When JMIL discusses Marshall's in-house engineering responses to the LA modder scene, the responsible named designer is Steve Grindrod — credited across multiple Marshall product lines that bracket the Jose era.
Per Dave Friedman in Amp Panel #14 (April 2026, ~[64:00, 107:52]):
> *"The guy who made these — Steve Grindrod — the guy who made the JMP, the Jubilee, he made all the 900s and he designed this."*
> *"This is the dude who made the JMP. He made the vintage 30. Like, he to me, he's a super legend."*
Grindrod-attributed designs in the Marshall lineage:
- JMP series (mid-70s onward) — the cosmetic-rebadge era of the Super Lead and the architectural baseline for the 2203 master-volume amp.
- Celestion Vintage 30 speaker (1986+) — designed by Grindrod for Celestion before he worked at Marshall. The most-cloned modern guitar speaker, used by everyone from EVH (5150 amps) to Pantera.
- Silver Jubilee (1987) — the LED-clipping JCM800 variant (technically LEDs are diodes, but the Silver Jubilee uses LED-pair asymmetric clipping in the lead channel — designer Steve Grindrod chose LEDs because of 12AX7-quality concerns at the time and they perform "the same thing as an extra tube would do"). Marshall's first factory production amp with hard clipping. Architecturally orthogonal to the 2203/Jose lineage but historically important.
- JCM900 series (1990–1999) — including the SL-X (2100/2500), the Mark III with diode clipping, the dual-reverb 4100.
Relationship to Jose: Per Friedman [Panel #13 63:44], Marshall had a Jose amp on the bench when designing the 900 series — *"I know this cuz I remember when they first came out and some guy from Marshall was talking about this with us"*. However, the 900 series's diode-clipping circuits were NOT copied from Jose — Marshall's implementation is asymmetrical and conceptually more derived from the pedal world (e.g., MXR Distortion+) than from Jose's symmetrical-Zener-across-MV-wiper topology.
Why naming Grindrod matters for JMIL: most JMIL discussions of Marshall's "in-house" or "factory" amps cite Marshall abstractly. Attributing specific designs to Grindrod adds historical fidelity and acknowledges the named engineering work behind the JMP-Jubilee-900 lineage that bracketed (and partially absorbed) Jose-era modder innovations.
Reference: For deep Marshall-side technical detail, Brent Ferguson's "SL-X Guide" on the Marshall Forum is the most-cited public technical writeup on Grindrod's later work — Friedman has endorsed it explicitly.