D-LA2A Support Thread

[[silent:arts]]

since more and more people will build the [silent:arts] D-LA2A version I thought I will start this thread.
please ask your questions here, no PMs please.

the Project started at Franks Forum, and there is already a huge amount of information over there:
http://www.nrgrecording.de/nrg/viewtopic.php?t=405

D-LA2A schematic
D-LA2A ground scheme
wiring the heaters
wiring the Rondo Müller PSU transformer
tube socket modification for 2RU cases

Rx25 (TBD) & Meter callibration by SSLtech
Limiter Response Calibration (RV137/RV237)
Stereo Balance Adjust (RV103/RV203)
comments about Cx04 & Cx14 (aka Arco caps) by Kingston
some very important things that all should be awared by poctop

compiled informations from this thread in a single PDF by sonicwarrior

BOM by Azone with additions by QNote

videos of a D-LA2A build and calibration by QNote

FINISHED UNITS:

[silent:arts]
waldorfcave
bernbrue
Infernal_Death
ChuckD
ChuckD (Numero deux) :shock:
geoff004
inputoutput
stitch-o
tskguy
Holger
stereokillah
USIEL
stereokillah  (Numero deux)
Silvas
crisotop (scroll down thru all those nice builds)
Kingston
alexc
electrisizer
Soeren_DK
horvitz
poctop
drgrateful
baadc0de
Audioman
creal
desol
Borja Lopez
sea_man
briomusic
Cardinen
etiefenthaler
MicDaddy
mrclunk

and many many more 8)

 

[MartyMart]

Great, thanks Volker ... it"s on my list !!

Marty.

 

[Kingston]

a useful looking link from that thread about grid stoppers:

http://www.groupdiy.com/index.php?topic=258781

but it's for the old prodigy pro forum version..

how do I make that link compatible with the one today?

 

[Audioman]

Hi All ,
Anybody have a BOM for the Dual LA-2A for the european customers including where to buy tubes and T4B cells ??
And also the right type of tubes
Thank you all !!
Fabio

 

[tskguy]

I would be interested in a USA bom as well.

Eric

 

[kazper]

What happened to the build thread from S.A. first build?

I just looked for it a couple weeks ago referencing the PCB I have from that buy.

 

[[silent:arts]]

What happened to the build thread from S.A. first build?
I just looked for it a couple weeks ago referencing the PCB I have from that buy.

there never was a build thread except the one at Franks place.

Anybody have a BOM for the Dual LA-2A for the european customers including where to buy tubes and T4B cells ??
And also the right type of tubes

here you find some links for the caps I used, and a BOM bernbrue once did.
T4Bs:
http://www.dripelectronics.com/t4b.html
http://www.studioelectronics.biz/sunshop/index.php?l=product_detail&p=1142

 

[tskguy]

Would any la2a bom work for most of this build? I have found some US friendly BOM's for diffrent layouts and was wondering if most of it would be the same?

Eric

 

[RAM]

It'll probably work for the resistors at least. But most of the electrolytic caps may not fit on the board. Plus the PSU is different.

Rob

 

[tskguy]

Thanks,

I actually orderd the PSU from the group buy so Im good to go there. As for caps I can figure that out pretty easily.

Im just being lazy Im sure I can get together a BOM onmy own pretty quickly.

Eric

 

[tskguy]

Hi all,

Will this work for the relays??

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=Z767-ND

Eric

 

[Silvas]

This thread is great news !!!

Now, to the questions :

Will the antek 1T250 work here?

Seems like an economical option...i think the voltages and VA´s are right

 

[[silent:arts]]

Will the antek 1T250 work here?

looks good to me, but you won't have any relay power for the bypass (actually those are "compressor in" relays.

Eric, your relays are fine.

 

[deuce42]

Great thread idea Silent Arts.

To everyone else, Silent Arts has been so helpful in my experience at the "Franks Place" forum for this project and I am glad the thread can continue here at groupdiy.

Now for my question, since these things put out huge amounts of gain, can I substitute input transformers and use 1:1 ratio transformers rather than the normal 1:4 to lower the amount of gain? Besides substituting the 100k gain pot for a the 25kpot/75k resistor as discussed at Franks Place , could I substitute 1:1 input transformers instead?  I have these Sowters lying around which are 600/600 ohms 1:1  and I would love to make use of them.

Thanks

 

[[silent:arts]]

Now for my question, since these things put out huge amounts of gain, can I substitute input transformers and use 1:1 ratio transformers rather than the normal 1:4 to lower the amount of gain?

yes you can

 

[tskguy]

Thanks,

I was wondering about the input iron also. Im considering using Lundhal transformers and Talked with Kevin the US distribitor and he suggested using 1:1 on the input as well.
Im working on a USA Bom and noticed I cant find the silver Mica caps. Does anybody have a usa source for those?

Eric

 

[[silent:arts]]

Eric, I doesn't have to be Silver Micas

 

[tskguy]

Thats what I figured but I thought that I would try and stay true to your original design.

Eric

 

[deuce42]

Awesome - thanks! These are special 4757 Sowters made for the BBC. Will givem them a go and then report back

 

[Silvas]

Will the antek 1T250 work here?

looks good to me, but you won't have any relay power for the bypass (actually those are "compressor in" relays.

Eric, your relays are fine.

But it is possible to steal some voltage from the heaters secondary to do this right? running the relays at 5v ? or i can use a second toroid (have lots of 10va anteks lying around).

Thanks !