Randall RB300, RB500, RB750 Instruction Manual

Table of Contents

FRONT PANEL FEATURES:

Input/dB Cut 3
Overdrive Controls 3
Compressor/Pre Gain controls 3
EQ Controls 4
Valve-Dynamic EQ Controls 5
Phones Jack 5
Power Switch 5

REAR PANEL FEATURES:

AC Power Input 6
Speaker Outputs 6
Footswitch Input 6
Direct Output/Level Control 7
Effects Loop 7
Tuner Output 7
Troubleshooting 8
Specifications 8
Warranty 8

RB S ERIES F RONT PANEL FEATU RES

INPUT/-10dB CUT:

The main guitar INPUT for the amplifier. Using a high quality instrument cable, simply connect your
guitar to this 1/4” input jack. The -10dB switch can be used with basses that use an on-board preamp
with active tone controls. You can use the -!0dB cut switch to prevent clipping at the first input stage
when using active basses or passive basses with hotter pickups. You will not need to the -10dB cut
when using basses with passive tone controls.

OVERDRIVE SECTION:

The footswitch able OVERDRIVE circuit can be used to add a little or insane amount of distortion to your
bass tone. You can activate the Overdrive using the front panel switch or the included Foot controller. Use
the LO CUT switch to remove sub low frequencies if the low end is too excessive. Now, adjust the
Overdrive level to the desired distortion then use the LEVEL Control to adjust the volume level. Use the
Overdrive and Pre Gain Level controls so that your Overdrive and Clean bass tones are similar volumes.

COMPRESSION/MUTE/PRE-GAIN CONTROLS:

Each RB Series amp is equipped with a footswitch able MUTE circuit for silent tuning. The Mute can be
activated by using either the front panel button or included footswitch. The RB Series were also designed
using “THAT” Compression chips, providing professional studio quality compression to your bass tone,
simply press the “Comp On” switch to activate. The Compression control works in conjunction with the Pre­Gain level, so you will notice the Compression is more or less active depending on where the Pre-Gain level
is set. If the Pre-Gain is lower the Compression level is lower, and as you increase the Pre Gain level you
will also increase the Compression. The Pre-Gain level controls the gain level before the EQ section, so it
can be used to add some grit or additional attack when set higher.

RB S ERIES F RONT PANEL FEATURES - c ont.

BASS CONTROL:

A passive low end control that adjusts the sub low frequencies of the preamp circuit. Set flat to start and
adjust to find the desired amount of low end.

TREBLE CONTROL:

A passive high end control that adjusts the amount of high frequencies of the preamp circuit. Set flat to start
and adjust to find the desired amount of high end..

MIDDLE CONTROL:

A passive mid-range control that adjusts all mid-range frequencies of the preamp circuit. Set flat to start and
adjust to find the desired amount of mid-range.

CONTOUR CONTROL:

A secondary mid-range control that works in tandem with the MIDDLE control allowing you to sweep between
different mid-range frequencies. With the MIDDLE control set flat you will notice the Contour is extremely
subtle, but as you adjust the MIDDLE control off of flat the Contour control will become much more active.
A lower Contour setting pin points the lower mid-range frequencies that the MIDDLE control will then cut or
boost. Set the Contour knob higher and the MIDDLE control will cut or boost the higher mid-range
Frequencies.

MASTER LEVEL CONTROL:

The knob controls the overall volume and output of the amplifier. Use this control along with the Pre-Gain
level control to achieve the desired volume level. Experiment with using different Pre-Gain and Master settings
as you will notice some tonal differences by how you set and balance the Pre-Gain and Master controls.

RB S ERIES F RONT PANEL FEATURES - c ont.

VALVE-DYNAMIC BOTTOM/DENSITY CONTROLS

This is the very unique section of the RB Series bass amplifiers. Each RB Series amp includes an active
Bottom and Density control which EQ’s the power section for more low end tube warmth and high end
shine. The tube driven MOSFET power section, includes a 12AT7 tube plus a built-in EQ for authentic all­tube tone and feel unlike any other tube, solid-state or hybrid power section. Adjust the Bottom control for
additional tube warmth and punch, then adjust the Definition control for more top end tonal attack. Use this
EQ in conjunction with the Preamp tone controls for unlimited tone shaping options.

PHONES JACK:

The filtered 1/4” Phones jack allow you to play or practice silently using a good quality pair of headphones.

POWER SWITCH:

This is the main power switch for the amplifier. Once the unit is plugged into an AC wall outlet or preferred
power strip conditioner, use this toggle switch to turn the unit ON & OFF. It will take 4-5 seconds,
like other all tube power amps, for the 12AT7 tube in the power amp to warm up and fully come on.

AC INLET:

Each unit includes an AC power cord for the country that you live in. Attach the included AC power cord from
this AC inlet to a standard wall outlet or preferred power conditioner. Once plugged in, the unit is ready for
power up. If the amp does not power up, please check the fuse located inside this AC inlet. It can be
removed using a small flat head screwdriver. Please refer to the fuse rating above the AC inlet if you need
to replace the fuse for any reason.

