MINI-MARSHMALLOW Vacuum-Tube Guitar Preamplifier

MINI-MARSHMALLOW 2-Channel Vacuum Tube Guitar Preamplifier (1U)

$2,130 (approx. $1,710 USD)

London Power Mini Marshmallow Preamp
MINI-MARSHMALLOW builds upon the tone legacy of Mr. Dumble's famous topology, providing classic warm clean tones, and an over-driven amp tone. Tubes create the entire sound while solid-state circuitry provides a low-noise effects loop, dual outputs, DI and buffered Link for connection to other preamps 

uses two of 12AX7 or any of 12AT7, 12AU7, 12AY7, 12AX7, ECC-81/-82/-83, or equivalent
low-gain channel has 2 voicing switches
high-gain channel has 2 voicing switches
front-panel effects loop controls
low-noise effects loop and output circuitry
dual impedance-matched ground-compensated TRS 1/4" outputs
impedance-matched ground-compensated XLR for D.I. output
front panel switches for channel and loop selection
remote control via TRS jacks or DIN6
regulated voltages
1U  3.4kg, 17"W x 1.7"H x 6.5" D (plus tubes)
120V, 240V range switch
rack-mountable with optional kit

MINI-MARSHMALLOW covers the range of pristine clean, warm clean, mild over-drive, to heavy over-drive that is smooth for jazz, blues or hard rock. Classic clean sounds and mild to heavy saturation are produced with low noise and excellent note articulation and sustain. The player can set the voicing and gain structure using the voicing switches and Drive and Level controls for each channel, then easily switch between a Low-Gain sound and a High-Gain sound using the front panel switch or remote control.

A shared EQ provides easy tone shaping, but each channel has its own "Rock/Jazz" switch and "mid-shift" switch. Set each channel how you like and use Loud to make everything louder or quieter without altering the channel balance. Our updating of the controls frees the player from having to set up the clean sound first, then set the over-drive sound: MINI-MARSHMALLOW gives new freedom to the player.

MINI-MARSHMALLOW has a full-feature effects loop that can handle line-level devices or pedals, as well as series or mxing modes. Front-panel Send and Return level controls combine with a rear-panel 20dB switch to accommodate any signal level, and any signal-handling capability of the external device. The loop is ground compensated and impedance matched to eliminate ground loops.

London Power Mini-Marshmallow rearMINI-MARSHMALLOW has two instrument input jacks, with the front panel jack over-riding the rear-panel jack. There is a buffered Link output to fan out the guitar signal to other preamps, tuner, etc. The buffered signal can be used to drive the tube stages if one wishes, by activation of the BF switch on the rear panel.

Dual main outputs allow many system connections, for use with multiple amplifiers or for split recording and monitoring. Each output has its own level control. The LP low-pass filter for the main outputs can be enabled for direct connection to a mixer or PA, or left 'off' to drive multiple guitar amps for a zoned stage. There is also a D.I. (direct injection) output that tracks the raw output after the effects loop. The main outputs use TRS 1/4" jacks where the D.I. has an XLR. All outputs are impedance matched and ground compensated to eliminate ground loops between equipment.

All of MINI-MARSHMALLOW's sounds and features can be accessed by front-panel switches. Standard 1-button and 2-button push-on/off foot switches can also be used for remote switching, connected by way of the TRS 1/4" rear panel FSW jack. More sophisticated control is tied in via the DIN6 connector, matching London Power's FS4-2W foot control (sold separately). FS4-2W provides direct-random access to either channel with or without the effects, so four system voices A,B,Ax,Bx; and it has 2-way communication: you can hit a switch on FS4-2W OR on MINI-MARSHMALLOW's face plate and the LEDs on both will change along with the system status selected. Of course, one can use the DIN6 to link to other types of controller.

MINI-MARSHMALLOW incorporates all of London Power's standard design and construction features:

toroidal power transformers
fusing for all transformer windings
Galactic Grounding
active hum filtering
long-life capacitors
low noise metal-film resistors
metal-oxide and wire-wound power resistors
zero wiring
zero standby power when switched 'off'

MINI-MARSHMALLOW can be rack mounted using the optional 1U6-BRKT, sold as pairs.

Photo gallery - click to enlarge

London Power Mini-Marshmallow front

London Power Mini-Marshmallow Preamp - inside


About London Power

London Power was founded in 1990 by Kevin O'Connor, after two decades of research into innovative audio amplification techniques. Kevin is an audio designer, author and speaker, known for his proprietary methodology called Power Scaling, and for his eleven books on audio subjects. Whether you seek amps, kits or information, you'll find useful answers here on not just the "how" but the "why" of audio amplifier design. Please enjoy the information on this site, and don't hesitate to contact us with questions.

Contact Us

(807) 473-0952
11 am - 6 pm, M-F
PO Box 10012, Thunder Bay, ON P7B 6T6 CANADA