LA500A opto comp leveling amp BUILD THREAD 500/51X

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

Postby rbkonline » Sat Dec 26, 2015 2:13 am

Hi Joe

I have built TWO LA500a kits. I am having the same calibration problem with BOTH the kits. Your help will be very much appreciated.

I am feeding a 1k sine tone from my RME fireface ufx at roughly -15dbfs which is giving an output of 1.23VAC in my DMM. According to the calibration procedure, The VU meter of the LA should be at 0VU at this level. But adjusting the 0VU trim pot in VU mode doesnt move the needle at all! The needle keeps staying a little over -20db as shown in the photo:
WP_20151225_21_06_56_Pro.jpg



IN GR mode, the needle went to 0VU after adjusting the GR Trim pot.

Obsevation 1: in GR mode the needle moves if I adjust the 0VU trim pot.

Observation 2: In VU mode, if I feed hotter signal to the comp, the needle moves towards the right. After that if the 0VU trim pot is adjusted in either direction, the needle moves accordingly!!!

Observation 3; Turning the VU meter OFF, the needle drops to the extreme left.

Observation 4: in GR mode, the threshold and makeup pots work. But the GR meter goes straight to the left after turning the threshold knob just a little (about 9'0 clock)

Though I have cross checked everything while/after assembly, I am still posting the PCB photos of the first LA comp incase anyone finds a fault. But the same fault cant happen in BOTH the units. So I am a little confused about the whole thing. Need your help.
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Postby Joe Malone » Sun Dec 27, 2015 9:18 am

rbkonline wrote:Hi Joe

I have built TWO LA500a kits. I am having the same calibration problem with BOTH the kits. Your help will be very much appreciated.

I am feeding a 1k sine tone from my RME fireface ufx at roughly -15dbfs which is giving an output of 1.23VAC in my DMM. According to the calibration procedure, The VU meter of the LA should be at 0VU at this level. But adjusting the 0VU trim pot in VU mode doesnt move the needle at all! The needle keeps staying a little over -20db as shown in the photo:
WP_20151225_21_06_56_Pro.jpg



IN GR mode, the needle went to 0VU after adjusting the GR Trim pot.

Obsevation 1: in GR mode the needle moves if I adjust the 0VU trim pot.

Observation 2: In VU mode, if I feed hotter signal to the comp, the needle moves towards the right. After that if the 0VU trim pot is adjusted in either direction, the needle moves accordingly!!!

Observation 3; Turning the VU meter OFF, the needle drops to the extreme left.

Observation 4: in GR mode, the threshold and makeup pots work. But the GR meter goes straight to the left after turning the threshold knob just a little (about 9'0 clock)

Though I have cross checked everything while/after assembly, I am still posting the PCB photos of the first LA comp incase anyone finds a fault. But the same fault cant happen in BOTH the units. So I am a little confused about the whole thing. Need your help.


This problem seems to be due to the wrong value caps being packed in the latest batch of kits. 3 x 100nF Caps should be marked 104 or 0.1u or 100n. A batch of kits has been packed with wrong value 102 1nF caps these will work fine for C14 & C15 but C18 will need to be 104 or 100nF or 0.1uF or larger. Can be any type of mono ceramic or MKT cap as it is only for the meter.
If C18 is smaller than 100nF you will not be able to calibrate the VU meter.
Joe :-)
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nenett
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Postby nenett » Thu Feb 04, 2016 8:10 pm

More photos and answer all questions below.

I need a photo of the underside of the LA500SC PCB and top and bottom of the POT PCB. Always best to send a fully built photo first.

Sounds like the bypass circuit is not working. Which is only the VU/GR switch 1k8 resistor and relay but this travels on the ribbon cable.

Does the meter pin to the right in both VU and GR?
Is the meter back to -20 fully left when VU/GR is off?
Have you got the ribbons plugged in correct positions?
Check you have +16v at pin 8 of the OPA2604AP measured from 0v?
Check you have -16v at pin 4 of the OPA2604AP measured from 0v?


Hi Joe,
let me try this again. I was moving house, so my last post was on Dec 15. The LA500A is not working after I put it together. Audio goes straight through, without being affected. Light on the meter comes on when the power gets turned on.

