LA-4 Help Thread!

Just to verify with everyone else...

Using NSL-32 the dot goes toward the Opto # on the pcb correct?

I'm going to try them in the 2nd position as someone mentioned and the 6910's in slot 1

Yes.

I don't think it's a good idea to mix the two optos. I think you'll have trouble adjusting it correctly because you need the meter to adjust it and with two different optos in there their difference in operation will give you a reading different from what's actually happening in the opto in the signal path. To me it's a weird disposition and I fail to see any reason why you would intentionally make it more about guesswork than actual measurement you can trust. But maybe that's just me...

BUT when using the NSL32 you also need to do one more thing!
Change R13 (the 82KΩ just above jumper 2 on the pcb) to a 16KΩ resistor. (Alternatively you can just mount a 20KΩ resistor in parallel with the existing 82KΩ. That's what I did and that works perfectly fine.)

That'll enable you to adjust to the correct ratio on the trimmer.

It's necessary because the NSL32 needs a lot less current to work and makes correct trimming impossible with the original value.

It also works just fine to replace the 500Ω ratio trimmer with a 2K5Ω trimmer, but the above method seems easier.

SaMpLeGoD said:

Hey LUny, what did you changed beside that? can you post it?

Click to expand...

Sorry, I haven't checked yet. I will as soon as possible.

kazper said:

Using NSL-32 the dot goes toward the Opto # on the pcb correct?
I'm going to try them in the 2nd position as someone mentioned and the 6910's in slot 1

Click to expand...

yeah-
don't do that because it won't work right.  What ever you use, put the same in both positions.
Personally I'd step up the ratio trimmer from the beginning - it'll make it easier when you decide that the 6910 is too slow on the release (IMO).

geoff004 said:

Luny Tune said:

We've discovered that when using the NSL-32 opto you need to modify the circuit a bit. Instead of the 500Ω Ratio trimmer you should put in a 2K5Ω trimmer. I believe a 1K trimmer would be just fine, but I have only tested with a 2K5 trimmer and that works perfectly.

Click to expand...

And all this time I though it was just me.

I finally swapped out the NSL-32 in my unit with the NSL-6910 + 10mm red LED and it sounds wonderfully amazing (superlative superlative).  No distortion even when smashing.
My suggestion is to use the NSL-32 for opto 2 and the 6910+LED for opto 1.
I also put a TLE-2074 in the IC1 position and it sounds so smooth.

Click to expand...

funny geoff004 you gave me the idea to try.

I'm waiting on some black PCV material to show up and take over to my friends house to have his Dad mill out to make a holder for the LED/Cell. I have some white nylon material but I wasn't sure if it would cause a effect on the NSL-6910's and the squishing function and you only get so many favors.

I ordered the NSL32's by mistake so I thought what the hell I'll try them or make the compressor squish this weekend.

http://www.twin-x.com/groupdiy/albums/userpics/Front_Parmetal_1U_LA4.zip

Untested, so verify your goodies will work.

Meter is a Sifam Retro Al-15, 2-56 screws holding it to the FP and it's for a Par-Metal 1U rack case.

You will need to adjust the lip's to make it work also... This is DIY.

I removed some of the markings and got the panel down to $60 which I will send in and test once I print it out full scale.

Also note you should remove the meter outline, will fix it later


Kevin

Hello all! I just wired one channel of my dual LA-4, and it's working perfectly... I didn't listen the audio , just saw the behaviour, and it's working propertly!

Luny, I just wired the OEP trafo as you said, reversed, and I think is working... please when you have some time, please post if did you modified something else beside that
Thanks a lot, it's a very nice project!

Cheers,

Eddie

Just a quick question: If I understood correctly when I read in the LA-4's manual, the Input range is

HI    = Balanced (but at 0dbm);
LOW = Unbalanced (-20dbm);

Right?

Eddie

Balancing doesn't change when you flick that switch.

It can be a little difficult to grasp the way to use that switch, but it really is quite simple. (Maybe you get it right away but I've had to explain it MANY times to some.)

The thing is that it works opposite of what some finds logical.

It's not an Input Sensitivity switch but an Input Range switch. If what you're pouring in is high level and you experience overload then switch to High. That ensures that R7 (30KΩ) is in play and pads the signal 20 dB. If your input signal is low level and you need more you then switch to Low and thereby bypassing R7 to give you 20 dB more signal at that point.

