D-LA2A Support Thread

[johnnyscotch]

Also, any hints about wiring the Meter LEDs?

I have the Hairball meter. Just wondering where to pull the LED power from?  ???

thanks

 

[kilmister]

Hi all!

Finally, after one year lazyness to do a front panel, I swapped temporary front panel to the decent one and finished my unit.
Nothing too fancy here except it's build in 2U case and that was a tricky part.
Urei T4's, caps russian PIOs and Wima 10u films (leftovers from PM670 project)
Stepped attenuators, Freq Response trimmer on the front panel.
Some extra filtering for HT and rectified filament voltages. Trafos from Edcor.

Once again, thank you sir [silent:arts]!

And here's the pictures (click for hi-rez)

 

[Hank Dussen]

Very nice!
Is that a silkscreened frontpanel? How did you do that?
It's nice to see a more 'non-chalant' font on a front panel!

 

[Uhl]

Nice build! The cutouts for the T4's look funny.

Where did you get the perforated board on which everything is mounted?

 

[kilmister]

Is that a silkscreened frontpanel? How did you do that?
It's nice to see a more 'non-chalant' font on a front panel!

Front panel is made by UV color (flatbed)printer. Very easy, very cheap. It need clear coating on it thought. I've made all my finished units (2x1176, PM670) with this kinda style. After I'll finish the PRR176 project we have quite nice looking row of units in our rack 8)

Nice build! The cutouts for the T4's look funny.

Where did you get the perforated board on which everything is mounted?

Theres also those rubber rings for 12BH7's... But yeah, cutout was only option left to fit everything in 2U because I used perforated plate which eats 5 to 7mm of the headroom.
I use Modushop cases. They are offering these perforated plates which are very handy in DIY.

Cheers,
Paavo

 

[johnnyscotch]

Hey guys, need some help here, desperately

So, I fired up the DLA2A, and I get power to all the tubes, neons, indicator lamp, etc.....and nothing blew up or smelled bad. Check.

It passes audio, I ran a 1k tone through it, and bypass works. It goes straight through unaffected in bypass, and when I switch it in I have gain control. LOTS of gain. Too much actually. I went with the 75k/25kPot thing and it still hits unity around 1.5 (8 o'clock), which is pretty useless. I guess I'll try 90k/10kpot, but later.

My big issue right now is the left channel gain seems to be greatly affected by the GR/Output VU switch. The wiring is the same on both channels and the Right channel seems to be working OK. The left channel works, but as soon as I switch the VU to "GR", the level shoots through the roof! Does anyone know why there should be a correlation between the gain and GR/VU switch?

Is there anything I can do troubleshooting-wise to check everything is OK before the wiring? I assume since I'm getting signal at all that my trafo and input wiring is fine. I guess I also assume since I'm getting power everywhere that my Power trafo and heater wiring is fine. I'm thinking about ripping out all the switch wiring and starting from scratch.

Also, I felt like my trimpots for 125/225 weren't making a good connection due to the way I mounted them, so I basically just took a pair of 100k pots and wired them to the board till I can get some more trim pots. I'm not even sure what these two are doing in the signal chain, they don't seem to affect anything in my preliminary gain tests.

I was really pretty bummed when I fired it up and already ran into issues. I really felt like I was patient and attentive with this build and I guess it didn't seem to matter.........

thanks

 

[dandeurloo]

I think you will find 15K pot the best.  You can get close to that by putting a 27K resistor across the pot.  Seems to be working good for me.  I did that on one channel.  Now I need to build my stepped switches.

I'm looking at the schematic trying to see if I can find a spot to look.  But in the meantime, keep one hand in your back pocket while trouble shooting!  No need to die trying to test it.  The good news is one channel is working so it will be a small fix more then likely.

Also, double check your wiring.  It is most likely in there some how.  I'll let ya know if I see something.  Someone smarter will probably come up with a trouble shooting suggestion for you.

Maybe check your resistor values around R128, R126, R127 and R125.  I believe those and the trimmer R104 are all in the meter circuit.  It would be good to rule those out.

 

[johnnyscotch]

I give up, can't spend any more time on this thing

http://www.groupdiy.com/index.php?topic=50367.0

Maybe someone will have better luck than me

 

[desol]

Sounds like you're frustrated. Maybe you should put it away for a bit...and forget about it.

Come back to it later, and get it going. It's worth it. 

 

[abechap024]

I give up, can't spend any more time on this thing

http://www.groupdiy.com/index.php?topic=50367.0

Maybe someone will have better luck than me

Man you did 99% of alll the hard work! Now forever you are going to have a bad taste in your mind about DIY. Its ALWAYS something simple....just a huge pain finding out what. Try switching around the tubes, connectors, anything you can. Its a sweet deal, but i bet you could get it going. Shoot me an email if you want, I just built a couple and am in the middle of one so maybe I can help trouble shoot.

 

[chris77]

Hi folks,

I've Just about completed my D-LA2A ,i have have to tidy the wiring up a little ,also have a hummmmmm  on the left channel which i'm trying to diagnose  i've swapped the valves one at a time also tried swapping the transformers ,heating wiring is ok (i think)and the channel is properly grounded,using a scope i have found some ripple on c105 which isn't there on c205 but i'm not sure if the cap is faulty? the hum stops when bypassed,the unit sounds great besides the hum and is compressing properly,i'll be doing the 25k pot+75k resistor mod for the gain also.

cheers !

 

[desol]

Try moving the wiring around a bit with a chopstick and see if the hum changes. Also, make sure the polarities are correct on the wiring. I had to remove and install sheilded wire in a few places. Wiring is pretty important in this build...can make all kinds of little noises and hum.

 

[dandeurloo]

Also, make sure you remove the paint on the back side of the front panel by the pots and on one of the side.  This helps a bunch with rumble.  Also I would make your twisted pairs much tighter.  That helps with the noise.  I bet a little clean up and you will have the noise worked out!

 

[jonathanmorbin]

Hi,

Does anyone know where i can get the PCB's for the D-La2a or the single La2a? I really want to build one of these.

 

[websoul]

If you look under the White Market, you'll see them offered in there
http://www.groupdiy.com/index.php?topic=39570.0 for example.

 

[jplebre]

Hey guys

doing some research and hoping to join the clan of successful D-LA2A builders.
Most of the builds I've seen don't have the meter adjust pot mounted, only PCB mounted trimpots.

Am I right to assume that the meters, because they use the Opto-cell as tracking won't need the same adjustments as often as the other fet "driven" models would? (eg. á-la 1176 where any change in temperature drifts the needle completely?)

I'm asking because I will be contacting some people to get the enclosure done so can't really experiment with this until its too late.

Wadda you think, boys?

Cheers

 

[desol]

I find with mine that the meter does drift with temperature change. Pretty sure the 6bq5 drives the meter as well...

 

[jplebre]

Desol, so you find yourself popping the hood all the time for the 1M?

 

[[silent:arts]]

The (GR) Meter (zero point) drifts with temperature.
Calibrate it after one or two hours and you are gone.
(I don't see any changes later on, once it has "temperature" it doesn't drift anymore)

This is no high end measuring system anyway, fun to see the needle move, but it doesn't matter if it is exact.
Can't see any reason to re-calibrate every few hours.

 

[ethervalve]

Just to add to what [silent:arts] said: I built my D-LA2A with panel-mounted zero-set pots but I've never had to adjust them after the initial calibration. For comparison's sake, my 1176 rev a and d clones have far more GR zero drift.