aci VGM-804 Guide

VGM-804 Gated Microphone Mixer
Installation and Use
ACI-AppliCAD, Inc.
Version 2.0
[phone] www.aci-applicad.co

Table of Contents
Introduction ---------------------------------------- 1
Features & Benefits
Quick Start Guide --------------------------------- 2
Connecting Your Co ponents
Installation Issues
Microphone Settings
Setting Audio Levels
Operator’s Guide ---------------------------------- 6
Basics
Managing Microphones
How Sound Gating Works
Opti izing The Sound Gating
In Case of Difficulty -------------------------------11
Troubleshooting
Phone Support & Warranty
Specifications -------------------------------------- 12

1
Introduction
Congratulations on your purchase of the VGM-804 Gated Microphone Mixer.
Because its design targets sound reinforce ent applications, your audience will enjoy higher
quality sound than with generic ixers or consoles. At first, you’ll find a refreshingly si ple
exterior. It’s straightforward to set up, and easy to use. Soon, however, you’ll co e to
appreciate how the ixer allows you to ake better use of your sound syste . Its rugged
construction should provide you with years of reliable service.
Features and Benefits
The challenges often encountered running a sound reinforce ent syste inspired
the features of this ixer, as shown below:
VGM-804 Feature What It Does User Benefit
Mic Sound Gating
with Last Mic ON &
Adaptive Threshold
Quiets idle ics by gating active
ones ON. The last live ic
re ains ON until another is used.
Reduces distracting noise,
allows ore volu e with less
reverberation.
Gate/Clip LEDs Green shows inputs gated ON,
red indicates clipping.
Identifies ics in use. Warns of
excessive levels.
Co pression Li its unusually loud sounds. Listeners re ain co fortable.
Co press LED Lights when loud sounds trigger
co pression.
Helps the operator keep levels
under control.
Balanced Lo-Z
Microphone Inputs
Rejects electrical noise picked up
by icrophone cables.
Reduces “hu ” and “buzz.”
Mic input bass rolloff Reduces bass response of ic
inputs only.
Mini izes “pop” and “boo ”
while preserving vocals.
Industrial-quality level
controls
Designed to withstand illions of
rotations.
Controls re ain s ooth and
quiet for any years.
Gain presets Adapts to any source level. Makes level setting easier.
LED Level eter Indicates overall sound level. Assists setup & operation.
Balanced Output Drives professional gear. Yields quiet, stable operation.

2
Quick Start Guide – Connecting Your Co ponents
Gather your input and output cables and ake the connections you need :
MIC 1
MIC 2
MIC 3
MIC 4
MIC 5
MIC 6
MIC 7
MIC
LINE OUT
POWER
AUX OUT
AUX 2
AUX 1
Line Output
Balanced line output connects to
pro-audio a plifiers, equalizers, etc.
1 – Ground (Shield)
2 – White wire
3 – Black wire
1 2
3
1 – Ground (Shield)
2 – White wire
3 – Black wire
12
3
Microphone Input Jacks 1 –
Inputs are Lo-Z, balanced XLR
Phanto power available for condenser ics (See page 4)
Standard wiring for microphone cables:
Auxiliary Inputs 1 – 2
RCA jacks to play line-level ono sources:
•CD player
•Telephone interface (receive)
Co bine stereo sources with “Y” adapters
(see page 3)
16 VAC Power
Plug in supplied AC
adapter here.
Auxiliary Output
RCA jack for connecting:
•A plifier with unbalanced RCA input
•Recording devices
•
Telephone interface, FM trans itter
Use “Y” adapters to connect additional devices

