D-LA2A Support Thread

[ethervalve]

it seems to need a pretty epic input signal before it does any compression

Hi Michael, as bernbrue said earlier in this thread "- verify that limiter response and stereo link potentiometer are trimmed correctly"
It's quite easy to hook these pots up backwards; having them turned all the way in the wrong direction would have a huge effect on the threshold of compression.

 

[django]

I can remember adjusting these a while ago (had this project on the shelf for a while) with little success. are there any other things i could be checking? Also whats the ideal input voltage?

 

[ethervalve]

That's the extent of my advice. Wish I could help you. But I'm still troubleshooting my own issues (crosstalk). Good luck! I'm sure the experts will chime in soon enough.

 

[django]

have you posted a picture of your layout? I can help with lead dress!

 

[django]

Got it working, I now have a similar problem to you ethervalve.

If i turn up the gain or compression to high i get oscillation. Turning on the stereo link seems to cure it a bit but it also lowers the amount of compression i can get. Going to spend a bit of time hunting it down tommorow but some ideas of where to start would be great.

ta,
michael

 

[ethervalve]

Hi Michael,
sorry i missed your previous message. thanks! i will take a photo. I'm woefully ignorant of the vagaries of lead dress (shorter wire vs wire routing etc).
I'm expecting a pair of 12ay7 and lower value c4 caps tomorrow. I'll report back how that works out.

 

[ethervalve]

Hi Michael,
I finally found time this weekend to work on my D-LA2A again.
The good news is that is that I was able to fix all the issues it was having.
Slight bad news: I was stupidly troubleshooting from the hip and I'm not certain exactly what it was that fixed things....
I basically did the following at the same time:
1) I installed sockets for C4 (C104 and C204 on the boards) http://i630.photobucket.com/albums/uu30/cejl/dla2aC4sockets.png
2) I performed the 12ay7 Mod (using 100k resistors for R9 and R13)
3) I replaced the neon lamps with zener diodes
4) I shortened the many of the wire runs (I did this before I saw your offer to check out the lead dress--here's what my wiring looks like in any event: http://i630.photobucket.com/albums/uu30/cejl/dla2ainnards.jpg )
Here's what it looks like (my letraset technique could use some work): http://i630.photobucket.com/albums/uu30/cejl/dla2aLidoff.jpg
Now everything works fine: I get no oscillation, hiss or noticeable crosstalk.
One curious thing tho: To get the frequency response equal between sides, I had to use a significantly smaller cap in ch1 (100pf) vs ch2 (250pf). Does anyone know if this is normal? (I'm using Edcors for inputs and outputs).

 

[audiophreak]

Hi All ,
        I spoke with Gregory  ( Drip Electronics )  today and he said about two weeks for the T4Bs 

 

[johnnyscotch]

Can anyone help with wiring up the Edcors for this guy, as it relates to the "Sowter" indications on the pcb?

Has anyone done a diagram?
I was trying to go off the tech docs on the Sowter site, but I'm still afraid I might confuse the pri and sec......

Thanks!

 

[abechap024]

Can anyone help with wiring up the Edcors for this guy, as it relates to the "Sowter" indications on the pcb?

Has anyone done a diagram?
I was trying to go off the tech docs on the Sowter site, but I'm still afraid I might confuse the pri and sec......

Thanks!

I'm getting ready to wire the edcor transformers in mine in the next couple days, I'll take note. But what I've had to do on previous builds of this unit is look at the original sowter info....

input tx 4383:
http://www.sowter.co.uk/conpics.htg/4383.gif

and output 8940:

http://www.sowter.co.uk/conpics.htg/8940.gif

I used both of these transformers in a build for a friend and they sounded gorgeous! The wait and money involved to get them though, I wasn't expecting anything less. It will be interesting to hear the edcors by comparison, I think they will work just fine.

 

[johnnyscotch]

Can anyone help with wiring up the Edcors for this guy, as it relates to the "Sowter" indications on the pcb?

Has anyone done a diagram?
I was trying to go off the tech docs on the Sowter site, but I'm still afraid I might confuse the pri and sec......

Thanks!

I'm getting ready to wire the edcor transformers in mine in the next couple days, I'll take note. But what I've had to do on previous builds of this unit is look at the original sowter info....

input tx 4383:
http://www.sowter.co.uk/conpics.htg/4383.gif

and output 8940:

http://www.sowter.co.uk/conpics.htg/8940.gif

I used both of these transformers in a build for a friend and they sounded gorgeous! The wait and money involved to get them though, I wasn't expecting anything less. It will be interesting to hear the edcors by comparison, I think they will work just fine.

