Surprise sound FLEX 15 User manual

FLEX 15 TM
Owner’s Manual
Revision 1.0
Description
The FLEX 15 is a 15 watt (Triode) or 25 watt (Ultralinear) vacuum tube
guitar amplifier. The circuit configuration is Class A single-ended. There
are 2 channels and an effects loop, all footswitchable. The tube-buffered
effects loop is both series and parallel with send and return level controls
and a wet/dry mix control.
Inputs and Outputs
INPUT: This ¼” jack is used to connect to a guitar or the output of an
effects pedal.
SPEAKERS: These three ¼”jacks are used to connect to a speaker
cabinet. The Rock Block can drive speakers of 4, 8 or 16 ohms
impedance. Only one speaker jack should be used at a time.
SEND: This ¼” jack is used to connect to the input of effects pedals or
rackmount effects.
RETURN: This ¼” jack is used to connect to the output of effects pedals
or rackmount effects. If no cable is connected to the RETURN jack then
the SEND is internally connected to the RETURN.
FOOTSWITCH: This ¼” jack is used to connect to the dual footswitch box.
The footswitchs control the channel selection and the effects loop.
AC POWER: This jack is used to connect a 3-prong power cord.
Controls
POWER: This is the ON/OFF power switch. Push to the up position to
powerup the tube heater supply.
STANDBY: This is the Standby switch. Push to the up position to
powerup the amp.
GAIN: These knobs are used to control the gain of the preamp for each
channel.
BRIGHT: These knobs are used to boost the upper treble response for
each channel.
CHANNEL: This switch is used to select the channel. It is nonfunctional if
the footswitch is connected.
BASS FREQ: These 3-way switches are used to set the bass rolloff
frequency for each channel.
BASS LEVEL: This knob is used to set the bass level for both channels.
BOOST: This 3-way switch is used to boost the gain of the amplifier for
both channels.
MID (CH1): This 3-way switch is used to set the mid frequency level for
channel 1.
MID (CH2): This 5-position rotary switch is used to set the mid frequency level
for channel 2.
TREBLE: This knob is used to set the treble frequency level for both
channels..
EFFECTS LOOP: This switch is used to enable/disable the effects loop. It
is nonfunctional if the footswitch is connected.
VOL: These knobs are used to set the master volume for each channel.
SEND: This knob is used to set the level for the SEND output.
RETURN: This knob is used to set the level for the RETURN input.
MIX: This knob is used to control the amount of the effects loop signal mixed
into the direct signal.
OUTPUT POWER: This switch is used to select the maximum output power
(5W or 15W). In 5W mode only 1 output tube is used. The 4 ohm speaker
jack should not be used in the 5 watt mode.
TRIODE/UL: This switch is used to select the operating mode of the output
tubes –Triode or Ultralinear. The maximum output power is 15W for Triode
mode and 25W for Ultralinear mode.
Operating Instructions
Connect the guitar or effects pedal to the INPUT jack using a guitar cable with
a ¼” mono plug. Also connect a speaker cabinet to the SPEAKER jack using
a speaker cable with a ¼” mono plug. If a speaker cable is connected to the
SPEAKER jack, then a speaker must be connected to the speaker cable to
avoid possible damage to the amplifier.
Turn on the amplifier with the POWER switch. After about 30 seconds toggle
the Standby switch to PLAY. When turning off the amp reverse the turn-on
sequence.
For a clean guitar sound: Turn the VOL knob maximum clockwise. Set the
BOOST switch to the left (minimum) position. Adjust the GAIN knob for
maximum volume without distortion. Adjust the BASS switch and TONE
knobs to taste.
For a “bluesy” or “crunchy” guitar sound: Turn the VOL knob maximum
clockwise. Set the BOOST switch to either the left or center position. Adjust
the GAIN knob for the desired amount of distortion.
For a “hi-gain” or “lead” guitar sound: Turn the VOL knob maximum
clockwise. Set the BOOST switch to either the center or right position. Adjust
the GAIN knob for the desired amount of distortion, sustain and feedback.
For reduced volume with high gain: Turn the VOL knob counter-clockwise.
This will reduce the overall volume of the amplifier. The distortion will
transition from output tube to preamp tube distortion as the volume is reduced.

Using the Effects Loop
The Effects Loop is panel or foot switchable and is both series and parallel
type. When the MIX knob is turned to the right (WET) the loop is series. As
the MIX knob is turned to the left (DRY) the loop combines the Dry and Wet
signal (Parallel mode).
To set the Effects loop Send and Return levels:
If pedals are used in the Effects Loop set the SEND knob to 12 0’clock and
the RETURN knob to Max.
If rackmount effects are used in the Effects Loop set the SEND knob to Max
and the RETURN knob to 12 0’clock.
The Effects Loop can be used as a Boost or Attenuator by connecting
nothing to the SEND and RETURN and adjusting the SEND and RETURN
knobs to the desired Boost or Attenuation. When the Effects Loop is
engaged the Boost or Attenuation will occur.
Vacuum Tube Selection
Make sure that the vacuum tube pins are straight before inserting the tubes
into the sockets. Apply a slight pressure but do not force the tubes into the
sockets or damage to the sockets may result.
The best vacuum tube to use for the preamp (V1) is an ECC83 (12AX7) or
5751, and the best tube for the preamp/driver (V2) is an ECC81 (12AT7).
For the effects loop tube (V3), an ECC81 (12AT7) works best. For the power
tubes (V4,V5,V6) 6L6GCs or EL34s are recommended. 6550s, KT66 or
KT88s can also be used. No re-biasing is required and different types of
power tubes can be used together. When the OUTPUT POWER switch is
set to the 5 Watt position only the power tube in the V6 position is activated.
Specifications
Switch Settings Clean Max
Output Power
15W / UL 25W 50W
15W / TRIODE 15W 30W
5W / UL 7W 14W
5W / TRIODE 5W 10W
Speaker impedance 4, 8, 16 ohms
Input impedance 770K ohms (IN and RETURN)
Output impedance 2K ohms (SEND jack)
Warranty and Repair
The warranty period is 2 years. If during the first 2 years your FLEX 15
needs repair, Surprise Sound Lab will repair or replace it at no charge. The
vacuum tubes are guaranteed for 90 days. The owner will be responsible for
shipping charges. Any problems due to misuse, abuse or modification will
not be covered under the warranty. Any repairs outside of the warranty will
be performed by Surprise Sound Lab for a reasonable fee. Please email
[e-mail] for any repair requests.
Tips for using your FLEX 15
Generally keep the VOL control at maximum for output tube overdrive.
However, for high GAIN settings, reducing the VOL by about 1/3 to 1/2 will
provide more TONE control.
Decreasing the BASS FREQ setting as you increase the BOOST and GAIN
settings will produce the best distortion.
Only use as much GAIN as needed for the desired distortion and sustain to
avoid unpleasant distortion.
For high GAIN settings bridge pickups seem to work especially well.
Recommended Settings:
Generally keep the VOL control at maximum for output tube overdrive.
Guitar Style Pickup GAIN BOOST BASS
Strat Clean any 11 o’clock min max
Strat Blues any 2 o’clock min mid
Strat Rock bridge 1 o’clock mid mid
Strat Heavy bridge 2 o’clock max min
Les Paul Clean any 8 o’clock min mid
Les Paul Blues any 12 o’clock min mid
Les Paul Rock bridge 11 o’clock mid min
Les Paul Heavy bridge 1 o’clock max min