LA500A opto comp leveling amp BUILD THREAD 500/51X
Moderator: Joe Malone
-
- Posts: 8
- Joined: Mon Sep 06, 2021 11:24 am
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Hi Joe,
Not seeing any voltage across the LEDs. I took it apart today to look for shorts, measured the resistors which were fine, checked the header orientations and everything looked good so I’m at a loss. Pics attached. Thanks,
Not seeing any voltage across the LEDs. I took it apart today to look for shorts, measured the resistors which were fine, checked the header orientations and everything looked good so I’m at a loss. Pics attached. Thanks,
You do not have the required permissions to view the files attached to this post.
- Joe Malone
- Site Admin
- Posts: 1984
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Need to see a photo of the main pcb top and bottom in focus helps.Taperocket wrote: ↑Thu Sep 09, 2021 11:01 amHi Joe,
Not seeing any voltage across the LEDs. I took it apart today to look for shorts, measured the resistors which were fine, checked the header orientations and everything looked good so I’m at a loss. Pics attached. Thanks,
BB3A1504-0337-4799-8D93-453BB1454A5B.jpeg2DFA11A2-CA26-415D-BFBD-861C1D05136D.jpegF4186741-32E5-496B-93E6-131AD42A9071.jpeg
You are pulling the makeup and threshold pots outwards so they switch on the leds?
Joe 
JLM Audio
Capturing Audio without Injury

JLM Audio
Capturing Audio without Injury
-
- Posts: 8
- Joined: Mon Sep 06, 2021 11:24 am
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Yes. I will have to reopen tomorrow to take some additional pics, sorry about the focus issue on the last few.
- Joe Malone
- Site Admin
- Posts: 1984
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
The main thing to check if it is back together is that you have +/-15v to 16v on the 2 x 10R at the end of the LA500SC pcb.Taperocket wrote: ↑Thu Sep 09, 2021 12:03 pmYes. I will have to reopen tomorrow to take some additional pics, sorry about the focus issue on the last few.
Can you calibrate the comp ok? Like does the meter light in VU or GR mode?
Joe 
JLM Audio
Capturing Audio without Injury

JLM Audio
Capturing Audio without Injury
-
- Posts: 8
- Joined: Mon Sep 06, 2021 11:24 am
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Here are the pics of the main PCB that you requested, Joe. My phone camera seems to struggle with focus on the back of the boards - I hope this works.
I ordered a 500 series extension cable to assist with further testing because I can't access the board with my test probes as is. All other functionality seems normal - the unit calibrated fine and meter lights on both GR and VU modes and works as it should as does the compression/makeup gain.
I ordered a 500 series extension cable to assist with further testing because I can't access the board with my test probes as is. All other functionality seems normal - the unit calibrated fine and meter lights on both GR and VU modes and works as it should as does the compression/makeup gain.
You do not have the required permissions to view the files attached to this post.
- Joe Malone
- Site Admin
- Posts: 1984
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Do the 2 LEDs test dead short?Taperocket wrote: ↑Fri Sep 10, 2021 8:18 amHere are the pics of the main PCB that you requested, Joe. My phone camera seems to struggle with focus on the back of the boards - I hope this works.
I ordered a 500 series extension cable to assist with further testing because I can't access the board with my test probes as is. All other functionality seems normal - the unit calibrated fine and meter lights on both GR and VU modes and works as it should as does the compression/makeup gain.
processed-d7efd685-c3fc-41ef-b961-22a541f32c8a_Opqt7d5Z.jpegprocessed-47950647-8c1c-4e53-abde-944b921d0683_NQOgSKEL.jpegprocessed-817d405f-acb8-43d1-bece-0f275a81264f_YQ3aaJ49.jpeg
Joe 
JLM Audio
Capturing Audio without Injury

