Bias Tremolo Transistor Question

[theIntrepidGuitarist]

As one of my first "original" pedal projects I've been trying to design a simple bias tremolo around the phase shift oscillator found in the BYOC Harmonic Tremolo. I've been using LTSpice to simulate the circuit and I can't seem to figure out how to apply the right amount of both current and voltage to the base of the transistor. The oscillator works perfectly with no load attached, but when it is connected to the base of the transistor the wave becomes centered at 0V, hits a ceiling of ~0.7V, and dips to a large negative value. I've tried using a voltage divider to both change the bias of the transistor and reduce the amplitude of the oscillator, but nothing seems to keep the voltage from going negative, or maybe I couldn't figure out the right resistor combinations. The current also never seems to reach any significant value, only -1.9uA. In short, I would appreciate any input on how I can get the transistor to best act like a variable resistor. Thank you all for your help!

Below is the circuit without anything to attenuate the oscillator voltage since I don't know what the best option would be:




In green is the unaffected guitar signal, in red is the oscillator voltage with respect to the transistor base, and in blue is the current across the BaseCurrent resistor.

 

[Noodles]

Not related to your question (and probably not any help at all), but check out a Bennett Trema-donna or Blues Pearl Tejas Trem circuit for ideas on bias vary trems, particularly if you can find schematics (I haven't yet). Some day I'll take my Trema-donna apart and try to figure it out. I *think* they are based on transistors.

 

[theIntrepidGuitarist]

Not related to your question (and probably not any help at all), but check out a Bennett Trema-donna or Blues Pearl Tejas Trem circuit for ideas on bias vary trems, particularly if you can find schematics (I haven't yet). Some day I'll take my Trema-donna apart and try to figure it out. I *think* they are based on transistors.

Thanks for the suggestion! I did a quick search as well and couldn't find any schematics specific to those pedals. But for this project I've mostly been using this and this video as references and they discuss how transistor based tremolos work. Unfortunately, I obviously still have gaps in my knowledge.