Koch TWINTONE II Bedienungsanleitung Seite 5

the cause, the amp should be taken to a qualified service center
for repair.
This fuse also must be replaced with the same type and value
in order to avoid damage to the amp and to prevent voiding
the warranty.
[3] FOOTSWITCH CONNECTOR: Provides an input for the FS5
footswitch and disconnects the CHANNELS switch on the front
panel [2] when the footswitch is plugged in.
FS5 FOOTSWITCH
The included FS5 Footswitch is equipped with five switches:
- Three CHANNEL switches for selecting channels [red LED
indicators].
- REVERB/FX switch for activating the reverb or the parallel effects
loop (yellow LED).
- SOLO/RHYTHM switch for activating (=Rhythm - green LED
OFF) or bypassing (=Solo - green LED ON) the Rhythm Volume
control [4].
[4] RHYTHM VOLUME: When activated (see FS5 Footswitch), this
control functions as a master volume and can be preset at a lower
(rhythm) volume.
NOTE: If the FS5 Footswitch is not connected, the RHYTHM
VOLUME is active.
[5] REVERB/FX MIX VOLUME: Controls the amount of the Spring
Reverb or Effects signal mixed with the original dry signal (see [8]).
NOTE: If the FS5 Footswitch is not connected, the Reverb/Effects
is on.
[6] SERIAL/PARALLEL - TO FX-IN (=SEND): This jack provides a
buffered mono output from the preamp of the TWINTONE II and
can be used to connect an external effects unit. This jack must be
connected with the input of the effects unit (see also
CONNECTION DIAGRAM).
[7] SERIAL - FROM FX-OUT (=RETURN): This jack provides an
input for an external effects unit and must be connected to the
output of the unit. When used, it disconnects the preamp of the
TWINTONE II from the power amp.
[8] PARALLEL - FROM FX-OUT (=RETURN): This jack provides
an input for an external effects unit and must be connected to the
output of the unit. When used, it disconnects the internal spring
reverb of the TWINTONE II. The REVERB/FX MIX control [5] then
allows volume adjustment of the external effects signal.
If this loop is used, direct signal must be taken off the effects
unit's signal. For example by turning the effects unit's
'dry/wet' control to 'wet'.
NOTE: The effect loops operate on a -10dBV signal level which
guarantees compatibility with both instrument-level effects like
floor-pedals and guitar-processors, as well as line-level effects like
professional 19 inch rack mount devices.
If connecting an effects unit to the TWINTONE II causes hum,
a ground-loop may be the cause of it.
[9] SPEAKER OUTPUT JACKS: Provided for connection of
speaker(s) or speaker cabinet(s). Minimum total impedance can be
set with the IMPEDANCE SELECTOR switch [10] at 4 ohms or 8
ohms.
The MAIN jack must be used for connecting the Combo's internal
speaker (8 ohms) or the Head's cabinet.
If the plug is pulled, the power amp's output automatically connects
to the internal POWER SOAK. This special feature has been
added for three reasons:
1. PROTECTION. The amp is always protected and can not be
damaged as a result of operation without a speaker or speaker
cabinet.
2. SILENT PLAYING. Silent practicing (with headphones) or home
recording can be realised easily: just pull the speaker plug! (and
set the impedance selector [10] to 8 ohms)
3. HALF-POWER OPTION / 25WATTS. The audible power can be
reduced to 25 watts by plugging the (8 ohm) the internal speaker
(Combo) or the external 8 ohms speaker cabinet (Head) into the
Extension jack, while leaving the Main jack unused.
The speaker / speaker cabinet is now connected parallel to the
Power Soak and the total output power is divided between the
Power Soak and the speaker / speaker cabinet. The Impedance
Selector [10] must first be set to 4 ohms.
The EXTENSION jack may be used for connecting an additional 8
ohms speaker cabinet, after setting the Impedance Selector [10] to
4 ohms (see also CONNECTION DIAGRAM).
[10] IMPEDANCE SELECTOR: Provided for matching the power
amps output to the speaker(s) and/or speaker cabinet(s).
[11] RECORDING OUTPUT: ThIs jack provides a mono output
from the power amp and includes Reverb and External Effects
signals. The signal is derived from the speaker output and filtered
by a special Filter which simulates the sound coming from the
speaker, so it can be fed directly into a recording or sound
reinforcement mixer. (see also [9] 'silent playing')
[12] HEADPHONES OUTPUT : Provided for the connection of a
set of headphones. The signal is filtered in order to simulate the
sound coming from the speaker. (see also [9] 'silent playing')
NOTE: A set of low/medium quality headphones will give the best
results. High quality headphones may sound to shrill with distortion
sounds as a result of their extended frequency response.
REPLACING TUBES
•
SAFETY FIRST: DISCONNECT THE POWER CORD FROM
ITS POWER SOURCE AND LET HOT TUBES COOL.
•
CHECK THE 'TUBE LOCATION DIAGRAM' ON THE
CHASSIS FOR THE CORRECT TYPE NUMBERS AND
LOCATIONS.
•
REPLACE TUBES ONLY WITH ORIGINAL KOCH HIGH
QUALITY TUBES. (IF OTHER TUBES ARE USED THE
WARRANTEE OBLIGATION EXPIRES)
•
BEFORE REPLACING THE POWER TUBES, REMOVE THE
CE SAFETY CAP FIRST.
•
AFTER REPLACING THE POWER TUBES, PUT THE CE
SAFETY CAP BACK IN PLACE.
NOTE: Always have the amp rebiased after peplacing the power
tubes. Biasing instructions can be found inside the amp. Rebiasing
the amp is not neccessary only if Koch power tubes are used with
the same type and bias-class number.
If you have any doubts, please take no risks and let a qualified
technician do the job.
Preamp and Power tubes wear out and have to be changed from
time to time to maintain the TWINTONE II's best performance.
Tubes behave like strings, they lose highs, lows and dynamics and
after a period of time they have to be changed. Exactly when is
hard to say but this is an indication: if you play almost every day
change tubes each year, if you play once or twice a week change
tubes every 2-3 years.
Tubes rarely fail. If they are bad, these might be the symptoms:
PREAMP TUBES (ECC83, 12AX7, 7025):
- Microphonic whistling or squealing on one or both channels.
- No or low amp volume on one or both channels.
- Excessive noise on one or both channels.
POWER TUBES (EL34):
- Loud crackling that is not affected by front panel controls.
- Intermittent or regular blowing fuses.
- Weird amp 'distorting'.
- Hum.
Changing a tube is a simple and quick fix for most problems in
your amp.
In case of failure, just one or both POWER TUBES can be
replaced without rebiasing only if KOCH tubes with the SAME
TYPE AND BIAS-CLASS NUMBER are used.
If EL34's with a different or unknown bias-class number are used
for replacement, BOTH TUBES have to be replaced and the amp
has to be REBIASED.
Please always use two matched EL34 (= one duet)
replacement tubes to obtain the amps best performance.
Again, if you have any doubts, please take no risks and
consult your dealer and/or a qualified technician