The VFE SPS Dragon is a do-it-yourself pedal project from Madbean Pedals: a printed circuit board version of the VFE Dragon, a dynamic overdrive designed by VFE. The circuit uses two mosfet clippers to create the overdrive, and the design's defining idea is control over tone shaping: VFE describes the Dragon as "a dynamic overdrive designed to give you ultimate power over the pre-gain bass cut (HPF) and post-gain treble cut (LPF)"1. If you are new to overdrive as an effect type, see Overdrive Pedals for how it sits next to Distortion Pedals and Fuzz Pedals.
What the circuit does
The Dragon's approach sets it apart from overdrives built around a single tone knob. As Delicious Audio's Paolo De Gregorio put it in 2018, the pedal "lets you play with it through separate knobs controlling a Lo-Pass and a High Pass filter," giving the player separate control of the pre-gain bass cut (the HPF) and the post-gain treble cut common to popular overdrive circuits2. In practice that means you can shape how much low end reaches the clipping stage and how much top end survives it, which is more surgical than the fixed tone stacks on circuits like the Boss SD-1 vs Ibanez TS9 Tube Screamer comparison covers.
The SPS version adds the TrueSoft 3.4 switching PCB with the voltage inverter, which handles the pedal's bypass switching and internal voltage conversion1.
Controls and switching
| Control | What it does |
|---|---|
| LEVEL | Output level, described by Madbean as self-explanatory1 |
| DRIVE | Overdrive amount, described by Madbean as self-explanatory1 |
| HPF (High Pass filter) | Adjusts the pre-gain bass cut2 |
| Lo-Pass filter knob | Adjusts the post-gain treble cut2 |
| IMPED trimmer | On-board trimmer, see below1 |
Switching parts for the build:
- S1: On/On/On DPDT, pin mount. A pin-mount On/On DPDT may be used instead1
- Footswitch: SPST, momentary1
The IMPED trimmer is a set-and-forget control, not a panel knob. Madbean's document suggests that if you are using guitars with single coils or humbuckers, you try the Dragon with the IMPED trimmer set very low, because it can make the circuit more interactive with guitar volume changes1.
Building it
Madbean rates the SPS Dragon at build level Intermediate1. Points to know before ordering parts:
- Enclosure: the project includes a 125B drill template, so plan on a 125B enclosure rather than a smaller 1590B1
- Power: the design runs on a 9.44vDC One Spot supply with a split-rail design, drawing about 50mA with knobs at 50% and the switch down1
- Main IC: the surface mount version of the Dragon uses a OPA4134 quad amplifier IC, which is only available as an SMD package. It can be subbed with a TL074 or any other quad amplifier that can handle 18v or more1
The OPA4134 substitution matters for through-hole builders: since the SMD-only chip cannot be hand-soldered easily, the TL074 or another 18v-capable quad op amp is the practical route1.
Support and terms of use
Madbean directs technical assistance for the SPS Dragon to the madbeanpedals forum rather than email1. On what you may do with a finished board, the terms are specific:
- Purchased circuit boards may be used for both DIY and small commercial operations1
- PCBs may not be offered for resale or as part of a commercial kit1
- Peer to peer resale is fine1
For other VFE designs in the same family, the maker's terms of use allow purchased circuit boards to be used for both DIY and small commercial operations, though the boards may not be offered for resale or as part of a commercial "kit"; peer to peer resale is fine1. Related VFE overdrive circuits covered elsewhere on this site include the VFE Blues King, VFE The Scream, VFE Ice Scream, VFE Pale Horse, and VFE Merman.
Questions
What does the IMPED trimmer do on the Dragon?
The IMPED trimmer sets an input impedance character that changes how the circuit reacts to your guitar. Madbean's project document suggests that with single coil or humbucker equipped guitars, players try the Dragon with the IMPED trimmer set very low, because it can make the circuit more interactive with changes to the guitar's volume control. It is set with a trimmer on the board rather than an external knob.
What enclosure size does the VFE SPS Dragon need?
Madbean's project document includes a 125B drill template for the SPS Dragon, so the build is laid out for a 125B enclosure. That is a larger pedal enclosure than the standard 1590B size, which leaves room for the pedal's extra controls and the switching board.
Where do I get help with a Madbean Dragon build?
Madbean Pedals directs technical assistance for the SPS Dragon to the madbeanpedals forum rather than email support. If a build does not work or you have questions about parts and assembly, the forum is the place the maker points builders to.
Can I sell pedals built on Madbean PCBs?
Yes, within limits. Madbean's terms say purchased VFE SPS Dragon circuit boards may be used for both DIY and small commercial operations, and peer to peer resale of a built pedal is fine. What is not allowed is offering the PCBs themselves for resale or as part of a commercial kit.
Sources (2)
- VFE_SPS_Dragon.pdf, madbeanpedals.com, 2024-04-26
- VFE Dragon Dynamic Overdrive, Delicious Audio, 2018-09-21
