Owner’s Manual
for the
BT-350
Bass Amplifier
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BT-350 ThunderBass Amplifier
Introduction:
The Crate BT-350 ThunderBass amp is a high-quality bass guitar amplification system that combines
extremely high power with very desirable features. Each feature and control is discussed in detail in the sec-
tions entitled “The Front Panel,” “The Rear Panel” and “Using the Biamp Capabilities.”
Crate offers a heavy-duty three rack space enclosure (Crate model #CR-3) which will house the BT-350
perfectly, providing the extra protection and convenience needed when you take your Crate on the road.
Also available is a five rack space enclosure (Crate model #CR-5) which is ideal for use when the BT-350 is
combined with a second amplifier for biamping.
The BT-350 is equally suited for use in the club, the studio or on the stage. When combined with Crate’s
line of superior bass cabinets, the results are nothing less than phenomenal. (But then, what else would you
expect from Crate?)
Features:
Additional information can be found on the pages indicated.
• Tube Preamp: Adjustable Drive control. Low, Mid and High frequency controls. Low and High Boost
switches. Normal (0dB) and padded (-15dB) input jacks. (page 4)
• Graphic EQ: 7 bands. 40Hz to 10kHz. 12dB cut or boost. Master Level control. Footswitch control-
lable. LED Indicator. (pages 4 and 5)
• Master Level: Peak (overdrive) LED indicator. Switchable Limiter circuit with LED indicator. (page 4)
• Chorus: Adjustable Depth and Rate controls. Variable cut-off (“Spectrum”) control. (page 5)
• Biamp: Adjustable crossover frequency control. Low-to-high balance control. Independent Line Out
level control. Balanced (XLR) and unbalanced (1/4”) outputs. (pages 5 and 6)
• Internal Amplifier: 350 watts into 4 ohms. 1/4” mono speaker output jacks. Extensive heatsinking.
Detachable AC power cord. (page 6)
• Effects Loop: 1/4” Send and Return jacks. Allows use of external signal processors. Return jack
doubles as input for power amp in Biamp mode. (page 6)
• Musician made in the U.S.A.
• Crate’s exclusive 5-year warranty (U.S. only, – see your dealer in other areas for warranty informa-
tion)
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BT-350 ThunderBass Amplifier
The Front Panel:
INPUTS:
1. 0dB INPUT: Connect your bass the impressive 8dB of gain added at seek a more traditional sound.
here using a shielded instrument cable. 20Hz, increasing the deep, “floor-shak-
8. HIGH BOOST: Turning on the High
Boost greatly enhances the upper-har-
5. LOW: Adjust the output level of your monic overtones of your bass, increasing
low-bass tones with this control: the cen- such subtleties as the sounds of your fin-
The output signal of your bass will run ing” sounds of your instrument.
full-strength into the amplifier, which is
fine for most basses having passive elec-
tronics and/or low-output pickups. If
ter position is “flat” (no boost or cut). gers on the strings or the strings striking
your bass has active on-board electron-
Turning the control to the left reduces the the fretboard. High Boost produces an
ics and/or active pickups, use the -15dB
low frequency output; turning to the additional 10dB of gain at 10kHz, mak-
input jack (#2) to avoid overloading the
right increases the low frequency output. ing the “crisp” characteristics of your
amp’s input stage.
The Low control primarily affects the bass even more pronounced.
2. -15dB INPUT: Connect your bass notes you feel, providing up to 13dB of
here if it has active on-board electronics boost or cut at 40Hz.
MASTER LEVEL SECTION:
9. PEAK LED: This LED indicator will
and/or active pickups. The bass’s output
signal will be attenuated by 15dB to keep
6. MID: Adjust the output level of your light when you’re nearing the highest
upper-bass tones with this control: the desirable level for your input signal and
it from overloading the amplifier’s input
center position is “flat” (no boost or cut). are in danger of overdriving the pre-
stage.