3
Quick Start Guide – Installation Issues
Low-i pedance icrophones with standard cable wiring plug directly into the
icrophone jacks without any odifications. Here’s how to handle so e circu stances that
ay affect your installation:
Replacing an old mixer – If your installation has fixed icrophone jacks with cables run as
part of the building (though walls, under floor, above ceiling), exa ine how these cables
ter inate at your old ixer. If they have ale XLR connectors, si ply ove the to your
new ixer. If they ter inate as screw ter inals, you’ll need to attach XLR plugs. We
reco end Neutrik NC3M connectors because they are easier to work with. If these are
not available, Switchcraft type A3M will do. Whether new or existing, connector wiring ust
atch the standard shown on page 2.
Mounting – The ixer fits into a standard 19" rack, taking up one space. It needs no support
beyond the panel ounting screws. Be sure to place it where it’s easily accessible to the
operator. It akes little heat, but allow one rack space between the ixer and equip ent
that does generate significant heat, such as power a plifiers.
Wireless mics – Most wireless icrophone receivers allow you to select a balanced,
icrophone-level output. Choose this output and connect each wireless receiver to a
icrophone input of the ixer. This way, the ixer handles each wireless ic as it does
other icrophones, providing the gating and selectable co pression features. Set any level
controls on the wireless receivers to atch their level to that of your wired icrophones.
Condenser microphones – Condenser icrophones feature excellent sound quality, but
require a power source to operate. So e use built-in batteries. Others expect to receive
power fro the ixer’s icrophone connection (this is called, phantom power). Your ixer
can provide phanto power at any or all icrophone jacks. To select phanto power, see
Mixer Settings, next page. Many condenser ics have a “hot” (loud) output – adjust your
ixer’s presets (see page 5) as needed.
Stereo Sources – Use a “Y” adapter to co bine the Left and Right channel of stereo sources
(such as CD players). Connect the resulting ono output to one of the two auxiliary inputs
at the ixer.
Multiple sources – If you have ore than two auxiliary (non- icrophone) sources, we
reco end using an external selector switch to select a ong the . Different sources ay
not perfor properly if paralleled with “Y” adapters.

4
Quick Start Guide – Microphone Settings
The ixer allows you to tailor operating features for each icrophone. Make these
selections with the botto -panel switches shown below:
The COMPRESSION and Phantom Power switch banks each have nu bered switches
corresponding to the eight icrophone channels (1-8). Set each switch using a pen or
si ilar pointed tool. So e suggestions for each feature:
Compression – The ON position is reco ended for ost situations. Co pression li its
unusually loud sounds fro each ic, increasing audience co fort. It works unobtrusively, so you can
enable co pression with confidence. However, we reco end you select no co pression (switch
OFF) for any icrophone where its user ay need extra level – for exa ple, speaking above the noise
to bring a eeting to order. Often this eans choosing co pression OFF for the “ ain” ic.
Phantom Power – Leave OFF for dyna ic or wireless icrophones. Select ON for each input
fro a condenser icrophone. If a particular icrophone input is used with a variety of icrophones
including condenser ics, choose ON. Most condenser icrophones require phanto power.
Dyna ic ics don’t need it, but should tolerate it.
Quick Start Guide – Setting Audio Levels
This ixer has a balanced line output for professional equip ent, and an auxiliary
output for consu er-grade a plifiers and other devices. The balanced output is capable of
a high level: +28dBv. Following equip ent should be capable of a si ilar axi u level.
When any equip ent is driven beyond its axi u level, it “clips”, flattening audio peaks –
resulting in a characteristic distorted sound. You get the least noise fro your equip ent
(best signal-to-noise ratio) when everything clips at the sa e level. Thus, it’s best if
following equip ent can handle at least +28dBv.
Check the specifications of following gear. If for exa ple your equalizer can handle
only +22dBv at its balanced input, you need to reduce your ixer’s output by 6 dB. Since
your ixer has an output i pedance of 600 oh s, you can reduce its output by loading it
with a resistor. A 600 oh load lowers the output by 6dB. Other values can be used, as
shown next page. Wire this resistor into the connector at either end of the cable between
the ixer’s balanced output and the balanced input of the next device, as shown:
Gating
Threshold
Compression
Phantom
Power
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
ON

