Ashly SC-50 User's Manual
Contents
1. The Ashly Audio SC 50 Peak Limiter Compressor is used to place a ceiling on the peak level of program material When peaks exceed this ceiling gain is reduced to keep peaks within specified limits The amount of reduction how fast reduction takes place and the speed at which levels are returned to normal are all precise and independent adjustments This makes the SC 50 extremely useful for loud speaker protection broadcast limiting or com pression tape to disc transfer special effects vocal level control and musical instrument sustain FEATURES Extremely low noise and distortion Detector patch point for frequency selective limiting Stereo tie patch point for accurate stereo or quad tracking when multiple units are used Double time constant release action e Accurate and specific control calibrations Inputs and outputs that can be used balanced or unbalanced e Rugged 16 gauge steel chassis e n out bypass switching Cun STEREO TE fo DETECTOR PATCH O0 Rome SEND RETURN RERUN aa 1 2 AMP NOVAC nW 3 y CTC SHOCEH ASHLY 00 NOT OF O USER SERVICARL 50 60 Hz p z OCH NY U ot SE FUSE MODEL x 6 rece The two important components of the SC 50 are the VCA Voltage Controlled Amplifier and the Detec tor The Ashly SC 50 VCA is an all NPN current ratio multiplier circuit using integrated supermatch transistor pairs It has low noise 90 dBV low distortion 05 excellent2. release time INPUT IMPEDANCE OUTPUT IMPEDANCE DETECTOR PATCH POINT 30dB 2 1 00 200uS 20 mS 400 mS 2S 10KQ balanced bridging 5022 term with 600 Q or more allows the connection of an equalizer in the detector loop to produce frequency selective limiting MAX IN OUT LEVEL 20dBm FREQUENCY 5dB 20Hz 20kHZ RESPONSE DISTORTION lt 05 THD OdBV 20Hz 20kHz no limiting lt 2 418dBV worst case HUM AND NOISE 90dBV unity gain POWER 120 VAC 50 60Hz 5W SIZE 19 L x 1 3 4 H x 6 D SHIPPING WEIGHT 8 Ibs
3. response time and track ing and does not suffer from thermal drift It is a little complex there are 5 supporting op amps involved but today s low cost high quality op amps make this feasible The circuit is consistant in mass produc tion with no trimming or hand selection of transistors necessary On the surface it would seem that the VCA is more critical than the detector since audio passes through the VCA and the detector only provides it with a control voltage However experience showed us that both are crucial to the overall sound The detector must constantly adjust the gain of the audio path ina manner which keeps the level under control while sounding acceptable to the listener This constantly changing gain is a DYNAMIC action and conventional audio measurements like noise and distortion checks are static constant level This led us to use a purely subjective approach in the design of the detector we did a lot of listening to determine what sounded good and what didn t As a result of this research we designed the detector to let the attack and release times speed up as more and more limiting occurs the compression ratio also increases and a double release time constant was incorporated to minimize pumping and breathing STEREO TIE Our RATIO ATTACK DETECTOR rere RELEASE GAIN REDUCTION INDICATORS LED s er SPECIFICATIONS CONTROLS defeat switch gain ratio attack time
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