Thank you, and congratulations on your choice of BOSS RT-20 Rotary Sound Processor.

Before using this unit, carefully read the sections entitled: “USING THE UNIT SAFELY”
and “IMPORTANT NOTES” (separate sheet).
These sections provide important information concerning the proper operation of the unit.
Additionally, in order to feel assured that you have gained a good grasp of every feature
provided by your new unit, this manual should be read in its entirety. The manual should
be saved and kept on hand as a convenient reference.

Main Features
● COSM Modeling faithfully creates the speaker characteristics, internal cabinet resonance,
rotation speed adjustments, and other particular elements of the rotary speaker to provide
realistic reproduction of the rotary speaker sound.
● Includes overdrive, a must for rock sounds.
● Features four internal sounds, from the conventional rotary sound to rock sounds and UNI-
V, a sound known and loved by many guitarists.
● Expression pedal can be used to freely control the rotation speed.
● Permits adjustment of the balance for the horn speaker and bass speaker volume levels,
something difficult to accomplish with the original speakers. Use the knob to make changes
in the tone, from sharp to mild, in real time.
● Features Virtual Rotor Display that displays the speaker rotation effectively as a visual
image.

COSM (Composite Object Sound Modeling)

Composite Object Sound Modeling (COSM) is BOSS/Roland’s
innovative and powerful sound modeling technology.
COSM analyzes the many factors that make up the original sound,
such as the electrical and physical characteristics of the original, and
then produces a digital model that can reproduce the same sound.

Copyright © 2005 BOSS CORPORATION

All rights reserved. No part of this publication may be reproduced in
any form without the written permission of BOSS CORPORATION.
 Contents
Main Features .................................................. 1
Installing Batteries ........................................... 3
Making the Connections ................................... 4
Mono Connection ............................................................................ 5
Stereo Connection........................................................................... 6

Operating the RT-20......................................... 7

Pedal Operation .............................................................................. 7
Panel Operation .............................................................................. 8
Adjusting the Balance of the HORN Rotor and BASS rotor volume ....... 9
Adjusting the Rotor’s Rotation Speed .......................................................... 9
Adjusting the Rate at Which the Speed Changes
When Switching from SLOW to FAST and FAST to SLOW ..................... 9
Mixing the Direct Sound................................................................................. 9
Operating the SLOW/FAST Pedal................................................................ 9
Operating the BRAKE ................................................................................... 10
Controlling the RT-20 with an Expression Pedal...................................... 10

Names of Things and What They Do............... 11

Front Panel .................................................................................... 11
Mode List ........................................................................................................ 13
Rear Panel .................................................................................... 14

Troubleshooting ............................................. 15
Sample Settings ............................................. 16
Setting Memo................................................. 17
Main Specifications ........................................ 18

2
Installing Batteries
Batteries are supplied with the unit. The life of these batteries may be limited,
however, since their primary purpose was to enable testing.
Insert the included batteries as shown in figure, being careful to orient the batteries
correctly.
fig.010

• When turning the unit upside-down, get a bunch of newspapers or magazines, and
place them under the four corners or at both ends to prevent damage to the buttons
and controls. Also, you should try to orient the unit so no buttons or controls get
damaged.
• When turning the unit upside-down, handle with care to avoid dropping it, or
allowing it to fall or tip over.
• Make sure the “+” and “–” ends of the batteries are oriented correctly.
• When the batteries run down, the POWER indicator gets dim. If this happens, replace
with new batteries.
• When replacing the batteries, use six AA type.
• Avoid using new batteries together with used ones. In addition, avoid mixing different
types of batteries. Doing so can result in fluid leakage.
• Battery life can vary depending on battery type.

Continuous usage time under battery power is about 10 hours with alkaline batteries
and about 6 hours with carbon batteries. (This may vary according to usage
conditions.)