Thanks, I was looking at those on the sowter site. I just don't want to botch it up.
Is black on the Sowter the other center tap? Or more specifically, if it's just a ground, can I use the other ct on the edcor for that lead?

 

[[silent:arts]]

We don't use any center taps!

 

[MicDaddy]

I've got the lid off of mine (I like to watch the street lights in tube city at night) I'll take a peek and relay what I find.

WSM600/15K
1--Brown
4--Green
5--Blue
8--Grey

WSM15K/600
1--Yellow
4--Green
5--Grey
8--Pink

Thanks again to the contributor that helped me with this when I was lost.

 

[dandeurloo]

I got mine up and running finally.  I still need to work my stepped switches up but its working great with the standard build.  Now its time to do some tweaking. 

Are you guys finding the 12Ay7 mod doesn't really give you enough gain for proper reduction or is it a different issue you are having.  I am thinking about trying it but not if it doesn't really work? 

Also, are any of you guys putting 600r on the outputs or are you running them with out a load?  I will test that for sure.

 

[dandeurloo]

A few more questions in regrades to my testing. 

1. Has anyone padded down the outputs of the D-LA2A?  If so how much pad did you add?  I have tested 20db and 5 db pads.  5db seems to be best.  You are then able to turn up the gain a little more and slightly more color form the outputs.  20db was way to much.

2. I am also testing loading the outputs.  So far the cinemags have sounded pretty good with a 1.8k.  Wondering if anyone else has done this as well?


Overall, I am wondering if just padding and loading the outputs would be a solution to the super high gain of the units.  Maybe a alternative to the 12AYY mod.

 

[desol]

I did the 12ay7 mod. Works good and there is still plenty of gain. I changed a couple resistors too that cj had mentioned. Plate bias resistors i believe....from 220k to 100k if i remember correctly. Twas a long time ago. 

Info is here and there somewhere. Otherwise, works great and sounds fine, still plenty of gain. Didn't fool with any zobels on the outputs....and i used the edcors. 15k... did test with some software and a 1k sine....looked pretty flat from bottom to top.

 

[Hank Dussen]

1. Has anyone padded down the outputs of the D-LA2A?  If so how much pad did you add?  I have tested 20db and 5 db pads.  5db seems to be best.  You are then able to turn up the gain a little more and slightly more color form the outputs.  20db was way to much.

I added a switchable 10db pad right after the output transformer. That way you can really push the output gain for some nice distortion without going over +4dB output.
I also added a switch that bypasses R6 (68k) at the input. This gives me some extra gain so I can also use it as a preamp.

With the combination of these added switches you can get some really fat distortion sounds...

 

[Kingston]

I added a switchable 10db pad right after the output transformer. That way you can really push the output gain for some nice distortion without going over +4dB output.
I also added a switch that bypasses R6 (68k) at the input. This gives me some extra gain so I can also use it as a preamp.

With the combination of these added switches you can get some really fat distortion sounds...

I've a similar case but would add that the distortion tends to be on the harsh side. The stock amplifier of LA2A is very linear and it's like a guitar lead channel when it clips. Useful as effect. Beatles revolution style guitar sounds are quite possible with it. The output transformers that we use for LA2A commonly are not clipping in this at all. All the distortion comes from the NFB tube amp. Output transformer clipping threshold is much higher/louder.

 

[Hank Dussen]

I did change the 12AX7 to an 12AY7 which should make the distortion nicer.
Still it's not a subtle harmonic distortion but I really like the combination of compression and distortion on for example a drum loop.

BTW, I also tried to replace the feedback resistor R11 with an 470K pot, but this didn't change a lot to the sound...

 

[dandeurloo]

I've been testing R11 as well and it doesn't seem to be much more then another volume control (I think Kingston mentioned this as well).  I was thinking I would see more harmonics but seems to be just gain.  Maybe if I try the tube switch.  I was also thinking it still had so much gain that the padded outputs plus the tube switch would allow for the tubes to actually start to put out some harmonics.

I have found the R37 on a switch and the output termination to have more of a sonic change on the comp.  I also have had interesting findings with different values of the Gain pot.  The 25k pot and 75k resistor only seems marginally better then the 50K pot and 50k resistor.  Maybe its because the pots I am test with don't have the best resolution.  I am hoping stepped switches will act a little better.