Tdale wrote:Unfortunately, tone stacks are the part of an amp where I understand the least..
Which one of the stacks that you mentioned, are close to the hybrid? Any schematics posted here that shows the "correct" one?
Tommy
Tommy, I can give you a crude description of how the TS works. I am not sure which ones are the Hybrid XX or not, I've never used those schematics, but the information I included in my previous post should let you see whether they are the same tone stacks shown in the Hybrid schematics or not.
Anyway, I see the TS in the following way: The signal hits the input of it, at the very output of the preceding 12AX7 stage (V1A in Dumble's case). From there, there are two options:
1. Travel through a small coupling cap (330pF) to the treble pot, which will feed the volume control and the next stage, V1B. It is intuitive at this point that
the bigger this coupling cap, which is the treble cap, the more lower-frequency content will be able to pass to the next stage at high treble settings.
2. Travel through the slope resistor to the junction of the bass and middle caps. Right off the batt, this is telling you that
the higher the slope resistor, the more isolation there will be with respect to the middle and bass controls, or in other words, the stronger the effect of the treble control.
2A. After the signal has passed through the slope resistor, one possible solution is that it travel to ground through the middle cap and pot. The pot is a variable resistor to ground, so the lower the setting of the middle pot, the more signal will go straight to ground. Also note that the smaller the value of the middle cap, the less amount of lower-frequency content will be dumped to ground. Or in other words,
the smaller the middle cap, the thicker the amp will sound.
2B. Also after the slope resistor, whatever doesn't go to ground via the middle cap + pot, will try to go through the bass cap. At the output of that cap, the signal has two choices: either choose to travel to the bottom of the treble pot -- in which case it will make its way to the preamp volume control and therefore to V1B (next stage) -- or go to ground through the bass pot, if this path offers less resistance (i.e., depending on the setting of the bass pot).
In short, I see the tone stack as a panning control thanks to the treble pot. Dial that up pretty high, and the treble cap will have a lot to say about what the sound will be like; dial that lower, and then it will be up to the bass and middle controls to determine what other frequencies pass to the next stage, V1B.
Hope this helps,
Gil
