The JCM 900 Dual Reverb was produced by Marshall during the 1990's. Marshall engineers voiced Channel A for sparkling clarity but added enough percussive punch to kick out every note. Channel B provided "potent gain and grinding aggression" for solos. Each channel has its own reverb control. The Dual Reverb sounds so fine that no less than ZZ Top bluesman extraordinaire Billy Gibbons used a quartet of model 4100 heads during the band's Recyler world tour.
- Separate preamp gain controls: Channel (A) 1-10, Channel (B) 0-20
- Tone network with Treble, Middle, Bass, and Presence controls
- Individual master volume controls for each channel
- Separate reverb controls for each channel
- Manual or footswitch operation for channel selection
- Effects loop with sensitivity control
- Direct and recording compensated line ouputs
- Impedance selection switching
- Two speaker outputs
- High/low power switching (pentode to triode)
- Valve failure LEDs
- Entirely wired and assembled by hand in England
- 100 watt models (model numbers 4100, 4101, 4102) feature 4 x 5881 output valves, 3 x ECC 83 preamp valves
- 50 watt models (model numbers 4500, 4502) feature 2 x 5881 output valves, 3 x ECC 83 preamp valves
- Note: some models came factory equipped with EL34 power tubes instead of 5881s.