Kursus Experimentele Muziek: Boekdeel 4b: Audiotechnologie
Hogeschool Gent : Departement Muziek & Drama
Ontwerp en realisatie van een studio-patcher/mixer met professionele specifikaties.
Cfr. elektronisch schema van de patcher + demonstratie van het toestel.
Inputs are to be used exclusively: either balanced or unbalanced. Never both at the same time on a same channel. On different channels balanced input and unbalanced ones may be mixed.
All inputs use instrumentation-amplifier circuitry in order to achieve full balance. There are no DC-blocking capacitors in the input and thus the signals have to be free of DC offsets.
Common-mode signal rejection ratio : >80dB
If the jack connectors for unbalanced signal sources are used, they should be of the monophonical type. Never use stereo-jacks, unless they are connected for balanced signal transmission.
All of the inputs can be send to any of the four main outputs in any volume relation. The four potentiometers to control the channel-attribution of every single input, are arranged in vertical rows above the input-connectors.
Every horizontal row is mixed down to one of the four outputs.
There are four signal outputs delivering the mix of the complete horizontal corresponding row. The outputs signals are simultaneously available as four active balanced outputs ( male XLR connectors on the left side of the frontpanel ) and as four unbalanced outputs using RCA phono plugs. One 5-pin XLR connector carries the unbalanced output signals of all four channel. The connector is provided to connect to 4-channel tape decks. The signal level is as the other outputs.
To make easy connection of stereo recording equipment possible, a stereo-mixdown circuit has been designed into this piece of equipment. The potentiometer on the front-panel above the RCA- and XLR connectors allows the user to make stereo mixdowns as follows
CHANNEL 1 + CHANNEL 3 mixed to LEFT CHANNEL output
CHANNEL 2 + CHANNEL 4 mixed to RIGHT CHANNEL output
(potentiometer fully counterclockwise)
or: CHANNEL 1 + CHANNEL 4 mixed to LEFT CHANNEL output
CHANNEL 2 + CHANNEL 3 mixed to RIGHT CHANNEL output.
(potentiometer fully clockwise )
If the potentiometer is in the mid-position, the signals patched into channels 3 and 4 will be found mixed together in the center of the stereo image. Of course all intermediate positions can be used. Both active balanced outputs and unbalanced RCA-outputs can be used.
4. POWER REQUIREMENTS
Voltage selection should be performed only by a qualified technician since it necessitates soldering on the power-supply printed circuit board mounted on the back panel. There are no user serviceable parts ( fuses) inside the machine.
The power supply is a precision symmetrical double tracking circuit. On its primary side, a mains filter had been inserted to suppress mains derived spikes, overvoltage and RF. In order to minimise induced hum, a toroidal transformer has been used.
The case is connected to the mains-earth, but the equipment can safely be used without mains-earth connection, if ground loop problems arrise from connections to other studio equipment. It is generally better to connect all studio-equiment at one point only to mains-earth ( i.e. at the power amplifiers). However all chassis ought to be at a same potential at all times.
If found defective , return equipment to Logotronics with a description of the failure. If you want to confine servicing to qualified technicians in your area, you can write to us to obtain schematics and part numbers. There is no copyright on any part of the circuit or the design. All components used are top-quality. All resistors low-noise metal film and 0.1% precision wherever necessary, all op-amps used are low-noise precision devices. (OP215, OP07, OP27) Whenever replacing components, make sure you are not degrading performance.
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