Mustang Communications Ltd
Issue No.2
Mustang Communications Ltd
Eastfield Industrial Estate
YO11 3UT
Telephone International
01723 582555
+44 1723 582555
[email protected]
Fax International
01723 581673
+44 1723 581673
Author: M. R. Tetley M. Inst. S. C. E.
Introduction ...............................................................
Carton contents
Warranty ...................................................................
Specifications ..........................................................
Front panel controls .................................................
Input level controls
Treble & bass controls
Master level control
Output level peak indicator
Mains power switch & indicator
Input facilities ...........................................................
Input connections and selection of cables
Input control removal
Priority control: Input No.1
Phantom powering of microphones ..........................
Input No.1 bass-cut option
Setting the input channel sensitivities
Connection of record deck - magnetic phono
Loudspeaker output .................................................
Typical loudspeaker arrangements
Selection of 100, 70V 50V, or 4 ohm outputs
Loudspeaker cables
Tape recording facilities ...........................................
Record/playback connections
Selection of recording take-off point
Slave amplifier facilities ...........................................
Installation ..............................................................
Installation checklist
AC Mains power input ..............................................
Fuses ......................................................................
Earthing & Hum loops ..............................................
Case removal ..........................................................
19” Rack bracket fixing ............................................
Fault checklist ..........................................................
List of drawings
PCB layout
Typical loudspeaker circuits & matching
Signal connections
Amplifier block schematic
(EMC directive
This equipment has been designed and manufactured to the highest standards. If connected and operated as set out in this manual, there should be no Electromagnetic
Compatibility problems.
If any aspect of operation gives rise to concern, then please contact the manufacturer for advice.
Thank you for purchasing this amplifier. You have made a wise choice. It is a purpose designed, British made, public address amplifier
which, if installed and operated correctly, will give many years of trouble-free and accurate amplification. Used in conjunction with good
quality loudspeakers and microphones etc., the MAESTRO series amplifier is capable of equalling or exceeding the performance of
more expensive units from our competitors’ ranges.
The Maestro 30 amplifier is manufactured entirely by Mustang Communications Ltd., in Scarborough, England, and meets the relevant
British Standards for safety and quality assurance.
The MAESTRO range is just one of many amplification ranges amongst the hundreds of items manufactured by Mustang Communications to meet the needs of the public address market. Your dealer will be pleased to advise you on the selection of the most suitable
equipment from the comprehensive Mustang catalogue should you have further amplification requirements.
By design, the Maestro amplifier range is a particularly versatile concept and may be applied to a wide variety of amplification projects
in locations such as schools, restaurants, theatres, churches, factories, recreation areas, etc., where high performance standards
should be expected.
Maestro amplifiers are designed to meet internationally agreed standards of signal level, impedance, sensitivity etc., and therefore may
be used successfully with all good quality public address loudspeakers, microphones, tape units and phono decks, of any origin.
Carton contents
On receipt from the manufacturer, this carton will contain:
installation & operation handbook
DIN input connectors: 5 pin, 180 degree pin format
DIN loudspeaker plug
front panel blanking plugs
AC mains connection lead
guarantee registration sheet
Rack mount brackets type BRK.20 may be purchased as a separate catalogue item to enable the Maestro 30 to be fixed in a standard
19" equipment rack, occupying 2U of panel space.
The Maestro range is carefully designed and budget priced. The amplifiers exhibit all the features required by the majority of simple
public address amplification installations. Various internal adjustments and options may be selected by the commissioning engineer to
suit the particular installation. The manufacturers are unable to undertake the consideration of any special options or modifications to
the standard Maestro format amplifier, as it is probable that an alternative Mustang amplification range may be more appropriate. Your
dealer will advise.
This amplifier should operate successfully for many years if installed correctly. However, should any fault occur within 24 months of
installation, irrespective of usage or application, the manufacturer undertakes to replace parts, or the whole unit, at their discretion, free
of all labour or parts charges. However, should investigation of such a fault indicate operation of the unit outside its specification, then
the manufacturer reserves the right to levy an appropriate repair charge.
