LA500A opto comp MAY 2021 BUILD THREAD 500/51X

[billface]

Probably the first in a series of stupid question from myself.

1) Do the J99 sockets get soldered into the board? I said on the instructions not to press them in and to use a piece of cardboard to hold them in, but now the J99 is inplace it seems a bit odd that is a bit loose.

2) I put the DIP8 socket in upside down. Any top tip on how to remove it? I have a solder sucker and some copper braid

[Joe Malone]

Probably the first in a series of stupid question from myself.

1) Do the J99 sockets get soldered into the board? I said on the instructions not to press them in and to use a piece of cardboard to hold them in, but now the J99 is inplace it seems a bit odd that is a bit loose.

2) I put the DIP8 socket in upside down. Any top tip on how to remove it? I have a solder sucker and some copper braid

Yes solder the sockets to the pcb. The 6 sockets fit the holes easy. Use a piece of cardboard to hold them in to flip the pcb and solder them on the bottom pcb side.

Don’t try and remove the dip socket unless you are very good at resoldering just put a white dot on the opposite end to remind you to put the opamp in the other way around. Best to fit the ne5532A now while you remember

[billface]

So just to be clear, are you saying this arrangement will work?

https://photos.google.com/photo/AF1QipM ... Fnyy24l0i9
https://photos.google.com/photo/AF1QipN ... TJ7D-JXn37

[Joe Malone]

So just to be clear, are you saying this arrangement will work?

Attach photos to your post. I cannot get to Google photos

[billface]

Here's the pics attached (sorry got confused by the img tag function). So quick recap, I put my dip8 upside down and you said to leave it in and match the orientation with the op amp. Have I understood correctly and if so will this affect stereo matching if I put the other one in correctly.

PXL_20240416_063203933-EDIT.jpg

PXL_20240416_063343561.jpg

[billface]

Sorry Joe,

I've just reread your post and engaged my brain. The 'other way round' means relative to the dip socket not its normal orientation

I'll flip the opamp to how i had it in the photos

[Joe Malone]

Sorry Joe,

I've just reread your post and engaged my brain. The 'other way round' means relative to the dip socket not its normal orientation

I'll flip the opamp to how i had it in the photos

You have the opamp facing the wrong way, so unplug and turn it 180 degrees

[billface]

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 the desired level for 0VU on the meter.
5. Switch Meter switch to GR and adjust Zero GR trim pot for 0VU on the meter.
6. Turn up Threshold pot until you have 5dB of compression on the meter.
7. Switch Meter switch between GR and VU and adjust the Balance trim pot until the same reading is seen in both GR and VU.
8. You're ready to rock.

Hey I've got two of these I'm trying to calibrate and have a few questions.

1) it needs a bit more gain to get one of the units to read 1.23vac. Should that be the case? If i'm setting a slighty higher amount of gain to equal 0vu presumably i need to adjust something to balance the two units. Would that be the front needle adjuster?
2) I would like -18db from my DAW to be 0vu but at the moment -16.6db is 0VU and i can't adjust the 0vu trimpot any higher. should adjust the screw on the front of the meter?

[Joe Malone]

Hey I've got two of these I'm trying to calibrate and have a few questions.

1) it needs a bit more gain to get one of the units to read 1.23vac. Should that be the case? If i'm setting a slighty higher amount of gain to equal 0vu presumably i need to adjust something to balance the two units. Would that be the front needle adjuster?
2) I would like -18db from my DAW to be 0vu but at the moment -16.6db is 0VU and i can't adjust the 0vu trimpot any higher. should adjust the screw on the front of the meter?

What is 0dBFS on your DAW = to in dBu?

It would need to be +22dBu for -18dB to = +4dBu

With 1.23vac between pin 2 & 3 on the output XLR you should be able to trimpot up to +2dB on the meter.

The mechanical adjust on the front of the meter is only for setting exactly -20 on the meter when the comp is not powered up before doing an alignment

[billface]

Yes the calibration on my system was a bit out. I've adjusted and its fine now. Next question:

The stereo link requires a link between adjactent units on the rack. My rack doesn't have this facility built in but apparently I can solder a link between pin 6 on adjacent slots. Does that sound right to you? i.e is pin 6 the right one? And do I count from the top or the botton of the unit?

[Joe Malone]

Yes the calibration on my system was a bit out. I've adjusted and its fine now. Next question:

The stereo link requires a link between adjactent units on the rack. My rack doesn't have this facility built in but apparently I can solder a link between pin 6 on adjacent slots. Does that sound right to you? i.e is pin 6 the right one? And do I count from the top or the botton of the unit?

Calibration is best done with the module warmed up for 30mins or so. And doing it twice is a good idea for stereo match.

Yes you just need a wire between pin 6 of the 2 slots for 500 series comp. Pin 1 is at the top. Set both comps to the same switch and rough threshold settings and then pull both makeup pots outwards so both blue link leds light up. And adjust both makeup pots to get the output level needed.

[billface]

Just doing my stereo calibirations. I don't understand what the instructions are trying to get me to do. But they seem to work in stereo with the Threshold of one unit controlling the threshold of the other. Could you perhaps do a laymans explanation of the procedure.

I have also noticed that with a 1khz sine wave at 1.228V input to both units with them both set to CCW thres & Makeup one gives aa output of 1.20V and the other 1.24V. Is that within tolerance?

[Joe Malone]

Just doing my stereo calibirations. I don't understand what the instructions are trying to get me to do. But they seem to work in stereo with the Threshold of one unit controlling the threshold of the other. Could you perhaps do a laymans explanation of the procedure.

I have also noticed that with a 1khz sine wave at 1.228V input to both units with them both set to CCW thres & Makeup one gives aa output of 1.20V and the other 1.24V. Is that within tolerance?

The cal is just setting the VU meter so 0VU = +4dBu (1.23vac) and then the second part is balancing so -5dB (5dB compression) on the VU meter = -5dB when switched to GR. The 1.24 to 1.2vac is a tiny difference but you can turn up the makeup on the lower level one slightly until you get 1.24vac on it as well.

[rohanz]

Hi Joe, successfully put mine together and it works except for one small issue. when in bypass, the gain is 4-5 db lower than it should be. also, when the gr meter gets ridiculously pinned, it gets stuck on the left. but it can be easily fixed by setting it to vu and back again. any idea what the fix for these are?

[Joe Malone]

Hi Joe, successfully put mine together and it works except for one small issue. when in bypass, the gain is 4-5 db lower than it should be. also, when the gr meter gets ridiculously pinned, it gets stuck on the left. but it can be easily fixed by setting it to vu and back again. any idea what the fix for these are?

Bypass is relay bypass so it would be very hard for that to be less than unity. Are you sure you do not have 4-5dB boost when the comp is switched in with makeup fully CCW?

The gr problem sounds like something wrong sidechain wise.

Best to send me clear in focus well lit top and bottom photos of the pcbs to check over.

Did the comp alignment work ok?