Chuck D. Bones
Circuit Wizard
I've been interested in the King of Tone for quite a while and finally got around to running sims and building a breadboard. The KoT is a pair of slightly modified Bluesbreakers in a single box. AnalogMan lowered the gain and added a charge pump for more headroom. He also added internal DIP switches for disconnecting the soft clipper and connecting a hard clipper. There is a Presence trimmer for increasing the brightness at the output. The two channels can be built the same, or there is a high-gain / low-gain option to make the channels different. The two channels are connected in series. The two stomp switches can engage either one, both or neither. Pretty cool design. By themselves, each channel has modest gain, around 40dB max. In series there is some serious gain and tone-shaping to be had. With the clippers disconnected, either channel can be used as a clean boost.
I saw some opportunities for mods. Here they are.
1. I kept the charge pump, but configured it to make ±9V in stead of +17V. Vref is now ground, which simplifies the biasing and removes the need for the output coupling capacitors. When we're building a circuit with opamps, it makes more sense to have split rails rather than one higher voltage rail and Vref.
2. I increased the gain of Channel 2 by cutting the impedances of C13, C14, R14 & R15 in half.
3. The Bluesbreaker and KoT roll-off the bass at the first stage to obtain the tone of a Marshall Hi-Treble channel. I added BOTTOM switches so one can add some or all of the bass back in, similar to bridging the inputs of a Marshall and turning up the Normal channel.
4. On channel 1, I moved the soft clipping DIP switch to the front panel and added an in-between selection. The soft clipping can be on, off or on but softer. This provides good control over the dynamics.
5. I replaced the hard clipping DIP switches with pots so we can blend in the hard clipping. It basically acts as a variable clean bleed on the hard clipper. This provides more control over the dynamics and tone.
6. I fiddled the impedance of the Presence filters a bit to make the presence trimpots more responsive.
Left side is the Rhythm channel (CH1), the right side is the Lead channel (CH2).
White knobs are VOLUME. Red knobs are TONE. Black knobs are HARD. Purple knob is LEAD DRIVE. Green knob is Rhythm DRIVE.
toggle switches L to R: LEAD BOTTOM, RHYTHM BOTTOM, RHYTHM SOFT CLIPPING.
The two trimpots are the Presence trims. I have them both set at 2 (9:00).
The schematic shows how the breadboard is configured, except I currently have NJM4580 dual opamps installed. I tried TL072s and they work well.
On the final version, I might add a SOFT CLIPPING switch to the Lead channel. So far, I don't think it's necessary. I'm considering adding an internal Volume Trim for the feed from the Rhythm channel to the Lead channel so that I can adjust how hard the Rhythm channel his the Lead channel without affecting the Rhythm volume.
Some of these mods are easily implemented on a Paragon board. The charge pump mod takes a little more effort, but should be doable. Most of these mods are also applicable to the Pauper. Many different clipping diode configurations are possible. The only caveat is that if we set the soft clipping threshold low, and the hard clipping threshold high, there is not enough signal to turn on the hard clippers. In the schematic below, if SOFT1 is switched to the right, D5 & D6 won't turn on. With SOFT1 in the center position (no soft clipping), it is possible to drive U1B to saturation if you dime DRIVE1 and have hot pickups or play aggressively.
I saw some opportunities for mods. Here they are.
1. I kept the charge pump, but configured it to make ±9V in stead of +17V. Vref is now ground, which simplifies the biasing and removes the need for the output coupling capacitors. When we're building a circuit with opamps, it makes more sense to have split rails rather than one higher voltage rail and Vref.
2. I increased the gain of Channel 2 by cutting the impedances of C13, C14, R14 & R15 in half.
3. The Bluesbreaker and KoT roll-off the bass at the first stage to obtain the tone of a Marshall Hi-Treble channel. I added BOTTOM switches so one can add some or all of the bass back in, similar to bridging the inputs of a Marshall and turning up the Normal channel.
4. On channel 1, I moved the soft clipping DIP switch to the front panel and added an in-between selection. The soft clipping can be on, off or on but softer. This provides good control over the dynamics.
5. I replaced the hard clipping DIP switches with pots so we can blend in the hard clipping. It basically acts as a variable clean bleed on the hard clipper. This provides more control over the dynamics and tone.
6. I fiddled the impedance of the Presence filters a bit to make the presence trimpots more responsive.
Left side is the Rhythm channel (CH1), the right side is the Lead channel (CH2).
White knobs are VOLUME. Red knobs are TONE. Black knobs are HARD. Purple knob is LEAD DRIVE. Green knob is Rhythm DRIVE.
toggle switches L to R: LEAD BOTTOM, RHYTHM BOTTOM, RHYTHM SOFT CLIPPING.
The two trimpots are the Presence trims. I have them both set at 2 (9:00).
The schematic shows how the breadboard is configured, except I currently have NJM4580 dual opamps installed. I tried TL072s and they work well.
On the final version, I might add a SOFT CLIPPING switch to the Lead channel. So far, I don't think it's necessary. I'm considering adding an internal Volume Trim for the feed from the Rhythm channel to the Lead channel so that I can adjust how hard the Rhythm channel his the Lead channel without affecting the Rhythm volume.
Some of these mods are easily implemented on a Paragon board. The charge pump mod takes a little more effort, but should be doable. Most of these mods are also applicable to the Pauper. Many different clipping diode configurations are possible. The only caveat is that if we set the soft clipping threshold low, and the hard clipping threshold high, there is not enough signal to turn on the hard clippers. In the schematic below, if SOFT1 is switched to the right, D5 & D6 won't turn on. With SOFT1 in the center position (no soft clipping), it is possible to drive U1B to saturation if you dime DRIVE1 and have hot pickups or play aggressively.