Should a fault be suspected, your dealer should be notified in the first instance. All returns should be made via your dealer, forward
carriage paid, and be accompanied by details of:
the reported symptoms
brief details of the installation.
details of the circumstances of failure
Following the routine warranty period, Maestro amplifiers may be returned via your dealer, to the manufacturer for any necessary
repairs or refurbishing. Details of the work required/reported fault must accompany the unit, and nominal charges will be levied.
Microphone input sensitivity: Inputs 1 - 3. (These inputs
may be operated in either balanced or unbalanced mode).
500uV @ 200 ohms
Switchable input attenuator - Inputs 1 - 3
Common mode rejection ratio @ 1KHz: Inputs 1 - 3
better than 95dB
Microphone overload level: Inputs 1 - 3
Signal to noise ratio: Inputs 1 - 3
better than 60dB
better than 65dB
Optional bass roll-off: Input No.1 Internal PCB switch
-3dB /octave below 200Hz
Input No.1 normal status
Input 2 balanced/unbalanced line sensitivity
775mV @ 220k
Input 4: either auxiliary line input unbalanced
or RIAA magnetic phono pick up: Internal PCB switch
100mV @ 47k
5mV @ 47k
Priority input channel sequence ladder
1 over 2/3/4
Inputs 2-3-4 muting during priority
Input 3 balanced/unbalanced line sensitivity
100mV @ 47k
Tape playback level via Input No.4 gain control. (Stereo
signals are mixed internally)
85mV @ 10k
Phantom microphone supply voltage: (optional) Inputs 1 - 3
+12V stabilised
Connectors: Inputs 1 - 4, and tape interface.
5 pin 180 deg. std DIN
Power output
Frequency response. -3db points @ full rated power
30Hz to 17kHz
Output matchings: selectable by internal PCB switch
4 ohms, 100V, 70V & 50V
100V line regulation load/no load @ 1KHz
Treble & bass equalisation (cut & lift)
+12dB @ 100Hz and 10kHz
Recording signal output/slave output: normally post-tone
control circuit: Internal PCB selector switch
775mV @ 600 ohms (0dB)
Power output connector
Signal to noise ratio: zero equalisation, gains set zero
2 pin DIN
better than 85dB
Supply voltage limits
180V to 250V AC 40/60Hz
Maximum supply consumption - at full rated power output
Overall width
(482.5mm with rack brackets)
excluding allowance for connectors
fascia to rear panel
Depth -
overall including control knobs
Total including removable feet
excluding allowance for connectors
88.5mm(main body 85mm)
In the interests of our policy of continuous improvement - any of the above specifications may be changed without notice.
Various front controls and facilities are provided to enable the user to obtain maximum clarity from the amplification system. The user
may adjust these at will.
Input level controls
Up to four input signals may be accepted by this unit and the corresponding input circuits of the amplifier are occasionally referred to
as input “channels”. Input level controls are used to set the relative sensitivities of the four input channels of the amplifier. Whilst
these controls are calibrated, the associated numbers are only arbitrary and should not be taken to indicate absolute output powers.
For instance: an unusually low level input signal will not necessarily cause the amplifier to be operating at maximum power even with
the corresponding input control fully rotated. The numbers are primarily to enable accurate re-setting, and the controls should be set
to provide the required sound volume from the loudspeakers.
Treble and bass controls
Treble and bass controls are provided to enable correct tonal adjustment to suit the characteristics of the input signals. Each operates
on a cut and lift principle, and when set to position “0” has no effect.
Master level control
Use this control to change the sensitivity of all four inputs simultaneously. It would normally be used to fade down the total output to
zero so set the control at about No. 8 or 9 before adjusting the individual input level controls. In this way the overall sensitivity may also
be increased slightly.
