tonestack questions

[myker]

hey guys im new here. i am interested in this active / plate driven tone stack. how does it differ from a regular marshall tonestack in the way it connects to the pots? i see the differences in the layouts and schems, but im not exactly sure but it looks like a regular marshall tonestack with the 100k not running to ground...
mike

[mhuss]

A plate-driven tonestack is 'less ideal' (whatever that means) then a cathode-driven one, because it has a higher output inpedance. That said, all mid-to-late period Fenders used plate-driven tone stacks, as did most other vintage amp manufacturers.

Grap Duncan's free tone stack calculator ()http://duncanamps.com/tsc/) to see graphically how changing the values change the response.

--mark h

[Moose]

A plate-driven tonestack is 'less ideal' (whatever that means) then a cathode-driven one,

Actually, what it means is simple. The lower the driving impedance before the tonestack, the less attenuation of the signal that occurs in the tonestack.

In other words, you get more signal after a tonestack when it's driven by a cathode follower because that circuit has a relatively low output impedance.

However, in the case of the 'wreck, the amount of attenuation is moot since there's a full on gain stage recovering the tonestack. In a normal marshall style (cathode follower) situation, the tonestack generally goes straight into the phase inverter, meaning the poweramp won't be overdriven at full volume if too much signal is attenuated there. We don't have that problem.

In fact, I have opined that one of the reasons this circuit is so amazingly touch sensetive is the fact that it can drive the PI better since there's nothing in the way right before it.

[s2]

The higher impedance of the plate driven stack also causes a shift in frequency response toward emphasizing bass. You will notice almost all amps that use this kind of stack use a 100K tone slope resistor to compensate, whereas cathode driven stacks usually use something along the lines of 33K or 47K as the lower impedance results in a flatter input curve.

How's it coming, Myker?