APHEX EQF-2 Parametric Equalizer Filter User Manual
- June 13, 2024
- APHEX
Table of Contents
EQF-2 Parametric Equalizer Filter
User Manual
EQF-2 Parametric Equalizer Filter
- Tunable Peak/Shelf EO
- Tunable Hi/Lo Pass Filter Modular (Retrofits to Industry Standards)
- Full Band (20Hz to 20kHz)
- Constant Bandwidth ( 1.5 Octave)
- Reciprocal Equalization Curves (Cut/Boost)
- Resolution (Expanded 600 Cut/Boost)
Well established in major studios internationally, the EOF-2 is available
through the worldwide sales offices of Apex Systems Ltd.
To fix that difficult guitar or that impossible bass drum, or simply to get
that “just right” sound, the EOF-2 has proven itself to be a powerful I and
creative tool.
The design engineers at Apex are also experienced musicians and studio
personnel, and they listen to what they design. One cannot determine what a
piece of gear sounds like by looking at a graph. The EQF-2’s curves were
chosen for the way they sounded not how they looked. The “music first”
philosophy carries through all Apex products, because good music is what it’s
all about in the first place.
SPECIFICATIONS
INPUT SPECIFICATIONS:
HIGH LEVEL INPUT Z = 34K OHM; MAXIMUM INPUT LEVEL = +30dBm LOW LEVEL INPUT Z =
IK OHM; MAXIMUM
INPUT LEVEL = +20dBm
OUTPUT SPECIFICATIONS:
HIGH LEVEL OUTPUT AT CLIPPING = +30dBm L.OW LEVEL OUTPUT AT CLIPPING = +20dBm
NOISE OUTPUT (INPUT SHORTED) HIGH LEVEL OUT = 93dBm LOW LEVEL OUT = -103dBm
TRANSFORMER (OUTPUT) RJE. 123 AL (OPTIONAL) (OUTPUT SPECIFICATIONS WITH
BIPOLAR 16 VOLT SUPPLY.)
FREQUENCY RESPONSE:
EQUALIZERS AND FILTERS OUT OF CIRCUIT +0.1 dB, 10 TO 20,000 HZ. EQUALIZERS AND
FILTERS IN CIRCUIT, MIN. 1MUM EQUALIZATION, MAXIMUM BANDWIDTH: -1 dB, 20 TO
20,000 HZ. FILTER AND EQUALIZER CHARACTERISTICS:
HIGH PASS TUNING (2ND ORDER BUTTER WORTH); = 20 TO 500 HZ FLAT PASS BAND.
LOW PASS TUNING (2ND ORDER BUTTER WORTH) I TO 20 KHZ FLAT PASSBAND, LOW
FREQUENCY EQUALIZER: 25 HZ TO $00 Hz ±12dB (PEAKING & SHELVING) MID FREQUENCY
EQUALIZER: 250 TO 5,000 Hz ±12dB
HIGH FREQUENCY EQUALIZER: I KHZ TO 20 KHz ±12dB (PEAKING & SHELVING) TRUE
RECIPROCAL BOOST/CUT SWITCHING ON ALL THREE EQ RANGES. SEPARATE EQUALIZER AND
FILTER IN/OUT SWITCHING, 
DISTORTION AND TRANSIENT RESPONSE:
HARMONIC AND L.M. DISTORTION ARE LESS THAN 0.I%
SLEW RATE: GREATER THAN IO VOLTS PER MICROSECOND.
OVERSHOOT ANT. RINGING: NEGLIGIBLE, WITH OR WITHOUT LOADING
MECHANICAL DATA:
THE EQF-2 I AN ELECTRO-MECHANICAL RETROFIT FOR AENGUS, APSI, AUTO-. MATED
PROCESSES, MODULAR AUDIO PRODUCTS, AND MELCOR EQUALIZERS. FRONT PANEL: 5.25 IN
» LS IN, (13.3 CM. 3.8 CM.)
DEPTH: 6 IN. (5.2 CM.)
WEIGHT: 2 LB. (0.9 KG.)
POWER REQUIREMENTS:
±12VOLTS TO ±I8 VOLTS AT 75MA MAXIMUM CURRENT AND 1% OR BETTER RIPPLE.