Operating the master at too low a setting (less than 4 or 5) will render the amplifier liable to distortion on sound peaks.
Output level peak indicator
To the right hand side of the front panel is a small LED indicator which illuminates momentarily when the amplifier is operating at the
peak of its output capability. Technically this is known as the “clipping level”. The input level, treble, and bass controls should be
adjusted such that this indicator is rarely illuminated. In these circumstances the amplifier will be at its most efficient, generating little
wasted power, whilst being free of distortion. Severe damage may be caused if the amplifier is used beyond this clipping level.
Mains power switch & indicator
A front panel rocker switch isolates the unit from the AC power input, and the adjacent LED illuminates to confirm that the internal DC
power supply circuit is operational.
The four input circuits of the Maestro 30 have been designed to enable the amplifier to be used in a wide variety of applications. Most
of the inputs will accommodate two different types of input signal as follows:
balanced microphone, optionally phantom powered, with optional priority over inputs 2-3-4
balanced microphone, optionally phantom powered, or balanced high level line
balanced microphone, optionally phantom powered, or balanced low level line
low level line or RIAA phono - mono/stereo
Alternatively, the balanced inputs may be used with unbalanced signals if required. See the drawing “Signal connections” at the rear
of this manual for further details
Input connections and selection of cables
It is essential that input connections are made carefully, using appropriate screened cable, soldered to the DIN connector plugs
supplied, and using the appropriate terminal numbers indicated in the “Signal Connection” drawing at the end of this manual. Unscreened
“telephone” type cables are NOT suitable. Either twin conductor, or single conductor types may be used depending upon the application. For long fixed cable runs, a cable with a conventionally braided outer shield is preferable to a lap-screened type. A conductive
plastic shield type is ideal for cables which will be subject to constant flexing such as those connected directly to microphones. For
guidance as to the installation and routing of input cables - especially microphone cables - please refer to section - INSTALLATION
LOCATION. Failure to meet these requirements will result in inferior performance, and at worst, damage to the amplifier.
It is not possible in this manual to be specific about the exact types of input cable for in any particular amplification system, as many
practical factors will need to be taken into account. However, as a guide, we would recommend the following:
Balanced microphone lines should be wired in twin, twisted core, screened cable with a conductor size of at least, and
preferably This is equally valid for dynamic or phantom-powered microphones.
Paging microphone lines will need an extra two conductors to operate the priority circuit of the amplifier. These need not be screened.
For short runs, (up to 2 mtrs), paging microphones may be connected using 4-core overall screened cable, and for longer runs, (up to
10 mtrs), 4-core individually screened cable. If it is necessary to run a cable over say 10 mtrs, then there may be some performance
advantage in using a separate twin-twisted screened cable for the audio, and a separate twin unscreened cable for the priority operate
Line level cables, such as those between a tape recorder and the amplifier, which may be up to a few metres in length are less critical
and may be run using lap-screened, single or twin cable with conductors of 7/0.1mm or 7./0.2mm.
Input control removal
Each of the four input level controls and the treble and bass controls and associated spindles may be removed, by pulling, to prevent
unauthorised tampering. Blanking plugs are provided. At any time in the future, the situation may be reversed, but care should be
exercised in correctly locating the spindle splines.
Priority control: Input No.1
A facility is provided whereby input No. 1 takes priority over the other inputs. This is particularly important for a paging system where
background music may, for example, be playing via input No 4. Operation of the microphone button will automatically mute the music
whilst the paging announcement is made. The priority circuit is operated by making a contact between pins 4 and 5 of the DIN input
plug. This would normally be done by the microphone “press-to-talk” button via the microphone lead.
The audio pre-amplification circuit for input No.1 is active (live) at all times, and therefore the “press-to-talk” button of the paging
microphone that is used should normally mute the microphone audio output. The Mustang DM/1 microphone has been designed with
this facility in mind.