Does the meter pin to the right in both VU and GR? => YES. The meter pins to the right for both VU and GR
Is the meter back to -20 fully left when VU/GR is off? => NO. The meter is still pinned to the right when VU/GR is off
Have you got the ribbons plugged in correct positions? => The ribbons are in the right positions according to the thread instructions. I will include several photos of the whole kit so you can have a look for yourself.
Check you have +16v at pin 8 of the OPA2604AP measured from 0v? => I am not quite sure how to do this part. Can you give me some instructions pls? I do have a multimeter that I could use
Check you have -16v at pin 4 of the OPA2604AP measured from 0v?

I will post the photos below, so you can have a look for yourself. I appreciate any help you can offer. I'm really keen to get the compressor working. Thank you in advance.

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

Postby nenett » Thu Feb 04, 2016 8:22 pm

And here is some more photos:
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nenett
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Postby nenett » Thu Feb 04, 2016 8:27 pm

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

Postby G-Sun » Fri Feb 05, 2016 2:42 am

Joe: I'm sure you've tried different optos for the LA500.
And, if choosing just one, I'd say you've found a very good all round performer.
Yet, if having many LA500, I wonder: Could it be realized with a very fast/ fast opto.
And have you considered selling part kits for something like this?

Second question: I never use anything but 3:1 ratio. Would it be technical possible to use the switch to switch between 3 different optos?

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

Postby Joe Malone » Wed Feb 10, 2016 10:22 am

nenett wrote:Hi Joe,
let me try this again. I was moving house, so my last post was on Dec 15. The LA500A is not working after I put it together. Audio goes straight through, without being affected. Light on the meter comes on when the power gets turned on.

Does the meter pin to the right in both VU and GR? => YES. The meter pins to the right for both VU and GR
Is the meter back to -20 fully left when VU/GR is off? => NO. The meter is still pinned to the right when VU/GR is off
Have you got the ribbons plugged in correct positions? => The ribbons are in the right positions according to the thread instructions. I will include several photos of the whole kit so you can have a look for yourself.
Check you have +16v at pin 8 of the OPA2604AP measured from 0v? => I am not quite sure how to do this part. Can you give me some instructions pls? I do have a multimeter that I could use
Check you have -16v at pin 4 of the OPA2604AP measured from 0v?

I will post the photos below, so you can have a look for yourself. I appreciate any help you can offer. I'm really keen to get the compressor working. Thank you in advance.

Damir


ok please answer this list of questions.
So when power is turned off the 500 rack the meter returns to -20?
Remove the OPA2604AP on the LA500SC PCB and power up the module does the meter stay at -20? or is it still pinned?
Refit OPA2604AP on the LA500SC PCB and power up the module and do measurements below on OPA2604AP on LA500SC PCB
Check you have +16v at pin 8 of the OPA2604AP measured from 0v? Turn meter to DC volts. Place black lead to 0v (pin 13 of the edge connector PWR GND will do). Place red lead on pin 8 of OPA2604AP)
Check you have -16v at pin 4 of the OPA2604AP measured from 0v? Turn meter to DC volts. Place black lead to 0v (pin 13 of the edge connector PWR GND will do). Place red lead on pin 4 of OPA2604AP)

Let me know the answers to these and we should be able to work this out.
Joe :-)

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

Postby Joe Malone » Wed Feb 10, 2016 10:28 am

G-Sun wrote:Joe: I'm sure you've tried different optos for the LA500.
And, if choosing just one, I'd say you've found a very good all round performer.
Yet, if having many LA500, I wonder: Could it be realized with a very fast/ fast opto.
And have you considered selling part kits for something like this?

Second question: I never use anything but 3:1 ratio. Would it be technical possible to use the switch to switch between 3 different optos?


You could try a pair of fast optos but you will only be able to run and calibrate one type at a time as each opto type will need a completely different calibration setup.

