LA500A opto comp leveling amp BUILD THREAD 500/51X

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nicsmith
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Joined: Wed Dec 11, 2019 3:53 am

Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by nicsmith »

Hi there!

I built a LA500 and to my amazement it worked straight away. It sounded fantastic, I was super happy with it and was gleefully using it as my main vocal compressor on the way in. I had it up and running for about 3 weeks. Since then I've had some issues. At some point the Rupert Neve R6 container I had it in seemed to develop a fault or at least showed a fault code (all power LEDs flashing intermittently) and no power was being supplied to any of the units. The needle pulsed slightly and the light came on intermittently with the flashing of the power LEDs of the R6 unit.

A few days later after testing it and trying to get in contact with RND about the R6 it just started working again. The LA500 functioned normally, all was well and I just thought heck, weirder things have happened.

A few days after that, it continued to appear like it was working. The needle still moves in accordance with the amount of gain reduction applied, the unit lights up, theoretically it all seems to be working, except, there is no output. Just nothing coming out.

Signal comes through perfectly in bypass. Needle moves in accordance with gain reduction and input signal, and make up gain controls. Simply no output.

Very small amount of bleed when gain is boosted drastically on interface, but predominantly electrical noise signal.

I'm hopefully sending the R6 in for a look over soon but waiting on a ticket and details from RND, they suggested perhaps an electrical issue or problem with the power supply. Regardless, I'm not the most amazing circuit builder and I wanted to check if you thought perhaps I may have made any mistakes with the build that could have caused this electrical fault in the first place. Sadly I have no alternative rack to test any of them on atm. If it's relevant perhaps, my EMS Neve 1073LB unit is not transmitting phantom power but is otherwise working fine as well as an API 560a unit, so I wonder if the two issues might be connected in some way.

Any thoughts?

Many thanks!

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Joe Malone
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

nicsmith wrote:Hi there!

I built a LA500 and to my amazement it worked straight away. It sounded fantastic, I was super happy with it and was gleefully using it as my main vocal compressor on the way in. I had it up and running for about 3 weeks. Since then I've had some issues. At some point the Rupert Neve R6 container I had it in seemed to develop a fault or at least showed a fault code (all power LEDs flashing intermittently) and no power was being supplied to any of the units. The needle pulsed slightly and the light came on intermittently with the flashing of the power LEDs of the R6 unit.

A few days later after testing it and trying to get in contact with RND about the R6 it just started working again. The LA500 functioned normally, all was well and I just thought heck, weirder things have happened.

A few days after that, it continued to appear like it was working. The needle still moves in accordance with the amount of gain reduction applied, the unit lights up, theoretically it all seems to be working, except, there is no output. Just nothing coming out.

Signal comes through perfectly in bypass. Needle moves in accordance with gain reduction and input signal, and make up gain controls. Simply no output.

Very small amount of bleed when gain is boosted drastically on interface, but predominantly electrical noise signal.

I'm hopefully sending the R6 in for a look over soon but waiting on a ticket and details from RND, they suggested perhaps an electrical issue or problem with the power supply. Regardless, I'm not the most amazing circuit builder and I wanted to check if you thought perhaps I may have made any mistakes with the build that could have caused this electrical fault in the first place. Sadly I have no alternative rack to test any of them on atm. If it's relevant perhaps, my EMS Neve 1073LB unit is not transmitting phantom power but is otherwise working fine as well as an API 560a unit, so I wonder if the two issues might be connected in some way.

Any thoughts?

Many thanks!
The LA500A only uses the +/-16vdc and only about 60mA per rails so is very easy to run and way under the API VPR standard. If the VU meter is still running it proves all the electronics is working. Only part after that point between the output XLR is the JLM111DC output transformer. Basically check the JLM99v is plugged in fully and all 10 pin headers are fully plugged in. Plus your soldering is all clean and no solder joint has been missed.

I would try another 500 rack to see if it works fine in there. Sounds like your rack power supply is SMPS type and has failed.
Joe :-)
JLM Audio
Capturing Audio without Injury

CasinoDeathfish
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Joined: Mon Jan 06, 2020 11:48 pm

Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by CasinoDeathfish »

Greetings.

