We have tested the entire system and aside from the normal wear and noisy pots most of these modules are in good working order.
Please note that 2 of the 903 Limiters have no output and a third module needs a replacement Bypass switch.
Here's some general information from dbx:
The Model 903 Compressor gives you all the features you'd expect from dbx. And then some. For starters, you
have at your command a unique new negative compression feature that actually begins reducing output volume once the threshold is exceeded. Signals are given a new and unusual sense of "punch." And the 903, like our acclaimed 165A is an Over Easy® compressor, with a soft knee threshold that increases compression ratio gradually over a range of several dB. It features true RMS level detection, continuously variable compression ratios, and a threshold that's adjustable from -40 dB to +20dB.
Input impedance: balanced = 25 k-ohms, un-balanced = 18.5 k-ohms
Output impedance: 22 ohms, designed to drive 600 ohms or more
Maximum input level: +24 dBm
Maximum output level: +24 dBm into 600 ohms or more
Frequency response: 20 Hz-20 kHz ± 1 dB
Distortion: at infinite-compression, 1 kHz, 0 dBm, typically 0.05% 2nd harmonic and 0.2% 3rd harmonic
Equivalent input noise: -88 dBm, 20 Hz-20 kHz, unweighted
Attack rate: program- dependent; to achieve 63% gain reduction, measured in the infinite-compression region of
the Over Easy curve, 15ms for 10dB above threshold and 5 ms for 20 dB above threshold
Release rate: 120 dB/sec
Threshold: variable from -40 to +20dBm (7.75 mV to 7.75 V)
Compression ratio: variable from 1:1 through infinity:1 to —1:1
Output gain: variable, -20 to+20dB
Detector input impedance: balanced = 250 k-ohms, unbalanced = 185 k-ohms
Controls: THRESHOLD, RATIO, OUTPUT
Switches: IN/Out
The Model 904 Noise Gate is the ultimate noise gate, with a combination of features not found on any other noise
gate, at any price. It features adjustable attack and release rates, threshold adjustment from -40 to +10 dB,
attenuation limit adjustment from 0 to 60 dB, with dbx Over Easy* downward expansion for a smooth sound. It also
features a KEY input that allows gating of one instrument by another.
The special PLM mode of the 904 allows users without automated consoles to put threshold programmed
muting on solo channels. After the user sets the correct solo level on the console, the 904 will automatically keep
the channel muted, eliminating spurious signals which frequently precede the solo itself. When the solo begins,
the 904 will un-mute the channel, allowing the solo into the mix at the pre-set level.
Input impedance: balanced = 25 k-ohms, un-balanced = 18.5 k-ohms
Output impedance: 22 ohms, designed to drive 600 ohms or more
Maximum input level: +24 dBm
Maximum output level: +24 dBm into 600 ohms or more
Frequency response: 20 Hz-20 kHz (+0,-1dB)
Total harmonic distortion (THD): less than 0.02% at 1kHz
Equivalent input noise: -82 dBm, 20 Hz-20 kHz bandwidth, unweighted
Attack rate: variable, 500 dB/ms to 2.5 dB/ms
Release rate: variable, 2.5 dB/ms to 22 dB/sec
Threshold: variable, -40 to +10 dB (7.75 mV to 2.5 V)
Expansion ratio: variable, 1.5:1 to 5:1
Maximum attenuation: more than 60 dB
KEY input impedance: balanced = 250 k-ohms, unbalanced = 185 k-ohms
Controls: ATTeNuation LIMIT, RATIO, THRESHOLD, ATTACK, RELEASE
Switches: IN/Out, PLM, KEY
The Model 905 Parametric Equalizer offers a unique degree of equalization flexibility in a high density format without
sacrificing true, fully parametric operation of all three filter bands. The overlapping bands each offer control of frequency, bandwidth (0), and up to 15 dB of reciprocal cut or boost to provide exact, complementary filter action for most equalization needs. For problem situations requiring the removal of spurious signals, each of the bands can be independently switched into "infinite notch" mode without affecting the operation of the others. In situations where a shelving equalizer will produce better results than a peaking one, the 905's high and low bands can be independently switched from peaking to shelving operation. The entire unit may be switch bypassed for instant before/after comparisons. The 905 is the complete equalizer package right at your fingertips.
DD Three bands of EQ in one package permit exceptional flexibility, allow precise shaping of frequency curve DD Each band has controls for reciprocal boost/cut (up to 15 dB), bandwidth (Q), and frequency center DD "Infinite" notch switch on each band lets you remove unwanted narrow-band signals without affecting adjacent frequency information DD Peak/shelf switch on high and low bands gives great flexibility in shaping the ends of the curve DD Panel layout allows easy access to all critical controls DD Multipoint overload sensing helps you eliminate clipping by showing when overload occurs at any point in the unit.
Input impedance: balanced = 25 k-ohms, unbalanced = 18.5 k-ohms
Output impedance: 22 ohms, designed to drive 600 ohms or more
Maximum input level: +24 dBm
Maximum output level: +24 dBm into 600 ohms or more
Frequency response: 20 Hz-20 kHz (+0,-1dB)
Total harmonic distortion (THD): under any boost or cut condition, less than 0.03% at 1 kHz
Equivalent input noise: -88 dBm, 20 Hz-20 kHz bandwidth, unweighted
Filter type: each band symmetrical peak/dip; each switchable to notch mode; high and low bands switchable to symmetrical shelving
Center frequencies: low band = 20-500 Hz; middle band = 200-5 kHz; high band = 800-20 kHz
Range: ±15 dB, peak or shelved
Notch attenuation: more than 40 dB at maximum Q, greater at minimum Qs (typically-70 dB)
Controls: FREQuency, Q, boost/cut (each band)
Switches: IN/Out, Shelving (two bands), "Infinite" notch (all bands)