So no you cannot reuse the ratio switch for this as a lot more switching and parts would be needed.
Joe :-)

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

Postby G-Sun » Wed Feb 10, 2016 8:47 pm

Joe Malone wrote:You could try a pair of fast optos but you will only be able to run and calibrate one type at a time as each opto type will need a completely different calibration setup.

So no you cannot reuse the ratio switch for this as a lot more switching and parts would be needed.

Ok, thanks!

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

Postby nenett » Fri Feb 19, 2016 1:06 pm

Joe Malone wrote:
nenett wrote:Hi Joe,
let me try this again. I was moving house, so my last post was on Dec 15. The LA500A is not working after I put it together. Audio goes straight through, without being affected. Light on the meter comes on when the power gets turned on.

Does the meter pin to the right in both VU and GR? => YES. The meter pins to the right for both VU and GR
Is the meter back to -20 fully left when VU/GR is off? => NO. The meter is still pinned to the right when VU/GR is off
Have you got the ribbons plugged in correct positions? => The ribbons are in the right positions according to the thread instructions. I will include several photos of the whole kit so you can have a look for yourself.
Check you have +16v at pin 8 of the OPA2604AP measured from 0v? => I am not quite sure how to do this part. Can you give me some instructions pls? I do have a multimeter that I could use
Check you have -16v at pin 4 of the OPA2604AP measured from 0v?

I will post the photos below, so you can have a look for yourself. I appreciate any help you can offer. I'm really keen to get the compressor working. Thank you in advance.

Damir


ok please answer this list of questions.
So when power is turned off the 500 rack the meter returns to -20?
Remove the OPA2604AP on the LA500SC PCB and power up the module does the meter stay at -20? or is it still pinned?
Refit OPA2604AP on the LA500SC PCB and power up the module and do measurements below on OPA2604AP on LA500SC PCB
Check you have +16v at pin 8 of the OPA2604AP measured from 0v? Turn meter to DC volts. Place black lead to 0v (pin 13 of the edge connector PWR GND will do). Place red lead on pin 8 of OPA2604AP)
Check you have -16v at pin 4 of the OPA2604AP measured from 0v? Turn meter to DC volts. Place black lead to 0v (pin 13 of the edge connector PWR GND will do). Place red lead on pin 4 of OPA2604AP)

Let me know the answers to these and we should be able to work this out.


Hi Joe,

answers to your questions below.

1.So when power is turned off the 500 rack the meter returns to -20? Yes. The meter returns to -20, when the power is off
2.Remove the OPA2604AP on the LA500SC PCB and power up the module does the meter stay at -20? or is it still pinned? The meter stays at -20 when the OPA2604AP on the LA500SC PCB is removed
3.Check you have +16v at pin 8 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is 0V
4.Check you have -16v at pin 4 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is ~44mV.

NOTE: I have included the photos of what I understood is the pin 13 of the edge connector and which are the pins 4 and 8 on the OPA2604AP.

Kind Regards,
Damir
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Re: LA500A opto comp leveling amp BUILD THREAD 500/51X

Postby Joe Malone » Fri Feb 19, 2016 3:00 pm

nenett wrote:3.Check you have +16v at pin 8 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is 0V
4.Check you have -16v at pin 4 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is ~44mV.

NOTE: I have included the photos of what I understood is the pin 13 of the edge connector and which are the pins 4 and 8 on the OPA2604AP.

Kind Regards,
Damir


Are you measuring on dc volts with your meter. As at least one of the pins must have volts on it otherwise the meter could not be pinned to the right when LA500A is powered up.

You have pin 13 0v correct.

Make sure LA500A is powered up by your rack. Meter light turns on and off.

3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v?
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v?
Joe :-)

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

Postby nenett » Sat Feb 20, 2016 1:32 pm

Joe Malone wrote:
nenett wrote:3.Check you have +16v at pin 8 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is 0V
4.Check you have -16v at pin 4 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is ~44mV.

NOTE: I have included the photos of what I understood is the pin 13 of the edge connector and which are the pins 4 and 8 on the OPA2604AP.

Kind Regards,
Damir


Are you measuring on dc volts with your meter. As at least one of the pins must have volts on it otherwise the meter could not be pinned to the right when LA500A is powered up.

