makes it pretty trebly.

[Decko]

So the Trainwreck is designed to bring the PT's to distort? Perhaps this is the magic that allows the amp to overdrive by turning the volume up on the guitar.

I am in process of building my own wreck. Procuring parts from Allyn that are detailed in yours and Ron's BOM. However, my desire in not only to build "copy exact" but also understand the the design topology. For example: Mesa Boogie Mark 1 uses a gain make up stage after pots then a cascading gain stage to get that sizzling distortion tone but one cannot control the distortion as well using the volume nob on the guitar like the wreck.

My first analysis of the Preamp Signal Chain:

1/4 inch input
1 meg resistor to prevent open-circuit hum

1st triode - the first gain stage
Pin 8 is the cathode which is biased with a 1.5 k ohm resistor and a 25uF/25V cap provides the low freqency roll off
Guitar Signal enters pin 7 which is the grid.
Then increases gain as it moves to pin 6 (plate)
From pin 6, signal travels toward the tone stack by way of two paths.
Path 1 toward Bass and Middle via 100K resistor split at the junction of two .022uF coupling caps.
Path 2 toward the Treble via 500pf cap.

I assume that the signal is then carved up at the pots by grounding bass, middle and treble frequencies then joined back at the vloume pot.

From the volume pot we go to the second gain stage
2nd triode
Pin 3 is the cathode which is biased with a 2.7 (lower gain? differs from 1st triode) k ohm resistor and a 25uF/25V cap provides the low freqency roll off
Volume pot signal enters pin 2.
Signal increases gain as it travels to pin 1 (plate).
From pin 1 signal goes toward the 3rd triode via .022pf cap (how does this cap affect the signal?)and 1.5k resistor then enter pin 2.

To be continued...wife is calling..

[flood]

From pin 1 signal goes toward the 3rd triode via .022pf cap (how does this cap affect the signal?)and 1.5k resistor then enter pin 2.

^^
i imagine you mean 0.0022 µF cap and 150k resistor - 0.022 pF would be like entering tinnitus country. this is highpass filter. roll off at about 483 Hz.

something i noticed is the use of two 10 nF caps in parallel for coupling, with different materials - this might contricute to the "organic" sound so many people talk about. i have never had the joy of playing a trainwreck, so i couldn't tell you...