Formula Sound Manual PM-100

Formula Sound Manual PM-100
PM - 100
PM - 100 Introduction
The Formula Sound PM-100 mixer is essentially the successor to our award winning PM-80 and
PM-90 mixers.
We believe that the experience we have gained over the past 21 years of producing the PM-80 and
PM-90 has produced a mixer that is equal to the challenges of the new millennium. We have
incorporated new features and innovations that have been in our file of wish lists from operators
around the world. We have tried to provide a tool that can be individual to the operator, We can
provide advice on how to achieve the best performance out of this equipment but when it comes to
mixing it becomes personal taste so we have provided the tools to do the job with choices where
possible. We believe that the equipment should not restrict the creative talent but help it.
General Description
The PM-100 is a compact modular production mixing system which combines exemplary technical
performance with the highest standards of mechanical engineering.
The system is totally modular each module being complete in itself. The connections to the modules
are via a flexible 34 way ribbon cable and gold plated computer grade connectors.
The chassis contains no electronics therefore upgrading to a larger chassis size is quite straightforward.
There are only three types of module, a universal input channel module, a blank module to fill unused
space in the chassis and the output module containing all the mixing, monitoring, and output
The mixer is factory assembled with the output module towards the right hand end of the chassis and
the input modules to the left. But in fact modules may be positioned in any format required.
Specific layouts may be ordered or engineers can easily change layouts to suit individual
requirements. Blank modules where fitted may be easily replaced by input modules at a later date if
The chassis is available in 3 standard sizes, 4 channel, 8 channel (19” rack mount) and 12 channel.
Larger sizes can be offered to special order.
Power Supply
The mixer requires an external power supply unit providing +/-17.5V for the audio electronics and 12V
for the working illumination socket.
A suitable power supply unit, the PSU5, is available. This unit is designed to be surface mounted
remotely from the mixer and features slow rise time characteristics to minimise turn on thrumps.
The unit is internally switchable to operate from 220-240V AC or 110-120V AC. Check that the
voltage selector switch is correctly set for the mains voltage available before connecting power.
Damage may result if the unit is connected to the wrong supply voltage.
It is important from a performance and safety aspect that the power supply is connected to a reliable
and suitable earth. Remember that this earth connection may also be providing the earth for input
sources connected to the mixer, turntables, microphones etc. For safe and reliable operation
adequate ventilation must be provided. Do not cover the power supply.
Mount the power supply in a suitable location bearing in mind that the captive connecting lead length
is 1.5 meters. Connect the mixer to the power supply ensuring that the connector is fully mated and
the securing screws fastened. (Do not over tighten the securing screws).
Input Sources. The design of this module allows almost any input source to
be used and further allows the operator to switch between any two input
This is achieved by providing a balanced low impedance low noise
microphone pre amplifier; a stereo RIAA equalised pre amplifier which also
may be configured as a normal flat response line level input; and a normal
line level input stage.
Input Connectors Rear panel mounted 1 - XLR Mic input socket, 1 - 3
pole jack insert socket (provides connection for external equipment into
the microphone channel).
Two pairs of gold plated RCA phono sockets are provided for the stereo
Input A may be the RIAA input or a normal line input as selected by 2
internal jumpers. The B input may be a microphone input or a stereo line
input as selected by a further internal jumper. Rear panel gain trims are
provided to set the maximum gain available on any input.
INPUT SELECTION A front panel mounted toggle switch allows rapid
selection of the A or B input. Red and Green led’s provide clear visual
indication of the input selected.
Adjacent areas are provided to label the input sources.
GAIN A control allows the operator to compensate for variations in programme material. (See later section on gain)
PEAK A red led indicates when the peak signal level in the module is just
below clipping.
Three band equalisation
HF (High Frequency or Treble)
This control provides +6dB boost -20dB cut @ 10kHz with a shelving
MID (Middle Frequencies)
This control provides +6dB boost -20dB cut @ 1kHz with a bell response.
LF (Low Frequency or Bass)
This control provides +6dB boost -20dB cut @ 100Hz with a bell response.
This response has been chosen so that sub sonic frequencies are not boosted
by this control.
All E.Q. controls have a centre detent at the (E.Q flat) centre position.
The E.Q. function may be disabled by the setting of internal jumpers (see
AUX 2 Push button with led illumination.
When depressed the signal in this module is mixed with any other source
selected. The resulting mix is available at the Aux 2 outputs on the master
module. Internal jumpers allow the source to be selected pre of post (before
or after) the channel fader. (See output section for more options on Aux2)
AUX 1 has a similar function to Aux2. A control replaces the switch so a
separate level mix of channels is available at the Aux1 outputs on the master
module. Internal jumpers are also provided for pre post selection.
