Studer 928 Service Manual
Professional Audio System Components
Technical Specifications
Audio: Power output 4 W/15 Ω
5 W/8 Ω
2.5 W/4 Ω, continuous, sine wave
THD < 0.1% @ rated output, 30 Hz...16 kHz
Frequency response ±0.5 dB, 30 Hz...16 kHz
Input impedance 10 kΩ, balanced
Sensitivity –17...+16 dBu (0.11...4.9 V
Maximum input level +24 dBu (12.3 V
) clipping point
rms
S/N 100 dB, linear to 23 kHz at normal operating gain (input +6 dBu)
85 dB, at maximum gain
Supply: ±15 V DC (40 mA idling; 400 mA @ 5 W/8 Ω)
Output stage quiescent current 23 mA
Dimensions: Euro-card 100 × 160 mm, 7M units wide
Weight approx. 210 g
) for rated output
rms
Ordering Information:
5 W amplifier with • transformerless input 1.915.410.xx
• input transformer 1.915.411.xx
• transformerless input and remote muting facility 1.915.412.xx
• input transformer and remote muting facility 1.915.413.xx
• transformerless input and remote gain control (VCA) 1.915.414.xx
• input transformer and remote gain control (VCA) 1.915.415.xx
E42 Date printed: 29.11.01
Professional Audio System Components
2.2.7 40 W Power Amplifier 1.915.440/441
For applications where higher power level is needed, a 40 W amplifier has
been realized on a Euro-card. Its width is 32 mm, which equals 7M widths
approximately.
Power is supplied from a separate 45 VDC source, as is contained in the
19” mounting frame 1.918.120.xx. Two amplifier cards will fit into that
frame, making it suitable for applications where stereophonic monitoring
is required.
Special Features • Transformerless version with electronically balanced inputs standard
• Version with balanced and floating inputs available
• Output stage protected from overload by momentary power limiting
• Temperature sensing avoids thermal overload
• High-end frequency response limited to prevent transient intermodulation
distortion
• Low distortion performance, even at low power output
• Operation with output transformer possible
Date printed: 29.11.01 E43
Professional Audio System Components
Technical Specifications
Audio: Power output 40 W/4 Ω, continuous, sine-wave,
THD < 0.1 %, 30 Hz...15 kHz (up to rated output)
Output impedance 0.1 Ω
Input impedance 10 kΩ
Common mode rejection > 50 dB, 30 Hz...16 kHz (with input transformer)
Input sensitivity –12...+18 dBu (0.195...6.2 V
in three 10 dB-increments, plus fine-trim range of 12 dB)
Frequency response +0.5/–1 dB, 30 Hz...15 kHz
S/N 105 dB @ maximum gain
90 dB @ minimum gain
) for rated output (adjustable with jumper
rms
Supply: 45 V
(70 mA idling, 1.5 A @ 40 W/4 Ω)
DC
Dimensions: Euro-card 100 × 160 mm, 7M units wide
Ordering Information:
Euro-cards • 40 W power amplifier with transformerless input 1.915.440.xx
• 40 W power amplifier with input transformer 1.915.441.xx
19”/1U standard products
40 W power amplifier • Mono version, 19”/1U 75.700.80311
• Stereo version, 19”/1U 75.700.80322
• 19”/1U mounting frame (without amplifier cards) 1.918.120.xx
E44 Date printed: 29.11.01
Professional Audio System Components
2.2.8 Monitor Switching Relays 1.915.601/602
Two different monitor circuit switching cards are available. They are
equipped with either five or eight relays for switching of a corresponding
number of stereo sources to one or two stereo outputs in monitor circuits.
The relays are available with coil ratings of 6 VDC or 24 VDC, depending
on the user’s requirement. Click-suppressing diodes are wired across each
relay coil. The relays are equipped with four double throw (change-over)
contacts each.
Isolation of the monitor lines from external circuitry is achieved by 5.6 kΩ
resistors in the “a” and “b” legs of each stereo line, thus a high impedance (bridging) load is presented to the outside source, even in deenergized (non-selected) status, when the respective pair of relay contacts
shorts the lines after the respective isolation resistors. With a relay energized, the corresponding stereo pair is routed to a stereo bus available on
four pins of the 32-contact edge connector (in case of the 5-input card
1.915.601.xx).
Date printed: 29.11.01 E45
Professional Audio System Components
Card 1.915.602.xx features a similar circuit configuration with eight relays,
to switch one unbalanced and three balanced stereo inputs. Two stereo
buses appear on eight pins of the edge-connector; in this way, the four inputs can be switched to either one or to both outputs, such as may be the
case with separate monitor circuits in the control room and in the studio.
Dimensions: Euro-card 100 × 160 mm, 4 M units wide
Weight approx. 250 g
Ordering Information: • Relay card, 5 IN/1 OUT 1.915.601.xx
• Relay card, 4 IN/2 OUT 1.915.602.xx
E46 Date printed: 29.11.01
Professional Audio System Components
2.2.9 Transistor-Driven Relays (7+2) 1.915.603
This Euro-card is supplied with nine transistor-driven relays with singlepole, double-throw (SPDT) contacts. For two of the relays, both normally-open and normally-closed contacts are routed to the edge connector;
for the remaining seven it is jumper-selectable whether the normally-open
or the normally-closed contact is used.
The relays are designed for operation on 6 VDC, and each relay coil is
bridged with a click-suppressing diode. PNP transistors in series with the
coils are blocking the current flow, because each transistor is normally biased off. By applying the output from the gate of an external control logic
to the base of a transistor, it is switched into saturation, thereby energizing
the respective relay. This arrangement of nine relays was designed for use
in signaling systems within a studio installation; however, it may find its
use for other applications as well.
