LA500 opto comp leveling amp BUILD THREAD 500/51X

Support for JLM Audio Kits

Moderator: Joe Malone

Stephen_Lam
Posts: 2
Joined: Mon Mar 19, 2012 11:15 am

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by Stephen_Lam »

Hello Joe,

I've recently purchased an LA500 (used, built by someone else) and ran into issues with calibration.

I followed the instructions you've outlined methodically. I used a 1kHZ sine tone generated by "Test Osc" in Logic Studio through my Digi 003 interface. When I set it to -18dBFS, which is what I'd like to calibrate the LA500 to, I couldn't get the meter's needle to go all the way up to 0VU before I reached the turning limit of the 0VU trim pot (I started to hear the click sound from the trim pot). The needle was staying somewhere in the -2dB and -3dB area.

On the other hand, I was able to calibrate the LA500 when I increased the signal to -14dBFS. The needle did go up to 0VU with a little room to spare, and I was also able to follow through the rest of the calibration (adjusting GR, then Balance).

Since the rest of my studio is calibrated to 0VU = -18dBFS, I would really like to be able to do so with the LA500. Is there anything I should check and is there anything I am doing wrong? Since I didn't build the unit myself I am not sure if there was anything wrong with the build itself.

Thanks,

Stephen Lam

User avatar
Joe Malone
Site Admin
Posts: 2068
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

Stephen_Lam wrote:Hello Joe,

I've recently purchased an LA500 (used, built by someone else) and ran into issues with calibration.

I followed the instructions you've outlined methodically. I used a 1kHZ sine tone generated by "Test Osc" in Logic Studio through my Digi 003 interface. When I set it to -18dBFS, which is what I'd like to calibrate the LA500 to, I couldn't get the meter's needle to go all the way up to 0VU before I reached the turning limit of the 0VU trim pot (I started to hear the click sound from the trim pot). The needle was staying somewhere in the -2dB and -3dB area.

On the other hand, I was able to calibrate the LA500 when I increased the signal to -14dBFS. The needle did go up to 0VU with a little room to spare, and I was also able to follow through the rest of the calibration (adjusting GR, then Balance).

Since the rest of my studio is calibrated to 0VU = -18dBFS, I would really like to be able to do so with the LA500. Is there anything I should check and is there anything I am doing wrong? Since I didn't build the unit myself I am not sure if there was anything wrong with the build itself.

Thanks,

Stephen Lam
HI Stephen
The lowest the LA500 can be calibrated normally is to +4dBM = 0VU = -14dBFS on Digi003 = K14 Scale. So from your description on the adjustment it sounds like the LA500 is working fine.

There is a track between IC1 pins 6 and 7 on top of the MAC PCB that can be cut and 2 x 10k resistors added. But this needs to be cut before the ic socket is fitted.

Since the LA500 is built already IC Pin 6 could be folded up and out so it doesn't go into the IC socket and a 10k resistor soldered between pin 6 and pin 7 of the IC and a second 10k resistor from pin 6 to 0v on the PCB. This will give the VU meter a 6dB boost and allow 0VU = 0dBM calibration to work.
Joe :-)
JLM Audio
Capturing Audio without Injury

Stephen_Lam
Posts: 2
Joined: Mon Mar 19, 2012 11:15 am

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by Stephen_Lam »

Hi Joe,

Thank you so much for your quick reply. Good to know that my LA500 is functioning correctly. I'm not familiar with the K14 and K20 calibration scales. Time to do some research online.

I would need to evaluate the difficulty of the surgical implants of the 10k resistors to see if it's something I can take on, or else I would need to live with it calibrated to -14dBFS. Would you mind clarifying for me a few things? How do I identify pins 6 and 7 of IC1? Also, where is 0v on the board (for the 2nd 10k resistor you said to solder between pin 6 and 0v)? If I don't attempt to do the mod myself, I know someone who should be able to.

Thanks again for your help! The compressor sounds killer and I might get another one just to be able to do linked compression/limiting!


Stephen Lam

kante1603
Posts: 86
Joined: Wed Jan 20, 2010 6:12 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by kante1603 »

Hi Stephen,

Identifying pins on op amps is easy.
Look at the ic,there's an orientation mark on it,sometimes a dot.
The pin to the left of it is always pin 1.Just count counterclockwise arround it.
Also you can have a look at the ic datasheet,it is described there very well.

Hope to have helped,

Udo.

permeke
Posts: 19
Joined: Sat Apr 09, 2011 10:35 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by permeke »

solved ( wrong resistor value :oops: )
Last edited by permeke on Sun May 20, 2012 6:43 am, edited 1 time in total.

kante1603
Posts: 86
Joined: Wed Jan 20, 2010 6:12 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by kante1603 »

Hi Joe,

finally I had the time to do some testing of my 2 LA500s.Have built them a while ago,but my students give me way too much work ("diploma time") :)
Now what can I say except of AWESOME!
Building:
It is really easy,everything is well documented,your help is super great as always.Adjusting the meter is really easy,anybody can do that I bet.
About sound:
When switching them in everything "glues" together immediately,overtones from the doa/transformer combination makes listening a breeze!
I do have a lot of compressors,I have heard a lot of them in my life and I´m quite experienced in using them.
But these guys are blowing me away!
It´s nearly impossible to dial them in a wrong way (except of people who don´t know how to use dynamics of course).
What I really like is how they act on complex material,the hpf in the sidechain at 100Hz and a ratio of 3:1 is simply a supertool to "compact" things without getting over-compressed but still staying "airy".Even at heavy compression it takes a certain amount of "cranking" the threshold until it starts to pump.If I had the money I would have tons of them!
I will definetely use them in our studios as well as in live situations like musicals.
About current:
Joe,I asked you a while ago what the approx. current would be for my calculations.I made a quick measurement today.Results are approx. 60mAs on positive and around 55mAs on the negative rail.So one can fill up two full 51x racks running from just one psu without even touching the +/-16v rails (from what I understood the LA500 pics up the higher rails in a 51x system,no?)