Bal - Pan (Stereo balance & Pan)
With a stereo source selected this control provides adjustment to balance
stereo signals.
With a microphone source selected or the mono switch depressed this control
allows the source to be positioned anywhere in the stereo image.
A centre detent is provided at the control centre position.
PFL (Pre Fade Listen)
Push button with red led illumination.
When depressed the signal in this module is connected to the PFL Mix Buss.
Any number of channels may be selected simultaneously, the sum of which
will be available in the master module for monitoring. An indicator led below
the Vu meters also illuminates if any PFL switch is depressed. (See
monitoring section on output module for more information)
MONO Push button with red led illumination.
When depressed this switch simply links left and right signals and allows
stereo signals to operate in mono.
XFA (Crossfade A select) Push button with red led illumination.
Depressing the switch routes the channel signal via the VCA controlled
crossfader channel A. XFA will take priority if both buttons are depressed.
XFB (Crossfade B select) Push button with green led illumination.
Depressing the switch routes the channel signal via the VCA controlled
crossfader channel B.
Red and green led switch illumination along with similar illumination on the
crossfader gives good visual indication of routing status.
If neither of the crossfade assign switches are depressed and a stereo source
is selected the signal will be routed via the stereo buss to the output section
bypassing the crossfade circuitry.
If a microphone source is selected the crossfade A&B assign switches will not
function and will not illuminate if depressed. The signal will be routed to the
output section via the microphone mix buss.
A 60mm studio quality linear fader is provided. This should be used to fade
up and down the volume of the channel. For normal production operation the
fader should be set at the top (No.9) and the gain control adjusted for normal
volume. The fader should be used to fade in the signal at the required time
taking the fader to the top. This lets you concentrate on the timing confident
that the volume will be correct. If you want to operate with some gain in hand
(e.g. mic mixing) operate with the fader set at No.7.
Always operate with the gain set as low as possible to achieve the desired
results. (See the section on gain)
Push button with red led illumination.
When depressed signal feeds to the programme busses are muted. AUX1
and AUX2 are not affected. An internal jumper allows this switch to be
(Factory option - the mute switch may be rewired to provide a low voltage
remote start switch wired to a 3.5mm jack socket on the rear panel.)
Internal Settings
Jumper links are used to select and
change functions.
1-5 uses 3 pin headers and the link
should join the centre pin to one of the
end pins.
6. Two pairs of pins - the link joins one
pair of pins. The various link positions are
also shown on the PCB.
If you are changing link positions
ensure they are seated correctly and
all necessary links have been moved
1. 1 Jumper link. The position selects
input B to microphone or stereo line input
(in the microphone position the Xfade
select switches are disabled.)
2. 2 Jumper links. The positions select
input A to be a Magnetic phono cartridge
equalised to RIAA or a normal flat
response line input. Move both links.
3. 4 Jumper links. The positions select
equalisation on or off (i.e. tone controls
disabled). It is vital that all four jumpers
are moved.
4. 2 pair of jumper links select Aux1
and Aux2 to be pre or post fader. (i.e. if
the selected aux function is affected by
the channel fader.) Move 2 links for AUX1
and 2 links for Aux2.
E.G. an auxiliary set up for use as an
echo send on a microphone channel
would normally be set to post, so if the
fader is closed no signal would be sent
to the echo system.
If the auxiliary function was in use as a
foldback or monitoring feed it would
normally be set to pre fader.
Aux sends can be used for many tasks.
5. 1 Jumper link selects Phantom power
on or off for microphone channels.
6. 1 Jumper link The position of this link
determines if the channel mute button is
enabled or disabled.
PM-100 Master Module
The master module contains all the
electronics required for the various
summing amplifiers, output stages, VU
meters, crossfade control circuits, etc.
The majority of connections are on the
rear of the unit.
The monitoring section of the PM-100 is
very comprehensive. Visual monitoring is
provided by a stereo 24 segment led bar
graph meter.
Two powerful stereo headphone amplifiers
are incorporated designed to drive
headphones of 32 ohms or greater.
Connections are via 3 pole jack sockets.
The main phones output is located at the
top right of the front panel, the second
output is on the rear panel.
The meter and the main phones output
are both connected to the same signal so
what you see is what you hear.
Mon Bal (monitor balance)
It is important that the function of this
control is fully understood.
The output from this control is fed to the
monitoring section (the led bargraph
meter and via the PHONES volume
control to the main phones output).
