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GTM 822 Handbook
Congratulations on your purchase of a GTM 822 console. I feel confident that you
will find that its many features and great "vintage" sound will help you to make
great mixes and recordings.
Please read through this handbook first to familiarize yourself with the controls
and optimal operating procedures.
1. Connecting the unit to your power source
The GTM has a remote linear power supply set at 120v. If it is to be used on
240v, select this value on the switch on the power supply rear panel.
The "power on" switch is also mounted on the power supply. It does the unit no
harm to be left on continuously, in much the same fashion as a vintage Neve
console. The VU and phase meters will light up when the unit is powered on.
2. Connecting the unit to your equipment
There are two sets of channel inputs to the unit...
a) The Channel XLR input connectors and
b) The 25 pin "D" style female connector
On each channel and on the monitor section is an illuminated blue push button
marked "TRACK". When this switch is selected, the channels will be sourced
from the Channel XLR's and it's anticipated that these will be used with
microphone pre amplifiers and other sources used for the "tracking" mode of
recording, sending to the DAW/MT tape m/c via the channel output XLR's or the
25 pin "D" output connector. Channels can be switched individually or globally.
If the "TRACK" switch is deselected then the channels are in default mix mode
and receive their input signals from the 25 pin "D" connector.
These D connectors are wired to standard workstation practice (see addendum
sheet #1) and are anticipated to be connected to a digital workstation or multi-
track recording system.
This represents the "mix" mode of recording where multiple channels are
mixed down to stereo. In both modes the mix and cue/aux busses are accessible
and can be used to send signals to effects paths or cue headphones.
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Summary of Contents for Aurora Audio GTM-822
- Page 1 GTM 822 Handbook Congratulations on your purchase of a GTM 822 console. I feel confident that you will find that its many features and great “vintage” sound will help you to make great mixes and recordings. Please read through this handbook first to familiarize yourself with the controls and optimal operating procedures.
- Page 2 All signal paths on the GTM (except the headphone jack socket on the front panel) are balanced line level (0VU = +4dBu = 1.228 volts ac). The XLR’s are pin 2 hot and the jack sockets are all 0.25” stereo tip/ring/sleeve type. Phone type jack plugs should not be used, as the smaller diameter tip will not connect properly with the TRS jack sockets.
- Page 3 The VU meter measures the signal level at the pre-fade insertion return point. This means that, with nothing plugged into the insertion, it will measure input level and with a device plugged into the insertion, it will measure the output level of that device.
- Page 4 4. The Monitor/Meter section The VU meters, phase meter, monitor output and headphone output all follow the monitor source selection switch. The source switch selects between 2T output (the stereo mix), 2T playback (the recorded mix), the Aux outputs and the PT Mix (that assumes that the digital mix output is assigned to channels #1 &...
- Page 5 As can be seen in the chart above, the power dissipated into headphones depends on their impedance. For a given output voltage… in this case +20dBu = 7.75 volts at 1KHz… the power is given by Voltage (squared) / load impedance. Thus 600 ohms headphones will produce around 0.08 watts while 150 ohm headphones will produce 0.30 watts.
- Page 6 In every case, the headphone level control should be set to zero before the headphones are plugged in and then gradually increased to a comfortable listening level. High levels can permanently damage your hearing (and wreck your headphones)! The Sifam VU meters are electronically buffered so that their internal rectifiers do not affect the distortion specification of the GTM.
- Page 7 The phase can usually be corrected by means of the phase switch on any external microphone pre-amplifier, a feature of the work station software, or, in the event that no other solution is available, the user can make a TRS to TRS cable with a deliberate phase reversal and plug it into the channel pre-fade insertion of the offending channel.
- Page 8 6. Adding extra channels Channels can be added, eight at a time, by connecting add-on units to the GTM master unit. The add-on units are basically identical to the GTM master unit, but there is no monitor/meter section or audio connections to the bus outputs. The only control to the right of the channels is the “TRACK”...
- Page 9 If all the studio equipment is bonded to a clean technical earth there is less likelihood of any difference in potential = ground hum, occurring. In the event that a loop exists between two items of equipment one should disconnect the ground on one end of the interconnecting XLR or TRS cable…...
- Page 10 There are external adjustments accessible on each channel via multi-turn trim pots above and below the stepped input gain control at the top of each channel. The lower preset trim pot sets the 0VU reference level of the LED VU display. It is factory set at 0VU = +4dBu = 1.228 volts ac when measured at the pre- fade insertion return.
- Page 11 8. More hints on using the GTM 822! My original design concept for the GTM was that it should be the CORE of a small, professional recording and mix down studio/room. The GTM is best used with an external patch bay that can provide the user with access to all the circuit paths.
- Page 12 A rough mix can be made from the channels to the stereo output so that the user can listen to the signals going to the workstation and send a stereo cue headphone signal to the performer. For mixing, the TRACK buttons are de-selected and the workstation can now mix down through the GTM channel paths, as relays would have switched the mic pre-amplifiers away from the channel inputs.
- Page 13 The above illustration represents how the GTM822 can be used as the CORE of a recording studio set up. In tracking mode, signals from the microphone preamplifiers can be sent to the digital editing system. In MIX mode, the digital editing system can mix down to stereo.
- Page 14 Connecting the Talk-back facility :- The external talk-back microphone and “press to talk” switch are connected via the male 9 pin D sub connector on the rear of the master unit. The wiring of the mating female D sub, viewed from the wiring side, is shown in the illustration.
- Page 15 Connecting an expansion unit to the master unit :- When connector expansion units to each other, or from an expansion unit into the master unit, the signal comes from the male 9 pin D sub connector on the expansion unit into the female 9 pin D sub on the master or slave unit. As there seems to be no standard thread length on D sub retaining screws, you may need to add washers to the screw if it is found to “bottom”...
- Page 16 When connecting unbalanced equipment to the GTM822's audio inputs, connect the wiring as follows :- XLR inputs :- Connect the signal's hot to pin 2, and the shield to pin 3. Leave pin 1 disconnected. TRS inputs :- Connect the signal's hot to tip, and the shield to ring. Leave the sleeve disconnected.
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Page 17: Warranty
VU Meter range :- Standard VU points from -20VU to +3VU where 0VU = +4dBu = 1.228 vac. Front panel trimpot to align the 0VU point. Input headroom :- At least 20dB above the red +3VU LED i.e. At 0dB input gain = 20dB above +3VU = +7dBu = >... - Page 18 Aurora Audio International warrants this GTM822 unit against defects in workmanship for a period of one year and parts for a period of one year from receipt by the original end user. This warranty shall not apply to damage resulting from misuse including water damage, in-transit damage, fire damage, improper maintenance, dropping the unit and operation or storage outside the environmental specification for the product.
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