LA500A opto comp MAY 2021 BUILD THREAD 500/51X

[Joe Malone]

I wish people who already did build the compressor would also be active here to help, like on other forums. Without this help there's no way I can finish the calibration procedure.
I'd do a video showing each step if I get to finish. This is the best way to know what to do and it saves further builders having to ask for help.

You haven't fitted the jumper shunt to short the 2 pins together so the balance pot is not connected on one side so calabration cannot be done.

missing jumper shunt.png

LA500SCv2 800 67.jpg

[batchas]

You haven't fitted the jumper shunt to short the 2 pins together so the balance pot is not connected on one side so calabration cannot be done.

Thank you very much Joe for your help. I thought the jumper was for stereo matching. I'll install tomorrow then and continue the calibration.

[batchas]

I installed the jumper and I was able to finish the first calibration part and move to the LA500A opto comp stereo matching mode part.

1. Check Both LA500 comp alignments are correct.
2. With 1k tone of the same level into both LA500 comps set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on the meter and switch to GR to check you have -5dB showing on both meters.

1 & 2 OK.

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.

When I link the 2 comps, both set set to -5dB, the second one is then now -2.7db. Which is more than +/-1dB difference.
The one showing more gain reduction is the first comp in my setup. But if I move the jumper to MATCH on this one, then the difference between both compressors will be even greater.
Do you think I didn't install properly the matched pair of optocouplers that came with the pair of comps?

BTW your text says:
"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"
But there's no image

[Joe Malone]

I installed the jumper and I was able to finish the first calibration part and move to the LA500A opto comp stereo matching mode part.

1. Check Both LA500 comp alignments are correct.
2. With 1k tone of the same level into both LA500 comps set 0VU on meter switched to VU and turn up Threshold pot to get -5dB on the meter and switch to GR to check you have -5dB showing on both meters.

1 & 2 OK.

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.

When I link the 2 comps, both set set to -5dB, the second one is then now -2.7db. Which is more than +/-1dB difference.
The one showing more gain reduction is the first comp in my setup. But if I move the jumper to MATCH on this one, then the difference between both compressors will be even greater.
Do you think I didn't install properly the matched pair of optocouplers that came with the pair of comps?

BTW your text says:
"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"
But there's no image

Sounds like the Optos are not in the correct places but first with the comps off check both meters show exactly -20. If not use screw adjust at the bottom of the meter front to set -20.

And recalibrate twice. If still out by greater +/-1dB then you can move the jumper over one pin so then balance / gr trimpot will set -5 gr and stereo match vu trimpot will set -5 vu and see if this then matches when linked.

[batchas]

Sounds like the Optos are not in the correct places but first with the comps off check both meters show exactly -20. If not use screw adjust at the bottom of the meter front to set -20.

And recalibrate twice. If still out by greater +/-1dB then you can move the jumper over one pin so then balance / gr trimpot will set -5 gr and stereo match vu trimpot will set -5 vu and see if this then matches when linked.

I had to check the text on the optos bags to be sure I didn't put 2 optos from bag 1 on first comp and 2 optos from bag 2 on second comp. But the text on the bag is very explicit, so I have no doubt I did it right.As I mentionned earlier though, having the white dot facing to the same direction for all optos, one of the 4 optos does not show the same orientation of the text on its surface.

So optos in the right place (if white dot on one of the optos is placed correctly).
I checked again and both meters show exactly -20.
I recalibrated twice.
And I go back to where I was.
I'm sending you a link to a video in private. Showing the all process in 2min40. And why I'm stucked.

[Joe Malone]

Sounds like the Optos are not in the correct places but first with the comps off check both meters show exactly -20. If not use screw adjust at the bottom of the meter front to set -20.

And recalibrate twice. If still out by greater +/-1dB then you can move the jumper over one pin so then balance / gr trimpot will set -5 gr and stereo match vu trimpot will set -5 vu and see if this then matches when linked.

I had to check the text on the optos bags to be sure I didn't put 2 optos from bag 1 on first comp and 2 optos from bag 2 on second comp. But the text on the bag is very explicit, so I have no doubt I did it right.As I mentionned earlier though, having the white dot facing to the same direction for all optos, one of the 4 optos does not show the same orientation of the text on its surface.

So optos in the right place (if white dot on one of the optos is placed correctly).
I checked again and both meters show exactly -20.
I recalibrated twice.
And I go back to where I was.
I'm sending you a link to a video in private. Showing the all process in 2min40. And why I'm stucked.

OK I watched the video but it doesn't show you recalabrating when you switched the BAL Match jumper over.

So the comp when linked that showed more compression has the BAL MATCH moved towards the back of the pcb and then using its ST MATCH VU trimpot while the comps are linked and switched to VU -5dB you can trim the VU to match the normal comp. Then switch both comps to GR and adjust BALANCE / GR trimpot so both comps GR -5dB match.

