LA500A opto comp MAY 2021 BUILD THREAD 500/51X

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

Dolbah wrote:
Sat Nov 06, 2021 8:30 am
I just built two of these units, and all seems fine. But, I am not able to get any reaction on the VU needle when turning the "Meter 0 VU" trim pot.
This applies to both units, I also tried to switch to GR and tested the GR pot, but still no reaction. I also tried putting the jumper over to "match" put I get nothing at all.
Threshold and all other functions react as expected and sound is flowing through.
  • I am sending 1000hz tone from my DAW, into the unit(s) and I have adjusted the input dB so that the LA output is showing exactly 1,23VAC, the needle is beyond 4dB on the VU.
  • All knobs counter clockwise
  • Ratio 3:1
  • Meter: VU
  • HPF: Flat

Any tips on this one?
First are you using the blue 0VU trimpot on SC PCB to set the +4dBu = 0VU? Some people mistakenly use the -20 mechanical set screw on the front of the meter which is only for setting the -20 point when the comp is off. If this set screw is moved it needs to be reset correctly before doing the calibration to the comp.

With 1.23vac on the LA500A output measured between pin 2 & pin 3 of the output XLR on first power up with no trimpots touched the VU meter will always read about -2VU and need to be turned up a couple of dB. If your VU meter reads higher usually you are reading the 1.23vac between pin 2 & pin 1 of the output XLR so really have 2.46vac.

In GR the meter will be off scale and need to be turned down several turns with Zero trimpot.
Joe :-)
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Dolbah
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Dolbah »

Joe Malone wrote:
Sat Nov 06, 2021 8:52 am
Dolbah wrote:
Sat Nov 06, 2021 8:30 am
I just built two of these units, and all seems fine. But, I am not able to get any reaction on the VU needle when turning the "Meter 0 VU" trim pot.
This applies to both units, I also tried to switch to GR and tested the GR pot, but still no reaction. I also tried putting the jumper over to "match" put I get nothing at all.
Threshold and all other functions react as expected and sound is flowing through.
  • I am sending 1000hz tone from my DAW, into the unit(s) and I have adjusted the input dB so that the LA output is showing exactly 1,23VAC, the needle is beyond 4dB on the VU.
  • All knobs counter clockwise
  • Ratio 3:1
  • Meter: VU
  • HPF: Flat

Any tips on this one?
First are you using the blue 0VU trimpot on SC PCB to set the +4dBu = 0VU? Some people mistakenly use the -20 mechanical set screw on the front of the meter which is only for setting the -20 point when the comp is off. If this set screw is moved it needs to be reset correctly before doing the calibration to the comp.

With 1.23vac on the LA500A output measured between pin 2 & pin 3 of the output XLR on first power up with no trimpots touched the VU meter will always read about -2VU and need to be turned up a couple of dB. If your VU meter reads higher usually you are reading the 1.23vac between pin 2 & pin 1 of the output XLR so really have 2.46vac.

In GR the meter will be off scale and need to be turned down several turns with Zero trimpot.


Yes, I'm on the Blue trimpots ;)

But, yes! I was using wrong pins, looks good now. Thanks!

kellyad33
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by kellyad33 »

Question about the POT board. When installing the IDC header one of the pics shows a linking wire to a hole from the center pin of the header (basically in the direct center of the board).

I only noticed in it in the picture, not instructions. Is this necessary? (maybe it's an older version?)

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

kellyad33 wrote:
Thu Dec 02, 2021 10:15 am
Question about the POT board. When installing the IDC header one of the pics shows a linking wire to a hole from the center pin of the header (basically in the direct center of the board).

I only noticed in it in the picture, not instructions. Is this necessary? (maybe it's an older version?)
That was only for the first batch. All pot PCBs since have the track on the pcb. You can actually see the track on the pcb going to the via pad.

No jumper is needed.
Joe :-)
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beatsnblunts
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by beatsnblunts »

what up Joe!

happy to report i was able to sell the LA500 i built 8 yrs ago and the 2 LA500A’s that i recently built are working great!

my only question is re: the calibration for the pair and how the linking actually works???

does it just link the detector circuit?
both units threshold and makeup still need to be set
the same?

reading the calibration thread what do you mean when u say adjust ‘the modified ‘ unit?

These kits rock!

thanks,
Steve

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

beatsnblunts wrote:
Sat Jan 22, 2022 11:53 am
what up Joe!

happy to report i was able to sell the LA500 i built 8 yrs ago and the 2 LA500A’s that i recently built are working great!

my only question is re: the calibration for the pair and how the linking actually works???

does it just link the detector circuit?
both units threshold and makeup still need to be set
the same?

reading the calibration thread what do you mean when u say adjust ‘the modified ‘ unit?

These kits rock!

thanks,
Steve
Yes 500 series uses edge connector pin 6 to link comp sidechains only. So all switches and pots on both comps need to be set to match. You have to make sure your rack has pin 6 linked on the 2 slots the comps are fitted and both makeup pots pulled out so blue link leds are both on.

