LA-4 Help Thread!

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Luny Tune

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Here is the documentation for the project with assembly notes:

http://www.tunetown.dk/download/LA-IV.pdf

Including a BOM, drawings of the board and a guide to connect the switches.
Missing is some pics from a stuffed board I made. I can't find the damn cable to go between the camera and the computer. I'll update the pdf with them of course when I find the cable later.

And here's the best manual for the li'l devil:
http://www.tunetown.dk/download/LA-IV%20Complete%20Manual.pdf

Including test and adjustment procedure.

Our version is the schematic on page 31. Numbers on the board for wiring corresponds with the numbers in the schematic so just work with that.

This version differs from the original schematic in the following ways:

1. RCA4136 quad opamps have been replaced with the TL074 quad opamp making the board pin compatible with even more esoteric quad opamps like the MC33079. (Pinout does not match the schematic. Refer to the datasheets for the two types of quad opamps when tracking errors. I will update the schematic with the pinout for TL074 and put it in the pdf-document at some point.)

2. Optos from the original as ordered from JBL as replacement parts can be fitted right into this board effortlessly, but with a few and easy modifications it's also compatible with other optos like the Vactec Vactrol VTL5C4/2.

3. The 2n6716 and 2n6728 transistors have been replaced with BD135/136 or BD139/140 transistors.

4. The output transformers I've tested are: OEP A262A2E and Cinemag CMOQ-2S which both work just great. I have both installed in two LA-4's and I don't prefer one over the other. I'm sure the Lundahl LL5402 will work just fine too as these three are interchangable in many designs.


Credits:
Thanks to Rasmus Fris for helping out with the prototype.
Thanks to Jakob Erland for great inspiration and general help.
Thanks to David "Craptical" Carlsson for kind assistance.
 

Luny Tune

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Which ones do you have?

I've tried the VTL5C4-2 and it sounded juuuust slightly different than the NSL32 in my prototype. It sounded much like the diy opto I made which also sounds slightly different than NSL32.

So yes you can use Vactec optos instead....but I'm not sure "which" Vactecs will work and which will sound good on top of that. I know the VTL5C4-s works and sounds good. Other than that...I recommend testing them out. They either work or they don't, I guess. You can't really damage anything by testing whatever optos you have.
 

pedroplanet

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I've downloaded all the info and I'd really like to build one of these - by the way thank you for the great work!

When will you have more PCBs??  8)
 

Luny Tune

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I'm not sure when there'll be a new batch made. I'll announce it in the Black Market when it happens.

@3nity
Check out the comparison chart on page 46 in this document: http://www.datasheetcatalog.org/datasheet/perkinelmer/VT500.pdf

I'm sorry but I have no idea how much these specs matter. Jakob E. told me that we're only using a little bit of the LDR's range.

The NSL32 is right on the money soundwise in my opinion and it's by far the cheapest opto too so though I certainly understand why you want to use the optos you already have, I don't see too much point in experimenting a whole lot. But hey, try 'em out! The worst thing that can happen is you get wiser and it'll cost you 5 bucks extra per limiter you build. :)

I'm probably cannibalizing my What? comps and replacing them with LA-4s in my setup. In that case I'll need six LA-4s in all. I believe I put VTL5C9 vactrols in them and I will of course test them in the LA-4 too and repoart back here.
 

Luny Tune

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Yes, I know it's fast and I worry that it'll distort more than we'll like.

I haven't checked with the NSL32 but the DIY opto has much the same attack and release times as the opto in the LA-2 as far as I can hear.
 

geoff004

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okgb said:
is there a North American source for the NSL32  , like digikey ?
[ i know i'll look but thought i'd ask first ]

http://www.alliedelec.com/

they've also got the 6910 if you go that route.

2 questions about the build:
Anyone plan on using the EA2503 from classic api?  It should work well, right?

and what about the idea of moving one of the LEDs (from the LDR section) to the front panel in place of a meter?  does it need 2 LDRs?



 

kazper

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If you revise the PCB I think making it setup for the NSL6910 and the Vectrol parts would be helpful.

Since I've been hanging out in a small machine shop lately, I'v been looking at getting a mini mill and lathe and will probably just build a tight fitting adapter for the NSL for my kits when I get there. But it would be nice to have a clean drop in solution that the Vectrol pieces can, thinking layout on DOAC PCB.

You may just as well bring up the Power rail to the top part of the pcb.

Kaz
 

Luny Tune

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I fail to see how four more holes would change the procedure:

Drop in the LED side first. (On the NSL32 the LED has the short, thin legs.)
Bend the LDR's legs and put them through holes in the PCB.

It's the exact same procedure with the original type opto.

The only difference is the 90 degree twist on the LDR. Oh, and the LED's legs on te NSL32 are slightly further apart.

But then again Vactec's optos are slightly different from the other two...

Dunno...let's hear what others have to say about it when people start assembling. :)

@gar381
Those look A LOT like the NSL32.... Maybe their actually NSL32s that didn't fall within tolerance or something... At that price I would certainly recommend testing them.
 

geoff004

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I wanted to add a bypass to this build.
I thought I'd just setup one of the power sections for +12v and use relays.
Is it as easy as putting in a 7812 in the spot for the 7818?
And can I just leave out all the stuff on the -v side?
any other changes?
thanks
 

Luny Tune

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geoff004 said:
and what about the idea of moving one of the LEDs (from the LDR section) to the front panel in place of a meter?  does it need 2 LDRs?
Yes, you can certainly do that. You won't be able to adjust the unit the way it's laid out in the manual though. But if you adjust it by ear or by ear and comparing it to the reference files I've uploaded for instance then you can certainly get it to work perfectly fine without the second LDR and the meter.
 

helterbelter

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Got my first la4 clone working.
The panel  is very temporary, haha, the panel's something that I'll do later this year. This LA 4 is built in SSL 5k module format, therefore the powersupplypart wasn't needed, so I cut it off (it'll live a life of it's own one day !). The Jensen output transformer is temporary as well, I have ordered an OEP for it. I used clarostat conductive plastic pots (from....SSL modules, ha), and Sueffer rotary switches (4mm shaft, and smaller bodies). The meters that I have are bought from a PP member, through ebay, for very little money. I think it came from a Sony or Teac machine.

When I received the OEP's and another pair of NSL32's, I'll finish the other LA4 board, and I'll make a dual mone/stereo cassette with an improved (but still temporary) frontpanel.

When I've finished reconstructing my SSL console, I'll order a decent frontpanel from schaeffer. And then I'll show the whole of it, haha

But for now, this LA-4 works !  :)

la42.jpg

la41.jpg


Thanks Luny Tune !
 

okgb

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looks like a 500 series module , nice ! [ neat & tidy ]

hey , i'm not close to stuffing my boards yet
but i have the  opto's and want to solder them on so i don't
misplace them , which way do the dot's go on the short leads ?
 

3nity

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Looks very neato...
However i dont really know how that meter tracks....

I see you used electrolytics where the true LA-4 used tantalums...

Thanks.
 
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