The Rocktron ValveSonic Plexi is an all-tube guitar preamp built as a rack unit, made by Rocktron in partnership with LA Custom. Rocktron describes it as capturing the vintage tones of the iconic British "plexi" amplifiers, from stacked amps and arena rock to the "Sunset Strip" era of rock and beyond1. MusicRadar's report on the announcement said the preamp aims to nail plexi tones spanning the 1960s to the 1980s and beyond2.
Where it came from
Rocktron announced the ValveSonic series in February 2018, developed with LA Custom, with the Plexi as one of the models in the line2. The series concept puts a tube preamp in a rack chassis while keeping a guitar-friendly input on the front panel: Rocktron notes that each ValveSonic model features a front panel input jack, so the unit can sit in a rack yet be played like a head1. The ValveSonic line also includes the Rocktron ValveSonic Black Plate +1.
Controls and connections
The front panel carries the input jack and the 1-2 switch. Rocktron explains that the 1-2 switch affects the input of the tube stage in the preamp: switched to "1", the unit provides the more "modern" British-style input, while position 2 gives a fatter "classic" vintage British input1.
The rear panel carries the fixed connections:
| Connection | Type |
|---|---|
| Input | 1/4-inch mono unbalanced, front and back1 |
| Output | 1/4-inch mono unbalanced, line out and instrument out1 |
The Afterburner circuit is the other tone control worth knowing. MusicRadar reported that Rocktron's Afterburner circuit, which adds an additional gain stage, helps to fine-tune the tone2. For a player, that means extra drive available beyond the preamp's own plexi-style gain staging.
Specifications
| Specification | Value |
|---|---|
| Tube type | 12AX7EH1 |
| Input impedance | 1M Ohms1 |
| Output impedance | <100 Ohms1 |
| Power requirements | 100 to 120VAC/1.0A, 220 to 240VAC/0.5A1 |
| Power consumption | 20W1 |
| Dimensions | 19 x 6.5 x 1.75 inches / 482.6 x 165.1 x 44.5 mm1 |
| Weight | 5.5 lbs / 2.5 kg1 |
The ValveSonic Plexi is a rack unit, not a pedal: Rocktron lists its dimensions as 19″ x 6.5″ x 1.75″ (482.6mm x 165.1mm x 44.5mm) and its weight as 5.5lbs (2.5kg)1, so it mounts in a standard rack rather than sitting on a pedalboard.
How it sits in Rocktron's range
The ValveSonic Plexi is a dedicated all-tube preamp, which sets it apart from Rocktron's programmable rack preamps such as the Rocktron VooDu Valve and the Rocktron Chameleon, which combine tube stages with digital processing and presets. Players after a single-purpose tube gain stage into a power amp or recording input are the audience for the Plexi approach, while players who want effects and MIDI memory in the same rack space are better served by those other units12.
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Questions
How much does the Rocktron ValveSonic Plexi cost?
MusicRadar reported at the February 2018 announcement that the ValveSonic Plexi was available then for $799. That was the list price at release, quoted in US dollars, and it is the only published price figure on record for the unit.
What tube does the Rocktron ValveSonic Plexi use?
Rocktron's product page lists the tube type as a 12AX7EH. That single tube runs the preamp's tube stage, which the 1-2 switch feeds at its input to shape the character of the gain.
Is the ValveSonic Plexi a rack unit?
Yes. It is a rack preamp measuring 19 inches wide by 6.5 inches deep by 1.75 inches tall, which is a standard single rackspace, and it weighs 5.5 pounds. Unusually for a rack unit, it also has a front panel input jack so a guitar can plug straight in.
What does the Afterburner circuit do?
According to MusicRadar's report on the announcement, Rocktron's Afterburner circuit adds an additional gain stage, which helps to fine-tune the tone. In practice it gives the player more drive on top of the preamp's own tube stage.
What is the input impedance of the ValveSonic Plexi?
Rocktron specifies the input impedance at 1M Ohms, with the output impedance under 100 Ohms. A 1 megohm input is high enough that a passive guitar's pickups are not loaded down, which keeps the tone intact going into the tube stage.
How much power does the ValveSonic Plexi draw?
Rocktron lists power consumption at 20 watts. The unit runs on mains power, with requirements given as 100 to 120VAC at 1.0A or 220 to 240VAC at 0.5A, so it is not a pedal-style 9V device and needs a wall outlet.
Sources (2)
- ValveSonic Plexi Tube Guitar Preamp, Rocktron (www.rocktron.com), 2024-08-28
- Rocktron aims to capture every era of Plexi tone with new ValveSonic all-tube guitar preamp, MusicRadar, 2018-02-22
