loop back and relay working.
also, cable shows continuity.
anything else to check out before i put it back together and give it another go?
I appreciate your help!
thx,
Steve
If the BIO500 and cable work it is only one side of the GR/OFF/VU switch and 1k8 resistor and meter led in series in the path to turn the relay on the BIO500 on and off. Check all IDC10 pins are soldered on all pcbs
Well…its all good now(minus the led)! not sure what happened maybe cold solder joints on the meter tabs?
Thanks for your support!
Joe Rocks! and so do most bands from down under!
loop back and relay working.
also, cable shows continuity.
anything else to check out before i put it back together and give it another go?
I appreciate your help!
thx,
Steve
If the BIO500 and cable work it is only one side of the GR/OFF/VU switch and 1k8 resistor and meter led in series in the path to turn the relay on the BIO500 on and off. Check all IDC10 pins are soldered on all pcbs
Well…its all good now(minus the led)! not sure what happened maybe cold solder joints on the meter tabs?
Thanks for your support!
Joe Rocks! and so do most bands from down under!
If you have 1.23vac = +4dBu on the balanced output between pin 2 and pin 3. The meter on VU for the first time will read bout -2dB and need to be turned up on the 0VU trimpot. The GR after that will be off the scale and need to be turned down by the zero gr trimpot a far bit to get back to 0VU
There is no gain difference between the LA500 and LA500A. The setup is identical.
So I have 1.23vac sending to both units and I have about a 7db difference between vu meters. There doesn't seem to be enough adjustment on the trim pot to make up for this. Any ideas of where I could begin troubleshooting since they're supposed to be equal in gain. Both units sound great by the way.
If you have 1.23vac = +4dBu on the balanced output between pin 2 and pin 3. The meter on VU for the first time will read bout -2dB and need to be turned up on the 0VU trimpot. The GR after that will be off the scale and need to be turned down by the zero gr trimpot a far bit to get back to 0VU
There is no gain difference between the LA500 and LA500A. The setup is identical.
So I have 1.23vac sending to both units and I have about a 7db difference between vu meters. There doesn't seem to be enough adjustment on the trim pot to make up for this. Any ideas of where I could begin troubleshooting since they're supposed to be equal in gain. Both units sound great by the way.
It doesn't matter what level you measure going in. You need to measure the level coming out and make sure it is +4dBu (1.23vac) between the output xlr pin 2 & 3. With makeup and threshold fully counterclockwise the input and output should be almost the same unless you have made a mistake.
If in and out levels are not same in an dout go back to loop test on LA500 / BIO500T pcb
It doesn't matter what level you measure going in. You need to measure the level coming out and make sure it is +4dBu (1.23vac) between the output xlr pin 2 & 3. With makeup and threshold fully counterclockwise the input and output should be almost the same unless you have made a mistake.
If in and out levels are not same in an dout go back to loop test on LA500 / BIO500T pcb
Ok gotcha. Level on the la500 is coming out at less than half of what's going in. I'll have to try the loop test...about to go to bed but I'll give it a shot tomorrow and let you know. Thanks for your help!
Well I'm not sure why but its now outputting correctly. I reseated everything so maybe that was it. Now I'm trying to get these compressors to track similarly..but I'm getting some weird behavior. They are currently always linked regardless of the link pull pot.. (I'm thinking that's the jumper on the la500) but when I pull out the slow attack pot on the la500a they delink?? not sure where to begin. Do you have any tips on getting an early la500 model to work well with what I think is the most current la500a model? sorry if this question is too broad..
Well I'm not sure why but its now outputting correctly. I reseated everything so maybe that was it. Now I'm trying to get these compressors to track similarly..but I'm getting some weird behavior. They are currently always linked regardless of the link pull pot.. (I'm thinking that's the jumper on the la500) but when I pull out the slow attack pot on the la500a they delink?? not sure where to begin. Do you have any tips on getting an early la500 model to work well with what I think is the most current la500a model? sorry if this question is too broad..
You will not get an early LA500 to match a later LA500A as firstly you need 2 matched pairs of optos split across the comps to get stereo match and slow attack and a few minor changes are different between them so will not work.
Well I'm not sure why but its now outputting correctly. I reseated everything so maybe that was it. Now I'm trying to get these compressors to track similarly..but I'm getting some weird behavior. They are currently always linked regardless of the link pull pot.. (I'm thinking that's the jumper on the la500) but when I pull out the slow attack pot on the la500a they delink?? not sure where to begin. Do you have any tips on getting an early la500 model to work well with what I think is the most current la500a model? sorry if this question is too broad..
You will not get an early LA500 to match a later LA500A as firstly you need 2 matched pairs of optos split across the comps to get stereo match and slow attack and a few minor changes are different between them so will not work.
