Over the past while I've been modding my MP1. It's really great!
- I unthrottled its drive circuit by getting rid of the clamping 8.2V Zener in the feedback of the op amp, replacing it with a 12V. I just the threshold of the clip LED accordingly.
- I changed the drive circuit's pre-eq band pass filter to be centered a little bit lower on around 1.6 kHz, down from 2.2.
- I redesigned the entire EQ. I no longer need an external equalizer!
- Bass rolls off lower. The -3dB point is 195 Hz rather than 312.
- Mid is wider and centered on 715 Hz rather than 560. It also has deeper cut/boost range. The bandwidth is from 320 Hz to 1.6 kHz
- Treble is no longer at 2.5 kHz. It is centered on 3.1 and is very narrow: from around 2.7 to 3.6 (Q factor of like 3.45 or so!). It sounds quite similar to a 3.15 kHz band on a 31 band EQ. (Edit: a week of playing showed that this was too narrow: I knocked the Q down to 2.0 (2.5 kHz to 4.0), while reducing the range for finer adjustment steps).
- Presence is no longer based on a band-pass filter centered on 5.7 kHz. I rearranged it to a two pole high pass making a shelving control. The -3 dB is at 5 kHz. This is intended for cutting. When you boost it it's freaking scary.
There's a lot more usable gain from the first tube being hit harder. Palm mutes are more meaty from the lowered frequency of the drive.
The EQ is such that I can go straight to a power amp. I have only one variable frequency low pass filter, in a mixer unit that sits between the MP1 and the power amp. That provides a bit of useful flexibility, like adjusting presence based on volume.
There's so much available mid scoop that I can use a solid state amp in voltage mode without any additional EQ needed to shape mids. This is not something I was specifically after but I just noticed it.
The ultra narrow treble control was intended for light boosting, to add some bite. It turns out to be very useful in creating a notch cut as well. With the Mid, Presence and Treble all turned down, those frequencies in the 1.6 to 2.5 kHz range receive emphasis, and Presence can be adjusted to bring some sparkle to that. It's a kind of nice surprise that there's this tonal flexibility.