5
2
3
1
3
2
1
R value: Atten.:
600 oh 6 dB
300 oh 10 dB
200 oh 12 dB
Because the VGM-804 can be set to co press excessively loud sounds to a consistent
level, you need to ad ust the rest of your system (power amplifier, etc.) to spot this level as
required. This is easy to do if you follow the procedure below. In fact, we reco end
following this procedure to get your levels “in the ballpark” even if you don’t plan on using
co pression in nor al operation (te porarily co press one ic input to perfor it):
•Start with your power a plifier’s volu e control at a low level.
•If your syste has an equalizer, set it to Bypass or Flat ode.
•Have so eone speak (reading a book works well) into a icrophone connected to any
channel that has co pression ON.
•Increase this ic channel’s gain control until you see the COMPRESS LED glow yellow and
red with the speaker’s voice. At this point, the ixer output has reached its
consistent co pressed level. The level display should peak within its yellow range.
•Now, turn up your power a plifier’s gain until your assistant’s voice fills your auditoriu
to a fully satisfying, but still co fortable, listening level.
•Enable your equalizer. The overall level shouldn’t change uch, but adjust as needed.
•You ay find that under actual use, when the auditoriu is filled, slightly ore volu e is
required. In that case, increase your power a plifier gain as needed.
Once you have found the right setting for your power a plifier, it should need little further
adjust ent. Instead, use your ixer to anage the volu e of all your sources. We suggest
you write down or ark the proper positions of EQ and a plifier controls for future
reference. To prevent unauthorized adjust ents, ount security covers over these panels.
In any installations, you’ll need ready access only to the ixer and your sound sources.
Your VGM-804 features a gain preset for each input. You can adjust these with a fine slot
screwdriver, to bring differing source levels into agree ent. These are factory set to
idrange, so si ply adjust any “low” inputs upward, and any “hot” inputs downward. Many
condenser ics, as well as so e wireless ics, output a very high level – go ahead and
“ta e” the with the presets. Ideally, you can adjust the presets to bring each source to a
usual, co fortable level when its knob is set to around “5”.
C OMPRESS
MIC
AUX 1 AUX 2
VGM804
AUX 1
Preset
AUX 2
Preset
MIC
Preset

6
Operator’s Guide – Basics
The power a plifier and preset adjust ents you’ve just co pleted, along with the VGM-
804’s icroprocessor “brain”, ake operation as si ple as it can be!
POWER Switch – At the far right of the panel. Switch ON for use. Many users prefer to plug
the ixer’s AC adapter (as well as the rest of their audio gear) into a switched outlet strip,
leaving the POWER switch on. Either way, the first green LED of the level display lights when
the ixer is powered up.
Gain controls – adjust as needed for good listening levels. You can apply labels on a blank
panel above or below your ixer (as shown above) to describe their actual use. Depending
on the icrophones and their place ent, about halfway up should provide good usable
level. If needed, adjust the presets (see the previous page). The gating and co pression
features ean you’ll do less knob-turning than would be needed with non-auto atic ixers.
Gate/Clip LEDs – under each icrophone gain control. Each lights green when the ixer
gates that icrophone ON. Use these LEDs to identify live ics. For exa ple, during a walk-
though test before the progra , have your assistant speak into each ic in turn – the LEDs
show which ixer channels are in use. These LEDs light red when their input channels are in
danger of clipping – reduce their gain to re edy this condition.
Clip LEDs – under the two AUX gain controls. Lights red when these channels are near
clipping. To prevent audible distortion, reduce gain should you see the clip indicators light.
If you still need ore sound, turn up your power a plifier instead.
The ic and aux input channels all feature sufficient headroo so you should rarely if ever
see red (clipping) lights.
C O M P R E S S
MIC AUX 1 AUX 2
VGM804
Gated
ON
Clipping!
POWER
Switch
Stage Left
CD Player
Phone

