LA500A opto comp MAY 2021 BUILD THREAD 500/51X

[Joe Malone]

Ok so there still appears to be a short - in addition to this I had to cut a couple legs to get it out so not exactly workable. My desoldering is getting better but this was a tricky one

Short on the PCB or the pot?

[Alex1990]

Actually - I am getting 2 x 20k measurements on the front lugs so maybe pot is fine after all? But can’t understand where issue would be on PCB. Perhaps it’s easier and quicker to get a new pot PCB at this point.

[Joe Malone]

Actually - I am getting 2 x 20k measurements on the front lugs so maybe pot is fine after all? But can’t understand where issue would be on PCB. Perhaps it’s easier and quicker to get a new pot PCB at this point.

OK email me so we can workout the pot kit or parts you need

[paulnajar]

Hi Joe,

I've just built my LA500A. Great build, great design but sadly I have a couple of issues.

What's working?
Both coloured LED's, meter LED, makeup gain, hardwire bypass. No smoke

What's not working?
Don't appear/ hear to be getting any gain reduction.
no movement on the meter regardless of switch position. Stays in far left position.Trim pots don't seem to change anything (I guess because meter is somehow not active even though LED light is on?
Threshold appears to have no effect.

It all seemed to be a clean straightforward build.Only thing I can think of is maybe I got the 2 optos around the wrong way? Could that explain the behaviour I'm getting?

Got the compressor output to read 1.23vac with makeup at 12 o'clock.

Here's some photos of the build.
<https://www.dropbox.com/scl/fo/jod8ulnx ... 9bfex&dl=0>

While I have you I notice the main PCB appears to have provision for a second DOA that could replace the NE5532AF. Is it possible or would the resistors need to change as well? I have a few different DOA flavours around that might be fun to play with once I get past my issues.

Kind regards
Paul Najar

[Joe Malone]

Hi Joe,

I've just built my LA500A. Great build, great design but sadly I have a couple of issues.

What's working?
Both coloured LED's, meter LED, makeup gain, hardwire bypass. No smoke

What's not working?
Don't appear/ hear to be getting any gain reduction.
no movement on the meter regardless of switch position. Stays in far left position.Trim pots don't seem to change anything (I guess because meter is somehow not active even though LED light is on?
Threshold appears to have no effect.

It all seemed to be a clean straightforward build.Only thing I can think of is maybe I got the 2 optos around the wrong way? Could that explain the behaviour I'm getting?

Got the compressor output to read 1.23vac with makeup at 12 o'clock.

Here's some photos of the build.
<https://www.dropbox.com/scl/fo/jod8ulnx ... 9bfex&dl=0>

While I have you I notice the main PCB appears to have provision for a second DOA that could replace the NE5532AF. Is it possible or would the resistors need to change as well? I have a few different DOA flavours around that might be fun to play with once I get past my issues.

Kind regards
Paul Najar

HI Paul the toggle switch pads on the toggle switch closest to the bracket needs some more soldering, especially the centre pin. See your photo. Otherwise the build is soldered very nice and neatly built.

So when you have the comp switched off with threshold & makeup fully CCW do you have 1.23vac at input and output in hard bypass? Y/N
and you switch to GR or VU does the level drop ? Y/N
If so check you have the 200k and 20k pots in the correct positions on the pot pcb? Y/N
With 1.23vac on the output does the meter move up towards 0VU at all? Y/N
If you switch to GR does the meter move up to 0VU at all? Y/N
Have you done the jumper loop test ont he BIO500T pcb to check it is working correctly by itself? Y/N

You can add sockets to the first opamp position to fit a DOA opamp without any other changes needed. This first opamp only runs a 47k load so even a NE5532A runs in class A at that load. Most DOA on the input will reduce the input headroom because they cannot swing rail to rail like the NE5532A.

[paulnajar]

Hi Joe,

thanks so much for the quick reply! and the tips regarding the DOA socket:-)

OK to your questions

I had another good go at all the toggle switch points with the solder iron.

Input to JLM Eleven rack measured the 1Khz sine wave at 1.228 volts
With rack power off or on and 500A connected via edge connector I measure 1.224 volts across edge pin 2 and metal chassis.
Comp is in full bypass, rack power on, comp output measures 1.208vac

switch to VU mode and output drops to 0.748vac

C20K pot is the output makeup pot and aligns with what is marked on the PCB and your build photos.

When 1.23vac is measured across output, meter needle in VU mode does not move at all. just sits at the bottom of the scale.

Same is true or meter needle when in GR mode - no movement. Also there appears to be no attenuation shown via external metering regardless of threshold setting.

So I did the voltage tests you describe on the NE5532A's and on both pin 8's the ac voltage on meter went to overload but when I tried to reduce the range of the MM I got almost no voltage. The meter is auto ranging but I'm not a super expert so maybe I did this test not right.

with everything still connected I set up a sine loop in out with comp in hardware bypass and can confirm it is a unity gain loop. -12dB sine in = -12dB sine out. With comp on and both knobs fully CCW the output becomes 0.2dB louder than the input. Turning up the output sees an appropriate increase in gain much the same as the 2 FC500A's I have.