JLM Audio
Capturing Audio without Injury
-
- Posts: 8
- Joined: Mon Sep 06, 2021 11:24 am
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
No, checked for continuity between them and they did not short together.
- Joe Malone
- Site Admin
- Posts: 1984
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
You are pulling the makeup and threshold pots outwards so they switch on the leds?Taperocket wrote: ↑Fri Sep 10, 2021 12:31 pmNo, checked for continuity between them and they did not short together.
Joe 
JLM Audio
Capturing Audio without Injury

JLM Audio
Capturing Audio without Injury
-
- Posts: 8
- Joined: Mon Sep 06, 2021 11:24 am
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Yes, I regularly keep the threshold pot pulled out for slower attack.
- Joe Malone
- Site Admin
- Posts: 1984
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
If you remove the leds and have the pots pulled what voltage do you see across the led pads?Taperocket wrote: ↑Sat Sep 11, 2021 4:45 amYes, I regularly keep the threshold pot pulled out for slower attack.
Joe 
JLM Audio
Capturing Audio without Injury

JLM Audio
Capturing Audio without Injury
-
- Posts: 8
- Joined: Mon Sep 06, 2021 11:24 am
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Looks like the issue resolved itself when I pulled the boards last time and reassembled. I'm guessing it's related to the ribbon cables somehow - either a loose connector on one of the headers or an intermittent lead. Either way, both LED'w are lighting now without any changes.
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Hi Joe
I recently finished an an LA500A. It compresses fine and all features work, however when I flick from bypass to GR/VU there is a small drop in level that doesn’t seem quite right. I was expecting unity gain when both pots are fully CCW. It’s not a severe drop but definitely there, maybe 2db.
In addition to this there is a distortion to the signal. This is even when both pots are fully CCW. I pulled another JLM99V from my MAC and nothing changed. I double checked all the PCB’s for stray solder/shorts but really couldn’t find anything with my admittedly unexperienced eye. The signal going in is not particularly hot and both the LA500 meter and my DAW meters are not going crazy. But the distortion is there all the time.
Just to say I received a 4-way pin header for the BAL MATCH part of the SC PCB in stead of a 3-way. In my efforts to break one pin off it snapped in two so I just went ahead and fitted two poles and added the jumper in the correct position (next to the BAL/GR trim). Let me know if I should acquire a 3 way and redo.
On a possibly related matter, I tried to calibrate the meter for 0VU and I adjusted my DAW tone generator level till I hit 1.2 on my multimeter. However the VU meter was pinned. I got down to about +2 before the trim pot ran out of turns.
Any ideas on where to start looking would be really appreciated! Sorry for the long post I just want to make sure you have the information!
Alex
I recently finished an an LA500A. It compresses fine and all features work, however when I flick from bypass to GR/VU there is a small drop in level that doesn’t seem quite right. I was expecting unity gain when both pots are fully CCW. It’s not a severe drop but definitely there, maybe 2db.
In addition to this there is a distortion to the signal. This is even when both pots are fully CCW. I pulled another JLM99V from my MAC and nothing changed. I double checked all the PCB’s for stray solder/shorts but really couldn’t find anything with my admittedly unexperienced eye. The signal going in is not particularly hot and both the LA500 meter and my DAW meters are not going crazy. But the distortion is there all the time.
Just to say I received a 4-way pin header for the BAL MATCH part of the SC PCB in stead of a 3-way. In my efforts to break one pin off it snapped in two so I just went ahead and fitted two poles and added the jumper in the correct position (next to the BAL/GR trim). Let me know if I should acquire a 3 way and redo.
On a possibly related matter, I tried to calibrate the meter for 0VU and I adjusted my DAW tone generator level till I hit 1.2 on my multimeter. However the VU meter was pinned. I got down to about +2 before the trim pot ran out of turns.
Any ideas on where to start looking would be really appreciated! Sorry for the long post I just want to make sure you have the information!
Alex
- Joe Malone
- Site Admin
- Posts: 1984
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Max level change should be less than +/-0.5dB depending on the input impedance of the gear plugged into the LA500A output.Alex1990 wrote: ↑Thu Jan 13, 2022 9:06 amHi Joe
I recently finished an an LA500A. It compresses fine and all features work, however when I flick from bypass to GR/VU there is a small drop in level that doesn’t seem quite right. I was expecting unity gain when both pots are fully CCW. It’s not a severe drop but definitely there, maybe 2db.
Test BIO500T by itself by doing the 2 wire loops test in the ribbon cable that would normally go to the SC so you can see if the fault is on the BIO or elsewhere in the build. Let me know what you find. Test BIO500/LA500 main pcb by itself by unplugging BIO500/LA500 main pcb ribbon cable from LA500SC pcb and fitting two cut off component leg loops as shown below.In addition to this there is a distortion to the signal. This is even when both pots are fully CCW. I pulled another JLM99V from my MAC and nothing changed. I double checked all the PCB’s for stray solder/shorts but really couldn’t find anything with my admittedly unexperienced eye. The signal going in is not particularly hot and both the LA500 meter and my DAW meters are not going crazy. But the distortion is there all the time.
You should have a unity gain audio loop if BIO500/LA500 main pcb is working. This test proves BIO500/LA500 main PCB and output transformer are both working.
You can plug the relay green wire loop in and out to switch between bypass and BIO500 audio path to check audio level is correct.
This is fine and will not be a problemJust to say I received a 4-way pin header for the BAL MATCH part of the SC PCB in stead of a 3-way. In my efforts to break one pin off it snapped in two so I just went ahead and fitted two poles and added the jumper in the correct position (next to the BAL/GR trim). Let me know if I should acquire a 3 way and redo.
With correct output of 1.23vac between pin 2 and pin 3 on output the meter will show roughly -2 to -3 on first power with new trimpot still in centre position. Sounds like you are measuring between pin 1 to pin 2 or pin 3.On a possibly related matter, I tried to calibrate the meter for 0VU and I adjusted my DAW tone generator level till I hit 1.2 on my multimeter. However the VU meter was pinned. I got down to about +2 before the trim pot ran out of turns.
You do not have the required permissions to view the files attached to this post.
Joe 
JLM Audio
Capturing Audio without Injury

