D-LA2A Support Thread

[[silent:arts]]

you might work too fast for slow vintage circuits 

 

[stereokillah]

in fact i'm happy to resolved this small problem, i'm building a third unit at time.

Great project.

 

[Audioman]

Hi All,
I'm looking for some tubes 6AQ5 for The D-LA2A but i have some difficult to find it
Can you please help me to find it ??
Let me know
Thank you
Fabio

 

[rob_gould]

There are lots on ebay

http://electronics.shop.ebay.co.uk/Vintage-Electronics-/14998/i.html?_nkw=6aq5&_catref=1&_fln=1&_trksid=p3286.c0.m282

 

[pilot]

Another is alive!

 

[rob_gould]

Good work!  Pretty neat

Can you tell us which transfomer combo you used? 
How is the gain on the unit?
Did you do do the 75k resistor / 25k pot mod?

 

[bernbrue]

Hi,
very nice built. You won´t be dissappointed in terms of sound, that´s for shure. Congrats!!
regards
Bernd

 

[[silent:arts]]

cool, have fun with it.
where did you get those T4Bs?

 

[Kingston]

a bit of info about the grid stoppers (those optional 1k resistors around 12BH7). I was asking about them long a go, but now I have all the info there is to them.

It has been said in the past one should use the grid stoppers when using Sowter 8940 output transformer, for example. It would otherwise oscillate.

It's not as simple as that. One can use those sowter outputs - even the more accurate utc A24 clone "sowter 1010" without grid stoppers.

You just have to calibrate C4 (feedback network high cut) accordingly. It should be replaced with a trimmer like Arco 465 (used in the originals as well). You get to tweak output high frequency response this way too.

The 300pF value might be too high for many builds, and too little low cut in the feedback network would result to oscillation. C4 to the rescue, tweak it down a notch.

Another choice is to knock down B+ some 10-20 volts. or use grid stoppers.

or do all of the above for bomb proof output gain stage.

 

[[silent:arts]]

thanks for the explanation Kingston.

fyi, my first build (no grid stoppers on rev01 PCBs) works fine without grid stoppers and sowter output transformer.
it oscillated only at stupid high gain settings I would never need / use.
the "gain pot mod" solved it while bringing a better adjustable gain range.

the grid stoppers have been added to rev02 since they are hard to implement to rev01 builds, but are easily bypassed if you don't want to use them.

the reason why there is no C4 trimmer is: I didn't find any easily available in europe. the 300pF is a guessed estimate I read somewhere in the long LA2A threads, but can easily exchanged to other values.

 

[Kingston]

it oscillated only at stupid high gain settings I would never need / use.
the "gain pot mod" solved it while bringing a better adjustable gain range.

I suppose that's fine if you only ever want to use it as a compressor.

But LA2A is a great preamp/lineamp as well, with some 40-50dB of gain, depending on transformer choices. Full pot range needed for this obviously. Actually the 68k input series resistor can be bypassed for some 5-6dB of extra gain.

 

[Silvas]

it oscillated only at stupid high gain settings I would never need / use.
the "gain pot mod" solved it while bringing a better adjustable gain range.

I suppose that's fine if you only ever want to use it as a compressor.

But LA2A is a great preamp/lineamp as well, with some 40-50dB of gain, depending on transformer choices. Full pot range needed for this obviously. Actually the 68k input series resistor can be bypassed for some 5-6dB of extra gain.

For a while, i wanted to add switchable +48v to the inputs for that purpose....but nah, not now. Maybe later when i´m finished and the baby is running smoothly.

 

[mjproc]

Hi.  I have some Elma's, and see some builds with these...

The Elma's I've got is "break before make"...  I'm not shure if "make before break" is better

http://www.elma.com/Admin/ProductionFiles1/ProductTypeFile/371/English/13%20Selector%20Switch%20Type%2004.pdf 

I'm trying to understand and calculate the different values for each step... 
Can the list below be used ?  Adding 4kOhm in series pr step

Target value 100 kOhm
Numer of steps 24
Value pr step 4,2

step kOhm Result
1 4 4
2 4 8
3 4 12
4 4 16
5 4 20
6 4 24
7 4 28
8 4 32
9 4 36
10 4 40
11 4 44
12 4 48
13 4 52
14 4 56
15 4 60
16 4 64
17 4 68
18 4 72
19 4 76
20 4 80
21 4 84
22 4 88
23 4 92
24 4 96


Hope someone can help my head with this, and suggest prper values pr step

Brgds
Ole Peder

 

[stereokillah]

hello,
in Pm670 thread there is a link where you can calculate if log linear or rev log, this how many step you search and give you the good value.

 

[mjproc]

Exxelent !!! I very much would like it log  ;D

Thnx for the link, and thnx to the author of the excelsheet!!!

 

[mjproc]

Hi.

Stuffing my dla2a cards and wonder what these components are.. GS101,GS102,GS201,GS202

Not mentioned in the bom, so I just want to make sure if they are "normal" 0,6W MF resistors

Brgds
Ole Peder

 

[Kingston]

Stuffing my dla2a cards and wonder what these components are.. GS101,GS102,GS201,GS202

They are the grid stoppers.

Read my posts above for a detailed explanation.

 

[mjproc]

Tried to PM you [silent:arts], but your inbox is full ....  Have you received the power trafo's for DLA2A yet?  Still interested in purchasing one or two.

 

[[silent:arts]]

Tried to PM you [silent:arts], but your inbox is full ....  Have you received the power trafo's for DLA2A yet?  Still interested in purchasing one or two.

full again ...
yes, I have received 85 kg of transformers last friday. due to the weight my wife didn't want to bring them in the house. but they over-lived 10 hours on the street ;D ;D ;D

will send you a mail later.

 

[staras]

Hi there,

I have few questions regarding this beuty. The first one, what actually the limiter response and stereo adjust trimpots do? I have plan to move these on the faceplate to make more useful. The other one, will the ecc802s tube will fit the 12ax7 situation?

Thanks!