PRS Guitars John Mayer J-MOD 100 User manual

Service Notes
Tubes
Tubes are consumables, as they have a given usable lifespan. They are part of the
heart of the tone, so keeping correctly operating tubes is essential. Tubes can fail
catastrophically or gradually, and it’s good to know what to look for if they start
to go bad. Periodically inspect them and look to see if anything inside the tube is
glowing cherry red other than the normal orange glow of the filament. This would
indicate a situation where the tube is conducting more current than it is capable
of handling and most likely about to fail. Two other conditions to observe are:
1) filaments not glowing or 2) a miniature fireworks display inside the tube. Any
of the above conditions indicate serious problems with the tube and should be
taken care of immediately. Tubes quite often are the cause of spurious noise in the
amp. Microphonic tubes will squeal or rale with the vibrations of the cabinet.
If suspected, tap each tube lightly with a pencil with the amp powered up—the
suspect tube will let you know. Note that there is a normal metallic clinking when
doing this, but a microphonic tube will be quite loud.
Replacing preamp tubes will not require any adjustment, but the power tubes will
need rebiasing to assure proper operation. After power tube replacement, initially
inspect the tubes often to assure there are no “cherry red” components within
the tube. Tubes today can have a wide variety of tolerances and a re-bias is highly
recommended with new ones.
Power tube bias should be adjusted to 30 mV, +/- 5 mV. If power tubes are
mismatched by less than 5 mV, average the two around 30. Mis-matched tubes
beyond 5 mV will induce noise and may cause a degradation of tone.
NOTE! Capacitors may retain an electric charge and can be dangerous even when
the unit is o, unplugged, and has not been played for an extended period of
time. USE CAUTION!!!!
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LIT-AMP-MAN-JMOD REV B
John Mayer J-MOD 100
User’s Manual

Using your PRS Amplifier
IMPORTANT: Before using your amplifier, refer to the IMPORTANT SAFETY
INSTRUCTIONS insert supplied with the product.
Powering Up:
1. Make sure your speaker or speaker cabinet is connected to the correct speaker output
impedance jack with a high quality speaker cable. Do not use guitar cords.
2. Make sure the power cord is connected to the correct grounded outlet.
3. Make sure there is at least 12 inches of clearance behind the amplifier to allow for
proper cooling. Never place the amplifier against a wall or other equipment, and keep
it clear of other heat sources, such as other amplifiers or stoves. Make sure there are
no flammable items, such as curtains, behind the amp. Do not drape items over the
amps that can prevent proper cooling. Do not set drinks or other liquids on top of the
amp that can spill into the amp.
4. To increase the life of the tubes, set the “Standby” switch to the STANDBY position
before powering on. Turn the POWER switch on and let the amplifier warm up for
2 minutes before seing the standby switch to “ON”. If this is the first time you are
turning on the amp, check to see if all of the tubes are glowing.
5. Plug in the guitar cable, turn the volume knob down, and turn the standby switch
on and wait a few seconds for the bias to sele. Bring the volume up and play some
tunes.
This equipment is capable of very high sound pressure levels. Prolonged
exposure may cause hearing damage.
This equipment contains no user-serviceable parts. Refer all repairs to qualified service
personnel.
Ensure that the mains plug is easily accessible to allow the unit to be switched o.
Only connect this unit to an earthed supply socket.
THIS UNIT IS CLASS 1 CONSTRUCTION AND MUST BE EARTHED!
J-MOD 100 Amplifier Front Panel Controls
Input: ¼” Standard Mono Guitar Cable.
Volume: Controls the overall volume of the amp. At extreme seings the amp will begin to
overdrive and distort.
Bright Switch: Adds high end to the overall tone with a capacitor bypassing the input of the
volume pot to the output. Brightness is more evident at lower volume control seings.
Treble Control: Adjusts the high frequencies within the overall tone. This adjustment
allows the tone to become warmer at low seings and brighter at higher seings.
