LA500 opto comp leveling amp BUILD THREAD 500/51X

[golddust]

I Presume you mean ohms not volts?

Yes.

The only reference to this on the thread I can find was the transformer which had its IDC header solder joints broken by pressing in the header to hard which was fixed with re-soldering the header.

I'm experiencing the same symptoms he had, which is a Level Drop and also Low End Rolloff with the compression engaged (meter switched to either GR or VU)

Are the 7 outside gold pins soldered on the transformer 10 pin header?

Yes

Below is the standard tests for output transformer and ribbon cable.

Simply test with the module off on the bench with a ohmmeter on the transformer terminal block between +P and -P to see if you get roughly 14ohms and between +S and -S to see if you get roughly 28ohms?
(This proves the ribbon and output transformer are both ok if measurements are correct)

They test 13.2ohm and 26.1ohm on my meter. I assume this is ok?

To test LA500 without output transformer unplug transformer from LA500 pcb and use a wire between P+ and S+ and 0- and S- as the overlay shows. This will allow you to fully test and use the LA500 module without the output transformer?

Will do this later and see. But it seems my transformer and ribbon is fine with the reading above?

[Joe Malone]

They test 13.2ohm and 26.1ohm on my meter. I assume this is ok?

Yes that is fine.

But it seems my transformer and ribbon is fine with the reading above?

Yes correct.

What type for rack do you have this in ?

What voltage do you get at pin 4 and pin 8 of the OPA2604AP?

What voltage do you get a -V and +V of the 99v sockets without opamp fitted?

Email me a couple of large clear well lit in focus photos of the top and bottom of the whole LA500 PCB with 99v opamp removed so I can check all parts values etc.

[golddust]

Many thanks Joe!

I will shoot some clear pictures tomorrow when I disassembled the unit tomorrow. I'm not sure how I could measure the voltage as I don't have an extender. I have this in a Radial Workhorse.

I have to mention that the compression works, makeup gain works. As soon as I switched the meter to GR or VU i'll get a level drop and a low end roll off.

Thanks AGAIN!

Jantzen

[golddust]

Having finally get it up and working properly, I couldn't say enough thanks to Joe here. Joe has been most helpful in getting my unit working. Being someone who has not much knowledge in electronics but handy with a solder iron from experience, this project has been very fun despite having problems that took a while to troubleshoot. Could not done it without Joe's generous help!!

[Joe Malone]

Many thanks Joe!

I will shoot some clear pictures tomorrow when I disassembled the unit tomorrow. I'm not sure how I could measure the voltage as I don't have an extender. I have this in a Radial Workhorse.

I have to mention that the compression works, makeup gain works. As soon as I switched the meter to GR or VU i'll get a level drop and a low end roll off.

Thanks AGAIN!

Jantzen

This ended up being the relay not pulling fully on due to the lower volts across the relay coil on the lower 500 series power rails. This was still above the supposedly guaranteed operate voltage stated by the relay manufacturer. But I recommend all 500 series builds from now on to change R14 on the MAC PCB from 2k7 to 1k8 which will give the relay its normal nominal voltage and it will operate normally in 500 and 51X racks.

[Joe Malone]

Added the stereo balance mod to the third post at the beginning of this build thread.

Direct link
http://www.jlmaudio.com/forum/viewtopic ... =187#p1709

[vernois]

Hey Joe,
I'm still having issues with not getting any GR with one of my units.
I've replaced suspect trim pots and swapped all known working parts from the other module, but still at -14 db's in Logics oscillator I get at best a 3 or 4 db's at 10:1 of momentary reduction before the signal returns to 0. These settings work as they're supposed to on the working unit. I've isolated the problem to the Comp board but I've not been able to find any solder bridges or missplaced parts, I've compared both units several times and keep finding no noticeable physical problem.