Doing your BIO500 test first with rack power off I just disconnected the ribbon and then ran the sine wave through without creating the orange and green wire loops you describe and the unity gain loop was still fully in tact. I then added the 2 loop wires and tested with rack power on and off and there was no change. The unity IO loop was always in tact.

Kind regards
Paul Najar

[paulnajar]

Also meant to say I've added another photo showing the underside of the BIO500 board.
https://www.dropbox.com/scl/fo/jod8ulnx ... 9bfex&dl=0

[Joe Malone]

OK main thing below is to test if the meter coil is intact. See below

I had another good go at all the toggle switch points with the solder iron.

Cool

Input to JLM Eleven rack measured the 1Khz sine wave at 1.228 volts
With rack power off or on and 500A connected via edge connector I measure 1.224 volts across edge pin 2 and metal chassis.
Comp is in full bypass, rack power on, comp output measures 1.208vac

switch to VU mode and output drops to 0.748vac

You have to measure the 1.23v between pin 2 and pin 3 of the output XLR as that is the balanced out. Otherwise the output transformer is floating and you will just get random meausrements

C20K pot is the output makeup pot and aligns with what is marked on the PCB and your build photos.

When 1.23vac is measured across output, meter needle in VU mode does not move at all. just sits at the bottom of the scale.

Does the meter needle move at all? Ever (like power up etc). If not unplug the module and ohms measure across the 2 inside metal tabs on the meter and let me know what ohms you get. Should be under 1k

So I did the voltage tests you describe on the NE5532A's and on both pin 8's the ac voltage on meter went to overload but when I tried to reduce the range of the MM I got almost no voltage. The meter is auto ranging but I'm not a super expert so maybe I did this test not right.

PIn 4 and pin 8 are +/-dc voltage for the opamp so you have to measure in dc volts on the meter.

Doing your BIO500 test first with rack power off I just disconnected the ribbon and then ran the sine wave through without creating the orange and green wire loops you describe and the unity gain loop was still fully in tact. I then added the 2 loop wires and tested with rack power on and off and there was no change. The unity IO loop was always in tact.

Can you hear the relay click on and off ? when adding the green jumper in and out

JLMIO loop test (1).jpg

[paulnajar]

You have to measure the 1.23v between pin 2 and pin 3 of the output XLR as that is the balanced out. Otherwise the output transformer is floating and you will just get random meausrements

OK as stated previously closest to 1.23vac I can get is 1.224vac. I send this 1Khz sine to FC500A input. In VU mode with both pots fully CCW the output xls pins 2&3 measure 0.395vac

Does the meter needle move at all? Ever (like power up etc). If not unplug the module and ohms measure across the 2 inside metal tabs on the meter and let me know what ohms you get. Should be under 1k

So I made a new discovery. If I press the bottom right corner of the board that has the pot adjusters on it in - that is the corner behind the output pot closest to the 500 module frame - when I do this the meter pins hard right so yes it does appear that the meter is working. Not sure what I'm shorting here.

Does the meter needle move at all? Ever (like power up etc). If not unplug the module and ohms measure across the 2 inside metal tabs on the meter and let me know what ohms you get. Should be under 1k

I did the meter Ohms measure anyway. With module unplugged the 2 inside tabs read about 19.4Kohms.

PIn 4 and pin 8 are +/-dc voltage for the opamp so you have to measure in dc volts on the meter.

Sorry about that. Did this test again NE5332A on BIO500 board reads:
Pin8: 15.12vdc
Pin 4: 15.35vdc

Readings for other NE5332A =
Pin8: 14.84vdc
Pin4: 15.45vdc

On the BIO500 board the NE5332A other pins all read either 0 ro .001vdc

On the other NE5332A the readings are somewhat different as follows
Pin1:14.33vdc
Pin2: 0.35vdc
Pin3:4.85vdc
Pin5: 4.97vdc
Pin6: 4.97vdc
Pin7: 14.3vdc

Can you hear the relay click on and off ? when adding the green jumper in and out

Yes every time.

Thanks again Joe for the help!

[Joe Malone]

You have to measure the 1.23v between pin 2 and pin 3 of the output XLR as that is the balanced out. Otherwise the output transformer is floating and you will just get random meausrements

OK as stated previously closest to 1.23vac I can get is 1.224vac. I send this 1Khz sine to FC500A input. In VU mode with both pots fully CCW the output xls pins 2&3 measure 0.395vac

Does the meter needle move at all? Ever (like power up etc). If not unplug the module and ohms measure across the 2 inside metal tabs on the meter and let me know what ohms you get. Should be under 1k

So I made a new discovery. If I press the bottom right corner of the board that has the pot adjusters on it in - that is the corner behind the output pot closest to the 500 module frame - when I do this the meter pins hard right so yes it does appear that the meter is working. Not sure what I'm shorting here.