3
 Making the Connections

• The use of an AC adaptor is recommended as the unit’s power consumption is

relatively high. Should you prefer to use batteries, please use the alkaline type.
• Noise may be produced if wireless communications devices, such as cell phones, are
operated in the vicinity of this unit. Such noise could occur when receiving or initiating
a call, or while conversing. Should you experience such problems, you should relocate
such wireless devices so they are at a greater distance from this unit, or switch them
off.
• Use a cable from Roland to make the connection. If using some other make of
connection cable, please note the following precautions.
• Some connection cables contain resistors. Do not use cables that incorporate resistors
for connecting to this unit. The use of such cables can cause the sound level to be
extremely low, or impossible to hear. For information on cable specifications, contact
the manufacturer of the cable.
• When the unit is running on battery power, the power comes on when you insert the
connector plug into the INPUT A (MONO) jack.
• To prevent malfunction and/or damage to speakers or other devices, always turn
down the volume, and turn off the power on all devices before making any
connections.
• If there are batteries in the unit while an AC adaptor is being used, normal operation
will continue should the line voltage be interrupted (power blackout or power cord
disconnection).
• Once the connections have been completed, turn on power to your various devices in
the order specified. By turning on devices in the wrong order, you risk causing
malfunction and/or damage to speakers and other devices.
When powering up: Turn on the power to your guitar amp last.
When powering down: Turn off the power to your guitar amp first.
• Always make sure to have the volume level turned down before switching on power.
Even with the volume all the way down, you may still hear some sound when the
power is switched on, but this is normal, and does not indicate a malfunction.
• When operating on battery power only, the POWER indicator will become dim when
battery power gets too low. Replace the battery as soon as possible.
• When moved from one location to another where the temperature and/or humidity is
very different, water droplets (condensation) may form inside the unit. Damage or
malfunction may result if you attempt to use the unit in this condition. Therefore,
before using the unit, you must allow it to stand for several hours, until the
condensation has completely evaporated.

4
 Making the Connections

Mono Connection
■ Guitar
fig.020

Set DRIVE TYPE switch

to GUITAR

AC Adaptor
PSA series
(sold separately)

Electric Guitar

Guitar Amp

■ Keyboard
fig.030

Set DRIVE TYPE switch

to KEYBOARD

AC Adaptor
PSA series
(sold separately)

Keyboard MTR Mixer

5
Making the Connections

Stereo Connection
■ Guitar
fig.060

Set DRIVE TYPE switch

to GUITAR

AC Adaptor
PSA series
(sold separately)

Effector
Guitar Amp
Electric Guitar

■ Keyboard
fig.070

Set DRIVE TYPE switch

to KEYBOARD

AC Adaptor
PSA series
(sold separately)

Keyboard MTR Mixer

6
 Operating the RT-20
Pedal Operation

When “ON” When “OFF” When set to “SLOW” When set to “FAST”

Lit Off Off Lit

EFFECT ON/OFF Pedal SLOW/FAST Pedal

Alternately switches the effect on or off Switches the rotor’s rotation speed each
each time the pedal is pressed. time the pedal is pressed.
When switched off, the sound input to the
INPUT jack is output without change.

7
Operating the RT-20

Panel Operation
For this description of using the pedals, first press the EFFECT ON/OFF pedal to
switch on the effect (ON/OFF indicator lit), and press the SLOW/FAST pedal to
switch the setting to SLOW (SLOW/FAST indicator off).
In addition, set the knobs to the positions shown in the figure.
fig.080

2 3

1. Set the DRIVE TYPE switch on the rear panel to match the type of instrument being
used.
Refer to “Making the Connections” (p. 5–p. 6).

2. Use the MODE knob to select the desired rotary speaker effect from the four types.

3. Turn the OVERDRIVE knob to adjust the amount of drive applied.

4. Adjust the EFFECT ON volume by turning the EFFECT LEVEL knob.

While the settings described above produce a rotary speaker sound, The RT-20 allows
you to control the following factors that are difficult to control with conventional
rotary speakers.
• Adjust the balance of the HORN rotor and BASS rotor volume
• Adjust the rotor’s rotation speed
• Adjust the rate at which the speed changes when switching from SLOW to FAST
and FAST to SLOW
• Mix the direct sound

8
 Operating the RT-20

Adjusting the Balance of the HORN Adjusting the Rate at Which the Speed
Rotor and BASS rotor volume Changes When Switching from SLOW
You can adjust the balance in volume from to FAST and FAST to SLOW
the horn rotor and bass rotor inside the
You can adjust the rate at which the rotation
rotary speaker with the BALANCE knob.
fig.081
changes from slow to fast and vice versa with
the RISE TIME knob.
Turn the knob to the left to slow down the
rate of change; turn the knob to the right to
increase the rate.
When this knob is at the center position, the
rise time is set to the standard setting.
fig.083

Adjusting the Rotor’s

Rotation Speed
You can adjust the rotor rotation speed using
the SLOW SPEED and FAST SPEED knobs.
Turning these knobs to the center position
sets the rotor speed to the standard rotation Mixing the Direct Sound
speed. If you want to retain the nuance of the direct
fig.082 sound used by the guitar or other
instrument, you can add the direct sound
using the DIRECT knob.