I hope that narrows things down a little, thanks for your help.
Gavin

[Joe Malone]

Hey Joe,
I'm still having issues with not getting any GR with one of my units.
I've replaced suspect trim pots and swapped all known working parts from the other module, but still at -14 db's in Logics oscillator I get at best a 3 or 4 db's at 10:1 of momentary reduction before the signal returns to 0. These settings work as they're supposed to on the working unit. I've isolated the problem to the Comp board but I've not been able to find any solder bridges or missplaced parts, I've compared both units several times and keep finding no noticeable physical problem.

I hope that narrows things down a little, thanks for your help.
Gavin

Have you swapped OPA2604AP between MAC PCB's?

What voltage is at pin 4 and pin 8 of the OPA2604AP to 0v?

There should be about 4volts between the end two solder pads of the zero trim pot?

Email me some clear in focus well lit large photos of the top and bottom of the MAC PCB so I can check it over.

[kante1603]

Added the stereo balance mod to the third post at the beginning of this build thread.

Direct link
http://www.jlmaudio.com/forum/viewtopic ... =187#p1709

Wow,cool!Tricky!
Thanks a lot Joe!!!

Udo.

[vernois]

Hey Joe, I've swapped opamps, read - 15v and +15v at pins 4 and 8, and 4.15V across the zero GR trim. So that all seems good. Ill send some photos when I get a chance. I really appreciate the time you put into support.
Thanks again, Gavin

[axel]

hi joe,have succesfully completed the first la500 and it sounds lovely and clear as i never heard before!
now i am up with the second and here is the problem with the output tranny: the middle yellow tube (in which the wire is covered) Is reaching about 1 mm over the niveau of the surface, i think the tube is abit to long.
my fear is that the wire could get damaged when fitting the tranny as this side will hit the bracket..
my idea is to desolder the wire, cut a little bit of the tube and refit ? -should have very safe hands there..
or should i just try to fit it ? i dont know how i could upload a photo
next : i fitted 2,7k to r14, don´t know how i could not read all the errata note..
so the unit is working awesome and debuilding and desoldering at this place with the switches from the other side would be a major pita..
so what does r14 and what will happen with the wrong value
-i will use this unit always whith +-24v from my 51xrack if this helps
if it is a greater problem i will try to paralel r14 with 4.7k from the upper side then....
thanks for advice and greets
axel

[vernois]

Hi Joe, I sent a couple of pictures to your "sales" email address. It's the only one I could find. If you get a chance, could take a look? Thanks, Gavin

[Joe Malone]

hi joe,have succesfully completed the first la500 and it sounds lovely and clear as i never heard before!
now i am up with the second and here is the problem with the output tranny: the middle yellow tube (in which the wire is covered) Is reaching about 1 mm over the niveau of the surface, i think the tube is abit to long.
my fear is that the wire could get damaged when fitting the tranny as this side will hit the bracket..
my idea is to desolder the wire, cut a little bit of the tube and refit ? -should have very safe hands there..
or should i just try to fit it ? i dont know how i could upload a photo

I saw the photo you sent me. Just lay the transformer on its side in the bracket and do up the bolts and the fibreglass wire tube will flatten out as the otherside it held by the the white bobbin. If you have any problem after that let me know.

next : i fitted 2,7k to r14, don´t know how i could not read all the errata note..
so the unit is working awesome and debuilding and desoldering at this place with the switches from the other side would be a major pita..
so what does r14 and what will happen with the wrong value
-i will use this unit always whith +-24v from my 51xrack if this helps
if it is a greater problem i will try to paralel r14 with 4.7k from the upper side then....
thanks for advice and greets
axel

R14 = 2k7 is perfect for 51X no need to change anything. On 500 series +/-16v if the relay is working it is ok to leave as 2k7.

If the relay is not working change to 1k8. For all new (not started yet) builds I just recommend using 1k8 resistor instead for 500 which will also work for 51X as well.

[Joe Malone]

Hi Joe, I sent a couple of pictures to your "sales" email address. It's the only one I could find. If you get a chance, could take a look? Thanks, Gavin

Ok I will check the photos over this weekend and let you know what I find.

[axel]

many thanks for your quick answer so now up for finishing the second unit !
greets
axel