Middle Control: Adjusts the midrange frequencies within the overall tone. This adjustment
allows the user to add fullness or body to the sound, or create a “scooped”, crisp sound.
Bass Control: Adjusts the low frequencies within the overall tone. Lower seings will
sound tighter, especially with more gain and higher seings will add deep fullness and
thump.
Gain Stage Switch: Activates the gain stage circuitry. Set switch in the down position when
using the footpedal to switch in the gain stage.
Gain Stage Volume: Increase this control to add volume, distortion and overdrive.
Gain Stage Output: Serves as a master volume control for the Gain Stage. Use this control
to set the relative volumes with the Gain Stage switched in and out.
Loop Bypass Switch: Set this switch up to bypass the loop circuitry and any eects in
the loop. Set switch in the down position to engage the loop use this function on the
footswitch.
Presence Control: Works in the power amp portion of the circuitry to add high end
sparkle.
Master Control: Sets the overall volume of the amp.
Power On/O and Standby Switches: Power on the amp first with the Standby Switch in
the OFF position. This eectively allows the tube filaments to warm up without applying
high voltage to the tubes. Wait about 2 minutes, then switch the Standby Switch in the ON
position to play the amp. The Standby can be used when not playing the amp for several
minutes.
Rear Panel Controls
Mains Socket: Always use the mains lead supplied. Your sales outlet can provide a
lead suitable for your country. Always disconnect the equipment from the mains and
ancillary units before moving.
Fuses: This amplifier is equipped with multiple accessible fuses. Replacement fuses
must be of the same type and rating as indicated. Failure to comply may result in
permanent damage to the product, and/or create a safety hazard. Always disconnect
the equipment from the mains supply before replacing a fuse.
Mains Fuses: These are located in the mains socket.
B+ Fuse: This fuse is located next to the mains socket and is accessible via a
screwdriver-turn fuse holder.
Bias Jacks and Pot: These jacks measure the power tube current draw in milliVolts.
1mV=1mA. Review the information on the back of this manual for guidance on replacing
tubes. Biasing and tube replacement should be performed only by a qualified
technician. Bias adjustments can be made with a small flat blade screwdriver.
Speaker Jacks: These are the main outputs for your combo speaker or cabinet(s). There
are 3 total jacks to use. A 4 ohm or 8 ohm selector switch is assigned to two jacks in
parallel, and there is a dedicated 16 Ohm jack. Determine beforehand what your total
speaker loading will be and use the appropriate jacks. Never use the 16 Ohm jack with
the 4 or 8 Ohm jacks at the same time. Examples of loads include two 8 ohm speakers
combine for 4 ohms. Set the selector switch to 4 Ohm and use the two parallel jacks.
For two 16 ohm cabinets creating and 8 Ohm load, set the selector switch to 8 Ohms.
Failure to correctly match the speaker load to the appropriate output jacks can cause
tube socket arcs, blown power tubes, or failure of the amp.
Eects Loop: This amplifier features a series eects loop that is integral to the overall
sound of the amp. Connect the Send jack with a 1/4” mono instrument cable to the
input of your pedal(s). Connect your pedal(s) output to the Return jack also using a
1/4” mono instrument cable. Use the loop Send and Return level controls to adjust
the signal to and from your pedals for minimum distortion. To minimize your cables
picking up hum, arrange the cables together for the first few feet away from the amp,
and move them away from the power transformer and mains power cable.
Footswitch Jack: Connect the included PRS footswitch to control Gain Stage switching
and Eects Loop Bypass. Do not use other footswitches as they can possibly damage
the amp. When aached, place the Gain Stage and Eects Loop Bypass front panel
switches in the correct positions to allow the footswitch to function correctly.
Safety Symbols: The following symbols mean:
Warning: read instructions to understand possible hazard
Danger: electrical shock hazard
Warning: This equipment is capable of very high sound pressure levels.
Prolonged exposure may cause hearing damage.