* If you want to reproduce the regular rotary

speaker sound, turn this knob completely to
the left to shut off the direct sound.
fig.084

Operating the SLOW/FAST Pedal

You can switch the rotor’s rotation speed by
pressing the SLOW/FAST pedal.
When set to SLOW, the SLOW/FAST
indicator is switched off; the indicator is lit
when the speed is set to FAST.

9
Operating the RT-20

Operating the BRAKE Controlling the RT-20

You can use the brake to stop the rotation of with an Expression Pedal
the rotor. You can connect an optional expression
Pressing both of the pedals simultaneously pedal (such as the Roland EV-5) to the rear
stops the rotation of the rotor. panel SPEED (EXP PEDAL) jack and use the
The SLOW/FAST indicator flashes rapidly pedal to control the rotor’s rotation speed in
while the brake is on. real time.
fig.100
The time required for the rotor to come to a
stop after the BRAKE is activated changes
according to the position of the RISE TIME
knob.
The time required for the rotor to stop
increases as the knob is turned further left
from the center position; turning the knob to
the right of the center position decreases the
time required for the rotor to stop. Expression pedal
fig.090 (Roland EV -5, etc.)

Flashes
rapidly With the expression pedal fully released, the
RT-20 switches to the value set with the
SLOW SPEED knob; depressing the pedal all
the way switches the RT-20 to the value set
with the FAST SPEED knob.
Both pressed * The SLOW/FAST indicator flashes when an
simultaneously expression pedal is connected.

* Operation of the SLOW/FAST pedal is disabled

To cancel the BRAKE, pressing either the
while the expression pedal is connected.
light pedal or both left and right pedals
simultaneously. * You can also use an expression pedal to operate
the BRAKE.
The rotor always faces directly in front when
stopped. * Use only the specified expression pedal (EV-5;
sold separately). By connecting any other
expression pedals, you risk causing malfunction
and/or damage to the unit.

10
 Names of Things and What They Do
Front Panel
RISE TIME Knob
This adjusts the rate at which the rotation changes from slow to fast and vice versa.
When this knob is at the center position, the rotary speaker rotation changes at the standard rate.

MODE Knob BALANCE Knob

Use this to select the rotary This adjusts the balance in volume from
speaker effect from the four the horn rotor and bass rotor inside the
available types. rotary speaker with the BALANCE knob.
“Mode List” (p. 13) * When MODE is set to IV, this knob adjusts
the intensity of the UNI-V effect.

OVERDRIVE Knob
This knob adjusts the
depth of the overdrive
effect. Switch to OFF
when overdrive is not
being used.

EFFECT LEVEL Knob

This adjusts the volume level
FAST SPEED Knob
of the effect sound.
This adjusts the rotor’s rotation
speed when FAST is selected.
When the knob is at the center
position, it sets the rotor’s
rotation speed to the standard
DIRECT LEVEL Knob rotation speed.
This adjusts the volume level of the
direct sound.
* If you want to reproduce the regular SLOW SPEED Knob
rotary speaker sound, turn this knob This adjusts the rotor’s rotation speed when
completely to the left to shut off the SLOW is selected.
direct sound. When the knob is at the center position, it sets
the rotor’s rotation speed to the standard
rotation speed.
Turn the knob completely to the left to have the
rotor facing directly toward the front when
stopped.

11
Names of Things and What They Do

VIRTUAL ROTOR Display

This display uses indicators and moving light beams to indicate the rotary speaker effect visually.
The HORN rotor is indicated with the red light, the BASS rotor with blue.

