Bogen MT250 Operating Manual

Page 1

250-Watt

Booster Amplifier

BOGEN.

A DIVISION OF LEAR SIEGLER, INC.

Model MT250

DESCRIPTION

The Model MT250 Booster Amplifier provides a rated out-
put of 250 watts (ms) at less than l.7z distortion over the
frequency range of40 to 14.000 Hz. and 300-watts (rmslat less
than 2% distortion between 50 and 12.000 Hz. Frequency
response of the Model MT250 is :2 dB from 20 to 20.000 Hz.

In addition to 8-ohm. 25 on the rear of the amplifier. a direct output is provided at a
rated impedance of0.75 ohms. A polarized output receptacle
also provides a source of 120 volt ac power. at any frequency
between 35 and l0 kHz. for shake tables and similarindustrial
applications.

The booster amplifier will accept a high-impedance un-
balanced input. or high or low impedance. balanced sources
by means of accessory plug-in transformers. Only 250 mil-
livolts input is reQUired for full-rated output.

A power switch and power indicator are provided on the
front panel. The rear panel has a screwdriver.adjustable level
control. a speech filter switch. and a circuit breaker that

prevents the amplifier from drawing excessive primary cur-
rent.

All internal circuitry is readily accessible from the top ofthe
unit. and the output transistors are located on heat sinks
secured to the sides. These heat sinks also contain a then'no-
stat that automatically cuts off the input signal when the heat
sink temperature reaches 95°C (203°F). An output bias com-
pensation transistor is located on the chassis wall close to the
heat sinks.

The amplifier. which normally operates from a l05- l 25 volt .
50-60 Hz source. is designed for emergency operation from a
dual (+ and -) Zd-volt battery supply (such as four lZ-volt
batteries). The amplifier is also equipped with power output
terminals which provide +22 and ~22 volts dc at IOO milliam-
peres for external equipment. regardless ofthe primary power
source to the amplifier. Overall dimensions of the amplifier
are 17% inches wide, 7V2 inches high and 11% inches deep.
The unit has mounting feet for bench or shelf installation and
may be rack mounted by means of the Bogen Model RPK-36
Rack Mounting Kit.

TECHNICAL SPECIFICATIONS

POWER OUTPUT: 250 watts (rms). 40 ~ 14.000 Hz @
less than l7r distonion; 300 watts (rmsl. 50 . l2.000
Hz Q: less than 27: distortion.

PEAK POWER OUTPUT: 600 watts.

POWER GAIN: 80 dB at 300 watts.

FREQUENCY RESPONSE: :2 dB from 20 - 20.000 Hz.

REGULATION: Better than 2 dB from no load to full
load.

SENSITIVITY: 250 mV for rated output.

NOISE LEVEL: -83 dB below rated output.

INPUT IMPEDANCE: Hi~Z. 50k: Lo-Z. 500/600 ohms
with TL600 xfmr; Bridging. 10k ohms with TLlOk
xfmr.

OUTPUT CONNECTIONS: 25V. 45V. 70V and 120V
balanced: 14V direct. unbalanced.

OUTPUT IMPEDANCES (Balanced and Unbalanced):
0.75. 1.0. 2. 2.5. 8. 16. 20. and 58 ohms.

AC POWER OUTPUT: 300 watts of [20th sine wave
power for industrial applications at variable fre-
quéncies between 35 and 10,000 Hz. when driven
from suitable input signal source.

CONTROLS AND INDICATORS: Front panel -
Power switch and power-on indicator. Rear panel -
Speech filter switch (-SdB @ 100 Hz). input level
control. and ac circuit breaker.

POWER REQUIREMENTS: 105-125 volts. 50/60 Hz
ac; or dual 28 Vdc 61' 8 amps.

LINE CORD: Three-wire type SJ with three-prong
grounded plug.

AUXILIARY RECEPTACLE: Three-wire grounded,
600 watts (q [20 volts.

POWER CONSUMPTION: 105-125 Vac 50/60 Hz;
750W @ full rated output. 75W ((1 idle. Dual (+ and -)
24 Vdc: 8A (1, full rated output. 500 mA @ idle.

CIRCUIT PROTECTION: IO-amp breaker for ac line:
electronic overload protection: thermostatic tem-
perature protection.

TEMPERATURE RANGE: ~20°C (-4F) to +55C
(+130°F).

SEMICONDUCTORS: Allsilicon. 27 transistors and 9
diodes.

DIMENSIONS: 17%" wide x 71/2 high x 11% deep.

RACK PANEL MOUNTING: RPK-36 accessory with
19" x 8% rack mounting adaptor panel.

FINISH: Low-lustre black.

WEIGHT: Shipping 55 lb.. net 50 lb.