You have pin 13 0v correct.

Make sure LA500A is powered up by your rack. Meter light turns on and off.

3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v?
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v?



Hi Joe,
you are right, the meter wasn't switched to DC Volts. I tried again today and got the below results

3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v? I get 0.8V on the pin 8 (the actual value might be slightly different, but it's definitely not 16V)
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v? I get 14.9V on the pin 4.

The rack is powered on. The meter lights go on when I switch it to VU or GR.

Damir

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

Postby Joe Malone » Mon Feb 22, 2016 12:11 pm

nenett wrote:
Joe Malone wrote:
nenett wrote:3.Check you have +16v at pin 8 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is 0V
4.Check you have -16v at pin 4 of the OPA2604AP measured from 0v? Not the case here. The voltage measured is ~44mV.

NOTE: I have included the photos of what I understood is the pin 13 of the edge connector and which are the pins 4 and 8 on the OPA2604AP.

Kind Regards,
Damir


Are you measuring on dc volts with your meter. As at least one of the pins must have volts on it otherwise the meter could not be pinned to the right when LA500A is powered up.

You have pin 13 0v correct.

Make sure LA500A is powered up by your rack. Meter light turns on and off.

3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v?
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v?



Hi Joe,
you are right, the meter wasn't switched to DC Volts. I tried again today and got the below results

3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v? I get 0.8V on the pin 8 (the actual value might be slightly different, but it's definitely not 16V)
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v? I get 14.9V on the pin 4.

The rack is powered on. The meter lights go on when I switch it to VU or GR.

Damir


OK that is the problem.

Check voltages using pin 13 as 0v for black meter lead and let me know what voltages you have at pin 12 & pin 14 at the LA500 back edge connector
PIn 12 ?
Pin 14 ?

If they have +16v and -16v then do below check and let me know results

Then check OPA2604AP on the LA500 main PCB
3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v?
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v?
Joe :-)

JLM Audio

Capturing Audio without Injury

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

Postby nenett » Mon Feb 22, 2016 1:24 pm

OK that is the problem.

Check voltages using pin 13 as 0v for black meter lead and let me know what voltages you have at pin 12 & pin 14 at the LA500 back edge connector
PIn 12 ?
Pin 14 ?

If they have +16v and -16v then do below check and let me know results

Then check OPA2604AP on the LA500 main PCB
3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v?
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v?


Pin 12 =>0V
Pin 14 => +16V


3.Check you have +16v at pin 8 of the OPA2604AP on LA500 PCB measured from 0v? NO. I measure +1V.
4.Check you have -16v at pin 4 of the OPA2604AP on LA500 PCB measured from 0v?NO. I measure +14.9V.

Damir

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

Postby Joe Malone » Mon Feb 22, 2016 1:56 pm

nenett wrote:
OK that is the problem.

Check voltages using pin 13 as 0v for black meter lead and let me know what voltages you have at pin 12 & pin 14 at the LA500 back edge connector
PIn 12 ?
Pin 14 ?

If they have +16v and -16v then do below check and let me know results

Then check OPA2604AP on the LA500 main PCB
3.Check you have +16v at pin 8 of the OPA2604AP on LA500SC PCB measured from 0v?
4.Check you have -16v at pin 4 of the OPA2604AP on LA500SC PCB measured from 0v?


Pin 12 =>0V
Pin 14 => +16V




3.Check you have +16v at pin 8 of the OPA2604AP on LA500 PCB measured from 0v? NO. I measure +1V.
4.Check you have -16v at pin 4 of the OPA2604AP on LA500 PCB measured from 0v?NO. I measure +14.9V.

Damir


Ok pin 14 should be -16v and pin 12 should be +16v. They cannot swap. So check you had you black lead on pin 13 all the time you were testing. But looks like you are missing the +16v rail form the rack power supply.

So remove everything from your 500 rack and check at the edge connector inside the rack that you have +16v at pin 12 and -16v at pin 14 when measured from pin 13 PWR GND 0v. See attachment.

Empty rack power supply test.
black lead pin 13.
Red lead to
pin 12 = ?
pin 14 = ?
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Joe :-)

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