McMartin MS-25B User manual

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MS-25B
25 WATT AMPLIFIER ·
•
• McMartin Industries
Inc.• 4500 South 76th Street• Omaha. Nebraska 68127• Phone [phone]

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MC Martin.
~c~arti
MS-25B
25 WATT AMPLIFIER
INSTRUCTION MANUAL
I SPECIFICATIONS
11 GENERAL DESCRIPTION
Ill INSTALLATION
IV
PART S LIST
WARRANTY
V SCHEMA TIC DIAGRAMS
page
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2
3
4
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MCMartin.
I. SPECIFICATIONS
POWER OUTPUT •..
DISTORTION ..... .
OUTPUT
REGULATION . . ..•
FREQUENCY
RESPONSE
Mualc Channel ..
Mic Channel •...
Aux Channel .•..
Mualc Tone
Compenaatlon
..•
HUM & NOISE
Mualc Channel . .
Mic Channel .•..
Aux Channel ....
INPUTS (4)
Mualc .........•
Microphone ..... •
(2
optional)
Auxlllary ...... .
GAIN
Mualc
Bridging
600-
ohm with
optional
MT-4,MT-6 .. .
Matching .... .
Auxlllary ...... .
Microphone .. ... .
OUTPUTS ........ .
......••.•.•...• 25 watts rms
35 watts music
50
watts peak
. . . . .
Less than 2% THD @rms
rated power 50-15000
Hz
...••... .. ••.•......... 2 dB
. •...... ±1.0 dB 30- 15000 Hz
±1.5 dB 20-20000 Hz
..•..•... Fl at response t2 dB
50-15000 Hz
Equalized for speech,
-12
dB @ 50 Hz
...•..... ±1.5 dB 20-20000 Hz
. .. ..... Bess ±15 dB I 50 Hz
Treble ±1 5 dB@ 15 kHz
........... 70 dB below rated
power output
•.......... 60 dB below rated
power output
.•......... 70 dB below rated
power output
..•........ 25K-ohm standard
10K-ohm bridging
or 600-ohm
matching
with optional MT-4
or MT-6 input transformer
......... 50-150-ohm balanced
... 40K-ohm nominal, auxiliary
gain control standard
. .
.. • • •• •. . . . . . • •. . . . .54 dB
.••.••.• • •••••••••••.• 64 dB
. ..••................. 44 dB
........•............ 108 dB
•..• 8 ohm unbalanced, 25 and
70.7 V balanced
11. GENERAL DESCRIPTION
BASIC AMPLIFIER
The amplifier consists of a complementary power amp-
lifler circuit, power supply, and speaker line matching
transformer.
This basic unit may be used for back-
4/75
ground music applications where microphones end tone
equalizatlon are
not required. Provision is made for two
medium level Inputs; (1) music Input -which may be
used unbalanced or balanced with the MT-4 or MT-6
(600 ohms or 10 K bridging) transformers, front and rear
panel control, (2)
auxiliary inputs which may be used
for an auxiliary program source. This Input is unbal-
anced
only and may be adjusted by a r ear panel screw-
driver adjust control which comes as standard equipment.
Output connections provide for
either 8 ohm unbalanced
load
or 25 volt and 70.7 volt balanced speaker systems.
A three wire unswltched utility outlet (300 watt capa-
city), . AC power indicator light and maximum output
indicator I ight also come standard with the basic amp-
1 ifier. Electrical protection is provided by AC fusing
as well es diode current limiting for short circuit fault
protection.
The
basic amplifier provides for insertion of additional
accessory modules such
as :me or two microphone pre-
amplifiers
with balanced input, telephone page adaptor,
feedback
type individual bass and treble controls and
en electronic page mute adaptor for controlling all input
muting.
See catalog sheets for full MSA-Module items.
For convenience, the most commonly used modules,
MSA-1, 2 & 3 are described here.
TONE CONTROLS (MSA -2)
A separate plug-in
circui t card (MSA-2) is available for
bass and
treble tone equalization for installa tions
where
this is desired. The tone controls affect the
music channel
only and provide 15 dB of bass boost or
cut and 15 dB of treble boost or cut. They are screw-
driver adjustable through the rear panel to prevent
tempering.