With the control turned fully clockwise
towards PFL, the meter will read the PFL
signal of any channel that has its PFL
button depressed, or the sum of channels
if more than one is selected. As a further
visual aid a red led beneath the meter
also illuminates if any PFL button is
depressed. If no PFL buttons are
depressed the meter reads the main
output level which is dependent on the
MASTER control setting.
Turning the monitor balance control
counter clockwise towards PGM feeds the
programme signal (pre master) to the
monitoring section. Therefore the
operator can quickly pan or mix between
the PFL and program.
It also facilitates the monitoring of a
recording being made with the master
turned down.
A SPLIT button is also provided (which is
the preference of some operators). This
provides a mono PFL signal on one side
of the monitor system and a mono
program signal on the other side. The
Mon Bal sets the balance of the two
signals in this situation. Practice and use
will determine the best mode of operation.
PM-100 Master Module continued
A.V.O. (Automatic Voice Over)
This function is enabled by the illuminated push button A.V.O. ON. When turned on any microphone
signal present will dim the music signals to allow talk over. The amount the music is dimmed is
determined by the attenuation control. The adjacent sensitivity control sets the triggering level of the
AVO system.
AUX RET (Auxiliary Return)
This is a basic stereo input configured to accept balanced or unbalanced input signals via 2 X 1/4” 3
pole jack sockets. (For unbalanced operation 2 pole jack plugs may be used). For mono operation
feed equally into both inputs. The input impedance is >20K ohms balanced and 10K ohms
unbalanced. This input is intended for simple no frills connection to the stereo buss for effects return
etc. If more facilities are required it is normal to use an input channel.
MASTER - This control sets the output level of the main balanced output available via 3 pole XLR
connectors on the rear panel. This output is monitored by the main phones and VU meter when the
MON BAL control is set to PFL and no PFL is selected. The VU meter is factory calibrated 0dB =
0dBu (775mV)
MONO - An illuminated push button switch located below the master control allows the master output
to be operated in mono mode. This switch only affects the main output.
ZONE -The zone output is almost identical to the main output in all respects except that the signal is
not available to the monitoring section and no insert sockets are provided. The output may also be
used in mono or stereo as set by a rear mounted push switch located between the XLR sockets.
AUX 1 MASTER - This master control adjusts the output level of the signals derived from the Aux1
sends on the input modules. The outputs are via 2 1/4” jack sockets a mono signal may be obtained
by using the left output socket only.
AUX 2 MASTER - This master control adjusts the output level of the signals derived from the Aux2
sends on the input modules. The outputs are via 2 1/4” jack sockets a mono signal may be obtained
by using the left output socket only.
An illuminated push button switch located below the AUX 2 Master control (PROG TO AUX 2) routes
the programme mix to the AUX 2 output. This is provided so that the AUX 2 output can be used as
yet another zone output should this be required.
Alternatively if the second phones output is set (via internal jumpers located on PC-344) to listen to
the AUX 2 output a second monitoring system will then be available which is totally independent of
the main phones output. This would provide for a second operator to have independent monitoring
facilities. In this mode AUX 2 jumper links on the channel modules would normally be set to pre fade.
The AUX 2 master control would set the phones level.
BOOTH - This control adjusts the level of the booth output which is a mix of music channels only.
The outputs are via 2 1/4” jack sockets. A mono signal may be obtained by using the left output
socket only.
CUE TO BOOTH - An illuminated push button switch located below the booth control. When
depressed this switch routes the mains phones signal to the booth output, so therefore all the phones
monitoring facilities become available on the booth outputs. Operators should be aware that in this
mode it is possible to have microphone signals present on the booth outputs which could be the
cause of acoustic feedback.
PM-100 Master Module continued
The XF-A and XF-B busses are fed to the crossfade circuitry. The crossfader is a 45mm fader which
can be used to smoothly fade between the XF-A and XF-B busses.
The crossfade system uses studio quality V.C.A.’s (voltage controlled amplifiers) to Improve
crossfader life and also ensure good attenuation at the ends of travel.
Red and green leds positioned at the fader ends correspond to the XFA and XFB routing switch
illumination colours which gives good visual routing status.
A contour control is provided which allows the operator to adjust the crossfader characteristics to suit
personal taste, from a gentle fade between A and B to a more aggressive fade towards the ends of
the fader.
A fast momentary action push button is fitted to provide rapid switching effects. The action of this
switch is to turn on both XF-A and XF-B busses irrespective of the fader position. Depending on how
channels are routed to crossfader this can provide several effects for the creative D.J.
Insert sockets in the form of 3 pole 1/4” jacks are provided for the connection of external signal
processing equipment. Located on the rear panel the connections are:Tip = send (mixer output)
Ring = return (mixer input)
Body = common (ground)
These sockets have switching contacts so that if a plug is not inserted the signal path is maintained.
