Marshall Bluesbreaker
Soft-clipping op-amp overdrive that became the blueprint for the King of Tone, Morning Glory, and every modern 'transparent' OD.
We don't ship reference schematics until they've been hand-authored against authoritative sources (manufacturer service docs, ElectroSmash analyses, GEOFEX writeups) and reviewed in the simulator. Until then, the BOM, signal chain, controls and mod notes below are accurate, and you can still add this pedal to a project — it just won't include a circuit yet.
About
A TL072 dual op-amp with a single non-inverting gain stage feeding back through two pairs of soft-clipping diodes (4× 1N4148, two each direction). The voicing is much more open than a Tube Screamer — gentler mid-hump and a wider low end — which is why nearly every 'transparent OD' on the market is some refinement of this circuit.
Signal chain preview
5 stagesQuick facts
- Originally a discontinued Marshall pedal sold in small numbers; soared in value after the Bonamassa endorsement.
- Analogman King of Tone, JHS Morning Glory, and Wampler Pantheon are all Bluesbreaker descendants.
- Uses a charge pump on later revisions to run the op-amp on ±9V for more headroom.
Controls
- Volume
- Tone
- Gain
Mod recipes Pro
3 mods- Morning Glory tone stack
More usable treble and a 'bright' switch.
How: Reduce the tone-cap to 220 pF and add an SPDT switch wiring a 470 pF cap across the input series resistor for the bright mode.
- Asymmetric clipping
Adds even-harmonic grit.
How: Replace one pair of 1N4148s in the feedback loop with a single LED — gives 2:1 asymmetric clipping.
- Charge-pump 18V
More headroom and dynamic response.
How: Add a TC1044S/MAX1044 charge pump to feed the TL072 with ±9V rails. Verify all coupling caps are rated >25V.