Lab systems 250B User manual

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INTRODUCTION AND OVERVIEW:
The Labsystems 250B has been specifically designed for the modern bassist that
requires a high performance bass head in a compact easy to handle package without
sacrificing quality or reliability. We at Labsystems feel that up until the introduction of the
250B, this goal had not been achieved by other manufacturers; compromise had always taken
precedent and reliability had been less than perfect. With the introduction of the 250B these
problems are now overcome.
Years of development and refinement have gone into the Labsystems unique preamp
design, which features radical pre shaping eq. to give you a great starting sound, with the front
panel equalisation controls set flat. From here the tonal possibilities are endless, with carefully
chosen centre frequencies on the equalisation and voicing controls, and massive amounts of
cut and boost available on each of the controls. The separate variable voicing controls give
you added flexibility in addition to the normal equalisation with radical changes in mid and high
frequencies, tailored over a broader spectrum.
On board compression is also standard on the 250B, incorporating Labsystems
unique bass detection circuitry. Sophisticated frequency filtration networks process the signal
for threshold sensing eliminating over compression of the lower notes. What this means in
sonic terms is the ultimate slap and pull sounds; the transient response of the bottom end
retained, whilst smoothing out the top end to eliminate that harshness, often heard with today's
aggressive bass techniques. The overall amount of compression is of course adjustable to
your taste, or if desired can be fully bi-passed.
Attenuation is also catered for in the form of a 10dB pad switch on the front panel,
allowing you to use basses with either active or passive pickups, whilst still maintaining correct
gain integrity to drive the preamp stage to the optimum.
A 600 ohm balanced D.I. output is provided, which is taken post eq., so you can be
assured the sound you are getting out front is the same as your stage sound, the way you
want it to sound. An effects loop is also provided, to allow you to correctly interface with the
vast array of signal processing devices available to the modern bass player.
Power output is achieved by the legendary Labsystems M4 modular mosfet output
module, this same module having been used extensively in our entire product range for many
years now with reliability un-surpassed and un-rivalled in other products. Current limiting
incorporated into the module provides a high degree of protection against speaker impedance
mismatch and short circuit, a common killer of "other" output stages. Also built into the 250B
are protection circuits for over voltage and spike suppression.
The 250B utilises a toroidal power transformer, and high grade capacitors to achieve
a power supply light in weight, low in noise, but heavy on performance, with adequate
reserves to deliver high speed voltage swing necessary for the transient attack demanded by
the bassist of the nineties.

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CONTROLS AND THEIR FUNCTION
1. COMPRESSION: When the compression control is turned fully anti
clockwise the compression will be fully bi-passed.Turning the control
clockwise will lower the threshold at which the compression begins to
operate. The yellow l.e.d. marked threshold will indicate the onset of
threshold detection and thus the start of compression. A subtle or
occasional flashing of the threshold l.e.d. will indicate subtle compression,
whilst the l.e.d. staying illuminated for longer periods will indicate heavier
compression. Adjust this control to your own taste.
2. PAD SWITCH: Depressing the pad switch will result in 10dB of
attenuation. This setting should be used if you have a bass with active
pickups or an on board preamp. For passive basses use this switch in the
out position.
3. BASS EQ. Controls the amount of bottom end present. With the
control set centre it is in-active. Turning the control left of centre cuts the
amount of bass, turn the control right of centre boosts the amount of
bass. The centre frequency of this control is 20hz, and is very effective on
five string bass.
4. LOW MID EQ. Controls the amount of lower mids. With the control set
centre it is in-active. Turning the control left of centre cuts the amount of
lower mids, turning the control right of centre boosts the amount of lower
mids. The centre frequency for this control is 400 hz, although due to its
wide bandshape, has a considerable response on most of the
fundamental frequencies on bass guitar.
5. HIGH MID EQ. Controls the amount of upper mids. With the control set
centre it is in-active. Turning the control left of centre cuts the amount of
upper mids, turning the control right of centre boosts the upper mids. The
centre frequency for this control is 1.5khz.
6. HIGH EQ. Controls the amount of top end. With the control set
centre it is in-active. Turning the control left of centre cuts the amount of
top end, turning the control right of centre boosts the top end. The
condition and age of your strings will affect how this is set.
7. MID VOICING: This control gives a more radical response than the mid
eq. due to its broader and tailored bandshape. Can be used to quickly
alter your basic sound without adjusting your initial eq. settings.
Centre frequency is around 1.2khz, although the band shape is quite
different to that of a conventional eq. control.
8. HIGH VOICING: Works in a similar fashion to the mid voicing but has a
higher centre frequency of 12 khz to control the amount of transparency
in your sound.

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* OUTPUT STAGE: M4 MODULAR MOSFET
* OUTPUT POWER 250 WATTS RMS INTO 4 OHMS
180 WATTS RMS INTO 8 OHMS
* EQUALISATION BASS 20HZ
LO MID 400HZ
HI MID 1.5KHZ
HIGH 7KHZ
* VOICING MID 1.2KHZ BROADBAND
HIGH 12KHZ BROADBAND
* SPEAKER OUTS 2 X 6.3MM JACK SOCKETS
*FUSE 3.15 AMP SLO-BLO LOCATED IN FUSE
DRAWER INTEGRATED INTO
LOWERPART OF I.E.C. POWER SOCKET
ON REAR PANEL
* CHASSIS POWDERCOATED BHP STEEL
* WARRANTY 2 YEARS PARTS AND LABOUR
AS PER DETAILS IN WARRANTY CARD
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