D-LA2A Support Thread

[peterc]

Very nice!

 

[hugo]

Hi there.. just wanted to introduce my D-LA2A which I finished last night. I used Sowter 1449 input TXs and 1010s output Txs.
Thank you, Volker for this amazing project and thanks everyone for documentation within this thread.

Just have a question, when I dial in the Link between the channels, the GR backs up a bit. Is this the regular behavior of the compressor?

Cheers,
Falk

STereo link (correct me if I am wrong), make the "peak reduction" matched between both channels, and it is influenced by Both pots. It makes an average. For example, when you have the same signal passing channel one and channel 2, if you apply the same compression, the stereo link will not change the GR..But if you set up both channels with only one pot, your GR will be different.

 

[cdeboda]

The BOM link on the first page seems to be broken. Anyone have an extra BOM in stock they'd be willing to sell me?


EDIT:
Got ahold of the BOM that’s missing from the first page, thanks to Volker. Figured I’d share for anyone looking. IIRC, there may be an error or two (# of tube sockets?)

https://www.dropbox.com/s/4rl0h4ffai83wu6/d-la2a_bom.pdf?dl=0

 

[QNote]

Thanks, cdeboda.  It slipped my mind to update my links on page 89.  But, they are updated now.

NEWS:  I will have one final video coming out late March 2018 that will wrap up my D-LA2A series.  Thanks to those that have viewed them and found them helpful!

 

[peterc]

Hi Prentice

Looking forward to that, the previous videos were excellent

Many thanks
Peter

 

[davidbonk]

Wow... over 90 pages.
Guys.. I'm new to this, recently finished 4 x g-1176 and wanted to try to build a stereo la2a and found this thread about the d-la2a now...

i managed to find the current BOM
https://drive.google.com/file/d/1MGCUw8NQSS-w_h11ELy2DpzwSmV0qQrM/view

the link to the case
https://www.diy-racked.com/dr-cases/

But im not sure about
1) where to find the pcb ?
2) where to find the schematics?
3) and is there any "building instruction"?

thank you so much for you help guys!

Regards,
David

 

[peterc]

Welcome David

Check out the first post, all will be revealed.....

Peter

 

[Mikolaj]

Peak reduction pot has to be rotated too much before gain reduction kicks in.

With a 0 vu 1k tone at input and gain set to unity it takes the peak reduction dial to be rotated nearly all the way clockwise before the meter starts to act. Seems strange compared to other la2a's I've used. It sounds fine but the controls seem a little off.
Could it be the peak reduction tube? Or is there some adjustment to make it more  responsive.

 

[[silent:arts]]

fully open the stereo trimpot

 

[Mikolaj]

Problem with Peak reduction not kicking in until pot is nearly all clockwise

I fully opened the stereo trimpot and it did help with peak reduction dialing to a lower setting.

But I still get no gain reduction until the peak reduction knob is at position 6 then I can dial in -20 db if I want.

( testing at 1.23 v and 1 KHz)

Can I modify something that will get the gain reduction to start working around the 2 position on the pot?
Thank You.

 

[[silent:arts]]

Before thinking about modifications better find the fault.
Sounds like a wrong potentiometer taper?
LIN instead of LOG?

 

[Mikolaj]

Thanks Volker
I tested the pot and wiring to make sure the 100k pot was tapered. Its is.
Here is the pot i installed https://www.digikey.ca/product-detail/en/precision-electronics-corporation/KA1041S28/KA1041S28-ND/523420
Something must be in common, because both channels behave exactly the same ( 60% on dial before gain reduction kicks in). Same pots & same parts on each channel.

Solved!
When Looking at the B.O.M from mouser the pots that they suggested were linear taper. ( not evident at the time)
Further down on the B.O.M list they recommended higher quality pots from DigiKey ( which are the ones I ordered) they were logrithmic pots.
Changed only the peak reduction pot to linear and I get perfect resonse when dialinging in the gain reduction.
The other pots are log pots.
Hope this helps other builders
P.S. Thanks SilentArts for all the help.

