- The over-whole MT2 tone (and the bass variation)
- The MT2 pedal sections: analysis
- Analysis of the Boss MT2 Metal Zone pedal (2)
- How to model an opamp? (the implications on simulation)
- Should I invert my matrix or not?
- Analysis of the Boss MT2 Metal zone pedal (1)
- From netlist to code: strategies to implement schematics modelling results
- From netlist to code: strategies to implement schematics modelling
- Analog modelling: The Moog ladder filter emulation in Python
- Analog modelling: A prototype generic modeller in Python
- Comparing preamps
- Triode circuit
- SD1 vs TS9
In the previous entry in this series, we saw the effect of the gyrator in a circuit. Now we can analyse each stage individually.
I will not show the individual circuit for each stage, but you can go on Github to download each circuit. I will use perfect opamp according to what I said previously in this series as well, so you will have to adapt the circuit to your LTSpice, or you can just use ATK filters as well and use the C++ code.
High pass
The first stage is a simple high pass and filters around 100Hz:
It’s very straightforward and only impacts notes on the first string of the guitar.
Pre-distortion tone-shaping
We now have a first non linear stage, as can be seen on a spectrogram:
The distortion is quite low but noticeable. The amplitude response shows a clear affinity for frequencies just below 1kHz, which is the meaty part of a guitar sound.
Band pass
The next stage is another linear one that slowly removes all frequencies above 100Hz:
Distortion level
The distortion level is a very aggressive amplifier with a small high frequency attenuation:
Distortion
Now we have the actual distortion stage. It has a small shelving effect:
And of course generates lots of odd harmonics:
Of course this stage is driven with the previous stage that has a huge amplification factor, so the effect will be more important that the one here with an input amplitude of 1.
Post-distortion tone-shaping
Now, we have the last stage that consists of a dual filter section:
This stage emphasizes frequencies around 100Hz and around 1kHz, which is very different from the SD1 and TS9 tone section (see previous entries in this series).
The spectrogram also shows additional harmonics generated by this stage:
Contrary to the first gyrator filter that was very quiet, this one generates far more harmonics, probably due to the higher Q factor of the low band pass section.
Conclusion
All things considered, there are three stages that generate distortion, almost all stages are filtering some frequencies one way or another and this can be heard in the pedal sound itself.
Of course, looking at each stage individually doesn’t tell us the full story. This is an investigation for next entry.