LA-4 Help Thread!

[Luny Tune]

1. That's not a diagram. That's a pcb layout.
2. Correct in what sense? What does the numbers mean?

 

[ilfungo]

I added numbers to identify  trimmers function

1) common mode adjust R4
2) zero adjust R51
3) meter tracking R49
4) threshold trim R57
5) ratio R34
thanks

 

[Luny Tune]

Oh, sorry. I didn't see the notes on te left.

Yes, that's correct. (As it says in the manual.)

 

[ilfungo]

I can not make the machines work properly in stereo ...
all resistors are 1% 1 / 2 w matched
any ideas?
where is the stereo tracking trimpot?
Thanks

 

[benlindell]

I believe it's R57

 

[ilfungo]

thanks  benlindell
I did all the settings but in stereo does not work ...
I used this switch could be the problem?

 

[Luny Tune]

When you say it doesn't work, do you mean that it doesn't link the two or does it compress in weird way? What happens/doesn't happen?

 

[ilfungo]

the link works but the two machines compress differently
GR-5db

LA4 1- 5db
LA4 2- 5db

GR-10db

LA4 1- 7dB
LA4 2- 10db
Help!!! ???

 

[ilfungo]

The strange thing is that in dual mono mode, the compressors are much more linked :'(
What can be?
thanks...

 

[ilfungo]

work after several hours of calibration
but works only with 8:1 ratio
other ratios have differences 3db....

 

[MrZpliff]

The strange thing is that in dual mono mode, the compressors are much more linked :'(
What can be?
thanks...

Hm.. same thing for me. Tracks fine in dual mono, but acting weird in stereo....

 

[Luny Tune]

Maybe that's the need for matched pairs of LEDs and LDRs spelled out for us?

I'm just guessing... Mine works pretty good in stereo too and I haven't even gone through the stereo adjustment for them. I'm not sure how close they are exactly but I'll check...

Weird stuff.

 

[ilfungo]

Hello and thanks Luny
I used Vactrol VTL5C4 / 2
how do I measure and I select them?
Thanks

 

[MrZpliff]

Maybe that's the need for matched pairs of LEDs and LDRs spelled out for us?

I'm just guessing... Mine works pretty good in stereo too and I haven't even gone through the stereo adjustment for them. I'm not sure how close they are exactly but I'll check...

Weird stuff.

Yup, could be some case of mismatch. I gave mine to an experienced tech-friend to have a look at it. It could've beenm doing something wrong when calibrating it. If he finds something strange, I'll let you know.
It sounds fine in dual mono, so it's not the whole world if it doesn't work in stereo but it would be nice...

 

[ilfungo]

I may have found the problem ....
I can not calibrate perfectly trim ratio
I can replace trim  2k5 with 4k7?
thanks

 

[Luny Tune]

I don't know how far we can push that. I'd say you should just try it out.

 

[ilfungo]

I would replace the trimmer because when I do the  ratio calibration
I can not have the +2.5 db REQUEST
but only + / - 1.5dB
I compared  2 UREI LA4 silver face with 2 clone
and the sound is very close ...
Good ratio 2:1
4-8-12-20:1 are different in the attack,
clones seem to attack faster, and  nearest point threshold
Am I wrong?
May depend on the Ratio and Threshold setting that I can not do well?
Thanks and I hope I explained ...

 

[Luny Tune]

I think you're right.

The original seems to have a slightly "beefier" sound. And it's like it's faster to get the perfect setting for your instrument.

I also thing there's a difference in the attack, but also in the release and I believe that it's because with the vactrol and the NSL 32 we're moving away from the specific range on the logarithmic curve on the LDR that they zoomed in on when they designed the LA-4.

I get the correct beefy sound with my DIY optos when I use the correct LEDs and I believe that's precisely because I'm hitting the right spot on the NSL 6910's logarithmic curve. With the DIY optos I get the right action on the meters too. Do you notice the difference in the needle movement between the originals and the DIY version? The original crawls back up when it has moved far downwards and my guess is that your needle moves faster, correct?

That's not a difference in the meters themselves but in the optos.

PS: Thanks, ilfungo. I appreciate this "back and forth" with our experiences. We WILL find the perfect combination of every relevant thing here!

 

[Rybow]

Ilfungo- I am having a similar issue with the ratio trimmer as well. I cannot get the needed 2.5db increase either, and I have already replaced the 500ohm trimmer with a 1k. This made a difference, but only a very small one. Also, no matter what the ratio is, the output increase is the same, but if I induce some limiting and select a higher ratio, I do see an increase in gain reduction. I was going to try adjusting the unit with only one opto installed, but I haven't gotten around to it.

I switched the wires on the primary of the transformer, so now the From transformer + is going to F2 and the other wire is going to S1. Went to check polarity only to find my multimeter missing. I was robbed recently, and it turns out $60 multimeters are a hot item! Anyways, I could be wrong, but my LA 4 seemed to sound fuller than it did before. Again, I could be wrong. I'll check on the polarity as soon as I get a new meter.

I started on my second channel the other day, and I just might rip the current channel out and put the new one in its place. I am still having a few interesting issues, and I think at this point I should rebuild it from scratch. This board was my second ever circuit board, so the soldering is less then awesome, and I have ripped it apart 3 times. Not a loss though! I learned a ton from this board. 

I have those other IC's on order right now, and some NSL 32's to try. I am going to hold off on the switching optos experiment for awhile as well. I think I'll reuse my DIY optos and double check those LED values. Thanks for all that info on the optos Luny!

 

[ilfungo]

Hello Luny
with NSL 6910 you are able to calibrate the Ratio?
what kind of LED did you use?
try first to replace the trimmer ratio with  greater one
you think I risk damaging something?
thanks