Does the meter needle move at all? Ever (like power up etc). If not unplug the module and ohms measure across the 2 inside metal tabs on the meter and let me know what ohms you get. Should be under 1k

I did the meter Ohms measure anyway. With module unplugged the 2 inside tabs read about 19.4Kohms.

PIn 4 and pin 8 are +/-dc voltage for the opamp so you have to measure in dc volts on the meter.

Sorry about that. Did this test again NE5332A on BIO500 board reads:
Pin8: 15.12vdc
Pin 4: 15.35vdc

Readings for other NE5332A =
Pin8: 14.84vdc
Pin4: 15.45vdc

On the BIO500 board the NE5332A other pins all read either 0 ro .001vdc

On the other NE5332A the readings are somewhat different as follows
Pin1:14.33vdc
Pin2: 0.35vdc
Pin3:4.85vdc
Pin5: 4.97vdc
Pin6: 4.97vdc
Pin7: 14.3vdc

Can you hear the relay click on and off ? when adding the green jumper in and out

Yes every time.

Thanks again Joe for the help!

We’re all the voltages actually +? The ones on pin 4 of the opamps should be -15v

Check all of the pins on the 2 x 10 pin headsers on the sidechain pcb are soldered and the correct way around

The voltages on the sidechain pcb ne5532 are wrong so going to need to see the full top and bottom photos of that pcb

[paulnajar]

We’re all the voltages actually +? The ones on pin 4 of the opamps should be -15v

Check all of the pins on the 2 x 10 pin headsers on the sidechain pcb are soldered and the correct way around

The voltages on the sidechain pcb ne5532 are wrong so going to need to see the full top and bottom photos of that pcb

Sorry my bad Joe.

Thought the + or - values were purely to do with which probe I used on the Opamp pin or 0v point. Here they are again for the side chain board.

Pin 1: +14.28vdc
Pin 2: -4.8vdc
Pin 3: -4.85vdc
Pin 4: -15.47vdc
Pin 5: -4.95vdc
Pin 6: -4.91vdc during this test the relay clicked a few times
Pin 7: +14.35vdc
Pin 8: +14.84vdc

OK so to remove the side chain board to check it all I had to unsolder the meter. I left the toggle pins in place. I discovered that the Dip 8 socket carrying the NE532A only had 2 of 8 pins soldered (doh!) so I fixed that. See new before and after photos here <https://www.dropbox.com/scl/fo/jod8ulnx ... 9bfex&dl=0>

The 10 pin header sockets appear to be well soldered and around the right way?

I've left it disassembled in case the new photos reveal something else.

Many thanks for this Joe!

[paulnajar]

Hi Again Joe,
apologies for all my bungling!

So I decided to put the compressor back together after soldering the dip 8 pins I had missed on the side chain board.

Good news is the meter appears to be working well now. the Sidechain NE5322A pin voltages all match the NE5322A on BIO500 board now as in pins 4 & 8 = 15.xxvdc and all other pins are now either 0 or 0.001vdc

Testing with 1Khz tone the meter behaves as expected and the compressor works well and sounds great.
With both pots fully CCW 1.23vac in = 1.23vac out

The only issue I now seem to have is the trim pots used to calibrate the meter don't seem to change the meter calibration in any way.

In VU mode and GR and Makeup pots fully CCW, 1.23 vac pushes the meter to read about +4
In GR mode with all the same settings the meter reads to the right of the +4 marking.

Over to you again please - hopefully for the last time:-)

Kind regards
Paul Najar

[Joe Malone]

Hi Again Joe,
apologies for all my bungling!

So I decided to put the compressor back together after soldering the dip 8 pins I had missed on the side chain board.

Good news is the meter appears to be working well now. the Sidechain NE5322A pin voltages all match the NE5322A on BIO500 board now as in pins 4 & 8 = 15.xxvdc and all other pins are now either 0 or 0.001vdc

Testing with 1Khz tone the meter behaves as expected and the compressor works well and sounds great.
With both pots fully CCW 1.23vac in = 1.23vac out

The only issue I now seem to have is the trim pots used to calibrate the meter don't seem to change the meter calibration in any way.

In VU mode and GR and Makeup pots fully CCW, 1.23 vac pushes the meter to read about +4
In GR mode with all the same settings the meter reads to the right of the +4 marking.

Over to you again please - hopefully for the last time:-)

Kind regards
Paul Najar

OK is 1.23vac measured with multimeter leads between pin 2 and pin 3 of the output xlr (not pin 2 to 0v or pin 1 etc)? Y/N
Remember the trimpots are 25 full turns. With the correct output level and trim pot fully turned up to short you should only get about +2 on the VU meter.

The GR once VU is set up correctly will need lots of zero pot turns down to get it back to 0VU especially if you have adjusted the pot while not working.

[paulnajar]

Total success!

Thank you Joe.

Amazing support. Loving the sound of this thing so far:-) Will most likely build another one before too long

Kind regards

Paul Najar

[Joe Malone]

Total success!

Thank you Joe.

Amazing support. Loving the sound of this thing so far:-) Will most likely build another one before too long

Kind regards

Paul Najar

Cool Paul. Great to hear you got it working and are liking the sound