The tone control network is of the active
feedback type having unity gain with the controls cen-
tered. Therefore, the input
sensitivity does not change
when the controls are
installed.
MICROPHONE PREAMPLIFIER (MSA-1)
The microphone preamplifier
is a se lf -contained plug-in
module (MSA-1)
with 40 dB gain, circuit board mounted
gain control,
end mu-metal shielded transformer accept-
ing lo-Z balanced microphones. The three stage preamp-
11 f ie r provides for 30 dB of overload, Instantaneous
overload recovery,
RF suppression, paging connection
(12
dB bass cut), two microphone input impedance taps,
and reversible front panel gain control for
either exter-
nal or concealed screwdriver adjustment. Either one or
two of these modules may be installed in the MS-25B.
Screw terminal connections are provided on the rear
panel for microphone termination.
PAGE MUTE MODULE (MSA-3)
Microphone and program muting
is accomplished by a
separate plug-in el
ectronic gating module. This circuit
when installed mutes both microphone channels and
leaves the
auxiliary input and music in put on. When
either or both microphone inputs are activated (by
grounding the appropriate mute connection) the music
end
auxiliary inputs are muted and the microphone
channel is activated. A screwdriver adjust control Is
also provided on the module (accessible through the
rear panel) to adjust the music level while the micro-
phone channel
is activated If complete muting of the
music Is not desired. By changing the location of one
resistor on the power amplifier board It is al so possible
to bypass the mute circuit on the auxiliary input chan-
nel to keep
this input open el ell times.
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If pr iority of Input Is desired {MIC-1 over MIC-2, etc.)
the 'ground' path Is simply run In series through the
muting contacts
as shown in Figure 1.
__ ,,.
RACK MOUNTING K IT (MRP -1 )
The MS-258 requires 3½" of rack space and may be
rack mounted by the addition of the optional rack
mounting
kit.
TB -1
--------,
M ic Sw itc h -· ~----- ..... --+..(:}-+---+
To M SA 3
_>--,.'~>-+---...- I IE
MSA
1
---
~--
----
PBX
PBX
I L ine I
Ck t
IR ly
by
1 Tel
co .J
.._ _______ _
NOTE: Se rles ground mu st originate at ampllfle r.
To MSA-3
MSA
4
Figure 1 CHANNEL 2 HAS PRIORITY
Ill. INSTALLATION AND OPERATION
The MS-258 is designed to operate from line voltages
of 105 to 125 volts AC. Both are equipped with power
transformer primary taps for 1
05 -115 volts AC and also
115-125 volts AC. T he amplifier is normally shipped
with the tap connected for 115-125 volts AC. Actually
higher fine voltages than this may be tolerated for short'
periods without endangering the safety of the amplifier.
The primary tap should only be changed to the 105-115
volt position in the event of sustained low line voltage.
After selecting a suitable location for the amplifier,
remove the top cover and
lnstal I the necessary acces-
sory circuit cards, fine transformer, etc. Connect the
speaker
lines to the 25, 70.7 or 8 ohm connections as
required.
Also connect all Inputs, unbalanced or bal-
anced music inputs, microphones, page mute, etc.
Balanced music Inputs may be connected for
either 10K
ohm bridging or 600 ohm matching Input (connections
are provided
on the rear chassis terminals). Unbalanced
program sources
may be fed to either the auxi llary Input
(phono plug)
or the 1 0K ohm terminals without the line
transformer installed. (Make sure jumpers are installed
in socket from pins 5 to 8 and 6 to 9). The 10K terminal
marked (G) Is the ground connection for unbalanced
input.
Balanced microphone inputs should be connected to the
appropriate screw terminals
on the rear of the unit. T he
ground connections are for shield grounds and for the
page mute ground returns. A three-<:onductor microphone
cord
with shield may be used with one lead for the page
mute Iine.
The page mute circuit may then be activated
by a remote microphone switch. NOTE : Always disable
the microphone audio Iine shunt switch when using the
MSA-3 mute
mOdule (See Figure 1)
Once all connections have been made , apply power and
set controls on front panel to the appropriate levels. A
gain I imit control Is provided on the rear of the unit to
set the maximum level of the music input. The gain
control tor the auxiliary input, the tone controls, and
the music mute level controls are also located on ·the
rear
of the unit. When maximum output of the amplifier
has been reached (with proper loading) the maximum
output Ilght
wi II flash, indicating the 70.7 volt line
level clipping point has been reached. This light may
flash occasionally with program peaks, but should not
stay on continuously. Overdriving the
amplifier in this
manner will cause excessive distortion.