Ah shoot, I was hoping you wouldn't say that haha.. the la500 does have the slow attack mod if that means anything. If I replace the optos, any chance I could get them close? Thanks again!
Well I'm not sure why but its now outputting correctly. I reseated everything so maybe that was it. Now I'm trying to get these compressors to track similarly..but I'm getting some weird behavior. They are currently always linked regardless of the link pull pot.. (I'm thinking that's the jumper on the la500) but when I pull out the slow attack pot on the la500a they delink?? not sure where to begin. Do you have any tips on getting an early la500 model to work well with what I think is the most current la500a model? sorry if this question is too broad..
You will not get an early LA500 to match a later LA500A as firstly you need 2 matched pairs of optos split across the comps to get stereo match and slow attack and a few minor changes are different between them so will not work.
Ah shoot, I was hoping you wouldn't say that haha.. the la500 does have the slow attack mod if that means anything. If I replace the optos, any chance I could get them close? Thanks again!
I would need to see photos of the original LA500 comp to work out what optos and version it is to see what could work
I build 2 x LA500A. They are up and running since 2 weeks.
Everything seems to be fine so far and they sound great.
All controls including trims react properly.
Now I am stuck in the calibration process.
I can trim the meter to 0 VU on both units 1K/1.23 Vac.
I can get the GR meter to show accurate GR values.
I can not get the VU meter to show accurate readings except for 0 VU.
- 1k -20 dBfs - meter shows 0 VU
- 1k -18 dBfs- meter shows almost +4 VU
- 1k -25 dBfs- meter shows almost -10 VU
I build 2 x LA500A. They are up and running since 2 weeks.
Everything seems to be fine so far and they sound great.
All controls including trims react properly.
Now I am stuck in the calibration process.
I can trim the meter to 0 VU on both units 1K/1.23 Vac.
I can get the GR meter to show accurate GR values.
I can not get the VU meter to show accurate readings except for 0 VU.
- 1k -20 dBfs - meter shows 0 VU
- 1k -18 dBfs- meter shows almost +4 VU
- 1k -25 dBfs- meter shows almost -10 VU
What am I doing wrong?
Wish you a nice slide into 2025!
Best Regards
The meters are faster than normal averaging VU meters so when showing VU level or GR the scale works to help show transients better in VU and more accurate GR reduction. If you try and do multipoint static level tests it will be out. Do the alignment as shown and enjoy the compressor as it will be more accurate metering on actual audio.
Normal VU meters are way too slow at 300mS attack and release, especially in showing GR. So when showing an average of 3-5dB GR an LA2A or LA3A type comp will usually be reducing transients 6-10dB.
I am sorry I don't understand the calibration procedure. Maybe because of my English, not my mother tongue.
I checked all the questions and answers in this thread one by one but I'm still stucked.
The build is pretty straight forward. I build the 2 compressors in a couple of hours. I think BTW that a calibration procedure shown on video would help and avoid misunderstandings. Not having the option to search the all thread for a keyword was also for me making things difficult.
EDIT/ I found the answer by myself to my question.
I had to turn up the volume of the 1khz signal until I get 1.23vac at pin 2/3 of XLR.
Last edited by batchas on Wed Feb 12, 2025 1:38 am, edited 1 time in total.
Hello! Not sure if this is the right place for this question.
I managed to complete and mostly calibrate two units. I made some silly errors earlier on, which Joe kindly helped me through via email. (Lesson learned there is that my mental facilities begin to decline sharply after midnight). It now seems both units work on their own.
Now I'm having some trouble with the stereo linking feature. I've gone back a few times and can't figure it out, especially since I'm not really sure how the linking feature is supposed to work on 500 series units in general.
Essentially when linking is engaged on the problem unit, pin 1 of the secondary op amp IC outputs a square wave at +/- 16V. This is also reflected on the meter, which jumps wildly with the voltage changes. When disengaged, the pin stays at 0V for a second and then returns to the signal it had before (some sort of oscillating signal). Note: this is with no signal on the input of the compressor.
How can I go about troubleshooting this issue? Any help is greatly appreciated.
I arrived with success to point 7 of Compressor setup procedure and stucked now with Balance trim pot doing nothing when the switch is set to VU.
I have 5dB of compression on the meter with switch set to GR and when I switch to VU the meter shows 0, as set in the previous procedure step. No change when turning the Balance trim pot. It remains there.
By the way, the orientation of the opto confuses me. It is not the same on the 2 x LA500A that I''m trying to calibrate.
Though I see the white dots on all vactrols aligned correctly to the dots on the boards. Still there's something I wish to understand. The white dot on the vactrol is not on the same side on all of them that I received and installed: https://youtu.be/X9J_bN7E7Mk
Is it because I have a pair of compressors that will work in stereo?
Orientation right or wrong, the issue is on both LA500A, so the issue comes from elsewhere.
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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.