ACCESSORIES: TL600 plug-in 500/600 ohms line
transformer. TLIOK plug-in l0.000 ohms bridging
transformer. RPK-36 19" x 8%" Rack Mounting
Kit.

Printed in ['8 A

904

54-5643-07

Page 2

INSTALLATION

UNPACKING

The power amplifier was carefully checked before leaving
the factory. Inspect both the amplifier and its shipping con-
tainer for indications of improper handling. Report any
equipment damage immediately to the distributor from whom
the unit was purchased. If the amplifier was shipped to you.
notify and place your claim with the shipping carrier without
delay.

NOTE
Do not discard the small envelope packed with
the amplifier.

EQUIPMENT CONNECTIONS

AC POWER CONNECTIONS. The ac line cord has a three-
prong plug which should be plugged into a three-Wire.
grounded 120-volt. 50/60 Hz outlet. This automatically will
ground the chassis. If a grounded three-wire outlet is not
available, install an adapter (e.g., Leviton No. 5017) and
connect the adapter pigtail to a reliable electrical system
ground (such as grounded wall-plate screw, separate ground
wire. etc.)

AUXILIARY DC POWER CONNECTIONS. The unit may be
powered from a dual (+ and -) 24-volt battery supply (28 volts
at full charge), such as four fully charged |2-volt automotive-
type storage batteries connected in series with center tap. The
unit is supplied with a three-pin male plug (in envelope) for
connecting the dc supply to the EXTERNAL DC OPERA-
TION receptacle (see figure 5). The power switch and the
Power On indicator are not functional with dc operation. An
emergency battery supply may be left permanently connected
to the amplifier via the circuit shown in figure 1. which also
provides a trickle charge for the batteries. It is important to
provide fuses or circuit breakers for the dc circuit.

Caution
Observe polarity on all dc power connections.

INPUT CONNECTIONS. There are two sets of input termi-
nals for accepting either high~impedance unbalanced. or
balanced inputs.

HI-Z Unbalanced Input. A high impedance (50000«ohm) un-
balanced input is available between the HI-Z and GND input
terminals (see figure 5). Minimum input level is 250 mV for full
rated output. Use singleAconductor. low capacity shielded
wire.

Balanced Input. A balanced input is provided at the BAL
INPUT terminals. Use two-conductor shielded wire. and
connect the shield to the GND terminal. The input requires

OPTiONAL CIRCUW

W \ CHASSIS
L ____________ EXTERNAL DC
3 C $ng Ft OPERATlON
a 12a Sfivcvnt 56V
>»-+-o~>- c
' * 35 " » +28ch
W

4506a: 85-1236-CI PLUG WlTH
85-1237-01 emswpscwaem

era-2:334!

7F0UR12V BATTERLES
Figure l - Trickle Charge Circuit for Auxiliary Supply.

.2.

W
PC. BOARD

REAR OF
AMPLIFIER

874-2378-01

O

TRANSFORMER
SOCKET
Figure 2 - Location of Accessory Socket.

installation ofa matching transformer on printed cirCUit board
A1 (see figure 2) which is accessible by removing the top
cover from the unit. Install either a Model TL600 for low-
impedance (500/600 ohm) or a Model TLIOK for high-
impedance (10.000 ohms) input.

C autian
All Ivork done inside the unit must be performed
by qualified personnel. Disconnect all power
sources before removing top cover.

OUTPUT CONNECTIONS. Figures 3 and 5 show the location
ofthe output connection strip. and the 120 Vac output recep-
tacle.

Caution
Many loudspeakers can be damaged ifuver-
driven. Do not connect speakers without firx/
checking the output level (refer to text under "In-
put Level Control". in Control: and Indicators
section).

RACK MOUNTING
The booster may be installed in a standard 19-inch rack
panel by means of a Bogen Model RPK-36 Rack Panel As-
sembly. To install the booster in the rack panel assembly.
proceed as follows:
3. Remove four front screws securing booster top cover (do
not remove cover).

LOAD MIME (ONMS)

«- INSTALL JUMPER FOR m L
BA RATING] LoAD

UNBALANC ED OUTPUT

o o o _ o 2 To
., \_,1(uvev)?-. ow/25
soow/z

25v eALANcso/ UNBALANCED

o o 2 o o 0-- is
" zsow/zo

now] Is

70v uunceo / UNBALANCED
o q o o 0-. a
tux?

SV BALANCED / UNBALANCED

? O O O O |
FEW/0.75

0.05

14v mater UNBALANCED 325,

I06! BS-oloI-OI'

(W I Pm-CCV.

cl mum-tum zscw/se
mow/so

Izov mmceo / UNHALANCED
c74-2364-al
Figure 3 - Output Options.