INSTALLATION ANO REMOVAL OF MODULES
To Install page-mute and tone control modules, it Is
necessary to remove the amplifier top cover, (remove
jumper from pins 4
and 7 and resistor from tone control
socket) and caretuI
ly plug the mOdu les in the approprl
ate sockets. Position the :,rinted circuit board mounting
stud over the chassis hole and secure board
with one
number 4-40 screw.
To
Install microphone preampllflers insert felt washers
over control shaft, remove hole plug and install preamp-
1 itiers; then proceed the same as above for the tone
controls. Afte r the preamplifier Is secured, place one
nylon washer over outside of control shaft and install
knob. Squeeze control and knob together gently and
tighten set screw. Be sure control Is turned full counter
clockwise and knob pointer Is set over O' mark. {7
o'clock position).
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MC Martin.
4/75
IV PARTS LIST
Non-Standard parts only ( all other parts available local ly)
Basic amplifier (Power amplifier, power supply and chassis)
SYMBOL
Q-1
Q-2, 3
Q-4, 6
Q-5
0-1, 2, 3, 4, 5
Z-1
R-15, 29,
30
R- 19
R-28
C-7
C-
11 , 12
F-1
PL-1
PL-2
SW -1
T-1
T-2
*
This value may vary from O to 10 ohms
P/ N
201050
201056
201067
20 1068
210008
220008
400042
502028
400039
600039
600040
280009
291001
291002
480011
900047
910043
PARTS LIST MSA-1 (MICROPHONE PREAMPLIFIER MODULE)
SYMBOL
Q-1
Q-2
Q-3
R-7
T-1
P/ N
201052
201050
201022
400039
910041
PARTS LIST MSA-2 (TONE CONTROL MODULE)
SYMBOL
Q- 1, 2
Q-3
R-2, 11
P/ N
201049
201022
400042
PARTS LIST MSA-3 (PAGE MUTE MODULE)
SYMBOL
Q-1 , 2, 3, 4
0-1,
2, 3
0-4, 5
R-3
PIN
201049
220003
220006
400042
DESCRIPTION
Transistor SE 4010
Transistor 2N 3569
Transistor MJE 2901
Transistor MJE 2801
Diode Rectifier 808 800 PIV at 750 MA
Diode Zener 36 Volts
Control 50 K Linear
*Resistor 3.3 ohm½ watt
Control 50 K
Audio
Capacitor 1000 MFO at 50 Volts DC
Capacitor 1000 MFD at 75 Volts Tubular
Fuse 0.75 Amp 125 volts slo blo
PI iot Lamp WHT Lens NE 2 PT
Red Lens NE 2 PT
Switch Rocker
Transformer 2-P-117 A
Transformer 2-A-93 A
DESCRIPTION
Transi stor SE 4010
Transistor 2N 4249
Transistor SE 4001
Control 50 K Audio
Transformer Input Microphone
DESCRIPTION
Transi stor SE 4002
Transistor SE 4001
Control 50 K
Linear
DESCRIPTION
Transistor SE 4002
Diode IN 462
Diode IN 87
Control
50 K Linear
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V. WARRANTY
McMartin products or e warranted to be fr ee from defects and work-
manship for a period of one year ofter shipping dote , when sub-
je cted to normal usage and se rvice . Al I warrant ies are void if (a)
equipment hos been altered or repaired by others without McMar-
tin's specific prior authorization; or (b) equipment is operated
under environmental conditions or circumstances other than those
specifically described in McMartin literature or instruction man-
uals.
Upon notification within the applicable warranty period, McMartin
agrees without charge, to repair, replace , or supply replacement
ports for any properly maintained equipment or port s that are de-
fective as to design, materials, or workmanship and that are re-
turned in accordance with McMartin's instructions to the Buyer.