SLOW/FAST Indicator
EFFECT ON/OFF Indicator Extinguished when SLOW is selected;
This lights up when the effect is on. lights when FAST is selected.

POWER Indicator
This lights up when the power
is on.

EFFECT ON/OFF Pedal SLOW/FAST Pedal

This alternately switches the effect on This alternately switches the rotor’s
or off each time the pedal is pressed. rotation speed to FAST or SLOW
When switched off, the sound input to each time the pedal is pressed.
the INPUT jack is output without
change.

12
 Names of Things and What They Do

Mode List
The rotary speaker sound is modeled on the famed vintage Leslie 122 speaker.
The MODE knob is used to switch between the rotary and overdrive tones.

* The trademarks listed in this document are trademarks of their respective owners, which are separate
companies from BOSS. Those companies are not affiliated with BOSS and have not licensed or
authorized BOSS’s RT-20. Their marks are used solely to identify the equipment whose sound is
simulated by BOSS’s RT-20.

Mode Descriptions
Combination of standard Leslie 122 sound and natural overdrive.
I
This is the mode with the broadest range of uses.
Combination of Leslie 122 with on-mic setting and natural overdrive.
II
This produces a sound with an emphasized sense of tremolo.
This mode combines the sound of the Leslie 122 with the distortion of
a Marshall 1959.
III
This is a whole new sound, unavailable with any regular system, with
a particularly intense distortion.
This sound combines the UNI-V, modeled on the “Uni Vibe” effect,
IV which recalls the late ’60s and the ’70s, together with the Marshall 1959.
The intensity of the UNI-V effect is adjusted with the BALANCE knob.

13
Names of Things and What They Do

Rear Panel
INPUT Jacks Headphone Jack (PHONES)
(INPUT A (MONO), INPUT B) You can listen through headphones by
These input jacks are used for connecting the headphones here.
connecting electric guitars, keyboards,
other instruments, and effects * Plug in the headphones only after turning
processors. on the power. When turning the power
Connect mono instruments or effects to off, unplug the headphones first, and then
the A (MONO) jack. turn off the power.
“Making the Connections” (p. 4)
* The A (MONO) jack also doubles as the
power switch when the unit is running on DRIVE TYPE Switch
battery power. The power comes on when
This sets the overdrive gain to levels
a plug is inserted into the A (MONO)
jack, and goes off when it is unplugged. appropriate for guitars or for
Unplug any connected cords when the keyboards.
unit is not in use. Set the switch according to the type
of instrument you are connecting.

AC Adaptor Jack
(DC IN)
This jack is for connecting an
AC adaptor (BOSS PSA-series,
sold separately).
SPEED (EXP PEDAL) Jack
Using an AC adaptor makes
Connect an optional expression pedal possible long performances
(such as the Roland EV-5) to this jack. with no worry about batteries
You can use the connected pedal to going dead.
control the rotor’s rotation speed in
real time.

“Controlling the RT-20 with an OUTPUT Jacks

Expression Pedal” (p. 10) (OUTPUT A (MONO), OUTPUT B)
Use these jacks to connect to a guitar amp or
keyboard amp or to an effects processor, mixer,
multitrack recorder, or other such device.
Connect to the A (MONO) jack when
outputting in mono.
“Making the Connections” (p. 4)

14
 Troubleshooting
The power doesn’t come on. Sound is distorted.
❍ Is the guitar or keyboard connected correctly ❍ Are the EFFECT LEVEL knob and DIRECT
to the INPUT A (MONO) jack? LEVEL knob positioned correctly?
→ Check the connections again (p. 4–p. 6). → Sounds may become distorted with the knob at
certain settings. Turn down the EFFECT LEVEL
* When running off batteries, the unit won’t switch
knob and DIRECT LEVEL knob to appropriate
on unless there’s something plugged into the
level. If in spite of these measures the sound is
INPUT jack. This helps conserve the batteries.
still distorted, lower the output level of the
❍ Is the plug connected to the INPUT B jack? device connected to the INPUT jacks.
→ When using battery power, connect the plug to
the INPUT A (MONO) jack. The volume level of the instrument
connected to INPUT jack is too low.
❍ Have the batteries run down?
❍ Could you be using a connection cable that
→ Replace with fresh batteries (p. 3).
contains a resistor?
❍ Is the specified AC adaptor (PSA-series sold → Use a connection cable that does not contain a
separately) connected correctly? resistor.
→ Check the connections again (p. 5–p. 6).

