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Model D Automatic Mixing Controller

Installation and Operating Instructions

August 2002

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1) Disconnect power cord.

2) Check line voltage setting. Units shipped to the USA are set for 115V. The 115V-230V selector switch is inside, located between the two power transformers.

3) Set the back panel NORMAL-SLAVE switch to NORMAL.

4) Inspect for broken knobs or switches. Place all front panel switches and knobs on the yellow marks exceptthe auto mix depth master should be set at at infinity (counter-clockwise).

5) Remove the top lid and press down on the motherboard power connector (white nylon connector with six fat wires). Press down on the orange multi-pin connector towards the rear nearby.

6) Check that all the front panel cable connectors (two per channel plus master board) are fully inserted both in the front panel boards and in the channel circuit boards.

7) If any of the ALC telephone jacks are not seated in the panel openings, re-seat the circuit boards.

8) Power up the unit and test the actions of the controls:

a) Try each channel's on, auto, and off buttons. On produces a full gain display. Leave channels in "auto" mode.

b) The auto mix depth master will produce full gain displays on all channels when rotated full clockwise. Leave it there for the next two steps.

c) The master gain limiting display should indicate -9 dB. Rotating the NOM control clockwise should reduce this display to 0. Return the NOM control counter-clockwise to "1".

d) The master mute and override buttons should fade all channels out. The master preset button should return all channels to auto mode. Return the Depth control to full counter-clockwise.

e) Hold down the master Preset button. Try all three positions of the preset switch on each channel, verifying that the channel modes follow. Leave preset switches in the auto position.

f) Hold down the master Override button. Try the Override switch on each channel to verify that the gains go full on and off accordingly. Leave the override switches in the off position.

g) As the unit warms up (with no audio connected) channel gain displays will show gradually increasing gain, up to about half when hot. This normal no-signal display condition will disappear when a signal higher than -50 dBu is applied to any input.

9) If a channel fails to respond normally, first recheck the positions of the front panel switches, then check that the front panel cables are fully inserted in the connectors on the channel boards and front panel boards. If difficulties persist please contact the factory.

10) Dugan Speech System™ performance can be tested with the following procedure:

a) Connect two different oscillators set for 1 KHz with a 0 dBu output level to inputs 1 and 2. Fine-tune the frequency of one oscillator so that the gain indicators bounce up and down at about 2 Hz. Adjust oscillator levels so that the gain displays are equal.

b) Leaving one oscillator in input 1, move the second signal to input 3, 4, and so on, observing the bouncing display. This is a good way to test linked systems.

Note: What is happening? The two inputs mix in the side chain control mix bus. The signal level on this bus will beat between no signal (subtraction) and +6 dB level (addition) as the waves phase against each other. When the two waves cancel in the control mix, gain in the channel will rise to full. When a channel sees 0 dB as its own level and a low level in the control mix, it will bring its gain up to full. Gains bounce down to -6 dB when the two waves add. When a channel sees 0 as its own level, and +6 on the control mix, it will attenuate to -6 dB.

11) Dugan Music System™ performance can be tested with the following procedure:

a) Switch all channels to "music."

b) Connect one oscillator to the channel 1 input, and the other to the Music System Threshold Input. Set the Music System Threshold Input control to "0" (2:00).

c) Raise and lower the Threshold control for channel 1. Above a point around 0, the gain will be full and stay full. Below that point gain will be reduced progressively as the knob is rotated counter-clockwise. Return the knob to 0.

d) Move the oscillator from channel 1 to channel 2 and repeat for each channel.

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1) Install the unit in the rack, or table-top next to the console, but don't connect audio lines yet. Allow one rack unit of vent space above and below the unit if possible. Taking extra care to position the unit close to the console and close to the operator's line of sight to the stage will pay off in smooth operation. As the power supply is in the right-hand end of the chassis, putting the unit to the right of the console will keep the hum field away from the mike preamps in the board.

2) a) Re-check the positions of all front panel controls per 3) above.

b) Make sure the back panel NORMAL-SLAVE switch is at NORMAL.

6) Test the action of the controls again. The auto mix depth master can be rotated clockwise to bring up full gain on all channels. Override and mute should fade out all channels. Return the depth control to full counter-clockwise for normal operation.

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1) The eight channel inputs and the Music System threshold input are female XLR receptacles, active balanced, pin 1 ground, pin 2 hot, pin 3 cool. Wire pin 3 to ground if the source is unbalanced. The eight channel outputs are male XLRs, unbalanced, pins 1 and 3 ground, pin 2 hot. Levels from -10 to +4 are expected. Clip lights flash at +21 dBu. The bypass relay connects all three pins through in balanced fashion when the channel is bypassed or the unit's power is off.