However, now that I'm writing this I get an idea. I notice that when switching to High, I believe that wire number 3 is picking up noise (it's now just lifted actually) and so I tend to just leave the LA-4 permanently in the Low position and control the input level elsewhere in my setup. What if we put in a 30KΩ potetiometer and move it to the front plate instead of the switch. Then there would never be any wires lifted and on top of that it would be possible to maintain max level without overload and not keeping an unnecessary 20dB headroom. I think I'll experiment with that.

Luny Tune said:

However, now that I'm writing this I get an idea. I notice that when switching to High, I believe that wire number 3 is picking up noise (it's now just lifted actually) and so I tend to just leave the LA-4 permanently in the Low position and control the input level elsewhere in my setup. What if we put in a 30KΩ potetiometer and move it to the front plate instead of the switch. Then there would never be any wires lifted and on top of that it would be possible to maintain max level without overload and not keeping an unnecessary 20dB headroom. I think I'll experiment with that.

Click to expand...

Thanks for the explanation, so, the Input range switch is nothing but a 20dB Pad switch... ok, I wired it in my back panel, just over the XLR's, maybe I'll leave as you said, in LOW mode and try to rise the gain somewherelse on the chain!
Thanks a lot Luny!

Eddie

See? You got it the other way around!

When leaving it in the Low position you don't need to boost the input signal anywhere but rather dampen it in case you're overloading. See?

Ok! finished min! is alive and kickin'! nice unit Luny!
I used the bypass PCBs that came with my DAOC... I'm not building that right now
I adjusted the unit following the manual, but I didn't touch the Ratio and common rejection trimmers... the manual just give a test procedure, not to regulate them... so as long I think it sounds and behave as it should, that's fine! I adjust the other ones for meter tracking, zero and stereo threshold issue

Nice! I'll post some photos

Thanks a lot for the great project!

Eddie

Hi everyone,

This might be a little of subject, but I wanna know what you guys think especially those that use this comp.

I'm getting ready to do some vocal recording sessions and I want to get a compressor build. I am currently working on a LA4A, Drip 175B and Mnats 1176 revA.

Given my limited time and budget, which compressor should I concentrate on finishing? The 175B has very expensive Sowter transformers and PSU, for the 1176 I wanna get all the goodies from hairball audio and I wanna take my time. So that leaves me with the LA4A...

In your experience is it a good comp for vocals? I'll be recording hip hop and I need slight level control / punch pre-converters.

What ya think???

J

Hey Matthew!

I builded some 1176 and just finished a dual LA-4! both are nice, but with the 1176LN you'll get some extra color to the sound because of the in and out transformers, they will add some mid range that is awesome for rock vocals, snares and so on. The LA-4 is transparent, soft when you need it and super hard when you want! talking about the price, the LA-4 is cheaper, because the expensiviest part is the OEP transformer for the output (€15), the rest is just the optocoupler (around €3), resistors, few caps, 4x 10k pots
Is really up to you, both are great!
Cheers,

Eddie

Thanks Eddie for that.

Sounds like the LA4A is a nice all rounder and is cheaper and simpler??? to build but the 1176 got some extra "grit" and "color" to it which makes it very temping for what I need. Just finished a G-Pultec to go with my G9 pre so I just wanna finish off my recording signal chain with a comp...

I wish I had the cash to do both... at the same time... lol ;D

BTW, have you tried your dual LA4A on vocals yet?

J

Matthew Jacobs said:

Sounds like the LA4A is a nice all rounder and is cheaper and simpler??? to build but the 1176 got some extra "grit" and "color" to it which makes it very temping for what I need.

Click to expand...

My LA4 kills my old 1178.  The only thing it doesn't do (that I care about) is variable release time. 
Other than switching between LDRs is there any way to change the release?

Matthew Jacobs said:

BTW, have you tried your dual LA4A on vocals yet?

Click to expand...

Hey! didn't try yet! only in a drum track! sounds awesome!
It's a really nice unit!

Eddie

Does anyone happen to have Eagle files for this project? I'd love to have a few printed up at a board shop - but I'm pretty new to all of this and haven't dug into pcb layout yet. . .

jmejia said:

Does anyone happen to have Eagle files for this project? I'd love to have a few printed up at a board shop - but I'm pretty new to all of this and haven't dug into pcb layout yet. . .

Click to expand...

White market.... there is a guy who sells them cheap... Names Gustav....

knock 3 times and don't ask for da Gerbers it will get ya shot around these parts kid...

Hi there...

I've got a few 6.8 uF Tantalums that I'd like to use, but they are 35V.
Is there any reason that the electrolytics are listed as 63V in the BOM ?

Looking at the schematic, I can't really see why 35V wouldn't be enough... then I might be missing something  :-\