MAKE OR BREAK CONTACTS
(7 ×)
4k7
10k
– 6 V
CHANGE-OVER CONTACTS
(2 ×)
4k7
10k
– 6 V
Polarity of the relay’s supply voltage must be observed when utilizing this
circuit.
Date printed: 29.11.01 E47
Professional Audio System Components
Technical Specifications
Contact Ratings: max. 1 A/30 VDC or 0.3 A/125 V
AC
Note: In this application 48 V must not be exceeded to avoid shock hazard.
Switching power 60 VA (AC)
100 W (DC)
Dimensions: Euro-card 100 × 160 mm, 4 M units wide
Ordering Information: Transistor-driven relays 1.915.603.xx
E48 Date printed: 29.11.01
Professional Audio System Components
2.2.10 Dual Limiter 1.915.700
In sound work there are numerous situations where the signal amplitude
has to be limited to a pre-determined level in order to prevent overloading
of succeeding equipment, such as light modulators in film work, or radio
transmitters. With this limiter, excessive levels are automatically reduced
to a preset level, and, since regulation is controlled by the program’s energy content, the performance of this limiter is free of any “pumping” effects. Gain reduction is achieved with a Studer Voltage Controlled Amplifier (VCA) which ensures low noise performance and negligible distortion.
Two identical, independent limiter circuits are contained on one Eurocard, plus additional, separate gain stages to drive peak program meters.
The perfect tracking of the two VCAs makes this Dual Limiter suitable for
stereo work as well, in which case a simple electrical connection is needed
to link the units.
Note: Gain reduction meters (not supplied) can be connected to the LINK out-
puts as well, if required.
Date printed: 29.11.01 E49
Professional Audio System Components
Technical Specifications
Input: Impedance 5.4 kΩ, balanced configuration
2.7 kΩ, unbalanced configuration
Overload point +20 dBu (7.75 V
Output: Impedance < 50 Ω, unbalanced
Frequency response +0/–0.5 dB, 30 Hz...15 kHz
+0/–3 dB, 2 Hz...200 kHz
Gain 0 dB, limiter off
Output noise level –102 dBu, Limiter on
–106 dBu, Limiter off
Limiting ratio 20:1
Threshold –15 dBu...+3 dBu, adjustable
Limited output level –14 dBu...+4 dBu, depending on threshold setting
Attack time 1 ms
Release time 50 ms...5 s, program-dependent
PPM Section: Output impedance < 50 Ω, unbalanced
Maximum output level +20 dBu
Gain 2.5 dB...27 dB, adjustable
Frequency response +0/–3 dB, 2 Hz...200 kHz
rms
)
Supply: ±15 V (100 mA)
Dimensions: Euro-card 100 × 160 mm, 7 M units wide
Ordering Information: Dual limiter 1.915.700.xx
E50 Date printed: 29.11.01
Professional Audio System Components
2.2.11 Telephone Hybrid 1.915.760/764
In order to record or transmit a conversation between the announcer in the
studio and a person outside the studio being interviewed by telephone, the
telephone line must be connected to the mixing console.
In such a case, the full conversation is transmitted, since both voice signals are carried on normal 2-wire telephone lines. However, also the voice
of the announcer in the studio is then transmitted in telephone quality
(300... 3400 Hz). By mixing the microphone signal of the announcer (in
studio quality) to the conversation, the addition of the “good” and “poor”
signals results in a distorted and untrue signal.
Principle of a telephone transmission via a mixing console
The telephone hybrid allows to greatly improve the quality of a telephone
transmission by selectively suppressing the undesired “poor” announcer
signal (side-tone attenuation). This side-tone attenuation is done in principle by a hybrid circuit which is a familiar feature in telephony.
Date printed: 29.11.01 E51
Professional Audio System Components
The Studer telephone hybrid permits high-quality transmission of telephone conversations with the announcer in the studio. Apart from connecting it to the telephone line, the hybrid works automatically.
Maximum side-tone attenuation of the studio voice signal in the receiver
line is achieved by automatically constituting a dummy load for the telephone line. This adjustment is performed electronically, the real (resistive)
and imaginary (capacitive) components of the telephone line impedance
being matched as near as possible. This automatical matching process begins as soon as an announcer signal is present.
Operation with a single Telephone Hybrid Board
The telephone set is used to establish a telephone connection (call). After
switching over to the mixing console, the holding current for the subscriber’s relay is maintained by a resistor on the hybrid board.
Versions: A variety of 19” Telephone Hybrid units with one or two channels is
available, consisting of the following versions:
• Standard version (ST) – 19”/1U Telephone Hybrid unit for direct connection to the telephone line and a relay to switch the telephone line from the
telephone set to the hybrid.
• Noise gate version (NG) – same as standard version, equipped with a
noise gate
• Current-adjustable version (CA) – same as standard version, but additio nally featuring adjustable holding current for the telephone line.
Ordering Information:
Euro-cards: • Telephone hybrid card 1.915.760.xx
• Telephone hybrid card with noise gate 1.915.764.xx
19” standard products: • Telephone hybrid 1CH-ST 75.700.89118
• Telephone hybrid 2CH-ST 75.700.89228
• Telephone hybrid 1CH-NG 75.700.89114
• Telephone hybrid 2CH-NG 75.700.89224
• Telephone hybrid 1CH-CA 75.700.89116
• Telephone hybrid 2CH-CA 75.700.89226
• Telephone hybrid 1CH-CA/NG 75.700.89117
• Telephone hybrid 2CH-CA/NG 75.700.89227
E52 Date printed: 29.11.01
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