The Vertex Steel String Drive MkII is a compact, 100% analog overdrive and clean boost pedal from Vertex Effects, voiced after the Dumble Steel String Singer amplifier1. It is the smaller sibling in Vertex's Steel String family: released in early 2020, it shrinks the original Steel String Clean Drive by about 33 percent while keeping the complete circuit, and adds a Jazz/Rock voicing toggle borrowed from the Dumble playbook123.
The pedal was designed alongside a real Steel String Singer, with reference unit serial #1, and Vertex owner Mason Marangella has said the company had access to Steel String Singer number one and used it to inform the design14. The amp it emulates is a rare thing: Guitar World notes Dumble's Steel String Singer was a 150-watt amp of which only 12 examples were made, and Stevie Ray Vaughan used one, as That Pedal Show pointed out when covering the original pedal5.
A Dumble Steel String Singer in a pedal
The Steel String line began with the original Steel String Clean Drive, which Vertex released in late 20166. Delicious Audio describes it as faithfully recreating the tonality and feel of the iconic Dumble Steel String Singer, and the MkII carries that voicing forward in a smaller box1. On That Pedal Show, Dan and Mick framed the original simply: "the steel string singer is like the legendary amplifier... the pedal that it's the dumbbell that Stevie Ray used"7.
The MkII update arrived in early 2020, adding a two-voice Jazz and Rock toggle, a feature Vertex also uses on its Special Overdrive series2. In Sweetwater's demo video, Marangella explained the shrink: "we took that original version and we shrunk it to about 33% smaller in size"8.
"I love the dynamic feel of this thing and how responsive it is and for me I like I like playing with a clean amp you know"
In that demo, Marangella described the pedal as working like a second clean amp on stage, with a dynamic, responsive feel8. Delicious Audio lists its roles as overdrive, fat boost, compression and EQ shaping, and says it delivers "Crystal-Clear Overdrive and Fat Clean Tones" through any clean amp platform, referencing albums like "Texas Flood", "Venus Isle", and "Continuum"1.
The controls and the Jazz/Rock toggle
The MkII keeps the layout simple: three knobs and one toggle1.
| Control | What it does |
|---|---|
| Gain | Below about 50% (before 1:00) the pedal acts as a clean boost with D-style coloration; above that it adds drive, and wide open there is enough gain for heavy drive tones38 |
| Filter | Tone control that helps focus the midrange19 |
| Volume | Sets the output level1 |
| Jazz/Rock toggle | Voices the low-end EQ; Jazz cuts a little bass, Rock leaves the low end fuller38 |
Vertex says the pedal can be quickly dialed in with the gain, filter and level controls, with the added Jazz/Rock toggle to better shape the low end3. In the Sweetwater demo, Marangella noted the toggle's Jazz position cuts a little bass8. Premier Guitar's reviewer found the filter knob "helps to focus the midrange" on the Steel String9.
The same Jazz/Rock voicing carries over to the larger Steel String Supreme, where Marangella confirmed "the jazz and rock work the same way as they do on the standard steel string mk2"4. On the Supreme, both toggle sets are three-way, with a middle position that bypasses those parts of the circuit4.
The MkII is a streamlined pedal by design. Players who want deeper tone shaping, including a Bright/Deep switch and an independent EQ section, are looking at the Steel String Supreme rather than this model1011.
MkII vs the rest of the Steel String family
The Steel String family now spans several models, and the MkII sits in the middle of them:
- Steel String Clean Drive (MkI): the original, released in late 2016, larger than the MkII6. A limited-edition gold version was made in only 200 pieces12.
- Steel String MkII: about 33% smaller than the MkI with the complete circuit, plus the Jazz/Rock toggle38.
- Steel String Supreme: the bigger sibling, described in Sweetwater's demo as what the MkII is the little brother of, "also great but without the expanded controls"4. It adds an independent EQ section and five extra tone-shaping controls over the MkII, including a Bright/Deep switch on top of the Rock/Jazz toggle, in the same enclosure size210.
- Steel String Slight Return editions: versions voiced for fatter lows and glassier highs, with the Rock/Jazz switch delivering "glassier highs and fatter lows"13.