When you link the meters will most likely move away from each other and while you are doing the adjustment they will both comp back to -5dB. So when linked out of adjustment normal comp could go up to -1dB and the second comp you are adjusting could go to -10dB. As you turn the trimpots as mentioned above the the 2 meters will head back to -5dB so no threshold or makeup pots should be touched after setting comps to -5 GR and VU.

Only trimpot adjustments are done on the comp you moved the BAL MATCH jumper on.

[batchas]

OK I watched the video but it doesn't show you recalabrating when you switched the BAL Match jumper over.

So the comp when linked that showed more compression has the BAL MATCH moved towards the back of the pcb and then using its ST MATCH VU trimpot while the comps are linked and switched to VU -5dB you can trim the VU to match the normal comp. `

This is what I am trying to say. I alm terribly sorry I can't find a better way to communicate. The ST MATCH VU trimpot does nothing if I turn it (I checked soldering it's ok). This is why I need confirmation about the details. Like which comp left (ch 7 in my setup) or right (ch 8 in my setup) we are talking about, not "the one with more compression" because obv. there's something I do not understand correctly and I need to understand.
Like for instance "BAL MATCH moved towards the back of the pcb". I'm not english speaking. For me the back of the PCB is parallel to the jumper, so it's either move left or right, not toward the back. I understand though that it needs to be moved from BAL/left to MATCH/right position.

I did another video because it seems it's the only way for me to communicate with showing which compressor we are talking about and so on. It's again very short and I cross fingers as explicit as possible. Thank you in advance:

[Joe Malone]

OK I watched the video but it doesn't show you recalabrating when you switched the BAL Match jumper over.

So the comp when linked that showed more compression has the BAL MATCH moved towards the back of the pcb and then using its ST MATCH VU trimpot while the comps are linked and switched to VU -5dB you can trim the VU to match the normal comp. `

This is what I am trying to say. I alm terribly sorry I can't find a better way to communicate. The ST MATCH VU trimpot does nothing if I turn it (I checked soldering it's ok). This is why I need confirmation about the details. Like which comp left (ch 7 in my setup) or right (ch 8 in my setup) we are talking about, not "the one with more compression" because obv. there's something I do not understand correctly and I need to understand.
Like for instance "BAL MATCH moved towards the back of the pcb". I'm not english speaking. For me the back of the PCB is parallel to the jumper, so it's either move left or right, not toward the back. I understand though that it needs to be moved from BAL/left to MATCH/right position.

I did another video because it seems it's the only way for me to communicate with showing which compressor we are talking about and so on. It's again very short and I cross fingers as explicit as possible. Thank you in advance:

OK this is not a comp link problem as both comps do not even have the there makeup pots pull out to link with the 2 blue leds on so are not going to the rack comp link at all.

I think you are switching a audio link switch on the back of your rack which will send the output from the first comp into the input of the second comp which is why the second comp is showing different comp amount as this is completely wrong. This is not a comp link on pin 6 in the rack. Some rack have audio link so you don't need patch cables between slots. This is not the comp link on pin 6 that link compressor sidechains.

What rack do you have?

Show me a photo of what you are switching on the back of the rack?

I am sure the comps are fine it is just your understanding of how your rack link functions work that is wrong. Restore both comps back to original alignment with no jumper moved over. And link the rack slots correctly and then pull both makeup pots out so both blue leds light and see what the meters show in VU and in GR

Also using so very long extension cables is not a good idea as it introduces noise and instability. keep extender cables to about 300mm long max.

[batchas]

Thank you for your help Joe. I appreciate.

OK this is not a comp link problem as both comps do not even have the there makeup pots pull out to link with the 2 blue leds on so are not going to the rack comp link at all.

I didn't know they need to be pulled out during this phase of calib procedure. I was meticulously trying to follow the procedure that was described, and it is not mentionned under the "Compressor setup procedure" or "LA500A opto comp stereo matching mode". I should have deduced it myself. Very sorry about that.

I think you are switching a audio link switch on the back of your rack which will send the output from the first comp into the input of the second comp which is why the second comp is showing different comp amount as this is completely wrong. This is not a comp link on pin 6 in the rack. Some rack have audio link so you don't need patch cables between slots. This is not the comp link on pin 6 that link compressor sidechains.
What rack do you have?

I did send to you the infos via email. Also showing what I think is now ok with calibration.

[Joe Malone]

Thank you for your help Joe. I appreciate.

OK this is not a comp link problem as both comps do not even have the there makeup pots pull out to link with the 2 blue leds on so are not going to the rack comp link at all.

I didn't know they need to be pulled out during this phase of calib procedure. I was meticulously trying to follow the procedure that was described, and it is not mentionned under the "Compressor setup procedure" or "LA500A opto comp stereo matching mode". I should have deduced it myself. Very sorry about that.