Turning the control to the left reduces the amp’s solid state circuitry. (This can
NOTE: Even if your bass has passive upper-bass output; turning to the right cause the output of the amplifier to
electronics, if the Peak LED (#9) flashes increases the upper-bass output. The sound distorted.) To get the maximum
at seemingly low levels when you’re Mid control provides up to 11dB of benefit from the BT-350’s tube preamp
plugged into the 0dB input, try using the boost or cut at 260Hz, which changes section (good, clean sound with the
-15dB jack instead.
the “voice” of your instrument’s sound. “feel” of natural tube compression),
By boosting the Mid control you can adjust the Tube Drive control (#3) until
make the sound of your bass cut through this LED begins to flash when you’re hit-
the rest of the band, without getting a ting your strings pretty hard.
TUBE PRE-AMP section:
3. TUBE DRIVE: This serves as the gain
control for the BT-350’s tube preamp
section, which gives you the natural
whole lot louder.
10. MASTER LEVEL: This is the BT-350’s
compression of a tube amplifier. For the 7. HIGH: Adjust the amount of high-fre- master volume control. The output level
best compression. adjust the Tube Drive quency overtones with this control: the of the amplifier through your main
control as you strike your strings (hard). center position is “flat” (no boost or cut). speakers, the Biamp Outputs and the
Watch the Peak LED (#9): when the Turning the control to the left reduces the Effects Loop Send are simultaneously
LED starts to flash, you’ve reached a high-frequency output; turning to the adjusted by this control: at the full-left
choice setting for the best signal-to-noise right increases the high-frequency out- position there will be no output; rotating
ratio and “tube feel.”
put. The High control allows up to 15dB the control to the right increases the vol-
of boost or cut at 5kHz, which allows you ume level.
to adjust the “crispness” of the sound of
your bass. Players looking for a sharp,
slapping sound may tend to want this
4. LOW BOOST: Switch on the Low
Boost and you’ll feel a large increase in
the very lowest bass notes, especially
noticeable when you hit the low B string
of a five or six-string bass. This is due to
control turned up farther than those who
4
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BT-350 ThunderBass Amplifier
The Front Panel (con’t):
11. LIMIT LED: The BT-350 offers a the Line Out Level control to the right control up from center boosts the output
special limiting circuit which helps to increases the output level; to the left at its given frequency; pulling it down
keep the output of the amplifier “clean” decreases it.
when played at extreme volume levels.
reduces that frequency. The 40Hz and
100Hz controls affect the lower notes of
your bass, changing how much bass is
felt. 250Hz through 1.6kHz affect the
upper notes, modifying the amount of
“punch” that comes across. 4kHz and
10kHz affect the upper harmonic over-
tones of your bass, such as the sounds of
your fingers in the strings or the strings
striking the fretboard.
NOTE: The Line Level signal is pre-
When the Limiter is engaged, the Limit
LED will come on as the power amp is
being driven to full output.
Effects Loop and therefore will not be
affected by any external signal proces-
sors connected to the Loop (see #33
12. LIMITER: When a power amplifier and 34).
reaches maximum output levels, it may
16. POWER: This heavy-duty rocker-
begin to “clip” its output signal, which
generates potentially speaker-damaging
distortion. The BT-350 has a special
APM (Automatic Power Maximizer) limit-
ing circuit which helps minimize this
problem by monitoring the power amp’s
output signal, keeping it below clipping.
This feature insures you that even as you
push your amplifier to its full 350-watt
output, the sound will remain clean and
pure. To activate the limiter circuit, press
the Limiter switch in until it locks in
place. The limit LED (#11) lights up
when the APM circuit is actually limiting
the signal.
type switch is used to turn the amp on in
the “up” position, off when “down.” The
switch lights up when the power is on.
20. ON: When this switch is in, the EQ is
active, and the settings of the controls
affect the sound of your bass.
17. FOOTSWITCH: A two-button
footswitch (such as Crate’s CFP-2) can
be plugged in here to give you remote
on/off control of the graphic eq and the
chorus. When connected, the footswitch
overrides the front panel on/off switches
for these features.