Phantom powering of microphones
Certain professional microphones require a small DC current to power a pre-amplifier within the microphone housing. The technique
normally adopted is known as phantom powering, whereby both of the two conductors of the standard two core microphone cable carry
a DC voltage generated in the amplifier, as well of the normal audio signal. The DC circuit is completed by the screening shield of the
cable. Either conventional dynamic microphones or phantom powered microphones may be used with the Maestro range of amplifiers
without any preparation. No damage will be caused to dynamic microphones but if this facility is not required, it may be disabled by
repositioning the small coloured jumper connector which is located on the PCB in line with sockets 2 and 3, and approximately 5cm
towards the centre of the board. Pull off the jumper from the two pins nearest the rear panel, and re-position it on the two innermost
pins of the assembly.
The phantom powering voltage is +12 Volts and is extremely well stabilised.
Input No.1 bass-cut option
For paging microphone applications, it is usually advantageous to introduce a small amount of attenuation of the bass frequencies bass cut - for increased clarity. Maestro 30 amplifiers leave the factory with all microphone inputs amplifying the full frequency range.
Input No.1 of the amplifier features an internally selectable bass-cut switch on the main PCB adjacent to the No. 1 input socket and
circuitry. Remove the coloured jumper from its position on the two pins closest to the IC, and reposition it on the two pins furthest from
the IC.
Setting the input channel sensitivities
The Maestro range is designed to be applicable to a wide variety of amplification situations. The level of the sound to be amplified may
vary enormously with consequent need for very different control settings. In a typical sound re-inforcement church installation, for
example, where the speakers may stand well back from the microphone, the input level controls will be set perhaps mid-position, (with
the master at its normal setting of 8-9). But in a stage sound installation where the microphones may be held close to the mouth, the
input level control settings could be as low as positions 1 to 2. It is not appropriate to reduce the Master Level control setting too far as
this may give rise to distortion on signal peaks. The Maestro 30 is fitted with input channel attenuator pads to resolve this problem, by
de-sensitising the channel, effectively spreading out the input control settings and easing their adjustment. A pad is fitted to each of
inputs 1 to 3 and may be set individually by internal ‘jumper link’ switches. The amplifier will be set for maximum sensitivity on leaving
the factory. To change the setting, remove the top cover of the case after first disconnecting the AC supply. The three switches are
located on the PCB directly behind the input level controls, and take the form of an assembly of three pins with a plastic jumper link
fitted across the left-hand two pins (furthest from the AC power switch). To change the setting to lower the sensitivity, pull off the
jumper, and re-position it across the right-hand two pins.
Connection of record deck - magnetic phono
Input channel 4 has been designed with a selectable dual function. Either to accommodate a magnetic phono pick-up, providing the
necessary sensitivity and RIAA tone equalisation, or to accommodate a low level line input. The latter is the factory setting. An internal
PCB switch is located close to the Channel 4 input socket/ tape interface socket. Remove the coloured jumper link from the two pins
nearest the amplifier rear panel, and replace it on the two pins furthest from the rear panel.
The output circuitry of the Maestro 30 amplifier is designed to be used with all internationally recognised loudspeakers, operating at low
impedance or 100, 70, or 50 Volt line level. The commissioning engineer is able to set the internal selector to suit the loudspeaker
system in use. On leaving the factory, the amplifier is set to match a 4 ohm loudspeaker load.
The use of 100/70/50 Volt line enables a greater number of loudspeakers to be connected accurately and at differing powers if required,
than would be possible with low impedance units. There is no limit to the number of 100/70/50 Volt line loudspeakers that may be
connected but the total collective consumption should not exceed the amplifier power output rating.
It is recommended that loudspeakers be wired in parallel wherever possible
See the drawings at the end of this manual for illustrations of typical loudspeaker connection arrangements.
