D-LA2A Support Thread

[audiophreak]

Look on the first page of this thread, Compiled Information PDF

 

[Foots]

Look on the first page of this thread, Compiled Information PDF

Oh Lord,  how did I miss that?? Thanks so much!!

 

[JW]

Here's some pics of mine. Just waiting on some more silver micas for the hf response caps.

 

[JW]

Inside. I just happened to have some .22ohm 10 watt resistors, amazingly. Which dropped the heaters from 7VAC to 6.2VAC. Nice.

I know they look kind of precarious, but they're pretty solid actually. I should probably put them on their own little breadboard or something.

 

[JW]

Guts 2.

 

[audiophreak]

Hello All 

    Well , its been a long time coming for my second D-LA2A ... actually its my first , I put the wrong bypass relays in , tried to reverse polarization , messed that up got disgusted and started over .. the second  one was a success  YAY !!!

  so I got tired of looking at those parts on that PCB, took my time , repaired some traces , came up with a plan , and over a few years even pieced together some UTC's .. and that might be my problem.

I was short an A-10 , saw some posts that an A-18  could be used as an input , got everything together and wired, all voltages look good,  just went through calibration and noticed some differences in channels.

  The channel I'm having problems with is the channel that has the A-18 as input - noticed during calibration that the  Peak Reduction pot had to be turned about 3/4 to get -5db of reduction on meter , were as the other channel with A-10 was at about 1/3 , with 0db 1k sine wave, but was able to calibrate  - with audio noticed that signal was clean but at a certain point adio started to get a little distorted and in +4 meter would peg to right , peak reduction at full and meter was just showing -1db / -2db reduction with meter in GR mode.

  I suppose it could be the T4B , I haven't swapped them yet , but was wondering if it could be the A-18 ?

I have it wired :

  PCB              A-18
Brown---------P
Pink --------- 2-3 connected 
Green---------B
Blue-----------G
Gray-----------G
Black----------Earth Ground/Shield

( F + F  connected )

  .. does this look right ??

  any help / suggestions appreciated 

 

[[silent:arts]]

I don't have the data sheets for your transformers handy, but if they do have different ratios you will have different gain settings for the same amount of gain reduction.

 

[audiophreak]

Thanks for the speedy reply 

  I realize the gain setting would probably be a little different , I was referring to this thread - https://groupdiy.com/index.php?topic=6518.0

  With 1k sine at 0db on input the position of the gain pot was slightly different between channels as I suspected , however continuing with the calibration the Peak reduction control was  around 3/4 up to get -5db of GR were as the other channel with A-10 was at about 1/3 up, and with audio passing had to bring the Peak Reduction control all the up to see -1 or -2db of GR on meter, so I believe I have wired the A-18 incorrectly ... not sure were to go from here.

  Here is a pic of the A-18 schematic on the transformer , any suggestions ??

EDIT :  I swapped in another T4B and condition was the same.

 

 

[audiophreak]

.... so looking at the specs, wire the secondary in parallel , or use a single winding for 40k ??  adjust R205 value ??  ... not sure what to do on Primary side  :-[

 

[Foots]

I received my Sowter trafos today, I see that there are two threaded screw holes on the underside of the inputs. How deep can one go before messing up anything inside??

 

[audiophreak]

Hello All

  OK, so I'm going to try and wire the A-18 Pri & Sec in parallel . 

connect P and 2 to BRN
connect B and 3  to GRN
connect G and F to BLU
connect F and G to GRY
Ground/Shield to BLK

... do I leave PNK on PCB  open/ no connection  ??

EDIT :    Aslo , will R5 (205) need to be changed ? .. and if so ,  to what value


  any help appreciated  ;D


    ... sorry Foots , I cant help , but if you PM a Pic , I can offer up  my 2 cents 

 

[[silent:arts]]

PNK isn't connected to anything on the PCB.

 

[audiophreak]

PNK isn't connected to anything on the PCB.

  Thank you !!  I will report back if this works / works better than when wired in series.

Also , do you think  R5 ( R205 )  value needs / should be changed ?

  Thanks again 

 

[Foots]

I am very close to finishing this baby! I have a couple questions that I hope you guys will help with.

1. I am wiring the IEC and the primaries now. I found Bartons drawing and Volkers response about switching L and N. I followed his drawing and planned out my wiring as attached. Can somebody confirm that this is correct for USA? Also, since this IEC has an embedded on/off switch, how should I jumper the pins in order to make it work?

2. I have 25k pots and 75k resistors for Gain. I am not clear on where to connect the resistor. All I have found is 'in line'. The one picture I found, I couldn't tell if the resistor was soldered to two of the pot pins or if it was connected to two wires and then to one pin. Please help!