Quick question. I've built a single LA500A. Great kit, great instructions. It went together pretty quickly and easily. The problem I've run into and can't seem to solve has to do with an issue I discovered when calibrating my unit. 1Khz tone passes through and I can measure 1.23vac on output. VU meter trim adjustment has no effect on VU meter; it stays all the way left. GR meter adjustment works as expected and I can adjust it to 0db. Threshold control allows me to adjust for 5db compression. Balance trim adjustment also has no discernible effect. Switching between VU and GR show needle all the way left for VU and back to 5db for GR. Running an audio signal through the unit in GR mode shows the compressor working with meter action clearly responding to changes in threshold and audio signal, so it would seem the unit is functioning, although I was not actually LISTENING to the output signal but rather watching it on my multimeter.

I then thought to test the VU and Balance trim pots and discovered they both were not working or measuring properly.

I've replaced BOTH the VU and Balance trim pots (1k) and have confirmed they are good. All voltage measurements with the opamps are correct as is voltage coming into the unit.

Thoughts?

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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

CasinoDeathfish wrote:Greetings.

Quick question. I've built a single LA500A. Great kit, great instructions. It went together pretty quickly and easily. The problem I've run into and can't seem to solve has to do with an issue I discovered when calibrating my unit. 1Khz tone passes through and I can measure 1.23vac on output. VU meter trim adjustment has no effect on VU meter; it stays all the way left. GR meter adjustment works as expected and I can adjust it to 0db. Threshold control allows me to adjust for 5db compression. Balance trim adjustment also has no discernible effect. Switching between VU and GR show needle all the way left for VU and back to 5db for GR. Running an audio signal through the unit in GR mode shows the compressor working with meter action clearly responding to changes in threshold and audio signal, so it would seem the unit is functioning, although I was not actually LISTENING to the output signal but rather watching it on my multimeter.

I then thought to test the VU and Balance trim pots and discovered they both were not working or measuring properly.

I've replaced BOTH the VU and Balance trim pots (1k) and have confirmed they are good. All voltage measurements with the opamps are correct as is voltage coming into the unit.

Thoughts?
Ok check the toggle switches gave all there legs soldered properly to the pcb or send me some photos to check them. Often see solder that has not taken to the pcb at all so one switch position doesn’t work. Also common is not all legs of the 10 pin headers soldered on pot and SC pcb. If stuck Email me clear in focus well lit photos of the assembled comp with no 99v fitted so I can see the top sides of the pcbs. Also remember these are 25 turn trim pots so may take several turns to see any change.
Joe :-)
JLM Audio
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dneilsen
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by dneilsen »

I am having an issue with on of my LA500A units.

I built my first LA500A several years ago and it has been great. Absolutely love it so I decided to buy a second one so I can have a linked pair (with a matched opto set) but now I am having trouble with the old unit
I am using a JLM 500 extension cable to make calibrating and measuring with multimeter easier

Unit 2 (new build).
Running the 1khz test tone I am getting 1.23VAC between output pins 2 & 3. I am also getting 1.23VAC between the input pins 2 & 3 (important for later)
I calibrate the unit and all is good

Unit 1.
The only changes I made to this unit was removing the original Optos and replacing them with the matched U1 and U2 optos. Two do this I utilised the second set of opto holes on the board.
Attaching it to the same extension cable, same socket in the 500 chassis with exactly the same tone I am getting 1.23VAC between the input pins 2 & 3 but I am getting 3.27VAC between output pins 2 & 3

Something is obviously not right with this. Any advice would be helpful

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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

dneilsen wrote:
Thu Jul 16, 2020 10:26 am
I am having an issue with on of my LA500A units.

I built my first LA500A several years ago and it has been great. Absolutely love it so I decided to buy a second one so I can have a linked pair (with a matched opto set) but now I am having trouble with the old unit
I am using a JLM 500 extension cable to make calibrating and measuring with multimeter easier

Unit 2 (new build).
Running the 1khz test tone I am getting 1.23VAC between output pins 2 & 3. I am also getting 1.23VAC between the input pins 2 & 3 (important for later)
I calibrate the unit and all is good

Unit 1.
The only changes I made to this unit was removing the original Optos and replacing them with the matched U1 and U2 optos. Two do this I utilised the second set of opto holes on the board.
Attaching it to the same extension cable, same socket in the 500 chassis with exactly the same tone I am getting 1.23VAC between the input pins 2 & 3 but I am getting 3.27VAC between output pins 2 & 3

Something is obviously not right with this. Any advice would be helpful
Is the makeup pot and threshold pot both fully counterclockwise? As you can turn up the output level with the makeup .