21. ENABLED LED: This LED will only
light when the EQ is activated, showing
you that the signal will be affected by the
settings of the EQ controls.
CHORUS section:
NOTE: This is a stereo 1/4” jack: “ring”
controls the chorus, “tip” controls the
eq, and the “sleeve” is ground. Use only
a footswitch equipped with a stereo plug
(such as Crate’s CFP-2).
22. ON: When pushed in, the on-board
Chorus is activated and the signal pro-
duced by your bass will have the Chorus
effect applied to it.
NOTE: The limiter may be defeated,
which allows higher power output, but
there may be more distortion than the
.2% shown in the specifications chart.
23. ENABLED LED: This LED will light
when the Chorus is activated, giving you
a visual sign that the Chorus is function-
ing.
EQUALIZATION section:
The graphic equalizer can be used in
two different ways: 1: To fine-tune
your sound, make small adjustments
at the desired frequencies and leave
the EQ on for the entire performance;
2: For a completely different sound,
make larger adjustments and only
switch the EQ on when you want the
radical change (such as during bass
solos).
BIAMP section:
13. FREQUENCY: This sets the
crossover point when using the BT-350
in the biamp mode (using two power
amplifiers, one for the low frequencies,
one for the highs). Please see the section
entitled “Using the Biamp Capabilities”
on pages 8 and 9 for more details about
biamping.
24. SPECTRUM: (or “crossover:”) This
unique feature allows you to adjust
which frequencies – either the entire
range or only the upper bass tones – are
enhanced by the Chorus effect. In the
fully counter-clockwise position the
entire range (or “spectrum”) will have
the chorus effect. As you rotate the con-
trol clockwise you change the roll-off fre-
quency for the Chorus, which allows the
lowest tones to come through “dry”
(without chorus applied). This is
extremely useful for maintaining full low-
end impact and definition during live
performances.
18. LEVEL: This serves as the overall
volume control for the BT-350’s on-
board 7-band graphic equalizer, and
only affects the signal when the EQ is on
(see #20). Use this control to adjust the
volume of the equalized signal: pulling
the Level control down from the center
position reduces the volume, pushing it
up from center increases it. The center
detent is “flat” (no increase or decrease
in level).
14. BALANCE: This adjusts the relative
level between the low frequency and the
high frequency biamp output signals.
Please see the section entitled “Using the
Biamp Capabilities” for more details
15. LINE OUT LEVEL: This adjusts the
output level for the Line Outputs jacks
on the rear panel (#31, 32), separately
and independently from the amplifier’s
Master level control (#10). The line out
feature can be used to send a low-level
(pre-amplified) signal to a mixing board,
recorder or external power amp. The
Line Out signal will have the same tone
and Chorus information as the Master
Level (speaker output) signal. Turning
25. DEPTH: Adjust the overall amount
of the Chorus effect with this control: to
the left for a little, to the right for a lot.
26. RATE: Adjust the speed of the cho-
rus effect with this control: to the left for
slow, smooth “phasing” sounds, to the
right for faster, “vibrato” sounds.
19. 40Hz – 10kHz: These slide controls
allow you to vary the output at the fre-
quencies shown under each control by
12dB. The center position of each con-
trol is “flat” (no boost or cut): pushing a
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BT-350 ThunderBass Amplifier
The Rear Panel:
27. SPEAKER OUTPUT jacks: Using a high-frequency power amplifier. See the NOTE: The Balanced Output jack is
1/4” mono phone plug, connect the out- section entitled “Using the Biamp wired as follows:
put of the BT-350 to your speaker cabi- Capabilities” on pages 8 and 9 for
PIN 1: GROUND
net(s) via these jacks. Be sure to use details.
heavy gauge speaker cable – not instru-
PIN 2: POSITIVE (+)
30. LOW OUT: When used in the biamp
ment patch cords – for these connec-
PIN 3: NEGATIVE (–)
mode, this output connects to the low-
tions. These jacks are wired in parallel:
frequency power amplifier. See the sec-
when connecting your speakers, keep
tion entitled “Using the Biamp
Capabilities” on pages 8 and 9 for
details.
