LA500A opto comp MAY 2021 BUILD THREAD 500/51X

[paullambert100]

Hi

I’ve recently built a pair of la500a’s and peq500a’s. Amazing sounds for sure. I’ve been reading about folks matching mono units with test tones for stereo work but can’t figure out what this actually means or how to do it. Any tips would be appreciated!

Thanks

[Joe Malone]

Hi

I’ve recently built a pair of la500a’s and peq500a’s. Amazing sounds for sure. I’ve been reading about folks matching mono units with test tones for stereo work but can’t figure out what this actually means or how to do it. Any tips would be appreciated!

Thanks

HI
If you bought pairs from us in the same order we hand-match all pots, transformers, optos and inductors for you to very tight specs. So PEQ500A pair should stereo-match extremely well. Also If you did the alignment and opto placement correctly in the LA500A they 2 should stereo match extremely well.

For checking EQ match or frequency response match of any audio path I can recommend plug-in doctor in hardware mode looped into your A/D D/A

When you want to stereo match settings of anything with pots you can get a result the same or better than fully switched equipment by
Set for example both EQs to the same-looking settings that sound about right.
Then switch your monitor controller hardware or software to mono and reverse phase on the right channel.
Now you will only hear the difference and by tweaking the right channel EQ pot controls you will be able to null this difference while playing the audio you are mixing.
Once the null seems to be the best you can then remove the right phase flip and remove the mono and your stereo match will be at its best.

[noahraimy]

Hey Joe just bumping my message. I have a lengthier write up back a page. Still can’t get compression to act how I’d expect it to despite everything else working. Please get back to me when you get a chance, thanks so much.

[Joe Malone]

Hey Joe just bumping my message. I have a lengthier write up back a page. Still can’t get compression to act how I’d expect it to despite everything else working. Please get back to me when you get a chance, thanks so much.

HI Ok doesn't make sense that you could cal the comp but then with audio not get audio compression. Are you sure you are putting in a +4dBu or more level signal.

Do the below and post the 4 photos here
Switch to VU and put in 1k tone (1.23vac on the output) so you have 0VU showing on the meter with Threshold and makeup CCW and take a photo of the front whole panel so I can see all pots and switch and meter positions.

Take a photo of the voltage showing on the multimeter from the output

Turn up the threshold until you have -5 showing on the meter and take a photo of the front panel.

Switch to GR and take a photo of the front panel.

These 4 photos will help me

[Alex1990]

Hi Joe - correct.

Can confirm the unit stays at unity gain with bypass wire in/out so the problem must not be on BIO PCB.

all the best!

Bump

[Joe Malone]

If it is assembled remove the BIO take a good couple of photos of the top of the sc pcb and bottom of pot pcb first and I will check it

[noahraimy]

Hey Joe just bumping my message. I have a lengthier write up back a page. Still can’t get compression to act how I’d expect it to despite everything else working. Please get back to me when you get a chance, thanks so much.

HI Ok doesn't make sense that you could cal the comp but then with audio not get audio compression. Are you sure you are putting in a +4dBu or more level signal.

Do the below and post the 4 photos here
Switch to VU and put in 1k tone (1.23vac on the output) so you have 0VU showing on the meter with Threshold and makeup CCW and take a photo of the front whole panel so I can see all pots and switch and meter positions.

Take a photo of the voltage showing on the multimeter from the output

Turn up the threshold until you have -5 showing on the meter and take a photo of the front panel.

Switch to GR and take a photo of the front panel.

These 4 photos will help me

Thanks Joe, just to clarify, I am getting compression it just isn’t functioning as it should. When turning the threshold pot compression gradually increases then sharply cuts out the signal when 3/4 of the way then when turned the rest of the way signal is not compressed just distorted.

I’ll do the tests soon and post a drive link.

[Alex1990]

If it is assembled remove the BIO take a good couple of photos of the top of the sc pcb and bottom of pot pcb first and I will check it

Here we go! I did try reflowing make up pot joints just in case but it didn’t help.