Have the ribbon cables been put back in the correct places? As the optos cannot turn up the level like that only the makeup circuit.

Otherwise send me some photos to check over for you.
Joe :-)
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dneilsen
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Joined: Tue Nov 28, 2017 8:53 am

Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by dneilsen »

Hi Joe

Photos
https://www.dropbox.com/sh/ewc0cxfvg8nf ... IT93a?dl=0

Obviously, it was not easy to remove/install optos without removing the board (soldered to switches) so positioning is not the best but I believe they are installed correctly.

Something else I have noticed just now. With the VU/GR switch in the off position there is 1.23VAC going to the output xlr.
(I dont think my other LA500A does that? but I might be wrong)

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Joe Malone
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

dneilsen wrote:
Thu Jul 16, 2020 12:20 pm
Hi Joe

Photos
https://www.dropbox.com/sh/ewc0cxfvg8nf ... IT93a?dl=0

Obviously, it was not easy to remove/install optos without removing the board (soldered to switches) so positioning is not the best but I believe they are installed correctly.

Something else I have noticed just now. With the VU/GR switch in the off position there is 1.23VAC going to the output xlr.
(I dont think my other LA500A does that? but I might be wrong)
The LA500A has hard relay bypass when in OFF or no power so that is correct the as the input and output are connected then.

I will check the photos once you have answered the questions in the previous post.
Joe :-)
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dneilsen
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by dneilsen »

Sorry,
Yes, both makeup and threshhold pots are bot fully anticlockwise.
Yes the ribbon cables are connected correctly.

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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

dneilsen wrote:
Thu Jul 16, 2020 12:57 pm
Sorry,
Yes, both makeup and threshhold pots are bot fully anticlockwise.
Yes the ribbon cables are connected correctly.
Ok it makes no sense as 2 x 200k threshold pot in parallel with and 100k resistor make a 50k load which drops the input signal -6dB. And the makeup pot with output amp will add 6db to make unity.

If the ribbon cable hidden under the pot pcb is plugged in fully this should drop the level to the correct unity.

Does the Threshold pot work and compress when turned up?

Does the makeup pot work and turn up the signal when turned up?
Joe :-)
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dneilsen
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by dneilsen »

I put some vocal audio through to test.
Sounds fine (as you would expect) with the GR/VU switch in the off position.

I move the GR/VU switch to the GR position with threshhold and makeup fully anti-clockwise.
Signal starts to distort. Lightly but certainly noticable.
Moving threshhold pot applies compression which can clear be heard (distortion still there) and makeup pot also seems to act as it should.

This unit has been operating prefectly since I made it in late 2017. Only changes I made was the optos

dneilsen
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by dneilsen »

Is it possible I damaged a component with the soldering iron / heat when removing / installing the optos?
I was careful but was quite fiddly and the angles for access were not great.

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Joe Malone
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

dneilsen wrote:
Thu Jul 16, 2020 2:42 pm
Is it possible I damaged a component with the soldering iron / heat when removing / installing the optos?
I was careful but was quite fiddly and the angles for access were not great.
I can see solder across linking 2 solder pads on the opto LDR end which is not a good idea it could short things as it covers the sodler mask.
I would be removing the LA500sc pcb and and fixing up the opto soldering and mounting and checking all the soldering under the pcb from the old optos. There would now seem to a solder short somewhere or a broken joint.

Is the new la500a kit working ok?

If so try swapping the BIO500 pcb to see if the fault stays with the old or moves to the new comp.

That way you can work out if the fault is on the SC pcb or the BIO.
Joe :-)
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dneilsen
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by dneilsen »

I completely removed the LA500sc pcb and used solder wick to remove all extraneous solder, including the short (cant believe I didnt see that before).
I reseated the optos at the same time and removed any logs from the underside.
Gave it a really close visual inspection and everything looks to be ok.
Put it all back together.
Exactly the same results as before.

I will try mix and matching pcbs tomorrow and let you know how I go.

Thanks Joe

dneilsen
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Post by dneilsen »

I have narrowed down the issue to the BIO500V2 pcb by swapping the pcbs and transformers.

I am at a loss as to how any issue has happened on this pcb because it was literally just unscrewed, placed on the bench and then screwed back into place. Not soldering or alterations at all.

Here are photos both sides of the pcb
https://www.dropbox.com/sh/ewc0cxfvg8nf ... IT93a?dl=0

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