DIY 3-channel guitar preamp, part 1

I am starting a new and ambitious DIY project : a 3-channel analog guitar preamp ! I listed here the goals or features that I need:

List of goals/features

  • MAIN GOAL : getting rid of amplifier simulations. I want my sound, more limited (no longer 56 amp types combined with 34 cabinet types) yet more authentic ! So it will be analog.
  • NO TUBES. I hate tubes. It will rely on JFET and MOSFET transistors.
  • 3 channels : Clean, Rhythm and Lead for solos. 3 stages of distortion
  • 3 independent tone stacks : VOX inspired for Clean, MARSHALL inspired for Rhythm and Lead
  • A treble boost will be included as very first stage
  • The channel selection will be MIDI controlled for live purposes
  • and no cabinet. It will be simulated with the RunOffGroove Condor circuit.

Some years ago, I crafted a pedal based on the CD4049UBE chip that had a great sound. Unfortunately and for an obscure reason, I dismantled it. However, the design was a success. Therefore is becomes now my main inspiration to design my 3-channel guitar preamp.

The blueprints

Based on the Double D design of RunOffGroove and also on the latest Hot Harmonics design from Frank Clarke, I am currently drawing the blueprints of my preamp.

Double D, by RunOffGroove

Hot Harmonics V3, by Frank Clarke

The Double D uses 5 inverters of the 6 available on the CD4049. I will use all of them!

  • 1 inverter for the Clean channel
  • 2 inverters for the Rhythm channel, based on the Jiggle channel of the Double D
  • 3 inverters for the Lead channel, based on the Hot Harmonics design, with 2 gain knobs

Regarding the treble booster, I crafted exactly - without any modifications - the Omega booster from RunOffGroove.

The tone stacks

For the tone stack, I used the very cool freeware Tone Stack Calculator by Duncan Amps (for Windows only) to design the two following tone stacks:

Treble Bass tone stack for Clean channel

Treble Mid Bass tone stack for Rhythm and Lead channel

As you may notice, I try to set a mid scoop frequency to 700-800hz for a best result to my ears. But as they are analog tone stacks, this frequency can move from 600hz to 900hz depending on the Bass and Treble knobs position.

The cabinet simulation

For the cabinet simulation, I already crafted a RunOffGroove Condor in stereo. I will re-use this version.

Now that I have all the information I need, the next step for me it to try and play with the CD4049 (=try different values of resistors and capacitors). And for this purpose, I need to create a fully equipped test bench. To be continued...