7
Level Bargraph Display – Shows the progra level. Its first yellow LED indicates a level of 0
VU, equal to +4dBv at the VGM-804’s balanced output. Each LED above or below this point
represents a change of + or – 3dB output level.
If your sound syste ’s level has been set up according to the reco ended
procedure on page 5, a co fortable level for spoken aterial often reaches the first or
second yellow LED. Dra atic or usical aterial can often be played louder, covering the
entire yellow range into the first red LED. Use the eter as a guide – although your ears,
and the audience response, are your best judge of how uch sound to provide.
COMPRESS LED – This LED displays the status of the VGM-804’s co pression syste . It
lights whenever co pression is li iting the sound level. For each icrophone channel with
co pression enabled, li iting begins to occur at approxi ately at 0 VU (roughly the first
yellow LED of the level display). The COMPRESS LED shows green at 3dB gain reduction,
yellow at 6dB, and red when co pressing by 9dB. The co pressor’s THAT® Analog Engine
IC co presses with virtually inaudible distortion.
To use the ixer’s co pressor, first ake sure that co pression is enabled on the
desired ic inputs (see page 4). Then adjust each ic’s level control until the COMPRESS LED
blinks green and perhaps yellow on level “peaks”. If totally dark, you ight want to turn up
that channel. On the other hand, if the COMPRESS LED illu inates red, the channel in use is
set too high and constantly “hitting” the co pression. In that case, reduce that ic level.
If you find that the COMPRESS LED re ains dark for all situations, or lights red even
though the sound is barely adequate, adjust the volu e of your power a plifier accordingly
– repeat the procedure on Page 5.
When the VGM-804 is driven into co pression by excessively loud ic(s), it regulates
its output level within the co pressed range. The resulting gain reduction affects all inputs.
For exa ple, loud speech into a co pressed ic can reduce the level of usic playing
through an auxiliary input (so eti es called talk o er operation).
AUX 2
COMPRESS
VGM804
Power
On
0 VU (+4dBv)
output
Co press
LED
Output Le el

8
Operator’s Guide – Managing Microphones
Your goal as sound operator is to provide sufficient, quality sound fro all progra
participants, to all in your audience. We’ve prepared this section to help you do this.
Your sound syste allows participants to speak naturally or even softly as their
aterial requires, confident that the audience hears every word clearly. To do this, the
power of the sound co ing fro the loudspeakers greatly exceeds that picked up by the
icrophones. However, this advantage is also a liability: When one or ore icrophones
receive enough of their own a plified sound fro the auditoriu loudspeakers, the result is
that fa iliar “howl” often called, “feedback”. Strictly speaking, a easure of feedback
occurs even when not enough for a full-blown “howl”. Lesser a ounts of feedback result in
a hollow sound, as if your participants were speaking into an oil dru . Pros call this effect,
ringing. Your audience would find it tireso e and distracting.
If you turn your ics down to zero, you guarantee no feedback and no ringing – but
no benefit as well. As you increase your level controls, the audience gets to hear ore of
the progra , as a plified sound overco es background noises. The sound beco es louder
than your participants could provide alone – your syste is producing “gain.” In fact, the
expression, “raising the gain” si ply eans turning up your level controls.
This graph shows that as you turn
up the ics, the desired sound
(blue line) steadily increases and
the audience hears better. At first,
the bad effects of feedback (red)
are ini al. Increase gain beyond
a certain point, however, and
feedback ultiplies. Once ringing is
heard, you ust reduce gain to
achieve clear, usable sound. The
dotted lines show when gain is set
properly – enough sound while
feedback re ains inaudible.
Ideally, your sound syste ,
roo acoustics, and the way ics are used, all allow you to provide plenty of sound without
ringing. Extra available gain is logically called, gain before feedback. Having extra gain
before feedback insures that you won’t have to co pro ise between quantity and quality
of sound. Your audience will benefit, and all will appreciate the results.
Gain
Sound
Ideal level
Quality
Sound
Feed-
back

