D-LA2A Support Thread

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Also of note, I tried running a pair of guitar tracks, and when I turn up the compression, I can hear a lot of distortion (like a bad fuzz pedal). So obviously something is messed up in my build. Anybody know of some spots where this could happen? Could the t4s be backwards?
 
From where can i order the trim resistors when they weren't included with the t4b's? Ordered them from igs Audio
 
weiss said:
From where can i order the trim resistors when they weren't included with the t4b's? Ordered them from igs Audio
Click to expand...
just use a standard 33K resistor

or use Mr. Andrews calibration:
http://groupdiy.com/index.php?topic=23253.msg276178#msg276178
 
brewbacca said:
  • First, using the 100K pots for gain, I'm getting +4dbu levels with barely turning up the gain. This is where the unit is at in the pictures. This thing is currently a hell of a mic pre ;). I'm assuming this gets more manageable with the 25K pot/75K resistor?
yes do this mod
  • When running a 1K tone at around +4dbu, I only get about 4 db gain reduction with the gr knobs cranked. It varies just a bit between compression and limiting. I assumed the limiting would be stronger than the compression setting, but I've never used a real la2a. In any case, my understanding is that this thing should be pretty noticeably compressing with the GR knobs all the way up. Any thoughts on what might cause this?
Check your wiring from the pots to the molex's.  Wiggle them and see if it affects the meters.  I had issues with the molex connectors. 
  • I'm getting around 280 VAC on the blue and red wire terminals (250V). Should I look into adding high watt resistors to get it down to 250V?
Not sure on this.
  • When I measure voltage on the heaters (at each terminal with the DMM common to ground), I'm getting around 3.5V AC. I've checked the heater wiring and it looks good so I'm not sure if there's a trick to measuring that.
as long as your tubes are glowing you should be ok
  • When I switch the VU to GR mode, the needle doesn't move at all and just stays at around -20 on the meter. My understanding is that it should move up to around 0 db (give or take)? Any thoughts there?
you need to adjust the trim pot to get GR to read zero on each channel, search this thread
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xCLUKI.jpg

ps88Nt.jpg
Click to expand...
 
Thanks for the response saxmonster!

  • For the second issue, it seems like more than a meter issue. It's more of a sound issue where I'm getting distortion when I compress and it doesn't compress the sound much. I check this against other meters (such as the one on my DAW). I'll check the connectors some more. The guy who invented molex connectors must have been some sort of sadist.
  • On the heater wiring, tubes are glowing except for the 6AQ5A, although I can't really tell on those because the tube mechanics are covered up. In any case, the 6AQ5A's don't get nearly as hot as the other tubes. They do get slightly warm though.
  • For the last one I can't get the meter to change at all. I guess I wasn't very clear about that. I've definitely been reading the thread and have tried changing the zero adjust both directions. It doesn't seem to have any effect.
 
So still no luck with getting this thing to compress correctly, although I've made a bit of progress with some of the other issues.
- I realized that I wired the dual switch incorrectly.
- I stuck a 33K resistor in R125 and R225 and am able to get the meter to zero in gain reduction mode,  but it doesn't move at all when it should be compressing (in theory).
- I went with the 25K pot with the 75K resistor, and yeah, that should be standard ;)

I haven't been able to give this too much time for troubleshooting, but have been able to figure a couple things out.

Here's a video if anybody wants to take a gander: http://youtu.be/FLgo-2fwWRA

If you have a couple free minutes I'd love it if you could take a look at the video and let me know if you have any input.

Thanks!
 
A few things that I noticed

The lights flickering on the board are ok thats normal.

Does your channel two work?  The same?

You need to reread the pdf and setting up the meter section found in this thread just do a search.

It sounds like it is compressing but your r37 limit response might be set the wrong way try turning it all the way the other way.

Basically use your daw to send 0db out and an adjust your meter to read zero then feed it back into the daw and it should still be 0db

Then flip the meter to GR mode and it should still read 0db.  If not fix that its in the pdf.

Then turn the peak reduction knob till you get about 5db of gain reduction back into your daw.

Then adjust the meter to read -5db.

Thats is just for one channel do the same for channel two.

Then reread the stereo adjustment procedure to get the two channels to be fairly close around -5db.

You might have to put a trimmer in the r25 spot to get them to track properly.

You will have to do this process a few time cause one turn affects the other spots, hahahah

I know its a lot but just reread everything until you understand it.


Have fun.
 
saxmonster said:
A few things that I noticed

The lights flickering on the board are ok thats normal.
I thought so, but I wanted to check

Does your channel two work?  The same?
Yes, they both function exactly the same as far I can tell.