We match the opto so tight these days you should only have to align both comp and they will link well in BAL mode. Do alignments a second time after the comps have been on for 30 minutes and this will usually make alignment between pairs even better.

Is is rare that you would need to use Matched jumper setting if you followed the opto info on the bag sticker.
Joe :-)
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beatsnblunts
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by beatsnblunts »

“You have to make sure your rack has pin 6 linked on the 2 slots the comps are fitted“
duh, i totally forgot about this! thx.

yeah, actually left them on overnight and re calibrated! Rock solid, no visible meter deviation between the two units , GR , link and outs!

thanks,
SteveMc

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

beatsnblunts wrote:
Sun Jan 23, 2022 12:59 pm
“You have to make sure your rack has pin 6 linked on the 2 slots the comps are fitted“
duh, i totally forgot about this! thx.

yeah, actually left them on overnight and re calibrated! Rock solid, no visible meter deviation between the two units , GR , link and outs!

thanks,
SteveMc
Cool great to hear the match is super tight :-) Enjoy
Joe :-)
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edwinhokk
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by edwinhokk »

I think I did every steps correctly, however it sounds like the thres and makeup are bypassed, they make no changes. The meter stays on the far left when the thres is min, when I turn the thres to max, the meter went to the far right. This happens in all off, GR and VU. Also the amber led is not working as well.

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

edwinhokk wrote:
Mon Jun 20, 2022 2:33 pm
I think I did every steps correctly, however it sounds like the thres and makeup are bypassed, they make no changes. The meter stays on the far left when the thres is min, when I turn the thres to max, the meter went to the far right. This happens in all off, GR and VU. Also the amber led is not working as well.
HI Does the vu meter light up when switched to GR or VU? If not the comp will never turn off the hard bypass to let you hear the comp.

If stuck email me clear in focus well lit photos of the built comp insides first so I can check them over for you.
Joe :-)
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BIO500T PCB with gold pin holes to tight

Post by Joe Malone »

Some BIO500T PCB batchs have had holes a bit to small for the gold pins strip
If so press the pins into the top of the PCB by hand so they stand by themselves and solder the top of the pcb under the black plastic strip.
Or 6 wires can be run directly from the large pcb holes to the top of the 6 solder pads along the front edge of the transformer.

Holes to small 1.jpg
Holes to small 2.jpg
Holes to small 3.jpg
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Joe :-)
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Shredso
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Shredso »

I built the LA500A, for the most part it was a breeze, much better lay out and instructions than the last 500 kit I built. I'm hung up on the setup. My extender should be here tomorrow. Is there a video, or some more detailed instructions on the setup? The only one that I'm really stumped on is step 2 (hopefully).

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.

I found a 1khz test signal on Youtube and I can send with my audio interface. Am I setting the volume output until I see that voltage on the XLR cable before I plug it in to the 500 box or are there test points on the LA500A? I'm assuming I can check that voltage with a basic multimeter.

Thanks!

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

Shredso wrote:
Sat Nov 12, 2022 1:03 pm
I built the LA500A, for the most part it was a breeze, much better lay out and instructions than the last 500 kit I built. I'm hung up on the setup. My extender should be here tomorrow. Is there a video, or some more detailed instructions on the setup? The only one that I'm really stumped on is step 2 (hopefully).

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.

I found a 1khz test signal on Youtube and I can send with my audio interface. Am I setting the volume output until I see that voltage on the XLR cable before I plug it in to the 500 box or are there test points on the LA500A? I'm assuming I can check that voltage with a basic multimeter.

Thanks!
Any 1kHz test tone will work. There are several free software tone generators out there including the one I have mentioned in the first page of the forum. You need to measure the output from the LA500A output XLR on the rack with the rack powered and comp switched to VU not the cable going into the LA500A input. Average multimeter on ac volts will work fine.
Joe :-)
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Shredso
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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Shredso »

OK, I just built my extender cable. I have 1.23v using the Audio Test program linked. Power on, VU lights up, no LEDs. Not sure if that is correct. VU is pegged to the right. The 0VU trim pot has no effect on the needle. If I switch to GR the zero GR trim pot does work, I'm able to zero that one. Turning up the threshold does bring the needle down, so something is working. Any ideas?

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Re: LA500A opto comp MAY 2021 BUILD THREAD 500/51X

Post by Joe Malone »

Shredso wrote:
Sun Nov 13, 2022 7:07 am
OK, I just built my extender cable. I have 1.23v using the Audio Test program linked. Power on, VU lights up, no LEDs. Not sure if that is correct. VU is pegged to the right. The 0VU trim pot has no effect on the needle. If I switch to GR the zero GR trim pot does work, I'm able to zero that one. Turning up the threshold does bring the needle down, so something is working. Any ideas?
If turning down the 1kHz level bring the meter down to 0VU then you have the wrong level.

With the correct 1.23vac on the output of the LA500A on first power up with the VU trimpot in the original Centre position and switched to VU you should have the meter sitting about -2.
Check you are measuring the the 1.23vac across the correct 2 pins in the output XLR 2 & 3 or pins 2 & 4 of the 500 edge connector on the extender cable.
Joe :-)
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