9
If you find it difficult to ake your sound loud enough without ringing, you need ore gain
before feedback. Here’s so e si ple ways to get it:
•Train participants and stage handlers so that everyone speaks between 4" and 6" fro their
icrophones. Ai boo ics so they point toward the speaker’s chin when the speaker is looking
straight out at the audience. Good iking lets everyone be heard with lower gain, resulting in
sufficient sound without feedback proble s.
•The VGM-804's sound gating auto atically increases your available gain before feedback, by uting
unused icrophones. Unneeded ics receive no useful sound, only feedback and noise. You win
about 30% ore headroo for each ic shut off.
•Don’t use excessive compression. If any ic input is causing the COMPRESS LED to glow red, reduce
that input’s level control.
•Anything you can do to provide a quiet auditorium directly adds to your available gain before
feedback. For exa ple, keep auditoriu doors closed during the progra , to deflect lobby noise.
If your HVAC syste akes excessive noise, see if anything can be done to quiet it.
Thanks to the sound gating feature, there’s far less need for you to turn ics up and
down during the progra . We still reco end, however, turning down ics that are
obviously finding only noise:
•Stand mics being moved by stage handlers
•Certain wireless receivers that pick up radio noise when their ics are switched OFF – turn up wireless
ics only after they’ve been switched ON.
In short, working this ixer is like driving with cruise control – it akes your job
easier, but you still have to drive. Here’s so e “safety tips.”
•When you hear ringing, reduce gain on the affected ic(s). You’ll know which ics are causing
ringing by watching the ixer’s GATE LEDs while listening for the ringing. Mics gated “off” cannot
contribute to ringing at that o ent.
•The COMPRESS LED ay glow green or perhaps yellow o entarily at “high points” in the aterial.
That’s good – it indicates you’re providing axi u usable sound.
•When accidents happen – a dropped ic, a cough, or a feedback howl – the ixer li its these nasty
sounds (the COMPRESS LED lights red).
•If the COMPRESS LED lights red for nor al aterial, your ic gain(s) are set too high! Turn the down
until the ixer indicates only a slight, inter ittent co pression. You’ll get clearer, ore natural
sound and less feedback. In this situation, turn up your power a plifier should you need ore sound.

10
Operator’s Guide – How Sound Gating Works
The VGM-804’s icrocontroller easures all input levels continuously, 2500 ti es per
second. It “learns” the a bient sound at each ic to ignore background noise such as fro
air conditioning. Any ic whose level is 6dB louder than the others, gates ON. Once live, a
ic re ains ON as long as at least one of the following three conditions are et:
•Its level re ains higher than the threshold described above
•Less than 0.2 seconds “hang ti e” has elapsed since being above threshold
•It is the last (and only) input still gated ON
Microphone inputs gate OFF when all conditions beco e false, re aining so until active
again. Gating works best for orderly discussions where generally, one person speaks at a
ti e. The two Auxiliary inputs are not gated, thus can operate along with ics.
Operator’s Guide – Opti izing the Sound Gating
Follow these instructions if you need to adjust your ixer’s sound gating:
First, be sure that your sound syste ’s audio levels are set up properly. When your
ixer is working near its design level, its icroprocessor receives detailed infor ation on
ic usage, thus can ake better gating decisions. Use your level display to verify this:
• Have an assistant speak or read into a ic while you slowly advance its control.
• As you turn up the ic, listen to the sound in your auditoriu while observing the
bargraph. The display should reach 1 - 2 yellow LEDs when your sound has found its
co fortable, custo ary level (if co pression is enabled on that ic, you’ll also see the
COMPRESS LED illu inate) . If not, repeat the adjust ent procedure on page 5.
Next, observe the sound gating perfor ance using two or ore icrophones
alternately. Note if the gating is operating to your satisfaction. If not, you can fine-tune the
icrocontroller’s decision process by turning the Gating Threshold control (botto panel) in
the direction reco ended below (use a fine slot screwdriver) :
• If your ics see to gate ON too easily, set
the Gating Threshold control clockwise
approxi ately one-quarter turn.
• If your ics hesitate to gate ON – especially
if you have increased the gating threshold –
reduce it by turning the Gating Threshold
control counter-clockwise.
•This control affects gating results especially
when roo sound is relatively quiet.
Gating
Threshold
Compression