Typical loudspeaker arrangements
The following are acceptable examples of loudspeaker loading arrangements for a Maestro 30:
30 x 1 Watt 100 Volt line loudspeakers = 30 Watts total load to the amplifier. Amplifier set to 100 Volt output
5 x 3 Watt 100 Volt line loudspeakers and 10x 1 Watt loudspeakers = 25 Watts total load, (and 5 Watts spare for future
application) . Amplifier set to 100 Volt output
60 x 0.5 Watt 100 Volt line loudspeakers = 30 Watts total load to the amplifier. Amplifier set to 100 Volt output
2 x 10 Watt 100 Volt line loudspeakers and 1 x 3 Watt loudspeaker = 23 Watts total load to the amplifier ( and 7 Watts
spare). Amplifier set to 100 Volt output
4 x 16 ohm speakers (rated at least 10Watts each) connected in parallel. Amplifier set to 4 ohm output
2 x 8 ohm speakers (rated at least 15 Watts each) connected in parallel. Amplifier set to 4 ohm output
1 x 4 ohm speaker (rated at least 30 Watts) Amplifier set to 4 ohm output
Most 100 Volt line loudspeakers use a transformer which can be ‘tapped’ at various Wattages so that each loudspeaker may be
adjusted individually to provide the sound level required.
See the drawing “Typical loudspeaker connections” at the rear of this manual for further examples of connection arrangements.
The amplifier may be operated indefinitely without any loudspeaker load connected. However if the loudspeaker load exceeds the
ratings of the amplifier, then it is likely that permanent serious damage and overheating will result, with inferior reproduction quality
Selection of 100, 70, or 50 Volt, or 4 ohm outputs
Maestro 30 amplifiers leave the factory with the internal selector set to match a 4 ohm loudspeaker load. It will be necessary to gain
access to the main internal PCB to reset the selector switch if 100, 70, or 50 Volt line loudspeakers are to be used:Remove power from the unit by disconnecting at the power point. Remove the top cover to obtain access to the PCB. The switch is
located immediately behind the output socket, and takes the form of a jumper link which may be positioned on any of four sets of PCB
pins. The rearmost pins are for 4 ohms. To change to 100 Volt line operation, remove the small coloured jumper link and reposition it
on the two pins towards the centre of the PCB. Replace the cover etc.
See the drawing “Typical loudspeaker connections” at the rear of this manual for examples of connection arrangements.
Loudspeaker cables
Use of an appropriate cable for the connection of loudspeakers to the amplifier will ensure that a minimum amount of audio power is
lost during transmission to the loudspeaker network. The loss will depend upon several factors - loudspeaker loadings, size of cable
conductor, length of cable, etc.
As a general rule, for any particular loudspeaker system, the longer and the thinner the cable, the greater will be the loss. We therefore
recommend, that the system is planned such that the amplifier is as near as possible to the loudspeakers, especially with low impedance loudspeakers, and that the cable used is as large as practicable.
Whilst it is not possible to be specific about the precise cable to be used in any particular system, we would suggest as follows:
for 100V or 70V line systems, with loudspeakers located up to 50 mtrs, twin conductors of cross-sectional area.
for 50V line systems with loudspeakers located up to 50 mtrs, twin conductors of 0.75
cross-sectional area.
for 4 ohm systems, twin conductors of 1.0 cross sectional area and the loudspeakers
should be no more than 30 mtrs from the amplifier.
Either solid or flexible conductor cables may be used, or a combination of both. It would be appropriate for a heavy duty cable to be
used between the amplifier location and the general loudspeaker location, and for the subsequent loudspeakers of the network to be
interconnected with thinner cable.
A tape recording/playback socket is a standard feature of the Maestro 30. Users may conveniently connect, by means of one standard
5 pin DIN connection lead, most standard domestic or professional tape decks. Operate the tape recorder at any time to record the
amplified program. As supplied, the amplifier treble & bass controls will be in circuit for recording purposes, though this may be
changed - see section below. The recorder may be played back through the amplifier at any time using input No.4 level control to adjust
the volume. Stereo signals are electronically mixed to mono within the amplifier.