[Joe Malone]

If it is assembled remove the BIO take a good couple of photos of the top of the sc pcb and bottom of pot pcb first and I will check it

Here we go! I did try reflowing make up pot joints just in case but it didn’t help.

If you measure the makeup pot outside pads with pot fully CCW and BIO unplugged do you read 10k?

[noahraimy]

Hey Joe just bumping my message. I have a lengthier write up back a page. Still can’t get compression to act how I’d expect it to despite everything else working. Please get back to me when you get a chance, thanks so much.

HI Ok doesn't make sense that you could cal the comp but then with audio not get audio compression. Are you sure you are putting in a +4dBu or more level signal.

Do the below and post the 4 photos here
Switch to VU and put in 1k tone (1.23vac on the output) so you have 0VU showing on the meter with Threshold and makeup CCW and take a photo of the front whole panel so I can see all pots and switch and meter positions.

Take a photo of the voltage showing on the multimeter from the output

Turn up the threshold until you have -5 showing on the meter and take a photo of the front panel.

Switch to GR and take a photo of the front panel.

These 4 photos will help me

Thanks for your help. Here are the pictures
https://drive.google.com/drive/folders/ ... FPVfwfmhfZ

[Joe Malone]

Hey Joe just bumping my message. I have a lengthier write up back a page. Still can’t get compression to act how I’d expect it to despite everything else working. Please get back to me when you get a chance, thanks so much.

HI Ok doesn't make sense that you could cal the comp but then with audio not get audio compression. Are you sure you are putting in a +4dBu or more level signal.

Do the below and post the 4 photos here
Switch to VU and put in 1k tone (1.23vac on the output) so you have 0VU showing on the meter with Threshold and makeup CCW and take a photo of the front whole panel so I can see all pots and switch and meter positions.

Take a photo of the voltage showing on the multimeter from the output

Turn up the threshold until you have -5 showing on the meter and take a photo of the front panel.

Switch to GR and take a photo of the front panel.

These 4 photos will help me

Thanks for your help. Here are the pictures
https://drive.google.com/drive/folders/ ... FPVfwfmhfZ

Without the threshold knob I cannot know if the pot is up a bit or lots so makes the photos not of any use? Also, would be good to see a photo of 0GR.

But if the threshold knob in the alignment shown is only turned up a bit then the alignment looks perfect.

What are you running into the LA500A that needs lots of threshold?
Does the signal you send in get the meter in VU to 0vu or more?

[Alex1990]

If it is assembled remove the BIO take a good couple of photos of the top of the sc pcb and bottom of pot pcb first and I will check it

Here we go! I did try reflowing make up pot joints just in case but it didn’t help.

If you measure the makeup pot outside pads with pot fully CCW and BIO unplugged do you read 10k?

Hi Joe

Do you mean these pads? Reading is 300ohm

Best,
Alex

[Joe Malone]

Here we go! I did try reflowing make up pot joints just in case but it didn’t help.

If you measure the makeup pot outside pads with pot fully CCW and BIO unplugged do you read 10k?

Hi Joe

Do you mean these pads? Reading is 300ohm

Best,
Alex

Yes unplug the BIO pcb ribbon cable and see if it changes to 10k?

If not unplug the pot ribbon cable from the SC PCB and see if it changes to 10k?

If it says at 300ohm then the problem is on the pot pcb and most likely some strange short in the pot or pcb.

If you have the pot pcb out and it measures 10k try measuring from the pot legs to the pot metal frame to see if there is a short.

Let me know what you find.

[Alex1990]

Hi- So with both SC and/or BIO boards unplugged it’s still 300ohm

[Joe Malone]

Hi- So with both SC and/or BIO boards unplugged it’s still 300ohm

Pull out the pot pcb out and if it measures 10k try measuring from the pot legs to the pot metal frame to see if there is a short internally in the pot.

Let me know what you find.