Insert sockets are provided for the following functions:XFA left and right for the connection of filters etc. into the XFA signal chain.
XFB left and right for the connection of filters etc. into the XFB signal chain.
MIC left and right for the connection of signal processing equipment, compressors, limiters etc. into
the microphone signal chain.
Master Insert left and right for the connection of signal processing equipment into the main output
Individual microphone inserts are also provided on the input channel modules.
RECORD OUTPUTS 2 pairs of gold plated phono sockets are provided for the connection of stereo
recording equipment. One pair provides the complete programme mix; the other pair provides the
mix of music sources only. AVO does not affect this output. All record outputs are unaffected by the
master controls.
SUB BASS OUTPUT A mono output via a 1/4” jack is provided for driving a sub bass loudspeaker
system to enhance low frequency performance. The filter allows frequencies below 70Hz to pass
through. An internal jumper located on PC-344 allows higher bass output if required.
LIGHTING TRIGGER A mono fully floating transformer isolated trigger output is available on a 1/4”
jack to provide safe connection to lighting equipment.
A priority input with adjacent level trim control and control socket are provided to help comply with fire
regulations. The fire alarm panel needs to provide a fully floating pair of contacts to join the two pins
on the control connector.
Internal jumpers located on PC-342 provide the option to mute all signals or leave mic signals active
and intoduce the priority signal.
The priority input may not be required if existing microphone inputs are to be used for evacuation.
This will depend on local fire regulations.
The position of these links selects microphone
status when priority is activated. Move both
NORMAL position microphone channels are
active. Priority acts as music mute.
MUTE position microphone channels are
muted. Connect evacuation message system to
priority input
PC - 344 1 1 JUMPER LINK selects sub bass
output level. (Access by removing back panel)
PC - 344 2 2 JUMPER LINKS selects AUX 2
phones to follow AUX2 output or follow main
phones output. (Access by long nose pliers or
tweezers from open end)
In an audio mixer different signal levels from various items of equipment need to be amplified or
attenuated to a common level so that they can be added or mixed together. These signal levels may
differ considerably depending on the equipment. The signal from a microphone for example may be
1000 times smaller than that from a CD player. For a mixer to be as flexible as possible and to
accept signals from a variety of equipment it is necessary for the first or early stage in the input circuit
to be a variable gain amplifier. The gain of this amplifier is set by the gain control.
The PM-100 universal input module has a combination of variable gain amplifiers to get the input
signals to the required operating level. 3 gain trim presets are fitted - 1 for each input. These are
accessable through holes on the rear of the module and are labelled accordingly. The stereo input
gain trims are conventional single turn controls. The Mic preset is a multi-turn trimmer. These trims
should be adjusted to set the maximum gain available for any input. The front panel gain control
works in conjunction with these presets. The system may be considered as coarse gain control on
the rear presets and fine adjustment on the front gain control.
When amplifier gain is introduced in a circuit noise is also introduced (this is a fact you cannot have
one without the other). The PM-100 has been designed to keep this noise as low as possible by
using the latest technology. For the best performance set the gain control as low as possible to
achieve the desired output level. Gain introduced into the system and then held on the channel fader
is a waste of performance. Too much gain could result in overloading the first stage causing
distortion and clipping.
A red peak indicator has been included and is located below the front panel gain control. This
indicator flashes when the signal level is close to clipping. It monitors the signal at various points in
the signal chain, therefore, gain introduced by the equalisation or tone controls is also considered.
The installation of professional audio systems should be left to experienced engineers wherever
possible. The interconnection of audio systems can be fairly complex depending on the type and size
of system and obviously well outside the scope of this handbook. We have included a few basic
points for information for anyone who is new to audio systems.
Good wiring practice should be observed when connecting any audio equipment. Good quality
connectors and screened cable should be used for all audio connections .
Twin screened cable should be used for all balanced lines particularly microphone connections.
Always ensure cable clamps in connectors are fully tightened and gripping the outer sheath. Good
strain relief and mechanically sound connections will increase reliability at virtually no extra cost.
In our experience this is the most common problem encountered when connecting together different
items of audio equipment. It is the most common cause of hum (50Hz noise) on a system and is
caused by incorrect system grounding.
