Compressor setup procedure
1. Set LA to Threshold pot fully CCW, Makeup pot to CCW. Ratio switch to 3:1, Meter switch to VU, HPF switch to FLAT.
2. Apply 1kHz tone to LA500A input so you have the reference level of +4dBu (1.23vac) on the LA500A output between pin 2 & 3 of the XLR.
3. Or plug LA500A output into VU or PPM meter that is calibrated to 0VU = +4dBu. If voltage not correct adjust 1kHz generator level until correct.
4. Adjust meter 0VU trim pot for desired level for 0VU on the meter.
5. Switch Meter switch to GR and adjust Zero GR trim pot for 0VU on meter.
6. Turn up Threshold pot until you have 5dB of compression on meter.
7. Switch Meter switch between GR and VU and adjust Balance trim pot until the same reading is seen in both GR and VU.
8. Your ready to rock
LA500A opto comp stereo matching mode.
1. Check Both LA500 comp alignments are correct.
2. With 1k tone of same level into both LA500 comps set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on meter and switch to GR to check you have -5dB showing on both meters.
3. Link the comps. If meters move away from each other by more than a +/-1dB move jumper to MATCH end on the compressor which shows more gain reduction on the meter.
NOTE: If comps were bought together you will have an already matched pairs . If comps are very different when linked due to be ordered at different times or batches it is best to swap U1 from one comp with U2 of the other and realign before resorting to stereo match mode.
Original balance trim pot will now adjust GR meter level when switched to GR (U2 audio opto) and new ST Match trim pot R18 will adjust VU meter level when switched to VU (U1 meter opto)
Image
1. Setup both comp with 1k tone and set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on meter.
2. Turn threshold pot off on modified comp (fully CCW)
3. Link the comps. Adjust modified VU trim pot until both comps show the same VU meter readings.
4. Switch both comps to GR and adjust modified comp new GR pot until both comps show same GR meter readings.
5. Your comps should be matched.
To check match
1. With 1k tone of same level into both LA500 comps set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on meter and switch to GR to check you have -5dB showing on both meters.
2. Link the comps. If meters move away from each other by more than a +/-0.5dB trim modified comps New GR & New VU trim pot until perfect match when linked.
—————————–
The link switches on the back of the 8 way API box are audio in and out linking between each modules in and out and have nothing to do with the compressor link.
The 8 way box like the New 6 way API box have all comp link edge connector pin 6 linked across the back panel by zero ohm resistors.
So if you have only one pair of comps in the rack you do not have to do anything to link a pair.
Set both LA500 to the same settings and adjust threshold for the same GR reduction and pull both makeup pots outwards so they are linked.
If you have more than 1 pair of comps in the rack cut out the link resistor between the pairs of comps to isolate the 2 sets of comps link edge connector pin 6’s
Usually when setting up racks here cut out ever second zero ohm link resistor so 1&2, 3&4, 5&6, 7&8 link pins are left connected in pairs.
The zero ohm resistors in the 8 way box are numbered R21 to R27. So to set for pairs like above. Remove R22, R24, R26.
——
if you have only one pair of comps in the rack, you don’t have to do anything to link a pair, they just need to be next to each other.
Set both LA500A to the same settings (switch and threshold) adjust threshold for the same GR reduction and pull both makeup pots outwards so both blue link leds are on.
The sidechains are now linked. Works like all old 1176 1178 LA2A and LA3A linking does.
Two linked compressors will both attenuate the signal the same amount if there’s a signal that goes above the threshold on the left (or right) side only.
That’s to avoid tilting the stereo image one way, which would happen if you only compress one side of the signal. (two unlinked compressors).