To me these guys are nothing but a masterpiece,thank you so much again for making this possible for us DIYers!

And now:People-Get started building some of them-you definetely will not regret it!!!

Congrats Joe and all the best whishes from munich,germany,

Udo.

P.S.:Attached a pic of mine,the right hand piece is just my headphone amp to prevent them from falling off my table (yes,that´s an amphead :lol: ).
You do not have the required permissions to view the files attached to this post.

vernois
Posts: 5
Joined: Sat Sep 18, 2010 12:20 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by vernois »

Hi Joe, I seem to be having some issues in setting up one of my LA500's. When going through the steps, I can't get any response When i turn the threshold up. Any ideas on what might be causing this issue.
Thanks, Gavin

permeke
Posts: 19
Joined: Sat Apr 09, 2011 10:35 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by permeke »

When unlinked , my 2 builds are compressing and tracking equal on both sides when feeding 1Khz.
When linked , master unit gives 3dB more compression, slave 3 less !
any idea ?

User avatar
Joe Malone
Site Admin
Posts: 2068
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

vernois wrote:Hi Joe, I seem to be having some issues in setting up one of my LA500's. When going through the steps, I can't get any response When i turn the threshold up. Any ideas on what might be causing this issue.
Thanks, Gavin
That doesn't give me much info to go on. So probably best to send me a couple of photo's of the MAC PCB and wiring to my email as usual.

Since you have 2 x LA500 swapping the LA500 PCBs, Ribbon cables and transformers would help to narrow down the fault.
Joe :-)
JLM Audio
Capturing Audio without Injury

User avatar
Joe Malone
Site Admin
Posts: 2068
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

permeke wrote:When unlinked , my 2 builds are compressing and tracking equal on both sides when feeding 1Khz.
When linked , master unit gives 3dB more compression, slave 3 less !
any idea ?
Ok to start with there is no master unit in old opto comps. Both comps need to be set to the same exact compression settings (switches and threshold pot) and GR Meter level before linking.

If one comp pushes the other out after a accurate full stereo alignment (which I will have up here in the next week) there is a simple mod with a extra 1k 25 turn pot that can be done to tame the heavier compressing comp to the match other comp.
Joe :-)
JLM Audio
Capturing Audio without Injury

kante1603
Posts: 86
Joined: Wed Jan 20, 2010 6:12 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by kante1603 »

Hi Joe,

Maybe you haven't seen my previous post.I'm about to calculate currents in my new 51x racks.Am I right thinking that when LA500s operated in a 51x rack they use the 24v rails and leave the 16v rails untouched?I'm thinking of a useful assignment of my mixed up audio modules,that's why.

And any news on the "1k pot mod" for better stereo operation?

Thanks in advance,

Udo :wink:

User avatar
Joe Malone
Site Admin
Posts: 2068
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

kante1603 wrote:Hi Joe,

Maybe you haven't seen my previous post.I'm about to calculate currents in my new 51x racks.Am I right thinking that when LA500s operated in a 51x rack they use the 24v rails and leave the 16v rails untouched?I'm thinking of a useful assignment of my mixed up audio modules,that's why.

And any news on the "1k pot mod" for better stereo operation?

Thanks in advance,

Udo :wink:
Thanks for the great review of the LA500 kit. I had missed it some how sorry.

Please feel free to put it up on the web shop review link below.
http://www.jlmaudio.com/shop/index.php? ... ite_review

I will get the photo's up of the pot mod up when I get back to the workshop tomorrow. Yes the LA500 only uses the highest voltage rails available.
Joe :-)
JLM Audio
Capturing Audio without Injury

kante1603
Posts: 86
Joined: Wed Jan 20, 2010 6:12 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by kante1603 »

Joe Malone wrote:
kante1603 wrote: I will get the photo's up of the pot mod up when I get back to the workshop tomorrow. Yes the LA500 only uses the highest voltage rails available.
Hi Joe,

Good to hear,this way I can distribute my currents better in my 51x racks,cool!

Thank you!

Udo.

golddust
Posts: 4
Joined: Tue Jun 12, 2012 8:38 pm

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by golddust »

Hello,

I've just finished assembling the LA500 and am having problems. In fact, I have the same problem as someone earlier in the thread in which level drops and low end seem to roll off (drastically) with compression engaged.

I've checked the transformer and measured 13.2V betwwen all -1/+1 -2/+2 and -3/+3. IDC10 header seems fine as well.

Help needed!!!

Many thanks!

Jantzen

User avatar
Joe Malone
Site Admin
Posts: 2068
Joined: Wed Jan 24, 2007 11:35 pm
Location: Brisbane, Australia
Contact:

Re: LA500 opto comp leveling amp BUILD THREAD 500/51X

Post by Joe Malone »

golddust wrote:Hello,

I've just finished assembling the LA500 and am having problems. In fact, I have the same problem as someone earlier in the thread in which level drops and low end seem to roll off (drastically) with compression engaged.

I've checked the transformer and measured 13.2V betwwen all -1/+1 -2/+2 and -3/+3. IDC10 header seems fine as well.

Help needed!!!

Many thanks!

Jantzen
Please give me a answer to each question below so I can help you.

I Presume you mean ohms not volts?

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.

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

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)

If not remove the transformer and test between +1 to -1, +2 to -2, +3 to -3 to see if they all test 14ohms or not?

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?
Joe :-)
JLM Audio
Capturing Audio without Injury

Post Reply