D-LA2A Support Thread

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Hi list,

I've almost ready with my D-LA2A, just missing the vu-meters, audio-transformers, pots and switches (in other words: no cords in the molexes yet).
The board is ready with all components and tube wires.

Would it be safe to power on for a quick test and some measurements?
If "yes" what would be good places to measure?
Was thinking of the zeners for voltages (the neon replacements) and tube voltages. other i should try out?

Gotta say, this has been a great build, can't wait for the real test with audio!

ps: i'm looking for the audio transformers, so if anyone can help with the sh--ty high postals from Edcor, much appreciated :)
 
thanks saxmonster, thanks harpo!

i will try the zener diode. does anyone have a 2u template for the frontpanel?

weiss
 
This guy does

http://www.don-audio.com/Dual-LA2A-frontpanel-2HE-two-color-silkscreened

I almost went this way.
 
djfatum said:
hello where can I buy this kit to build ??
Click to expand...

there is no kit. you have to buy all the parts separately on your own.
but there is a bill of materials which includes a list of all parts. pcb (and optional transformer) is made by silent arts
 
weiss said:
djfatum said:
hello where can I buy this kit to build ??
Click to expand...

there is no kit. you have to buy all the parts separately on your own.
but there is a bill of materials which includes a list of all parts. pcb (and optional transformer) is made by silent arts
Click to expand...

Also in the b.o.m there are mouser order codes, so it's super easy to get correct parts (or replacements)...
Please note that one condensator is missing in the bom but it's mentioned somewhere...
 
Hi Guys,

Having a slight issue with my unit.

I am seeing that my GR zero on the meters are walking.

I have set them a few times after the unit has warmed up and then put it back in the rack and then a day or two later the have moved off the zero line and to the left a little bit.

What is causing them to "walk" of off zero?

Thanks
-Scott

 
is there actually any wiring guide or a schematic? what means tbd resistor? and what modifications do i need to fit my tubes in the 2u case? all the links to the threads on nrg-forum in the opening post are down...
 
There is a PDF in the beginning of the thread with all the wiring for the front switches and a few threads that talk about the different transformer wiring.  You will just have to reread and copy and paste what you need, thats what i did.

THe TBD means "To be determined".  You use a trimmer to find the value that you need and then if you choose you can take it out measure it and then replace it with the correct resistor.

I don't have a 2ru case mine is in a 3ru but from what I remember  you have to shave the sides of the pins to the tube and t4bs sockets so that they fit flush with the pcb giving you the extra mm clearance you might need in a 2ru case.

HTHS.
-Scott

 
hey thanks for your answer!

saxmonster said:
You use a trimmer to find the value that you need and then if you choose you can take it out measure it and then replace it with the correct resistor.
Click to expand...

and how do i know when the value is correct? what resistor do you have there?

weiss
 
When you set the gain reduction to zero on the meters you use the trimmers to adjust that and get them both on zero.  also you use them on RX25 to set the same compression levels on the meters.  I didn't replace mine yet with actual resistors.  I will probably just leave the trimmers in incase I have to readjust maybe down the line.

 
Here is my d-la2a. Currently using edcors. Panel made by frank. But still some wiring to do and not all parts arrived yet..
Enjoy.

54909-230814122727-2261180.jpeg


 
Hey all, I'm throwing my hat into the ring here

Just finished (ish) a "telronix" unit and it's working (ish). Here are some key parts I've used

  • igs t4bx opto cells
  • Silent Art's power transformer
  • Cinemag 9589L output transformers
  • 1009f Teltronix LA-2A 1968 Input transformers
  • 1 MOhm pots on front panel instead of trimmer for RV137/237

The rest was mainly what was in the US BOM. It seems like that thing could use a bit of updating.

Some odd things to note that I was hoping to get feedback on:

  • 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?
  • 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?
  • 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?
  • 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.
  • 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?

xCLUKI.jpg

ps88Nt.jpg
 

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