EDGE CONNECTOR:
I5 PIN, A4MM SPACING
| 1 | CHASSIS GND |
|---|---|
| 2 | HIGH LEVEL OUTPUT |
| 3 | LOW LEVEL OUTPUT |
| 4 | OUTPUT LOW SIDE |
| 5 | POWER COMMON |
| 6 | SPARE |
| 7 | SPARE |
| 8 | INPUT Low SIDE |
| 9 | LOW LEVEL INPUT |
| 10 | HIGH LEVEL INPUT |
| 11 | GAIN TRIM |
| 12 | POWER IN |
| 13 | POWER SUPPLY |
| 14 | COMMON |
| 15 | POWER IN |
| 16 | SPARE |
GAIN ADJUSTMENT IS ACCOMPLISHED BY
RESISTOR TO POWER COMMON. GAIN INCREASES AS FOLLOWS
4.7K = +2dB, 16K + +4 dB,
0.62K = +6dB, 0.IK = +8 dB
EOF-2 BLOCK DIAGRAM
EO-F 2 SIGNAL PATH
NO TRANSFORMER **
**
DC OFFSET CALIBRATION PROCEDURE
If it ever becomes necessary to replace one of the op-amps, this procedure will re-null the overall d.e. offset of the EQF-2. See drawing for test points.
- Attach noise filter to input of oscilloscope.
- Set scope on 5mv. per division scale and DC.
- Ground scope to an audio Gnd. on EQF-2 test cable.
- Turn all EQ knobs fully clockwise.
- Attaches. lead from noise filter on scope to either of the center pins of SW2 (“EQ” switch) on EQF-2.
- Engage “Filter” on EQF-2 and adjust “Position” knob on scope for center or “p’ line of the screen. This is your DC reference.
- Disengage “Filter” and adjust ‘Trumpet One” on EQF-2 so line matches with reference. When aligned properly, line will not move when ‘Filter” is engaged/disengaged.
- Engage “EQ” on EQF-2 and adjust ‘Trumpet Two” so line matches with reference. (As in step #7).
- Double check that when “EQ” or “Filter” is engaged or disengaged the line stays stationary.
NOTES ON ABOVE
- If DC is so far out of alignment that it cannot be calibrated by either trimpot, try swapping some of the #351 IC’s around (usually #2 with #9 or ll with #9 works best). After moving IC’s around re-calibrate DC.
- If possible, avoid calibrating so trimpot is at end stops. You should have enough adjustment left in trimpot to be able to pass reference line by at least 5mv. If this is not possible see “Note One”.
DC CALIBRATION HINT
To aid in getting accurate DC readings with high scope sensitivity, we
recommend constructing a simple low pass (noise) filter as described below .
APH€X SYSTEM LTD.
R-1 MODULAR INTERFACE
The R-1 is a compact rack mount package designed to hold ten EOF-2 or CX-1
size packages. The R-1 backplane provides barrier strip access to all inputs
and outputs; power and ground are bussed.
PS1 POWER SUPPLY
The PS-1 is a rack mount power supply designed to complement the R-1 in
looks and function. Its ± 16V @3.0 Amps will adequately power anything the
RR-1 can hold. Your modules are protected by built – in Over Voltage
Protection and illuminated circuit breaker/power switch. 
- SUPPORTS 4 APHEX AUDIO MODULES
- ALL PATCH POINTS ON REAR (¼” and T-T SIZES)
- SELF-POWERED FOR 115-230V
- EXTREMELY COMPACT AND PORTABLE FOR THE ENGINEER/PRODUCER ON THE GO
- HI/LO LEVEL SELECT FOR EACH INPUT/OUTPUT
SPECIFICATIONS
DC SUPPLY –REGULATED ± 16V @ 500mA
POWER REQUIREMENTS- 115-230 V.A.C., 25 WATTS
SIZE -5. 75″ H x 11 WX 7 .75″ D (EXCL. KNOBS)
WEIGHT- (EMPTY) 9 lbs., 2 oz.
4B-1 SELF POWERED
MODULAR MINI-RACK
7801 Melrose Avenue · Los Angeles, California
90046·213-655-1411·
TWX:910-321-5762