Marshall

JMP 1992 Super Bass 100W – 1974 – Japanese Export Specification

A superb 1974 Marshall JMP 1992 Super Bass 100-watt head, built for the Japanese market and representing a particularly interesting variation of Marshall's legendary early-'70s Super Bass.

The 1992 Super Bass is one of the great vintage Marshall circuits. Originally developed as the bass counterpart to the 1959 Super Lead, it quickly became a favourite among guitarists looking for a bigger, warmer and more rounded response than the brighter, more aggressive Super Lead.

With its 100-watt all-valve output stage, four-input layout and non-master-volume circuit, the Super Bass delivers enormous headroom, exceptional dynamics and a wonderfully rich, full-bodied sound.

This example dates from 1974, placing it firmly within the highly regarded metal-panel JMP period, and carries serial number 6488F. The circuit is very original with red shellac present on most solder joints and the amp comes with a period Rose-Morris/Marshall sticker on the front(see pictures).

Japanese Export Specification

This particular amplifier was originally manufactured for the Japanese market and features several differences from the more familiar UK and European models.

Most notably, it has a hardwired mains cable rather than a detachable IEC connection, and there is no external voltage selector on the rear panel.

These are features associated with certain export-market Marshall amplifiers of the period and form part of what makes this example particularly interesting.

For customers in North America, our amplifier engineer can configure the amplifier for 110V operation before shipping. This work will be carried out professionally, ensuring the amplifier is correctly configured for its destination.

Please contact us before purchasing if you require a different mains voltage configuration.

Classic Super Bass Tone

Although originally designed as a bass amplifier, the 1992 Super Bass has long been one of the most desirable vintage Marshall circuits for guitar.

Compared with the equivalent 1959 Super Lead, the Super Bass generally offers a warmer, fuller response, with a thicker bottom end and a slightly smoother, less aggressive top end.

There's enormous clean headroom available, but when pushed, the amplifier develops a wonderfully rich, harmonically complex overdrive with incredible depth and authority.

The two channels can also be jumpered, allowing the brighter and darker inputs to be blended for additional tonal flexibility.

Whether paired with a vintage Greenback-loaded 4×12 or a more powerful G12H cabinet, the Super Bass delivers that unmistakable early-'70s Marshall sound — huge, open and exceptionally responsive to the guitar.

Recently Professionally Serviced

The amplifier has recently undergone a comprehensive professional service by Dave Wittering, former Marshall senior service engineer.

The work was completed in September 2026 and included:

• Replacement of the bias circuit smoothing capacitors
• Replacement of the polarity decoupling capacitor
• Installation of a dedicated chassis earth
• New matched quartet of OEM Marshall EL34B output valves
• Three new OEM Marshall preamp and phase inverter valves
• Replacement OEM Bulgin HT fuse cap
• Electrical safety inspection
• Full operational testing

The amplifier has therefore benefited from a fresh complement of Marshall valves alongside important electrical maintenance, ensuring it is ready to be enjoyed as intended.

Specification

• Model: Marshall JMP 1992 Super Bass
• Year: 1974
• Serial Number: 6488F
• Power: 100 watts
• Circuit: Non-Master Volume Super Bass
• Configuration: Four-input, two-channel head
• Power Valves: 4× new OEM Marshall EL34B
• Preamp Valves: 3× new OEM Marshall ECC83
• Market: Japanese export specification
• Mains Connection: Original-style hardwired mains cable
• Voltage Selector: No external rear-panel selector
• Voltage Conversion: 110V configuration available before shipping
• Professionally Serviced: September 2026
• Dedicated Chassis Earth Fitted
• Fully checked and tested

The 1974 JMP Super Bass is a fantastic example of Marshall's golden era, offering a slightly different flavour to the more familiar Super Lead while retaining all the power, dynamics and unmistakable character of a proper 100-watt vintage Marshall.

The Japanese export specification adds another interesting element to this particular amplifier, while the recent comprehensive service and fresh set of OEM Marshall valves make it a very appealing example for players looking for authentic early-'70s Marshall tone.

Whether you're after enormous clean headroom, thick vintage crunch or simply the sound of a great 100-watt Marshall being pushed hard, the 1992 Super Bass is an exceptional amplifier.

Worldwide shipping available. The amplifier will be carefully prepared and securely packed using purpose-made Overdrive Guitars packaging, with the valves protected for transit and shipment fully tracked and insured.

For international customers, we can arrange for the amplifier to be configured for 110V operation by our engineer before dispatch.

Collection and demonstration are also available from our West London showroom.