In MusicRadar's 2024 A/B test, Marangella used Steel String pedals, including the Slight Return MKII mini, to recreate Dumble Steel String Singer multitrack tones from SRV, Eric Johnson and John Mayer recordings, and the piece describes the series as Vertex's Dumble-inspired Steel String preamp and overdrive pedals14.
What reviewers said
Vertex's own demo video, presented by Mason Marin, the owner of Vertex Effects, covers the Steel String Drive MkII, which he describes as based on the Dumble Steel String Singer amp8. In it he says he likes the pedal's dynamic feel and responsiveness, comparing it to playing with a clean amp8. The MkII was released in 2020 and adds a toggle for Jazz and Rock voicing, just like the original Dumble amps1. Vertex says the pedal was voiced after the legendary Dumble Steel String Singer, with the reference unit they used reportedly serial #11.
Sweetwater's demo video, presented by Vertex Effects owner Mason Marangella, walks through the gain, volume and filter controls, the Jazz/Rock switch, and how the pedal responds at different gain settings8.
Videos
Vertex Effects
Vertex Effects
Questions
Is the Vertex Steel String a clean boost or an overdrive?
It is both. Vertex says the flexible gain control allows use as a clean boost or an overdrive: below about 50 percent (or before 1:00 on the knob) it works as a clean boost with D-style coloration, and above that it moves into light overdrive territory. Wide open, it has enough gain for heavier drive tones.
What is the difference between the Steel String MkI and MkII?
The MkII, released in early 2020, is about 33 percent smaller than the original Steel String MkI while keeping the complete circuit, and it adds a Jazz/Rock voicing toggle for the low-end EQ, a feature Vertex also uses on its Special Overdrive series. The core three-knob layout of Gain, Filter and Volume carries over.
What does the Jazz/Rock switch do on the Steel String?
It voices the low-end EQ. In the Jazz position it cuts a little bass, while Rock leaves the low end fuller. Vertex describes the toggle as a way to better shape the low end, and the same Jazz/Rock voicing appears on the larger Steel String Supreme, where the toggles are three-way with a middle position that bypasses those circuit parts.
Is the Vertex Steel String Drive true bypass?
Yes. Vertex lists true bypass switching, mechanical, on the Steel String MKII product page, and press coverage of the MkII also describes it as true bypass. The original Steel String Clean Drive and the Slight Return editions are true bypass as well.
Steel String MkII vs Steel String Supreme
The Supreme is the bigger sibling: it keeps the MkII-style circuit but adds an independent EQ section and five extra tone-shaping controls, including a Bright/Deep switch on top of the Rock/Jazz toggle, in the same enclosure size. The MkII is the streamlined version, with three knobs and one toggle.
Sources (14)
- Vertex Steel String Drive MkII, Delicious Audio, 2020-10-14
- Vertex Steel String Supreme, D-Style Drive, Delicious Audio, 2021-09-16
- Steel String MKII, vertexeffects.com
- Vertex Effects Steel String Supreme Demo, Sweetwater, 2020-10-14
- Guitar World's 30 favorite guitar pedals from the past 5 years, Guitar World, 2025-06-02
- Delta Amp Overdrive / Vertex Steel String, Aion FX, 2020-06-05
- TPS Pick’N’Mix: Orange Fur Coat, Vertex Steel String, Walrus Audio Julia, Sinvertek FluidTime II, That Pedal Show (youtube.com), 2017-10-03
- Vertex Effects Steel String Drive mk 2 Overdrive Pedal Demo, Sweetwater, 2020-03-14
- Quick Hit: Vertex Effects Steel String Review, Premier Guitar, 2017-10-23
- Vertex Effects Steel String Supreme SRV Preamp Pedal Demo, Sweetwater, 2021-11-16
- Steel String Supreme (Slight Return Edition), vertexeffects.com
- Gold Steel String Clean Drive, www.vertexeffects.com
- Steel String (Slight Return Edition), vertexeffects.com
- Can a $249 preamp/drive pedal and a few commonly found stompboxes nail the Dumble amp tones of classic SRV, Eric Johnson and John Mayer tracks?, MusicRadar, 2024-02-16