At McMartin 's sole discretion , the Buyer may be requested to re -
turn
the defective port of equipment to McMartin, FOB Omaha,
Nebraska. Ports or equipment may be returned only with McMar-
tin's prior authorization and must be identified by o return auth-
orization number issued by McMartin's Customer Service Deport-
ment. All merchandise so returned must be sent transportation
prepaid, at Buyer's risk . Full details of the failure or malfunction
should be included so as to expedite repair or replacement. Re-
pair parts or repaired or replaced equipment wi 11 be returned to
the Buyer, FOB factory.
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MCMartin.
4/75
IV PARTS LIST
Non-Standard parts on ly (alI other parts avaiI able locally)
Basic ampI lfler (Power amplifier, power supply and chassis)
SYMBOL
0- 1
0-2, 3
0-4, 6
0-5
0-1, 2, 3, 4, 5
Z-1
R-15, 29,
30
R- 19
R-28
C-7
C-11, 12
F-1
PL-1
PL-2
SW-1
T -1
T-2
•This value may vary from O to 10 ohms
P/N
201050
201056
201067
201068
210008
220008
400042
502028
400039
600039
600040
280009
29 1 00 1
29 1002
480011
900047
910043
PARTS LIST MSA -1 (MICROPHONE PREAMPLIFIER MODULE)
SYMBOL
0- 1
0-2
0-3
R-7
T-1
PIN
201052
201050
201022
400039
910041
PART S LIST MSA -2 (TONE CONTROL MODULE)
SYMBOL
0- 1, 2
0-3
R-2, 11
P/N
201049
201022
400042
PARTS LIST MSA -3 (PAGE MUTE MODULE)
SYMBOL
0-1. 2. 3, 4
D-1, 2, 3
0-4, 5
R-3
P/ N
201049
220003
220006
400042
DESCRIPTION
Transistor SE 4010
Transistor 2N 3569
Transistor MJE 290 1
Transistor MJE 2801
Diode Rectifier 808 800 PIV at 750 MA
Diode Zener 36 Volts
Control 50 K Linear
•R esistor 3.3 ohm½ watt
Control 50 K Audio
Capacitor 1000 MFD at 50 Volts DC
Capacitor 1000 MFD at 75 Volts Tubular
Fuse 0.75 Amp 125 volts slo blo
Pilot Lamp WHT Lens NE 2 PT
Red Lens NE 2 PT
Switch Rocker
Transformer 2-P-117 A
Transformer 2-A-93 A
DESCRIPTION
Transistor SE 4010
Transistor 2N 4249
Trans
is tor SE 4001
Control
50 K Audio
Transformer Input Microphone
DE SC RIPTION
Trans is tor SE 4002
Tr ansistor SE 4001
Control 50 K Linear
DESCRIPTION
Transistor SE 4002
Diode IN 462
Diode IN 87
Control 50 K Linear
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V. W ARRANTY
McMartin products are warranted to be free from defects and work-
manship for a period of one year ofter shipping dote, when sub-
jected to normal usage and service. All warranties ore void if (a)
equipment has been al tered or r epaired by others without McMar-
tin's specific prior authorization; or (b) equipment is operated
unde r environmental conditions or circumstances other than those
specifically described in McMartin literature or instruction man-
uals.
Upon notification within the applicable warranty period, McMartin
agrees wit h out charge, to repair, replace, or supply rep l acement
por ts for any properly maintained equipment or ports that ore de-
fective as to design, materials, or workmanship and that are re-
turned in accordance with McMartin's instructions to the Buyer.
At McMartin's sole discretion, the Buyer may be requested to re-
turn
the defective port of equipment to McMartin, FOB Omaha,
Nebraska. Ports or equipment may be r eturned only with McMar-
tin's prior authorization and must be identified by o return auth-
orization number issued by McMartin's Customer Service Depart-
ment. AlI merchondi se so returned mu st be sent transportation
prepaid, at Buyer's risk. Full details of the failure or malfunction
should be included so as to expedite r epair or replacement. Re-
pair parts or repaired or replaced equipment wi 11 be returned to
the Buyer, FOB factory.
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MCMartin.
4/75
MSA-1
MSA-2
MSA-3
MS-25B
V. SCHEMATIC DIAGRAMS
MIC PRE AMP MODULE
TONE CONTROL MODULE
PAGE MUTE MODULE
MASTER SCHEMATIC
P/N 000400
PIN 000401
P/N 000402
E-2706
page
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