I've done some more tweaking of the circuit. I first tried replacing C8 with a .01, thinking it would get me more highs. It did, slightly, but it didn't cure the muffled/muddy sound I'm still getting from the amp, and worse reduced the audible effect of sweeping the tone knob to almost nothing.
So I did some more reading and finally figured out how to use LTSpice to do more than just draw circuit diagrams. I made a schematic of just the tone stack starting at C7 and ending at the wiper of VR3, then did an AC analysis with sweeps for a few different positions of the wiper of VR3 to see just what the heck the tone stack is doing. I'm actually amazed by its simplicity. At one end of VR3's sweep the tone stack is a simple high cut filter. At the other end, it is a notch filter with the notch gradually shifting forward flattening out to smoothly transition into the high-cut filter. Thinking about how I run my EQ's on the other amp, it actually makes sense. Clean sounds tend to have a mid-range scoop to counter the mid-range emphasis that magnetic pickups supposedly have for a more natural, balanced sound. But when running heavy distortion, I tend to pull my highs back a bit to keep the distortion from sounding too harsh. So yeah, once again, the First Act designers knew exactly what they were doing.
By changing C8 to the same value as C10, I pretty much flattened out the mid-range notch. All lows and mids with rolled off highs sounds pretty muffled. Playing with a few values in the simulation I found out I actually want C8 to be a larger value than C10. Yes, a larger C8 rolls off more highs, but the greater the difference, the notch gets narrower and shifts it down in the frequency range. There are other places in the circuit I can get my highs back or reduce lows to keep the amp from sounding muffled. Also, changing C7 to a smaller value has a negligable (<-3dB) on the bass until the cap gets down into the .1µF range and lower. If I change C5 and C7 to 1µ, I get the bass down about -1.5 dB. I think I'd have to change C15 and C24 to 1µF to as well to see a -3dB reduction in bass. It'd be easier to change the input caps at each gain stage from .022µF to .01µF, methinks. So I'm not going to bother with C7 just yet. I'll play around with the values of C8, C10 and R7 in the simulation and see if I can't tweak the tone stack to my liking in the simulation, then I'll try it and report my findings.
Yes, I know I'm wasting my time. This is a fun learning experience.
So I did some more reading and finally figured out how to use LTSpice to do more than just draw circuit diagrams. I made a schematic of just the tone stack starting at C7 and ending at the wiper of VR3, then did an AC analysis with sweeps for a few different positions of the wiper of VR3 to see just what the heck the tone stack is doing. I'm actually amazed by its simplicity. At one end of VR3's sweep the tone stack is a simple high cut filter. At the other end, it is a notch filter with the notch gradually shifting forward flattening out to smoothly transition into the high-cut filter. Thinking about how I run my EQ's on the other amp, it actually makes sense. Clean sounds tend to have a mid-range scoop to counter the mid-range emphasis that magnetic pickups supposedly have for a more natural, balanced sound. But when running heavy distortion, I tend to pull my highs back a bit to keep the distortion from sounding too harsh. So yeah, once again, the First Act designers knew exactly what they were doing.
By changing C8 to the same value as C10, I pretty much flattened out the mid-range notch. All lows and mids with rolled off highs sounds pretty muffled. Playing with a few values in the simulation I found out I actually want C8 to be a larger value than C10. Yes, a larger C8 rolls off more highs, but the greater the difference, the notch gets narrower and shifts it down in the frequency range. There are other places in the circuit I can get my highs back or reduce lows to keep the amp from sounding muffled. Also, changing C7 to a smaller value has a negligable (<-3dB) on the bass until the cap gets down into the .1µF range and lower. If I change C5 and C7 to 1µ, I get the bass down about -1.5 dB. I think I'd have to change C15 and C24 to 1µF to as well to see a -3dB reduction in bass. It'd be easier to change the input caps at each gain stage from .022µF to .01µF, methinks. So I'm not going to bother with C7 just yet. I'll play around with the values of C8, C10 and R7 in the simulation and see if I can't tweak the tone stack to my liking in the simulation, then I'll try it and report my findings.
Yes, I know I'm wasting my time. This is a fun learning experience.