The dbx Model 160/161 are single-channel compressor/limiters designed for professional and semi-professional audio applications. They combine sophisticated technology with user-oriented features in a compact package, distinguishing themselves from conventional compressor/limiters through unique circuit designs such as true RMS level-detection and feed-forward gain reduction.
Function Description:
The primary function of both models is to control dynamic range by compressing or limiting audio signals. A compressor reduces the gain of an audio signal as its input level increases past a set threshold, thereby decreasing the dynamic range. A limiter is a type of compressor with a high compression ratio (typically 10:1 or greater, up to 120:1 for these models), maintaining an essentially constant output level despite significant increases in input level above the threshold. This helps prevent clipping distortion, raise average audio levels, and improve overall sound quality, making them suitable for recording, broadcast, and sound reinforcement applications.
The true RMS level-detection closely simulates the response of the human ear, resulting in a highly listenable and natural-sounding gain change, even at high compression ratios. The feed-forward gain reduction approach ensures complete stability and inaudible distortion, allowing for infinite compression (approximately 120:1) without the instability or oscillation issues common in conventional feedback-loop designs. This approach also enables the attack and release times to automatically "track" the signal envelope, eliminating the need for manual attack/release adjustments and preserving the naturalness of the sound.
Beyond compression/limiting, both the 160 and 161 can function as high-quality line amplifiers due to their low noise, low distortion, and high output drive capabilities.
Important Technical Specifications (Model 160):
- Input Type: Balanced (differential) transformerless.
- Input Actual Impedance: 50K-ohms (25K-ohms in unbalanced mode).
- Input Connector: Jones-type barrier strip.
- Input Maximum Level: +21dB (8.7V).
- Output Type: Single-ended, ground-compensated; suitable for driving balanced or unbalanced loads.
- Output Actual Impedance: 25 ohms (typical).
- Output Connector: Jones-type barrier strip.
- Output Max. Level Bridging (10K-ohm or greater Z): +26dB (15.5V).
- Output Max. Level Matching (600-ohms): +24dBm (12.3V).
- Output Level Adjust: ±20dB from unity gain point.
- Distortion: 0.075% 2nd harmonic at infinite compression at +4dBm output; 0.5% 3rd harmonic typical at infinite compression ratio.
- Equivalent Input Noise (Unweighted): -78dBm, typical (input shorted).
- Attack Time: Automatically varies with program level change. Examples: 15 milliseconds for 10dB level change above threshold; 5 milliseconds for 20dB level change; 3 milliseconds for 30dB level change.
- Release Rate: 120dB/second (automatically varies with program level change).
- Compression Ratio: Continuously variable from 1:1 to 120:1 (infinity).
- Threshold: Continuously variable from 10mV (-38dB) to 3V (+12dB).
- Power Requirements: 117V AC, 50 or 60Hz, 8 watts maximum.
Important Technical Specifications (Model 161):
- Input Type: Unbalanced.
- Input Actual Impedance: 25K-ohms.
- Input Connector: RCA pin jack (phono connector).
- Input Maximum Level: +17dB (5.5V).
- Output Type: Unbalanced.
- Output Actual Impedance: 100 ohms (typical).
- Output Connector: RCA pin jack.
- Output Max. Level Bridging (10K-ohm or greater Z): +18dB (6.16V).
- Output Max. Level Matching (600-ohms): +16dBm (4.9V).
- Output Level Adjust: ±20dB from unity gain point.
- Distortion: 0.75% 2nd harmonic at infinite compression at +4dBm output; 0.5% 3rd harmonic typical at infinite compression ratio.
- Equivalent Input Noise (Unweighted): -78dBm, typical (input shorted).
- Attack Time: Automatically varies with program level change. Examples: 15 milliseconds for 10dB level change above threshold; 5 milliseconds for 20dB level change; 3 milliseconds for 30dB level change.
- Release Rate: 120dB/second (automatically varies with program level change).
- Compression Ratio: Continuously variable from 1:1 to 120:1 (infinity).
- Threshold: Continuously variable from 10mV (-38dB) to 3V (+12dB).
- Power Requirements: 117V AC, 50 or 60Hz, 8 watts maximum.
Usage Features:
- Controls: Both models feature adjustable Threshold, Compression Ratio, and Output Gain controls.
- Threshold: Continuously variable from 10mV to 3V, determining the level above which compression or limiting occurs.
- Compression Ratio: Continuously variable from 1:1 (unity gain) up to 120:1 (infinity), allowing for a wide range of compression effects from subtle to hard limiting.
- Output Gain: Adjusts the output stage gain by ±20dB, independent of Threshold and Compression settings.
- Metering: An illuminated meter displays a full 60dB range and is switchable to read input level, output level, or gain change. The meter's sensitivity is continuously variable, allowing "zero VU" to be adjusted from +10 to -10dB.
- LED Indicators: Two LEDs indicate whether the input level is BELOW or ABOVE the set threshold.
- Model 160 Specifics: Features a balanced differential input, an automatic ground-loop compensated output (attenuates hum by at least 40dB), and a special protection circuit that blocks power turn-on/turn-off transients from the output. Input and output connections are via barrier strips.
- Model 161 Specifics: Designed for smaller studios or semi-pro users, it has unbalanced inputs and outputs terminated in RCA-type phono jacks. It lacks the turn-on/turn-off transient protection and ground-loop compensation of the 160.
- Stereo Tracking: Neither model is equipped for stereo strapping. dbx made a deliberate engineering decision to omit this feature, arguing that accurate stereo tracking between two separate units requires extremely tight component tolerances, which would make the units prohibitively expensive or lead to inferior performance. For precise stereo tracking, dbx recommends their Model 162, a dedicated two-channel unit.
- Physical Design: Attractively styled, both models can stand alone or be mounted in a standard 19-inch rack. Two units can be mounted side-by-side in 3½" of panel space with the optional dbx RM-150-C rack mount kit; the RM-150-D is for rack mounting a single unit.
Maintenance Features:
- Meter Calibration: The meter is factory calibrated to read "0" at +4dB (1.23V) output level. It can be recalibrated by the user via a rear panel potentiometer to match desired nominal operating levels (from -10dB to +10dB).
- Warranty: All dbx products are covered by a Limited Warranty. Users are advised to consult their warranty card or local dealer for details.
- Factory Service: For additional assistance, service information, or special applications, users can contact the dbx Customer Service Department. If factory service is needed, units should be repacked with a note describing the problem, shipped freight prepaid and insured to the dbx Repair Department. For international service, contact the nearest dbx dealer.
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