SPEAKER OUTPUTS:

Each RB Series amp is equipped with dual 1/4” and dual Speak-on Speaker outputs jacks. You can use a
high quality 1/4” speaker cable or high quality speaker cable with locking Speak-on connectors and connect
to one or two external speaker cabinets. Keep in mind the output of your this bass amplifier depends on the
ohm rating of your cabinet/s. See the specification page for ohm ratings & power output.

Fuse

Fuse

FOOTSWITCH INPUT:

Each amp comes with a 2-button foot controller that activates the OVERDRIVE mode and turns the MUTE
function On and Off for on-stage tuning purposes. Simply plug the 1/4” foot controller cable into the
foot switch jack for remote switching of the OVERDRIVE and MUTE functions.

RB S ERIES R EAR PANEL FEATURES

Speak-on Speak-on

DIRECT OUTPUT:

A preamp output that allows you to send a balanced signal using an XLR cable to either a house mixing
console for live stage use, or to a studio recording console. This section includes a Pre/Post loop
option if you are using the Effect loop. The Ground Lift is if you should encounter a hum when connecting
the XLR output to a live or studio mixing console. This should eliminate most ground loop type noise from the
Direct out signal. If the Ground loop switch does not eliminate the hum then look at other units that may be
causing a ground loop. Use the Level control to adjust the amount of direct signal output.

EFFECTS LOOP:

The Effects loop allows you to interface external effects or processing units via the Return and Send jacks.
The Return is a patch point between the preamp and power amp section for returning a processed signal
from any external processing gear. Using a 1/4” cable, connect from the Output of your external unit to this
Effects Loop Return jack. The Send is the output of the preamp allowing you to send a signal to any effects
unit or external processor. Using a 1/4” cable, connect the Input of your external effects unit to this Effects
Loop Send jack

Fuse

TUNER OUTPUT:

A preamp send allowing you to connect directly to any rack mount or standard tuner for silent tuning at any
time. Using a 1/4” patch cable, connect this Tuner Output to the Input of your tuner.

RB S ERIES R EAR PANEL FEATURES

TROUBLESHOOTING GUIDE

TUBE NOISE:

Because Valve-Dynamic is tube hybrid design, you may encounter some usual tube noise and/or microphonics over time.
As with any tube amplifier we recommend that you carry a spare 12AT7 for this amp as the tube will need to be replaced. You
can diagnose a tube related problem if the amp begins to make a crackling or microphonic type noise. If the amp has lower
than normal output this can also be caused by a defective tube.

AMP DOES NOT POWER UP:

If the amplifier will not power up after you have plugged it into a known working power strip or wall outlet the first place to check
is the main fuse located inside the AC Inlet on the rear panel. Remove the fuse from the fuse holder and replace the fuse using
the same size and value of the existing fuse. If the amp still will not power up, contact your local Randall Dealer or Service Center.
Find your local dealer on our website at www.randallamplifiers.com

SPECIFICATIONS

Below are the main specifications for each RB Series Bass amplifier with Valve-Dynamic power. For full power output please
remember that you must use a single 4 ohm cabinet or two 8 ohm cabinets totaling 4 ohms.

RB750

750 Watts RMS @ 4 ohms
380 Watts RMS @ 8 ohms
175 Watts RMS @ 16 ohms

RB500

500 Watts RMS @ 4 ohms
270 Watts RMS @ 8 ohms
130 Watts RMS @ 16 ohms

RB300

300 Watts RMS @ 4 ohms
150 Watts RMS @ 8 ohms
80 Watts RMS @ 16 ohms

Randall guitar amplifiers, bass amplifiers and speaker enclosures are warranted to be free of defects in materials and
workmanship in normal use for a period of three (3) years from the date of original purchase. The manufacturer warrants
Jaguar speakers for a period of two years. The manufacturer warrants tubes for a period of sixty days. Rental stock is
Warranted for one year from date of invoice to dealer. Warranty on rental units is not transferable. During that period,
Randall will repair or replace, at Randall's option, any Randall product or part thereof which is found by Randall to be defective.
The customer pays transportation to and from Randall factory service or any Randall Authorized Service Center. Randall
reserves the right to use materials readily available at the time of the repair. Warranty service requires Proof of Purchase
(sales receipt) to be presented at time of service request.

REGISTER YOUR WARRANTY ON-LINE AT www.randallamplifiers.com/about/warranty/randallreg.asp

RANDALL WARRANTY

WWW.RANDALLAMPLIFIERS.COM

Randall Amplifiers is a Division of U.S. Music Corp

444 East Courtland Street. Mundelein, Illinois USA 60060

E-mail: [e-mail]

Phone: [phone] Fax: [phone]

Register your Warranty on-line at

www.randallamplifiers.com/about/warranty/randallreg.asp