3. I have 12v VU bulbs and need to figure out where to pull the voltage for these. I have not researched this yet so my answer is likely in the thread somewhere. Never the less, if somebody would like to weigh in that'd be just fine with me  ;D

Thanks guys!!!

 

[audiophreak]

I don't have the data sheets for your transformers handy, but if they do have different ratios you will have different gain settings for the same amount of gain reduction.

OK , wiring the A-18 in parallel fixed the behavior I was seeing and calibrated better, but there are still the differences you pointed out    ... so if anyone has a spare A-10 I have a A-18  and A-20 to trade or will purchase outright ... I haven't seen any in Black market or US Evilbay these past weeks. 

  Thank you for your help , much appreciated 

  Foots :  in the drawing you posted the live main is going strait to PT , use a DPDT switch , mains L&N to bottom pins of switch , Primary lines from PT go to poles ( middle) pins  ---------------- BE CAREFULL ---------, the 75k resistor runs between the red wire to the gain pot pin that it goes to in the wiring PDF graphic, as far as the  12v VU bulbs - replace them with 6v and run them from the 5v for relays but make sure you have enough amps for the draw.   

 

[Foots]

OK , wiring the A-18 in parallel fixed the behavior I was seeing and calibrated better, but there are still the differences you pointed out    ... so if anyone has a spare A-10 I have a A-18  and A-20 to trade or will purchase outright ... I haven't seen any in Black market or US Evilbay these past weeks. 

  Thank you for your help , much appreciated 

  Foots :  in the drawing you posted the live main is going strait to PT , use a DPDT switch , mains L&N to bottom pins of switch , Primary lines from PT go to poles ( middle) pins  ---------------- BE CAREFULL ---------, the 75k resistor runs between the red wire to the gain pot pin that it goes to in the wiring PDF graphic, as far as the  12v VU bulbs - replace them with 6v and run them from the 5v for relays but make sure you have enough amps for the draw. 

Thanks Audiophreak! Unfortunately, I am still unclear on this and am reaching out to a buddy that does a lot of this stuff for some remedial help. Total newbie here, but I know lots more than when I started! 

 

[Foots]

IT'S.....ALIVE!!

I got everything (mostly) wired and fired her up. No explosions, no smoke! All the tubes and the neons lit and she is passing signals and compressing/limiting on both channels!! I am waiting for a couple of 6.3v bulbs to arrive so that I can light the VUs. I will pull the voltage from the heaters. I am also waiting on trimpots for R125/225 so that I can calibrate this girl!!

A couple questions on the trimmers if somebody would be so kind as to answer:

1. My bourns trimpots for R137/237 and R103/203 are supposed to be 12 turn components, however they never stop. I've gone way past 25 as well. Could I have somehow killed them with too much heat?

2. Is there any fancy way to mount a 3 pin pot into the two holes for R137/237?

Thanks guys! Looking forward to my banner!!

 

[audiophreak]

Congratulations Foots !! 
  The trimmers I have make a tiny "click" as you pass the end of travel , but only in one direction , I think they are Bourns .  The two hole thing I just bend the wiper pin tight to the bottom of the housing and solder to one of the other pins.
  Hope this helps 

 

[Foots]

Congratulations Foots !! 
  The trimmers I have make a tiny "click" as you pass the end of travel , but only in one direction , I think they are Bourns .  The two hole thing I just bend the wiper pin tight to the bottom of the housing and solder to one of the other pins.
  Hope this helps 

Thank you sooo much Audiophreak!That did the trick! I've got the trimmers installed for Rx25 and they work beautifully. Also got the 6.3v bulbs installed and lit by pulling power from heaters. I had to trim away some plastic from the VUs as these bulbs are a bit longer, but NBD.

A couple of last issues that I have:

1. Channel 1 GR needle drifts +-1db after 5-10 minutes, sooner if I play with the Zero Adj. Does not do it on Ch2. I have swapped all tubes, T4B and even Zero Adj trimmer with no difference. I read in the thread that having the outputs trafos too close to the XLRs can be an issue, but even with them out of the case the problem still persists. Heat is not an issue as the top is off the case and I have plenty of ventilation. Any other suggestions on where to look?

2. Channel 2 GR needle tracks fine, but bounces back and forth a mm or so wherever it sits. Wouldn't really impact the functionality, but it doesn't do it on Ch1. More annoying than anything. Any thoughts on this issue?

Thanks folks!!
f

 

[Foots]

Looks like I solved both issues by replacing (more likely reflowing) the neon bulbs. Still a tiny bit of drift on ch1, but not near as much. Gonna order some zener diodes to replace the bulbs. My original searches came up short, but once I used the keywords 'neon' and 'drift' found lots of useful info.

So my build is officially done. Many thanks to those that helped!!!