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510021
A68 PROFESSIONAL POWER AMPLIFIER
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A professional studio power amplifier
The A68 studio power amplifier has been developed to conform in every respect to professional audio standards. In addition to high quality transmission, the primary aims were reliability, stability and fail-safe protection.
Experience in professional use has provided the proof that the A68 power amplifier, with its advanced design concept, is ideally suited to other studio equipment. Dependable in continuous operation, even under extreme loading, it meets the most exacting safety requirements imposed by monitor speakers. Under sustained load conditions the A68 satisfies the stringent FTC specifications. Ample reserves are designed into the system to give excellent results and a generous safety margin in all applications and with any kind of program material.
The A68 is the ideal power transformer for studio monitoring, sound reinforcement and public address duties (in mono).
Fully complementary push-pull amplifier
The A68 studio power amplifier is fully complementary throughout all stages, from input to output. Each individual amplifier stage has strong negative feedback and employs the active push-pull principle for both positive and negative half-waves. The result is very low distortion figures even under "open loop" conditions. This means that at rated output a constant feedback factor of only 26 dB, and extending well beyond the audio range, is enough to keep distortion below 0.1%. This low "closed loop" feedback factor makes sure that the A68 performs without transient intermodulation distortion (TID). A further feature is a phase-linear low-pass filter (50 kHz) which limits the slew rate of the input signals. This filter also provides effective protection for the tweeter sections of the speakers if an amplifier ahead of the A68 should happen to oscillate. To achieve very low crossover distortion, the power transistors (6 per channel with 200 W specifications) operate with high quiescent currents. All harmonics of the fourth or higher orders are thus suppressed by more than 90 dB relative to the fundamental.
With the aid of a switch on the rear panel the A68 can be used as a mono output stage in a push-pull bridge configuration.
The output stage of the A68 is in no way critical and can handle even complex loads without difficulty. Not only can all kinds of speakers be connected, but also transformers (in mono) for 100 V PA systems (such as the STUDER line transformer 1.068.550).
High-performance protection for amplifier and speakers
Several protection circuits look after the entire amplifier and the connected loudspeakers. Being fully electronic, they are without contacts or relays.
The power dissipation of the power transistors is monitored continuously, and limited to the maximum permissible values.
The power protection circuit operates with a time lag so that, in the event of steep pulses and capacitive load, high currents can flow for a short time without the protection system responding. Limitation of the absolute current (40A), however, functions without delay. A sequence of current surges slightly below the response level also causes the system to respond, since these are integrated by the protection circuitry. The final touch is that, once the protection circuit responds, the amplifier is blocked for about 10 ms. This protects the tweeters by preventing any oscillation within the response range. The temperatures of the power pack and of the heat sinks for both channels are constantly measured. Should natural cooling be restricted and cause the temperature to reach 90°C, despite the enormous cooling area, the amplifier is muted and "Overload" is indicated. No quiescent currents then flow, so cooling is then rapid. If the temperature rises still further, perhaps because of a defect, the electronic crowbar circuit intervenes at 110°C. A powerful thyristor then short-circuits the power pack, and the main fuse blows
The loudspeaker outputs are also continuously monitored for DC components. If a DC voltage which might endanger the speakers is present for more than one second, the crowbar circuit again intervenes. The speaker outputs are then momentarily de-energized, thus safely protecting your valuable monitor speakers.
A mains supply unit with ample reserves
The power pack is a critical factor in sustained performance under load, and also in "music power" performance at low frequencies. For this reason, the A68 has a generously rated supply unit with an unusually powerful transformer and a total of 60 000 µF for the driver and output stages. The operating voltage for the other amplifier stages is provided by a separate, stabilized and short-circuit-proof power pack.
The A68 power transformer and the 100 V line transformer have the same front dimensions and both fit into a 19" rack. Brackets and rugged fixings are incorporated for this purpose. Rack mounting is easy by simply turning the brackets.
100 V line transformer (mono)
A high-performance 100 V line transformer has been developed so that the studio power amplifier can be employed in PA systems. It is designed to be used with the A68 in mono, which means that the A68 and 100 V line transformer need to be duplicated for stereo operation. This combination makes available a total of at least 700 watts rated power output (music power of over 1000 watts!).
The front dimensions of the A68 and the 100 V line transformer are identical. Both are for fitting in a 19" rack.