Alternatively, this playback connection may be used to amplify any suitable input signal - from a tuner for example - and similarly the
record output signal may be used to drive other amplification systems. The signal levels and impedances will match most professional
Record/playback connections
A standard 5 pin 180 degree line plug should be connected as follows:
Pin 1
Pin 4
Record signal from amplifier to tape deck
Record signal from amplifier to tape deck
Pin 3
Pin 5
Playback signal from tape deck to amplifier
Playback signal from tape deck to amplifier
Pin 2
Cable braid/screening
Your dealer will be able to make up or supply a lead fitted with suitable connectors.
Please note that certain domestic recorders present a short-circuit at the recording terminals during playback. This will reduce the
sensitivity of the Maestro 30.
Selection of recording take-off point
The recording signal is normally sampled within the amplifier signal path at a point following the treble and bass tone control circuits.
If preferred, this may be changed to a point before those circuits, by adjusting an internal PCB jumper switch as follows: Remove AC
power from the amplifier by disconnecting. Remove the top cover and identify on the PCB a small assembly of six pins with a plastic
‘jumper’ link between the treble control and the No.4 input control. As supplied the central two pins will be linked by the jumper. Reset
this switch by pulling the jumper off and re-positioning it on the two pins furthest from the power switch to change the sampling point to
before the treble and bass controls. Conversely, the two pins nearest the power switch are for sampling after treble-bass-master
The Maestro 30 amplifier may be used as a slave amplifier by utilising a suitable input channel (or the tape playback connection), or it
may be used to derive a suitable low level drive signal for use with another slave amplifier. In the latter case, refer to the above section
“TAPE RECORDING FACILITIES” for details and connections. The output level or the ‘recording output’ is nominally 775mV with a
source impedance of 600 ohms and this is usually known as 0dB. All professional amplification equipment is designed to accommodate signals to this specification.
No two installations are identical. We recommend that all aspects of installation should be carried out by a competent engineer or
dealer who will have the experience to enable him to recognise potential trouble spots, and the symptoms of existing ones. He will be
able to advise on the selection of loudspeakers and their locations for best results. The use of a dealer will also provide the user of the
system with a contact should a problem occur in the future.
The installation environment for a Maestro amplifier is not critical but in general we would recommend a location that will:
avoid dampness or heavy vibration
prevent unauthorised adjustment
prevent heat build-up around the amplifier casing or heatsink
separate microphone cables from loudspeaker cables
separate microphone cables from mains cables
prevent microphone cables passing strong magnetic fields
avoid long microphone leads - over 50 Mtrs
avoid long, low impedance loudspeaker leads - over 50 Mtrs
We also recommend that when Maestro 30 amplifiers are fitted into rack cubicles, the top casing is removed to assist heat dissipation.
Installation checklist
During the commissioning of the amplifier, various options are available to the engineer to enable him to meet various technical
requirements and the operating requirements of the user:
Bass cut on paging microphone
Recording output pre- or post tone control circuits
Slave amplifier output pre- or post tone control circuits
Input 4 for RIAA phono deck, or for level response
Use of signal priority for input No.1
Selection of appropriate loudspeaker output matching
Removal of front control knobs
The standard UK power requirement for the Maestro range is 230V 50Hz though correct operation is possible between 180-250V and
No special consideration of the power supply is necessary though it is good safety practice to fit a small AC fuse in the supply to the
unit. The amplifier may be switched on/off remotely, by interruption of the supply, without any adverse effects.
Mains power transformers for supply voltages other than the UK standard are available.
Fuses are fitted to electronic equipment to isolate damaged circuitry thus preventing further consequent damage, and to avoid excess
consumption from the AC supply. The failure of a fuse is far more likely to indicate a problem with the amplifier circuitry or the
loudspeaker network rather than a ‘weak’ fuse.
In the unlikely event of an AC fuse failure (rear panel), it is acceptable to replace the fuse using the correct type, and try to run the
amplifier again. If the fuse fails again, refer to your dealer.