2) Connect the audio channels in the insert loop (send-return) of each console input strip. If there is sound in bypass but no sound in on or auto, check that your cables conform to the standard PIN 2 HOT, and that you have correctly identified the send and return connections at the console. Some boards send from the tip, some from the ring.

3) Adjust console input gain trimmers so that talking signal levels at the sends are between -10 and +4 dBu, and room noise at the sends is higher than -50 dbu.

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Multiple Model D units are linked so that they operate as one system. The units are linked in daisy-chain fashion.

1) Link cables may be made from mass-terminated DB15 connectors and ribbon cable. The cables are male at one end and female at the other, with the pin numbers all wired through, pin 1 to pin 1, etc. Make the link cables one foot in length. Note that many computer cables with DB15 connectors do not wire all pins straight through, so you shouldn't use a computer cable unless you're sure it's wired correctly.

2) Leave one rack space between units for ventilation.

3) Switch the back panel NORMAL-SLAVE switch of the bottom unit to NORMAL. Switch the NORMAL-SLAVE switch of all units above the bottom one to SLAVE.

4) Connect the LINK OUT of the top unit to the LINK IN of the next unit down. Continue on down the stack. The link input of the top unit is not used, and the link output of the bottom unit is not used. Check that all units except the bottom are the slave mode, and the bottom unit in the normal mode.

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Switch channels which are not used to the off (red LED) mode. Set the bottom row of switches to match the modes of the channels. When the system is powered up, the system will start up with the channels in the modes set on the preset switches.

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The Model D Automatic Mixing Controller has three patented automatic mixing functions, the Dugan Speech System,™ the Dugan Music System,™ and Dugan Gain Limiting.™ The Speech System is usually used by itself, and is the best choice for "talking heads." If you're impatient, just set all the controls on the yellow marks, switch unused channels to the off mode, and the Speech System will probably work for you without your having to read further.

The Music System and Gain limiting are usually used together, for singing voices or instruments. The Speech and Music systems are independent, and one group of mikes can be doing the Speech System while another group of mikes is doing the Music System.

In addition to these main functions there are some convenience functions:

• Each channel fades between on, auto, and off modes when the buttons are pressed.

• A master override button momentarily fades the channels to whatever combination has been preset on the channel override switches while the button is held down.

• A master preset button sets the channels to the modes which have been preset on the channel preset switches.

• A last hold function is available for use when constant ambience is desired with the Music System.

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The Dugan Speech System spreads the gain of one open mike over the whole system, so a natural one-mike ambience is maintained. This is not a gating system! When someone speaks, the controller very rapidly fades that mike up and the others down. When the talker pauses, all the mikes come up again to a medium gain. Thus all mikes are equally available and sound normal when they are in use, but they don't add up in noise or feedback. It always sounds like one mike is open; when no one is talking, it's a mix of all the mikes at lower gain. While someone is talking, that mike becomes the only one in the system.

Switch the system to speech for all the desired channels. Press the off buttons for all the channels that are not being used. Also set the preset switch to off on the channels not being used. Put all the live mike channels in auto.

Adjust console trimmers, controller threshold controls, and console faders to achieve the following objectives:

a) Console input trimmers are at as high a gain as possible without clipping. This will insure the most sensitive automatic mixing operation.

b) Console faders are at your normal operating marks.

c) Input trimmers and controller threshold controls are balanced so that ambient noise produces approximately equal gain on the controller's gain displays for all channels with mikes.

Start by setting all the auto mix threshold controls to 0 (2:00) and balancing the console trimmers for approximately equal ambience as seen on the auto mix gain displays when no one is talking. This will set all your mikes to equal acoustic gain. Flickering is normal in the ambient noise condition, but try to get the channels to average about the same gain on the displays. You will note that raising the threshold of one channel will cause its gain to rise, and the others to fall. It's a balancing act.

This will set all your mikes to equal acoustic gain. When you discover that some mikes must be at lower gain for louder talkers, turn down the console trimmers to get the level you want, and then when no one is talking, turn up the threshold of the channel you trimmed down to compensate and regain the ambient noise balance. In the Speech System the threshold controls do not affect the audio mix directly, and they do not control any kind of gating; they determine the weighting of each mike in the automatic mixing function. Note that raising the threshold for one channel will raise the ambient noise gain of that channel and reduce the others. When the thresholds are balanced each mike has an equal opportunity to take over the system. Now when a person talks at one mike the others will go down.