11
In Case of Difficulty – Troubleshooting
When the sound syste ’s down, one’s first instinct is to panic. It’s better, though, to
work the proble and find out what’s wrong:
Power – Are all your power indicator lights illu inated? So eone ay have inadvertently switched
OFF a co ponent.
Sources – Is part of your syste working? Is the proble li ited to one ic or one auxiliary source?
Outputs – Do you have a FM trans itter or recording device connected to your Auxiliary output? If
so, see if it works. If it does, this indicates that the proble is ost likely after your ixer – in the
equalizer, power a plifier, or speaker wiring.
Low volume – Mic inputs turned down cannot gate “on” or be heard. Check that your ixer’s level
controls are “up” on desired inputs. Verify that any level controls between the ixer and your
loudspeakers (a plifier, EQ, etc.) are set to their nor al positions.
Excessive volume – This ixer’s balanced output is very powerful, so your power a plifier’s gain
control often requires a lower setting than with other ixers you ay have used. Set it according to
the instructions on Page 5. If any input(s) see excessively loud even at a low setting (“3” or less) at
your ixer’s level control, reduce the preset(s) for the affected channel(s) – see Page 5.
In Case of Difficulty – Phone Support & Warranty
Please note that this product uses surface ount technology extensively. We don’t
reco end you atte pt internal repairs yourself, even if you’re co fortable around
electronics.
You ay call ACI-AppliCAD at [phone] during nor al business hours (Eastern
ti e) to get help with installing, using, or troubleshooting your ixer. If it appears that your
ixer is defective, we’ll issue a RMA (Return Material Authorization) nu ber for factory
service. Your warranty is one year fro date of purchase. Out of warranty, our current
repair charge is a flat rate of $65. plus shipping (subject to change). Whether in or out of
warranty, you’ll receive fast, courteous service. Like the VGM-804 itself, we are devoted to
solving proble s in sound reinforce ent.

12
Specifications
Inputs & Outputs:
8 MIC inputs. Balanced, Low-Z, XLR-F. Bass rolled off to ini ize boo iness.
Individually selectable co pression and phanto power.
2 AUX inputs. Unbalanced RCA. Flat, unco pressed.
2 Outputs, RCA unbalanced, XLR-M balanced.
Front Panel Controls:
Level controls on all inputs.
Preset gain adjust ents on all inputs.
Power Switch.
Front Panel Indicators:
LED indicates gating (MIC inputs) and clipping status of each input.
Co pression LED indicates co pression is active.
Level display bargraph with power indicator.
Installation Option Settings (accessible fro underneath):
Two 8-switch banks nu bered by MIC channel
Co pression: Enables co pression.
Phanto Power: Provides 15VDC for condenser ic.
Gating threshold adjust ent fine-adjusts the gating decision process.
Power:
9 Watts fro 18VAC wall transfor er.
Audio Specs:
Max Output Level (balanced) +28dBv at clipping, unloaded (less 6dB @ 600 Ω load)
Meter zero VU (first yellow LED) = +4dBv (less 6dB @ 600 Ω load)
AUX Output Level (unbalanced) +12dBv at clipping
MIC Gain (To balanced output, level and preset axi u ) 80dB
AUX Gain (To balanced output, level and preset axi u ) 37dB
Available preset attenuation (all inputs): 34dB
Co pression Ratio (MIC inputs, when active) 3:1
Equivalent Input Noise
MIC inputs: -118dBv
AUX inputs: -85dBv
Total Har onic Distortion < 0.05%
Frequency Response (-3dB):
MIC inputs: 150 Hz – 18KHz
AUX inputs: 25 Hz – 20KHz
THAT® is a registered trade ark of THAT corporation (for erly dbx).