In the unlikely event of an internal fuse failing, it is pointless and possibly dangerous to attempt replacement. Consult your dealer.
UNDER NO CIRCUMSTANCES use fuses of a higher value than those specified.
If the amplifier is interconnected with other earthed equipment using unbalanced screened connections, it may be possible to form an
earth hum loop. The symptoms would be that of a soft low-level humming audible on the loop programme, which is uneffected by the
front control settings.
Such problems may be resolved easily by the use of the balanced line input signal connections. If the interconnection is via the ‘Tape’
socket - which does not feature a balanced input connection - then it should be possible to resolve the hum loop by lifting the internal
signal earth of either the Maestro amplifier or the other unit. The signal circuitry within the case is earthed to the chassis via an internal
green wire signal earth link which is located between the PCB and an adjacent chassis earth lug, near to input socket No.1.
As supplied, the amplifier chassis and casing is electrically earthed via the AC supply lead and connector.
Where the unit is to be powered from a two-wire AC supply, the rear screw earth terminal must be permanently connected to a suitable
earth point.
This terminal is indicated by the symbol -
To gain access to the inside of the amplifier for any adjustments which may be required, firstly remove the AC mains supply to the unit,
then remove the 7 securing screws holding the top cover. The cover is earthed by a push-on tab connector which must always be in
place when the AC supply is connected.
The optional rack bracket kit - BRK.20 - is fitted by first removing the four small plastic covers from the sides of the amplifier. These are
a push fit. Then using the screws provided, fasten one angle bracket and one handle to each side of the amplifier. These brackets are
not intended to support the full weight of the amplifier, but to fasten it securely into the front of the rack. A pair of chassis runners would
normally be required to support the rear of the unit, enabling the amplifier to be slid out using the front handles.
For rack mounting, it may also be necessary to remove the self-adhesive feet.
We would always recommend calling your dealer if any problem is experienced though an initial check through
the following list may enable you to provide him with valuable time saving information.
Sound off, power lamp off
Sound off, power lamp on
Sound faint
Sound loud & distorted
Sound loud & distorted even
with input control set low
Inappropriately high input signal for the input in use
Distorted input signal
Distortion and insufficient volume
System requires more powerful amplifier unit
100 Volt loudspeakers set too low
Incorrect internal loudspeaker matching selection
Excess loudspeaker load: consult dealer
Sound distorted on bass
peaks only
Extreme case temperature
Mains supply
Mains fuse
mains switch
Input level controls rotated
Input connections secure
Loudspeaker circuitry connected
Priority input is operating
Internal DC fuse fail: consult dealer
Input level controls rotated
Inappropriate input signal
Incorrect input connection
Tape record socket partial short
Loudspeaker line fault
Inappropriate input signal
Input level control rotated
Incorrect loudspeaker connection
Incorrect internal output matching selection
Loudspeaker line fault
Distorted input signal
Poor quality loudspeakers
Bass control set too high
Excess loudspeaker load: consult dealer
System working very hard
9 Extreme case heat, LED “PEAK” indication
leads : without corresponding signal,
possible soft hum/distortion
System oscillation due to proximity of microphone leads to loudspeaker
Input lead security
Internal circuit fault: Consult dealer
11 Persistent hum, input
controls set to off
Earthing hum loop. Consult dealer
Nearby electrical appliance
10 Persistent hum, input
controls set normal
12 Persistent faint buzz
13 Intermittent loud crack
14 Howling/ringing
15 Record deck input giving
low level, poor quality sound
Incorrect input cables used
Incorrect input connections
Nearby electrical appliance
Earthing hum loop: consult dealer
Nearby faulty electrical appliance
Interference from lighting dimmer
Interference to sensitive input cables
Faulty AC supply connection
Input connector security
Faulty input signal
Acoustic feedback due to proximity/angling of microphones relative to loud
Internal selector switch incorrectly set. (Input channel No.4 only)
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