DIY 3-channel guitar preamp, part 2

In every project, there is a "doubt stage". This happens when after some tests, you wonder whether this whole project is a really good idea or just a huge waste of time.

The tests

It happened to me. After the original excitement, I tested on my breadboard the CD4049 based 3-channel circuit and honestly, I was not amazed at all. The sound that I liked years ago did not have the same "waow" effect : too fuzzy, not very vivid or open, rather flat and sometimes harsh. I has to be honest with myself: the CD4049 is not the right thing for this 3-channel preamp project !

Aouch! This IC was the core of the project! I have to start from the beginning, which brings me to the question: why do I want all this?  I am (quite) happy with my sound now. OK, my Boss GT-PRO might be a little old, and its sound is not that "open", but thanks to an DIY analog booster before and a double (stereo) analog DIY cabinet simulator after, the sound is not digital anymore and is fully playable. So what's the point?

Yes, but... 

After years of playing with the GT-PRO, I feel like the sound is always the same. There are tons of amp simulations and I used only 3 or 4 of them... So what do I want ?

(New) list of features

  • Simpler interface with only 3 main sounds, Clean, Rhythm and Lead
  • An integrated treble boost with a variable frequency filter
  • A real Clean sound, open, chimy, with singing tones, ready to break-up a little with high output pickups or the on-board booster of my Lady Blue guitar
  • A Rhythm sound that is not so much driven, but thick and mellow, very Brian May-ish, and very (very) sensitive to the guitar volume pot. I want a clean sound when the volume pot is at 1 or 2 on the guitar.
  • A Lead channel that is naturally compressed, with a good note-to-note separation and a good sustain (though it is very guitar-dependent...)
  • A MIDI controlled channel selection
  • A stereo output using a pseudo-stereo image: adding 10-20 ms of delay on one output
  • The possibility (inspired by Steven Wilson) to assign one channel on the left and another one on the right. Imagine a clean-overdriven sound!

Instead of relying on ONE circuit for all 3 channels, I will search for one circuit per channel. I preselected the following pedal schematics as a short list. Maybe that the next step is to build them all and to compare them.

Some inspiring schematics

RunOff Groove Azabache for Clean Channel

Dr Boogey for Lead Channel

Nobels ODR-1 for Rhythm Channel

Fulltone OCD for Rhythm Channel

Wampler Plexi Drive for Rhythm Channel

Zendrive for Rhythm Channel

ZVEX Box Of Rock for Rhythm or Lead Channel

As you can see, wide is the choice! And I guess that I will add a very open yet warm compressor at the very beginning of my signal chain. The Orange Squeezer is a good candidate.

Orange Squeezer compressor

New feature : I want to be able to select left and right channel independently. Which gives the overall architecture:

As a conclusion: I am far away from having my preamp ready or even completely imagined. Stay tuned, I will keep you posted of the evolution of my project.