The A68 power amplifier in service in the STUDER local stereo studio
Technical data of STUDER A68 studio power amplifier
Technical data of STUDER 100 V line transformer
|
Rated power output:
(30 Hz 15 kHz, both channels modulated simultaneously) |
100 W per channel (8 ohms)
175 W per channel (4 ohms) |
|---|---|
|
Rated power output mono:
(30 Hz 15 kHz) |
350 W (8 ohms) |
|
Power output
at threshold of limiting: (1% THD, one channel modulated) |
150 W (8 ohms), typ.
250 W (4 ohms), typ. |
| Frequency response: |
30 Hz 15 kHz +0, -0.5 dB
20 Hz 20 kHz +0, -1 dB |
|
Inputs:
Input impedance: Input sensitivity: |
balanced and floating
≧ 5 kohms (stereo) 0 dBu +17 dBu (0 dBu ≏ 0.775 V) |
| Harmonic distortion: | less than 0.1% at all power levels up to rated output (0.05% at 1 kHz typ.) |
|
Signal to noise ratio:
(unweighted rms reading) |
better than 100 dB
referred to rated power |
|
Crosstalk attenuation:
(30 Hz 15 kHz) |
better than 60 dB (typ. 80 dB at 1 kHz) |
|
Damping factor:
(30 Hz 15 kHz) |
better than 75 (250 typ. at 1 kHz) |
| Level controls: | accessible on front panel |
| Mains connections: |
100, 120, 140, 200, 220, 240 V
Fuses: 100 140 V: 8 A slow-blow 200 240 V: 4 A slow-blow |
| Power consumption: | 100 800 W |
| Dimensions: | 483 x 133 x 335 mm (w x h x d) |
| Weight: | 20 kg |
| Test conditions: | |
| Mains voltage: | 220 V |
| Input voltage: | +6 dBu (0 dBu ≏ 0.775 V) |
| Source Impedance: | 50 ohms |
|
A68 amplifier mode:
(same level on both channels |
Bridge connected (mono) |
|---|---|
|
Rated output voltage:
(30 Hz 15 kHz) |
100 V (🛆 357 W on 28 ohms) |
|
Frequency response:
(load 28 ohms) |
30 Hz 15 kHz +0, -0.75 dB |
|
Harmonic distortion:
(30 Hz 15 kHz) |
less than 0.1% |
|
Input:
Input sensitivity: (regulated on A68) |
terminals, balanced
0 +17 dBu |
|
Output:
for loading: impedance (1 kHz): |
XLR LNE, balanced
(high-voltage version) ≥ 28 ohms < 2 ohms |
|
Dimensions:
(transformer only) |
483 x 133 x 251 mm (w x h x d) |
| Weight: (transformer only) | 22 kg |
Dimensions of A68 power amplifier
Dimensions of the 100 V line transformer
Block diagram of the A68 power amplifier
Designed and Manufactured in Switzerland
Worldwide Distribution: STUDER INTERNATIONAL AG Professional Audio Equipment CH-8105 Regensdorf, Althardstrasse 10, Switzerland Phone 01 840 29 60, Telex 58489 stui ch
STUDER REVOX AMERICA INC. Nashville, Tennessee 37210, 1425, Elm Hill Pike Phone (615) 254-5651. Telex 065230/554453 studer nas
New York Office New York N.Y. 10013, 155 Avenue of the Americas Phone (212) 255-4462
Northern California Office Walnut Creek, California 94596, 954 Hawthorne Drive Phone (415) 930-9866
Southern California Office Van Nuys, California 91401, 14046 Burbank Blvd. Phone (818) 780-4234
Dallas Office Dallas, Texas 75208, 831 Woodlawn Avenue Phone (214) 943-2239
Chicago Office Barrington, Illinois 60010, 111 South Drive, Tower Lake Phone (312) 526-1660
Obeim Hersteller Archiv Michael Otto
STUDER REVOX CANADA LTD. Toronto 17, Ontario M4H 1E9, 14, Banigan Drive Phone (416) 423-2831, Telex 06-23310 studer tor
STUDER FRANCE S.A.R.L. F-75015 Paris, 12-14, rue Desnouettes Téléphone (1) 533 58 58+, Télex 204744 studer f
STUDER REVOX GMBH D-7827 Löffingen, Talstrasse 7 Phone 07654/1021, Telex 7722118 rvox d
F.W.O. BAUCH LTD. Boreham Wood, Herts. WD6 4RZ, 49 Theobald Street Phone 01-953 0091, Telex 27502 bauch g
STUDER REVOX WIEN GES.M.B.H. A-1180 Wien, Ludwiggasse 4 Phone 47 33 09/47 34 65, Telex 11/5275 studr a
AUDIO INTERNATIONAL SRL I-20133 Milano, Viale Campania 39 Phone 02-738 47 51, Telex 335230 audiom i
STUDER REVOX FAR EAST LTD. Hong Kong, 2-12 Queen's Road West 25th Floor, Arion Commercial Centre Phone 5-441 310, Telex 60185 srfel hx
STUDER REVOX AUDIO PTE LTD. Singapore 1130, 173, Goldhill Centre Phone 2507222/3, Telex 50830 sra rs
STUDER REVOX JAPAN LTD. 1-22-2 Yoyogi, Shibuya-Ku, Tokyo 151 Phone 03-320-1101, Telex 27618 rfent j
CENTELEC EQUIPAMENTOS E SISTEMAS ELECTRONICOS LTDA. 22440 Rio de Janeiro-RJ, Av. Ataulfo de Paiva 135/1710 Phone (021) 259 36 99, Telex 2130842 cosl br
We reserve the right to make alterations as technical progress may warrant.
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