When several items of audio equipment are connected together with unbalanced connections (i.e. 2
connections, single screened cable, etc.) the signal common connection is the screen and this will be
connected to mains earth at some point. If several items of equipment have their signal common
connected to mains earth this will form a loop (hence ground loop). Current will flow in this loop and
appear in the form of hum (50Hz mains frequency) added to the audio signal. The problem is
aggravated if the equipment is located a distance apart as the loop is larger. It is possible to have
several ground loops within a system. The solution is to connect the system to mains ground
only once. This is usually done at the mixer. You will need to investigate the various items of
equipment you are using and isolate their signal common from mains earth. Many manufacturers fit a
ground lift switch for this purpose. On some equipment this is in the form of a removable link.
Unfortunately with some equipment you have to get inside to identify where the connection is and
remove it.
You must not disconnect the mains earth wire from the mains plug of any equipment. This is
fitted for safety reasons and must be connected to ensure that the case is earthed.
PM-100 Specifications
Frequency response
E.Q. set flat
20Hz - 20kHz +/-0.5dB
Maximum output level
Main output and Zone output active balanced.
Stereo, auxiliary, mic busses etc. to related O/P’s
< 0.01% typically <0.005%
Noise measured 20Hz-20kHz
Stereo inputs e.q. flat gain set to max
RIAA stage ref. 5mV 1kHz Input shorted
Microphone input (ref 150R)
EIN < -98dB
-80dBV “A” weighted
EIN < -124dBU
Stereo inputs rear trim @ max
Stereo inputs rear trim @ min
Microphone input max
Microphone input min
+/- 15dB
+ 0dB -20dB
+ 75db
+ 0dB
Maximum input level
Stereo input A (line)
Stereo input A (RIAA)
Stereo input B
-8dBV 400mV
+4 dBV
Input Impedances
Stereo input A
Stereo input B
Microphone input
> 47k ohms
> 10k ohms
> 2k ohms active balanced
3 band e.q. per channel
+5dB -20 dB @
Treble 10kHz
Bass 100Hz
Internal channel jumpers allow the e.q. stage to be disabled if required.
(Exc. Knobs & connectors):
8 Channel
4 Channel
12 Channel
Height 312mm (12.25"-7RU)
Depth 110mm (4.33")
External PSU - PSU5 Width 175mm
Width 483mm ( 19" )
Width 330mm ( 13” )
Width 635mm ( 25” )
Height 75mm
Length 230mm
Installation Cut-out
Height 312mm Width:- 4 channel 280mm. 8 channel 433mm. 12 channel 585mm
Balanced outputs For unbalanced operation strap pins 1&3 to ground and use pin 2 hot. This will result in no
loss of output level or performance.
The chassis is constructed from custom aluminium extrusions and is available in 4, 8 and 12 input module
configurations. Finish is gun-metal grey anodised aluminium.
Module metalwork is also constructed of custom aluminium extrusions and is silver anodised. The module
colour and notation is by inset reverse printed polyester film, which provides a hard wearing attractive finish.
Removing and Re- fitting Modules.
A removable cover on the rear of the mixer provides access to the ribbon cable which connects to all
the modules. This cover is secured by 2 screws. Although modules can be removed and replaced
from the mixer front when necessary removing the rear connector cover makes disconnecting
modules easier particularly if more than one module is being removed.
To remove an input module from the chassis first disconnect all connections from the module and
ensure that the power supply is turned off. Input modules are secured by 2 screws, removing the
screws will release the module. Carefully ease the module out of the chassis and disconnect the
ribbon cable connector.
The output module is secured by 4 screws and connected by 3 connectors to the ribbon cable
assembly. We recommend that the rear connector cover is removed to facilitate disconnection of the
ribbon cable if this module is removed.
The master module is normally factory fitted to the right hand end of the chassis although the design
of the ribbon cable allows modules to be fitted into the chassis in any position. The output module is
the width of 3 input modules and uses 3 of the connectors for its operation.
Ensure that the connectors are fully mated before refitting the rear cover.
The modules have a clearance of approx. 0.25mm. This is deliberate to allow the modules to be
easily removed and refitted to the chassis. Use a strip of thin card (postcard) to set the spacing
between the modules when reassembling. Do not push all the modules tightly together as this will
make them difficult to remove and leave an unsightly space. Remember 0.25mm is only 1/1000”.
This is the normal spacing clearance but in an 8 channel chassis, if you push the modules tightly
together the resulting space will be 2.5mm which is 1/10” and looks unsightly.
Formula Sound reserve the right to alter specifications at any time without notice.
All Formula Sound products are designed and manufactured in our own factory which enables us to
maintain strict quality at every stage of manufacture. This attention to detail has helped to win us 14
industry awards to date and has earned us a world wide reputation for the high quality and reliability of
our products.
Formula Sound Ltd.
Ashton Road,
Tel +44 (0)161 494 5650
Fax +44(0)161 494 5651
E-mail [email protected]
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