With four open mikes, the ambient gains will ride around -6 dB. With eight mikes, they will flicker at around -9 dB, and with sixteen live mikes, around -12 dB. If the threshold controls are turned down too far, the inputs will appear to gate. This is NOT desirable.

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Because on most boards the faders are after the insert patch points, mikes must be muted not by pulling the faders down, but by using the off buttons on the controller. Leave the faders up; move the faders to adjust levels while people are talking, and kill mikes by pressing the off mode button. When people are ready to speak, put them back into auto mode so the system can cue them in when they talk.

The controller helps you locate a mike which is making an unwanted noise. Look at the gain displays to see which mike is active, and hit its off button.

If the last hold function is on with the Speech System, the system gain will rise to the 2-mikes-on level, the one mike being held on and the others in the speech group adding up to another one. Last hold is not recommended with the Speech System.



The natural ambience transmission of the Speech System in the Model D is one of its most valuable features, but in some cases it's desirable to expand the ambient noise downward. Of course, the trade-off for doing this is the sound of noise breathing up when someone talks!

To suppress ambient noise, send a pre-amplified mike from the room into a Model D channel, but keep the fader down for that mike. Adjust the gain of the mike preamp until you see the gains of the live channels go down the desired amount. If all Model D channels are used, it's still possible to insert this signal into the system via pin 1 of the LINK IN connector, with the ground going to pin 10.

If the ambience is constant, a fixed downward expansion threshold could be set by feeding an audio oscillator into an unused Model D channel.

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The Dugan Music System is a soft-gating system with an automatic threshold that follows the ambient noise. Each channel is 2/1 expanded below the floating threshold. The threshold is controlled by the sound level monitored at a sensing mike in the stage area. This mike is only needed for the Music System, as the Speech System has no threshold.

Install the noise sensing mike in the same area as the program mikes, but not close to any of the program sound sources, or close to any particular noise source. The idea is to get a balanced pickup of the general sound level onstage. Don't put it in the back of the house because of the time delay. Patch the preamplified mike to the MUSIC SYSTEM THRESHOLD INPUT of the Model D. Typically the direct output of a console input strip is used, with the mix buses deselected. This input is typically set with 10-15 dB more gain than the program mike inputs.

Switch the system to music for all the desired channels. Press the auto buttons for all live channels. Press the OFF buttons for channels not in use. Also set the PRESET switches OFF for channels not in use, and AUTO for the channels in use.

Adjust the auto mix THRESHOLD for each channel so that the bottom LED of the gain ladder is flickering. The MUSIC SYSTEM THRESHOLD INPUT knob is a master for all the channel thresholds, as is the noise mikes's console preamp gain trimmer. If all the channel auto mix displays just stay up, the reference signal is missing or too low.

If the gating of the ambience is annoying, the effect can be smoothed by either turning LAST HOLD on to keep one mike always open, or turning the DEPTH knob clockwise to around -10 dB to mix in a steady level of ambience.

The Music System may also be used with individual or group reference mikes for channels or groups of channels. To do this, move JP3 on the channel board one pin left to the NC pin. Then either an independent audio reference signal may be input for the channel or the music system threshold bus may be looped back in from contacts on the REMOTE CONTROL connector. Note that the Music System will not work on a channel with JP3 in the left-hand position unless a reference signal is input to the remote connector; the channel gain will simply stay up in music mode.

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With manual mike on-off selection, or in the Music System, the system gain increases as each mike comes on. The Gain Limiting System may be used to keep the gain below the feedback threshold. Gain Limiting is a number-of-open-mikes (NOM) master gain control. Since there is no master audio channel going through the Model D, it acts by reducing the gain on all the input channels together. The Gain Limiting function turns down the master gain when more than a desired number of microphones are open. It doesn't just count how many mikes are on; it actually sums the gains of all the channels and compares them to a threshold, and thus the gains of channels which are partially attenuated are accounted for also.

Set the gain limit threshold to the number of open mikes (NOM) that you can have before feedback. Set it to "1" if you want maximum gain for every mike when it's solo. The NOM switches for each channel must be on. The master gain display will show you 3 dB of gain reduction when two mikes are on, 6 dB of reduction with four mikes on, and so on.

Gain Limiting may be used with manual mike switching. Press the off buttons for all channels, and then try turning on one, two, four and eight mikes. Note the appropriate master gain reduction on the master display.