I did some more testing because SilentArts schematic calls for a Log pot for the peek reduction.

I drew a graph of resistance vs degrees rotation for the pots that were giving me problems and compared with other log pots in my parts bin.
The graph showed an obvious manufacturing quality control error. It was not a logrithmic shape. It was 1k ohm flat until the pot was turned past 60 degrees then it jumped to 100k ohms in a linear fasion.
I guess the batch I ordered from digikey was a faulty manufacturing run.

 

[ilan]

Hello everyone!
Here's my finished D-LA2A with IGS T4Bs and NOS Tubes.
It worked like a charm and sounded brilliant until a couple of days ago....
well it still sounds great but doesn't compress on BOTH channels.
There's no differnce weather i link the channels or not.

can anyone please point me in the right direction to find the error!?
Unfortunately i'm not too good with electronics so i really need some help here.

thanks in advance guys!

best
ilan

 

[Rob Flinn]

Hello everyone!
Here's my finished D-LA2A with IGS T4Bs and NOS Tubes.
It worked like a charm and sounded brilliant until a couple of days ago....
well it still sounds great but doesn't compress on BOTH channels.
There's no differnce weather i link the channels or not.

can anyone please point me in the right direction to find the error!?
Unfortunately i'm not too good with electronics so i really need some help here.

thanks in advance guys!

best
ilan

Have you been playing with the stereo adjust pots ?  If you turn them fully one way you will get no compression.

 

[Apache5]

Hi all! Finally I finalised my D-LA2A. I had the pcb from a few years ago(white christmas edition). I used some things that I have at hand like the big 32pos switches, MCI Vumeters and audio trafos... The T4Bs I built from pieces that I bought on a website, dont remember wich one, wich sells all parts necessary. After de calibrating it works well and sounds good too.
The panel is from Schaeffer AG using digital print on it. Now it's in a friend's studio and he is very happy with it. The first 2 photos are not of the  completely finished unit.
I have to thank  [silent:arts] and  all the people who  wrote about it on that help thread that is full of good advices and help.

 

[stitch-o]

Hi all!

9 years of awesome compressor!!
But now I have small DC 'blip' on both audio channels
every 2 min or so...
Cracked the lid and noticed the neon on chn 2 is flickering slightly.

Tube maybe?

edit: well swapping tubes seem to change the time and nature of the issue...
Ill find a quad of good 7025s or such

 

[maumet]

you already implemented it...

That's just the 1meg trimmer/rheostat of the sidechain (R37), right next to C12.

You can play with the values in any way you like, try 0k, 500k and 1meg for starters...

Hi Kingston, is that all that it's needed to implement that HPF on the DLA2A? Any other useful info I can forward to my tech guy on how to do that?

Thanks in advance!
M

 

[cdeboda]

After running some tests, I found that in order for R37 to have some reasonable kind of functional range it should be a logarithmic steps (or a log pot). I did five steps with a Grayhill 71 series rotary using these values:

1. Short (flat)
2. 86.6k
3. 240k
4.511k
5.1M

Edit: Here's a frequency response graph showing the 5 positions. pretty cool that the center frequency changes in addition to the amount of low end attenuation.

 

[Rlucas41]

Howdy folks, does anyone have a Mouser cart for this project they would be willing to share?

 

[elpapadelcrio]

Hi Rlucas41

I never created a cart (s) since I bought the components little by little as money was flowing. I created and used this Excel BOM for the three units that I built so far, is not a cart per se but it contains all the mouser part numbers, you just can copy and paste, it's very complete with prices and everything (is not only the Mouser stuff but the complete BOM), It should be pretty close, I don't remember errors on it but be careful,  I'll leave this link a couple of weeks, I hope that helps.



https://www.dropbox.com/s/xvr7nroz63k0wg3/dual%20la2a%20marco%20bom.xlsx?dl=0

Cheers

Marco