HOC1 Opto Compressor/Limiter User Manual: REV 2014A

HOC1_OM_03

OVERVIEW

The Hamptone HOC1 opto compressor limiter has pure discrete class A JFET, transformer balanced (In and Out) signal path.  It provides parallel gain paths for the direct and compressed signals via independent JFET amplifiers (to maintain optimum phase alignment), which are then summed in a final JFET gain stage.  Each gain stage has independent bias and gain control for precise internal factory calibration.  Each unit can be operated independently, or as a stereo pair with a sophisticated yet easy to set up stereo linking circuit.  When linked, all compression settings are passed to one set of controls (on the “send” unit) for accurate matching, and can be easily toggled to the other unit to create two settings (by toggling simultaneously the “send” / “receive” switches on both units).  This provides “A/B” settings, and can be toggled on the fly without artifacts to instantly change the compression characteristics between two different settings.  Unique to the HOC1 is the SHAPE control, which applies a mathematical transfer function to the detector output changing the compression vs input signal.  Rather than the characteristics being set, or a simple “knee” control, the detector voltage has 4 curves that are “morphed” with the shape knob in pairs: Exponential vs. Logarithmic, and Hard limit vs. Linear (depicted by the two small graphs on the front panel).  Though the HOC1 can create a vast palette of compression characteristics, the main design philosophy was to make it simple and intuitive to use.

FRONT PANEL CONTROLS:

  1. MAIN IN/OUT: True balanced hardwire bypass.
  2. DIRECT SIGNAL: Gain control of direct signal.
  3. COMPRESSED SIGNAL: Gain control of compressed signal.
  4. FF/FB: Feedforward vs. Feedback.  Feedforward is where the signal that drives the compression circuit is taken before the opto compression circuit, or equivalently from the “direct” signal path.  In this mode, the signal sent to the compression circuit is not affected by the amount of compression.  In Feedback, the signal sent to the compression circuit is taken after the opto compression circuit, making the signal dependent on the amount of compression.  That is when the unit compresses, the signal into the detector is reduced due to the compression, and the overall compression decrease.  This results in a feedback loop which has certain sonic consequences.  On some signals, there may be little difference, but on certain signals (like drums), the difference can be profound.  Both methods have there place historically and today, so the unit was designed with the option.
  5. THRESHHOLD: Input gain to the detector circuit, defines the threshold at which compression begins.
  6. RATIO:  The output gain of the detector circuit, defines the maximum range the opto pad will compress.  Threshold and Ratio work in concert to produce the total overall compression, but just like the “pre” and “post” knobs on an amp, have profoundly different consequences when one is set hi and the other low.
  7. SHAPE:  Applies a mathematical curve to the output to the AC to DC detector.  There are 4 internal curves (which are mathematical algorithms) that are grouped in pairs: Exponential/Logthrithmic and Hard limit/linear.  The shape knob varies continuously between them.  Like the FF/FB knob, on certain signals the difference is subtle, but on others it has been described as “I feel like I am moving the mic around”, where difference transients begin to “pop”.  For advanced users, we can provide a spreadsheet that you can design your own curves for a minimal re-programming fee.
  8. ATTACK: Attack time of the detector circuit.  The compression circuit uses two cells running in a “servo”, which has numerous benefits: vastly increased response time (1.5mS for -20dB comp), temperature stability, and improved linearity.  Attack times on the front panel indicate the time it takes to achieve the target compression point (not 90% which is often used).
  9. RELEASE: release time of detector circuit.  The release of the opto circuit is designed to be linear dB/sec.  Release times on the front panel are the time it takes to release from a full -20dB compression.
  10. STEREO LINK: Enables the link control logic (LCL) allowing two units to operate in unison.
  11. LINK STATUS DIODE (LSD):  Tricolor Led indicates control mode: off=no linking, green=”send”, red = “Receive”, toggle red/green= error: both units in “receive”, yellow= other error conditions:  link cables (two TRS) not connected, TRS cable is actually a TS, open or shorted cable, one unit off.…
  12. SEND / RECEIVE: determines which unit “sends” information and which one “receives” it.  In addition to the typical stereo linking mode, there are several valid “1/2” modes listed in the “ADVANCED STEREO LINK” section found later in this manual.
  13. DET HP: Pre detector hi pass filter.  Internally adjustable (see ADJUSTMENTS and CALIBRATION)  from -6dB @ 75Hz to 150Hz, factory set to 75Hz.
  14. METER MODE:  Selects the mode of the 20 segment display: Gain reduction -> Gain reduction with peak hold -> VU -> VU with peak hold.  Each time the button is pressed, the meter mode advances, the mode is indicated with a brief “blink” of the -20 (“GR”), -18 (“GR PK”), -17 (“VU”) or -16 (“VU PK”) led with text written to the right.  When in the peak hold modes, holding the button for longer than 0.7 seconds will reset the peak, but not advance modes.  The Led next to the appropriate peak mode will blink briefly to confirm the mode has not advanced.  The VU meter circuit measures the balanced signal at the output connector.  Therefore, when the unit is bypassed (in/out switch “1” out), the VU meter displays the input signal, when the unit is engaged, it displays to output.
  15. 20 SEGMENT METER: Hi accuracy multimode Led display.  Though mechanical meters are “sexy”, they are generally inaccurate in comparison, fragile, and limited in response time.
  16. VU CAL:  Allows the VU modes to be calibrated for external devices.  Factory set to hit the first red LED at 20Vpk-pk, which is the point where the compressor itself begins to enter its non linear region.  This is generally well beyond the level needed for DAWs and Tape machines.  Beyond this point the compressor still has good linearity and low THD for another 6dB, but will begin to exhibit some JFET compression, which many people find to be both musical and often desirable.
  17. SHAPE MODE:  Selects between the two curve sets, Exp/Log, Limit/Linear.  The two graphs on the front panel show the various curves.  Beneath the SHAPE control are two symbols, the blue circle (bunny hill) and the red rotated square (red diamond) that show which curve is which.  The compression characteristics are designed to get more pronounced as you turn the SHAPE knob CW.