There is no sound.
❍ Is the other equipment connected correctly?
→ Check the connections again (p. 5–p. 6).

❍ Is the volume turned down on the connected

guitar/keyboard, effects processor, or other
device?
→ Check the settings on the connected equipment
(p. 4–p. 6).

❍ Is the effect level (EFFECT LEVEL knob) set to

minimum?
→ Operate the EFFECT LEVEL knob to adjust the
effect level (p. 8).

15
 Sample Settings
* Set the DRIVE TYPE switch on the rear panel to match the type of instrument being used.

■ STANDARD SOUND

■ TREMOLO CHORUS

■ WILD SPIN

■ UNI-V

16
Setting Memo

17
 Main Specifications
RT-20: Rotary Sound Processor Power Supply
DC 9 V: Dry battery (R6/LR6 (AA) type) x 6,
Nominal Input Level
AC Adaptor
-20 dBu
Current Draw
Input Impedance
85 mA (9 V max.)
1 MΩ
* Expected battery life under continuous use:
Output Impedance Carbon: 6 hours
1 kΩ Alkaline: 10 hours
Recommended Load Impedance These figures will vary depending on the
10 kΩ or greater actual conditions of use.

Display Dimensions
VIRTUAL ROTOR 173 (W) x 158 (D) x 57 (H) mm
6-13/16 (W) x 6-1/4 (D) x 2-1/4 (H) inches
Controls
Weight
EFFECT ON/OFF pedal
SLOW/FAST pedal 1.1 kg / 2 lbs 7 oz (including batteries)
OVERDRIVE knob Accessories
BALANCE knob
Owner’s Manual
RISE TIME knob
Leaflet (“USING THE UNIT SAFELY,”
MODE knob
“IMPORTANT NOTES,” and “Information”)
FAST SPEED knob
Dry battery (R6 (AA) type) x 6
SLOW SPEED knob
DIRECT LEVEL knob * We recommend that alkaline batteries be used
EFFECT LEVEL knob when replacing the batteries.
DRIVE TYPE switch
Options
Indicators
AC Adaptor (PSA-series)
POWER indicator Expression Pedal (Roland EV-5)
(serves also as battery check indicator)
EFFECT ON/OFF indicator * 0 dBu = 0.775 Vrms
SLOW/FAST indicator
Connectors
In the interest of product improvement,
INPUT A (MONO) jack (1/4 inch phone type) the specifications and/or appearance of
INPUT B jack (1/4 inch phone type) this unit are subject to change without
SPEED (EXP PEDAL) jack (stereo 1/4 inch prior notice.
phone type)
PHONES jack (stereo 1/4 inch phone type)
OUTPUT A (MONO) jack (1/4 inch phone type)
OUTPUT B jack (1/4 inch phone type)
AC Adaptor jack

18
 For EU Countries

This product complies with the requirements of European Directive 89/336/EEC.

For the USA

FEDERAL COMMUNICATIONS COMMISSION

RADIO FREQUENCY INTERFERENCE STATEMENT
This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to Part 15 of the
FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential
installation. This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in
accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee
that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or
television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the
interference by one or more of the following measures:
– Reorient or relocate the receiving antenna.
– Increase the separation between the equipment and receiver.
– Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
– Consult the dealer or an experienced radio/TV technician for help.

This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions:
(1) This device may not cause harmful interference, and
(2) This device must accept any interference received, including interference that may cause undesired operation.

Unauthorized changes or modification to this system can void the users authority to operate this equipment.
This equipment requires shielded interface cables in order to meet FCC class B Limit.

For Canada

NOTICE
This Class B digital apparatus meets all requirements of the Canadian Interference-Causing Equipment Regulations.

AVIS
Cet appareil numérique de la classe B respecte toutes les exigences du Règlement sur le matériel brouilleur du Canada.

* This device features light emitting diodes (LEDs), which with certain settings may repeatedly flash on and off at a
rapid rate. Some persons may experience headaches or nausea by staring at such flashing lights. Cease looking at the
LEDs immediately if this occurs.

19
G6017153R1