I think you are switching a audio link switch on the back of your rack which will send the output from the first comp into the input of the second comp which is why the second comp is showing different comp amount as this is completely wrong. This is not a comp link on pin 6 in the rack. Some rack have audio link so you don't need patch cables between slots. This is not the comp link on pin 6 that link compressor sidechains.
What rack do you have?

I did send to you the infos via email. Also showing what I think is now ok with calibration.

Watched video and if VU and GR track the same on both comps as you show at the end of the video when linked everything is working

[beb]

Hi Joe,
I finally took the time to assemble the LA500. Unfortunately, the sound drops significantly as soon as it’s switched to VU mode, lacking low end, as in GR mode with the VU meter maxing out in the red.

Troubleshooting done :
* checked all sockets, polarities, and solder joints = everything appears to be in place
* read all 13 pages of this thread = two similar cases, unfortunately both resolved without explanation
* "meter led lights when switching to GR or VU" = done, ok
* "add a wire link across the outside meter terminals" = not yet, see below
* both "NE5532A voltage check" = done, ok (LA500 = 0,0,0,-15.39,0,0,0,15.53 ; LA500SC = 7.8,0,0,-15.48,-8.2,-8.4,-8.4,15.54)
* "orange and green wire" = done, ko : the sound drops significantly when green is connected, lacking low end
* "relay clic green wire" = done, ok

Could the P-12 relay be faulty, despite the clic? Any help would be greatly appreciated.
Photos in attachments.

Kind regards

[Joe Malone]

Hi Joe,
I finally took the time to assemble the LA500. Unfortunately, the sound drops significantly as soon as it’s switched to VU mode, lacking low end, as in GR mode with the VU meter maxing out in the red.

Troubleshooting done :
* checked all sockets, polarities, and solder joints = everything appears to be in place
* read all 13 pages of this thread = two similar cases, unfortunately both resolved without explanation
* "meter led lights when switching to GR or VU" = done, ok
* "add a wire link across the outside meter terminals" = not yet, see below
* both "NE5532A voltage check" = done, ok (LA500 = 0,0,0,-15.39,0,0,0,15.53 ; LA500SC = 7.8,0,0,-15.48,-8.2,-8.4,-8.4,15.54)
* "orange and green wire" = done, ko : the sound drops significantly when green is connected, lacking low end
* "relay clic green wire" = done, ok

Could the P-12 relay be faulty, despite the clic? Any help would be greatly appreciated.
Photos in attachments.

Kind regards

OK the fault is with the BIO500T since you have a level drop with the loop back test. From your description one of the output transformer legs is not connected to the output cable. First check none of the 6 wires are broken off on the top of the transformer.

What are you connecting the output to a fully balanced XLR cable to a balanced input? Remember if unbalancing you will need to connect pin 1 & 3 on the output xlr or you will only get very low level and no low end.

The telecommunications relays we use are extremely reliable so if soldered well and clicking should be no problem. But you could test with a ohm meter that both sides of the DPDT are switching over.

[beb]

What are you connecting the output to a fully balanced XLR cable to a balanced input? Remember if unbalancing you will need to connect pin 1 & 3 on the output xlr or you will only get very low level and no low end.

Quite simply... it’s true that most problems come from a connection issue. And indeed, I used a disassembled API 500-B4 for the tests, which doesn’t have XLR connectors. However, I thought the TRS connections were identical. Stacked in a OST4v2 behind a Tonelux preamp, the LA500 works flawlessly using XLR or internal rack link. I now have to find a way to deal with the tiny screws without dissambling all my stuff.
“Remember”: sorry, but I didn’t find this explicit condition mentioned anywhere on the forum. I've surely missed somehow.

[Joe Malone]

What are you connecting the output to a fully balanced XLR cable to a balanced input? Remember if unbalancing you will need to connect pin 1 & 3 on the output xlr or you will only get very low level and no low end.

Quite simply... it’s true that most problems come from a connection issue. And indeed, I used a disassembled API 500-B4 for the tests, which doesn’t have XLR connectors. However, I thought the TRS connections were identical. Stacked in a OST4v2 behind a Tonelux preamp, the LA500 works flawlessly using XLR or internal rack link. I now have to find a way to deal with the tiny screws without dissambling all my stuff.
“Remember”: sorry, but I didn’t find this explicit condition mentioned anywhere on the forum. I've surely missed somehow.

Output transformers are fully floating so if running unbalanced you must connect -out pin 3 to 0v pin 1 or there is a hole in the audio path. Unlike electronic balanced out were you will only drop 6dB in level. If the TRS is fully balanced is should work fine and can be unbalanced by using a mono jack with tip and shield as the shield will short the -out to 0v automatically. Some old API racks provide unbalanced jacks but they run from a different output pin that is not used in modern 500 racks and modules.