REAR PANEL INPUTS/OUTPUTS:

  1. IN: Transformer balanced input.  Connected directly to OUTPUT when I/O switch is out (i.e. hardwire bypass).  Tip=audio+, Ring=audio-
  2. OUT: Transformer balanced output.  Connected directly to INPUT when I/O switch is out (i.e. hardwire bypass). ).  Tip=audio+, Ring=audio-
  3. COM2: Connect to COM2 on second unit with a TRS cable for stereo linking.  Also see “ADVANCED STEREO LINKING” section for additional modes.
  4. COM1: Connect to COM1 on second unit with a TRS cable for stereo linking.  Also see “ADVANCED STEREO LINKING” section for additional modes.
  5. PRE DETECTOR INSERT: TRS, Tip=send, Ring=return, unbalanced.  Can be used to patch an external EQ prior to the detector circuit to make the compression frequency selective.  The HP control on the front panel follows the insert, and works independently.
  6. MAIN POWER SWITCH: Turns the power on/off (duh).
  7. FUSE HOLDER: 0.5A, slow blo
  8. AC POWER INPUT (IEC): 110/120vac or 220/240vac power input.  Hardwired internally, can be easily changed.

ADVANCED STEREO LINKING:  Two HOC1 units can be stereo linked to operate as a pair.  Linking is performed by connecting COM1 (communication1) on one unit to COM1 on the second, and COM2 to COM2 via two TRS cables.

COM1:  carries the Feedforward (tip) and Feedback (ring) voltages, fed from each unit through equal resistance values.  The result is the signals on the Tip and Ring will be the FF and FB voltages from one unit, the second, or the sum of the two depending on the link switch settings.  You should not connect this jack to anything but “COM1” on another HOC1.

COM2:  The Tip is a bidirectional pin (direction relay controlled within each unit) that carries the DC modulation voltage for the Opto pad circuit.  Its range is 0-5VDC, 0vdc=0dB compression, +5vdc=-20dB (or 4dB/VDC).  The ring is a multistage logic pin, whose voltage is dependent on the position of each units SEND/RECV switch.  The Link Control Logic (LCL) in each unit knows its own switch position, and can determine the other units switch position by the DC voltage on the shared node. .  You should not connect this jack to anything but “COM2” on another HOC1.

LINK ENABLE SWITCH OFF NOTE:  To keep the setup intuitive, yet offer various linking options, when the “Link Enable” is out or off, a few things happen: the unit runs solely off its own internal modulation voltage (ignores COM2-tip), it will be fixed in send mode (though led is off), and all compression settings will come from its own controls.  This way, if a unit is not link enabled, it cannot be affected by settings on the second unit.   In addition to the normal stereo link mode, there are several valid “1/2” or “sidechain” modes.  Table 1 summarizes the modes.

 

TABLE 1: HOC1 STEREO LINKING MODE TABLE vs FRONT PANEL SWITCH POSITIONS REV_E.01
2/3/2014
FRONT PANEL SWITCH SETTINGS RESULTING CONFIGURATION
HOC1 #1 SWITCHES HOC1 #2 SWITCHES UNIT #1 UNIT #2
MODE LINK ENABLE SEND/RECV LINK ENABLE SEND/RECV LED COMP SOURCE LED COMP SOURCE
1 OUT X OUT X OFF #1 OFF #2
2 IN X OUT X RED #2 OFF #2
3 OUT X IN X OFF #1 RED #1
4 IN SEND IN RECV GREEN SUM #1 & #2 RED SUM #1 & #2
5 IN RECV IN SEND RED SUM #1 & #2 GREEN SUM #1 & #2
6 IN SEND IN SEND GREEN SUM #1 & #2 GREEN SUM #1 & #2
7 IN RECV IN RECV R / G #1 R / G #2
MODE DESCRIPTIONS X=DON’T CARE
1 LINKING OFF
2 HOC1 #1 CHASES #2 (i.e. sidechain), #1 AUDIO DOES NOT AFFECT COMPRESSION
3 HOC1 #2 CHASES #1 (i.e. sidechain), #2 AUDIO DOES NOT AFFECT COMPRESSION
4 HOC1 #1 CONTROLS BOTH UNITS, COMPRESSION IS BASED ON THE SUM OF BOTH UNITS, NORMAL MODE OF OP
5 HOC1 #2 CONTROLS BOTH UNITS, COMPRESSION IS BASED ON THE SUM OF BOTH UNITS, NORMAL MODE OF OP
6 #1 AND #2 CONTROLS BOTH ACTIVE, EACH UNITS WORKS OFF ITS OWN CONTROL SETTINGS, COMPRESSION BASED ON THE SUM
7 INVALID: BOTH UNITS CAN’T RECEIVE, LOGIC FORCES EACH UNIT INTO “SEND”, LED TOGGLES GREEN/RED TO INDICATE ERROR
ADDITIONAL NOTES
1 LEDs WILL TURN YELLOW FOR MOST INVALID WIRING CONNECTIONS

HOC1 Opto Compressor/Limiter User Manual: REV E.01B