JLM Audio
Capturing Audio without Injury
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Hi Joe, thanks a lot for this.
The level drop when flicking between bypass and GR/VU is pretty much exactly 2db. I believe the BIO500 board is the culprit as the ribbon test showed the same results - 2db when Ii pulled out the bypass wire.
What's the best way to get images to you? I'm pretty confident with the component placements but not 100% pro at so soldering may have to revisit. Any ideas on where to focus would be great.
I am definitely measuring pins 2/3 if that's helpful in narrowing down an issue.
Thanks Joe!
The level drop when flicking between bypass and GR/VU is pretty much exactly 2db. I believe the BIO500 board is the culprit as the ribbon test showed the same results - 2db when Ii pulled out the bypass wire.
What's the best way to get images to you? I'm pretty confident with the component placements but not 100% pro at so soldering may have to revisit. Any ideas on where to focus would be great.
I am definitely measuring pins 2/3 if that's helpful in narrowing down an issue.
Thanks Joe!
- Joe Malone
- Site Admin
- Posts: 1984
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
Re: LA500A opto comp leveling amp BUILD THREAD 500/51X
Clean the bottom of the PCB with alcohol and old toothbrush and remove JLM99v and send me clear in focus well-lit photos of the top and bottom to my email joe @ jlmaudio . com to check. Make sure you include your forum user name as well.Alex1990 wrote: ↑Fri Jan 14, 2022 4:30 amHi Joe, thanks a lot for this.
The level drop when flicking between bypass and GR/VU is pretty much exactly 2db. I believe the BIO500 board is the culprit as the ribbon test showed the same results - 2db when Ii pulled out the bypass wire.
What's the best way to get images to you? I'm pretty confident with the component placements but not 100% pro at so soldering may have to revisit. Any ideas on where to focus would be great.
I am definitely measuring pins 2/3 if that's helpful in narrowing down an issue.
Thanks Joe!
Joe 
JLM Audio
Capturing Audio without Injury

JLM Audio
Capturing Audio without Injury