Individual channels may be exempted from either actuating or being affected by the the Gain Limiting function by turning the channels' NOM switches off.

Gain Limiting won't do anything when you are using the Speech System. The Speech System maintains NOM = 1 all the time anyway, so Gain Limiting can't sense any excess gain. Therefore it doesn't matter where the NOM controls are set in speech mode. It's recommended, however, to keep the NOM switches on and the gain limit threshold at 1 when using the Speech System, so that the system won't go into feedback if some mikes are manually punched into on mode, or the override button is pressed with multiple mikes selected to come on.

If the unit is being used "split" with some mikes on the Speech System and some mikes on the Music System with Gain Limiting, you may turn the NOM switches of the Speech System channels off if you don't want the master gain reduction caused by multiple active Music System mikes to affect them.

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The override button in the master control section is a momentary function, active while the button is held down. It fades all the channels full up or off, depending on how the override switches for the individual channels are set. Set the channel override switches to the pattern of mikes on or off that you want when you override the automatic system. The override button may be remoted for use as a chairperson's button to silence all other mikes.



The preset button sets the modes (on-auto-off) of the channels according to the "memory" set in the bottom row of switches. Set these switches to your normal pattern of channel usage. This pattern may be restored at any time by pressing the preset button.

The channels will be in the preset modes when the unit is powered up.



The mute button fades all channels out as long as it is held. It may be remoted to the podium to enable the chairperson to shut off all the mikes.



Each channel has bypass relays. A channel may be patched directly through with the bypass switch. Panel lights extinguish and the bypass LED illuminates to indicate this condition. When the power is off, all channels are bypassed, so it is not necessary to unpatch when the unit is not in use.



These front panel functions may be remoted using back-panel connections: mode buttons on, automatic, and off, mode LEDs on, automatic, and off, and the VCA control voltage output for a remote display. Additional functions available at the remote connector are channel override up, channel override off (both overrides are momentary and affect only the channel), logic out (true when the channel is near full gain), and control voltage in.

In the master section, the override, preset, and mute buttons may be remoted, and their three indicator LEDs.

After you have become accustomed to using the automatic mixing controller, you may wish to make the operation more convenient by integrating the controls into your console. All necessary connections are provided on the REMOTE CONTROL connectors on the back panel. You may even be able to use your board's channel mute buttons if they are a logic pull-down to ground.

If you use the Dugan Speech System™ most of the time, you may wish to re-wire your board's insert patch points to be post-fader. This would enable you to pull down the faders to kill mikes rather than using mute buttons. The on, auto, and off buttons, their LED's, and the auto mix gain displays may all be duplicated on your console. Please contact the factory for assistance in customizing.



The model D has a logic output which is true when the gain of an individual channel is high. This output may be used to switch off speakers near the mike, or to switch cameras. The logic output normally has about a half-second of delay before it is true. It is an open collector transistor switch, grounding when active, so whatever is reading it needs to pull up.

For speaker switching, instant response is desired. Clip out the logic delay capacitor C6 near the top of each channel board.

For camera switching, you probably want to leave the delay caps in to prevent switching from momentary noises like paper flaps. With cameras you should either use the Music System with the last hold function on, or program a logic controller like a Crestron system to hold the camera on after a momentary logic signal from the Model D.

The logic output is true (low) whenever the gain of a channel is above the logic threshold. This is factory set at -3dB gain, approximately the top light on the auto mix gain display. If you are using the logic outputs, you may need to adjust the logic thresholds (an internal adjustment) depending on how many mikes there are in the system. If there are only two mikes in auto mode, their average gain during ambient noise would be around -3dB each, so the logic outputs would be both true much of the time. In this case the logic threshold should be set to -1dB or even -0.5dB. Conversely, in a system with a large number of mikes and high gain, feedback may prevent channels from coming all the way up, and the logic output as set at -3dB gain may not be activated when someone speaks. In this case you should set the logic thresholds down to -4 or -5dB.

The logic threshold is on the master board of each Model D. It is not linked, so the adjustment must be made for each 8-channel chassis. The pot is on the top edge of the master card, labeled "LOGIC & HOLD THR." Observe the DC voltage to chassis from pin 2 of U4 on any mike channel while adjusting the trimmer on the master card. This voltage will be 0.3V as factory adjusted, for a threshold of -3dB. The scale is 0.1V per dB, so 0.4V would be a threshold of -4dB, and so on.


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