EFFECTS LOOP:
the total impedance at or above 4 ohms.
The chart below can help you determine
the total impedance load when connect-
ing various combinations of speakers in
parallel.
33. SEND: When using an external sig-
nal processor with the BT-350, connect
a shielded cable between the Send jack
of the amplifier and the input of the
effects unit. This “sends” the pre-ampli-
fied bass signal to the device for process-
ing.
NOTE: You may access the BT-350’s
internal power amp through the Effect
Return jack (#34), for either the high or
low signal. This is covered in the section
entitled “Using the Biamp Capabilities”
on pages 8 and 9.
SPEAKER
IMPEDANCE
NUMBER OF
SPEAKERS
TOTAL
IMPEDANCE
4 OHMS
8 OHMS
8 OHMS
16 OHMS
16 OHMS
1
1
2
2
4
4 OHMS
8 OHMS
4 OHMS
8 OHMS
4 OHMS
34. RETURN: When using an external
signal processor, connect a shielded
cable between the output of the effects
unit and the Return jack of the amplifier.
This “returns” the processed bass signal
to the BT-350’s internal amplifier.
LINE OUTPUTS:
31. UNBALANCED: This 1/4” mono
phone jack supplies an unbalanced out-
put signal for connecting to an external
power amplifier. Very short runs (under
20’) to a mixer or recorder having unbal-
anced inputs can also be made from this
jack; for longer runs use the Balanced
output (#32). The output level at this
jack is adjusted by the Line Out Level
control (#15) on the front panel.
28. AC Line cord: Firmly plug the sup-
plied, heavy-duty grounded power cord
into this receptacle. When in use, be sure
this cord is properly plugged into a safe-
ly-wired, grounded 120 volt, 60Hz AC
power outlet. Do not attempt to defeat
the ground connection on this cable!
32. BALANCED: This XLR-type con-
nector supplies a balanced signal for con-
necting to an external mixer, recorder or
power amp which has balanced inputs.
The output is adjusted by the Line Out
Level control (#15). Use the Balanced
output when the distance between the
BT-350 and the mixing console or
recorder is over 20’.
If your BT-350 was purchased outside of
the United States, see the unit’s rear
panel for its power rating and follow the
above guidelines.
BIAMP OUTPUTS:
29. HIGH OUT: When used in the
biamp mode, this output connects to the
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BT-350 ThunderBass Amplifier
System Block Diagram:
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BT-350 ThunderBass Amplifier
Using the Biamp Capabilities:
Your BT-350 can be used along with an additional power amplifier, to “biamp” your system: that is, using two ampli-
fier/speaker combinations to share the task of reproducing the full range of your bass. Due to increased efficiencies, the
combined output may sound cleaner and more powerful than that of a single-amped system, especially during high-vol-
ume, live performances.
Using the BT-350 as the low-frequency power amplifier:
In the biamp configuration shown below, the BT-350 serves as the system preamp, biamp crossover, and low-fre-
quency power amplifier. A second power amp of 75 to 200 watts (such as the Crate model SPA-200) may be used to
amplify the upper frequencies. The crossover frequency (that point where one amplifier ends and the other amp takes
over) is set by adjusting the BT-350’s Biamp Frequency control (#13).
To connect the unit for biamp operation using the BT-350 as the low-frequency power amp, refer to the diagram below:
1
Connect a shielded cable from the BT-350’s Biamp HIGH OUT jack and the input of the amplifier which
will be used for the upper frequencies.
2
3
Connect a shielded cable from the BT-350’s Biamp LOW OUT jack and its Effects Loop RETURN jack.
Connect the Speaker Outputs of your high-frequency power amp to the speaker cabinet(s) that will be
used to reproduce the upper frequencies. (10” or 12” drivers work well for this.)