You need to reread the pdf and setting up the meter section found in this thread just do a search.
I'll be sure to give it another read through, but the meter stuff isn't really my main concern. I was going to hold off on that until I was sure it was compressing correctly

It sounds like it is compressing but your r37 limit response might be set the wrong way try turning it all the way the other way.
So it's only going down about 3 or 4 db with the compression turned all the way up. Is that normal? It seems like it should squash the signal more. The signal running into the compressor is a ~+4dbu 1K sine wave coming from my daw(as you described above) through my mixer which has meters . I have a 1meg pot on the front panel attached to r37(s) and adjusting that makes a slight difference, but not a ton.

Have fun.
Thanks ;)
Click to expand...
 
Try using a 440 signal and see if you see anymore of a difference.

Sending a 1khz tone at 0db out of my digital performer daw I have to set my gain to about 20 (I did the mod also)

Going thru the la2a with the peak reduction at 50 I am getting a little over 5db of gain reduction back into my daw and the meter on the la2a says -5db even.

With the peak at 75 I am getting about -10.5 of reduction in my Daw and about -10 on my meter.

I don't think its an accurate science but its close.

I am using T4B's from drip.  Let me know how you make out.

Can you post  a photo of the outside of your panel and the inside so I can see how you did the R37 limit response pot.  I would love to do it but I am afraid I might mar my beautiful front panel.

-Scott
 
I'll try the 440 and see what happens. I'm also going to try downloading a LA-2A plugin of some sort so I can compare. I had an LA-610 and the compression on that would do waaaaay more gain reduction with grain reduction turned up, although I know that's different than an actual LA-2A.

You can see the pot/knob I'm using for r37 in the pics I posted above. I can get some more detailed picks, but basically I just drilled a 1/4-3/8" hole over the gain reduction  pot. If you haven't drilled a panel make sure you get a center punch of some sort and then start with smaller bits and gradually go to larger bits.
 
Sorry didn't see the pics, looks great though.

I think i am hearing harmonic distortion when you turn the peak reduction all the way up. 

Hopefully someone else will chime in to help you.

Maybe just double triple check all you connections and wiring.  It has to be something simple. It always is.
 
WSM600/15K
1--Brown
4--Green
5--Blue
8--Grey

WSM15K/600
1--Yellow
4--Green
5--Grey
8--Pink
Click to expand...

Does this also work for 10k/600 and vice versa? Can i combine 600/15k and 10k/600 audio transformers?
 
djfatum said:
Hi, where can I buy good T4B cell to build D-LA2A  ??

Andrzej
Click to expand...

how about google?

IGS: http://www.igsaudio.pl/en/product/others/70-photocell-t4bx
Kenetek: http://www.kenetek.com/T4AT4BUnits/KenetekT4BModules/tabid/300/Default.aspx
Drip: http://www.dripelectronics.com/index.php?option=com_content&view=frontpage&Itemid=1
 
hey guys. i got some issues with my la2a. I think it is obvious, that i can't continue with calibration in this condition.
I made a video showing what doesn't work: http://youtu.be/Kdk6pENa4aY

To sum it up:

- Audio is going through while unit turned off (is this normal?)
- When turned on, only left channel works
- Potentiometers don't work properly, weird behaviour (shown in the video)
- No audio is being processed at all (compression, limiting etc)
- Left meter does not output vu signal

Here are some pictures as well:

http://www.imageupload.co.uk/images/2014/09/23/IMG0430.jpg
http://www.imageupload.co.uk/images/2014/09/23/IMG0431.jpg
http://www.imageupload.co.uk/images/2014/09/23/IMG0432.jpg
http://www.imageupload.co.uk/images/2014/09/23/IMG0433.jpg
http://www.imageupload.co.uk/images/2014/09/23/IMG0434.jpg
http://www.imageupload.co.uk/images/2014/09/23/IMG0435.jpg

Still need to power the led's btw.

thanks for your help
weiss
 
Hi,
would be nice to have bigger pictures of your built. The picture you posted cannot be found (Error 414). I had a look at the video. A few things to consider (maybe too obvious, but we have to start somewhere):

< Audio is going through while unit turned off (is this normal?)>
yes, we call this true relay controlled bypass

< When turned on, only left channel works>
In the video I saw that the meter starts to peg when turning up the gain . Check wiring of the potentiometers. The shield of the wire has to be connected to ground. Have a look at the pcb layout, which pin of the molex connector goes to ground. There is a complete wiring guide somewhere. Check this out.

< Potentiometers don't work properly, weird behaviour (shown in the video)>
wrong wiring, see above

< No audio is being processed at all (compression, limiting etc)>
Maybe a silly remark, but did you do the heater wiring underneath the pcb?
Try to make your left channel work properly. Then compare it to the right channel

- Left meter does not output vu signal
3K6 resistor installed? Toggle switch wired correctly? Molex connector plugged into the right place?

I bet there are some very simple things gone wrong! Read the wiring & calibration guide attached.
Bernd
 

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