4
Connect the Speaker Outputs of the BT-350 to the speaker cabinet(s) that will be used to reproduce the
low bass notes. (Woofers in the 15” to 18” range work well for these low notes.)
Use the BT-350’s Balance control (#14) to adjust the relative level of lows to highs: to increase the level of low fre-
quencies in the mix, rotate the Balance control to the left (towards “LOW”). To increase the amount of highs in the mix,
rotate the control to the right (towards “HIGH”).
8
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BT-350 ThunderBass Amplifier
Using the Biamp Capabilities (con’t):
Using the BT-350 as the high-frequency power amplifier:
In the biamp configuration shown below, the BT-350 serves as the system preamp, biamp crossover, and high-fre-
quency power amplifier. A second power amp of 200 to 500 watts may be used to amplify the low frequencies. The
crossover frequency (that point where one amplifier ends and the other amp takes over) is set by adjusting the BT-350’s
Biamp Frequency control (#13).
To connect the unit for biamp operation using the BT-350 as the high-frequency power amp, refer to the diagram below:
5
Connect a shielded cable from the BT-350’s Biamp LOW OUT jack and the input of the amplifier which
will be used for the low frequencies.
6
7
Connect a shielded cable from the BT-350’s Biamp HIGH OUT jack and its Effects Loop RETURN jack.
Connect the Speaker Outputs of your low-frequency power amp to the speaker cabinet(s) that will be
used to reproduce the low bass notes. (Woofers in the 15” to 18” range work well for these low notes.)
8
Connect the Speaker Outputs of the BT-350 to the speaker cabinet(s) that will be used to reproduce the
upper bass notes. (10” or 12” drivers work well for this.)
Use the BT-350’s Balance control (#14) to adjust the relative level of lows to highs: to increase the level of low fre-
quencies in the mix, rotate the Balance control to the left (towards “LOW”). To increase the amount of highs in the mix,
rotate the control to the right (towards “HIGH”).
9
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BT-350 ThunderBass Amplifier
Some Suggested Settings:
ROCK:
Biamp and Chorus controls optional. You can crank the Tube Drive even more for distortion; if you do, back off the
EQ level.
JAZZ:
This will produce a very smooth sound with a minimum of percussive tones.
10
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BT-350 ThunderBass Amplifier
Some Suggested Settings:
COUNTRY:
Increasing the EQ Level produces more clean volume. Set the Master Level to taste.
FUNK “POPPING”:
Chorus is a great effect with this setting.
11
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BT-350 ThunderBass Amplifier
Technical Specifications:
Output Power Rating
350 watts @ 0.2% THD, 4 ohm load – 120VAC
200 watts @ 0.2% THD, 8 ohm load – 120VAC
Gain @ 1kHz
61dB, tones at “5”
Tone Control Range
Low Boost
Low
+8dB @ 20Hz
13dB @ 40Hz
11dB @ 260Hz
15dB @ 5kHz
+10dB @ 10kHz
Mid
High
High Boost
Graphic EQ Level
Graphic EQ Range
Signal to Noise Ratio
Input Impedance
+8dB, -10dB
12dB @ 40Hz, 100Hz, 250Hz, 625Hz, 1.6kHz, 4kHz, 10kHz
84dB typical
0dB input: 1M ohm
-15dB input: 122k ohm
Maximum Signal Level Accepted
0dB input: 2.5V peak to peak
-15dB input: 14V peak to peak
Tube Type:
12AX7 (preamp)
Effects Loop Level
1V RMS for full power output
Power Requirements
Domestic
Export
120VAC, 60 Hz, 10A
240VAC, 50 Hz, 5A
Size and Weight
5.25”H x 19”W x 15.75”D, 36 lbs.
CRATE continually develops new products, as well as improves existing ones. For this reason,
specifications and information in this manual are subject to change without notice.
CRATE/SLM ELECTRONICS, A DIVISION OF ST. LOUIS MUSIC, 1400 FERGUSON AVENUE, ST. LOUIS, MO 63133
47-599-02 • 02-96
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