D-LA2A Support Thread

[MiamiBoy]

Hello guys.
I'm almost ready to built a dual LA2A.

As i look through this thread, i couldn't find specific links for purchasing or the step-by-step guides.
This thread is 10 years old and most links are dead. But i managed to download the BOM.

Can someone help me get started?
I'm not an advanced builder (just yet) and i don't know anything about electronics.
But i'm good with the solder iron  ;D

Please, any advice is much appreciated.
What i would love is, if someone could provide me with links for purchasing and perhaps answers some of my questions.
(kinda like Hairball Audio's guides+purchase lists)

The idea is to start off with this 2U front-panel from Don Audio:
https://www.don-audio.com/Dual-LA-2A-frontpanel

Please don't send me back to the threads first page 

 

[Rlucas41]

Howdy folks, a couple questions...
What voltage does C8 need to be, Will a .1uf 100v film capacitor do?

Also, NE2 beside C115 & C215
Is that where the neon bulb goes?

 

[[silent:arts]]

C8 won't see more than 5V.
NE2 is the neon bulb.

 

[Rlucas41]

I have a green and yellow single wire that is first in the order of my Rondo power transformer... is that to be grounded ? Just don't see it in the first images of transformer wiring... sorry for the dumb question ;D

 

[ron_swanson]

I have a green and yellow single wire that is first in the order of my Rondo power transformer... is that to be grounded ? Just don't see it in the first images of transformer wiring... sorry for the dumb question ;D

The green and yellow wire indicated by the arrow (see pic) is ground....

 

[Rlucas41]

Hello again folks,
need some help wiring the xlr's;
from left to right with + on the left and - on the right...
do I wire it:
+ = xlr pin 2
middle = xlr pin 3
-= xlr pin 1 (shield)?

also for the VU led lights and power light indicator... is it okay to use the 6.3 heaters power supply?

I know I've read it through the many pages of notes... sorry for redundancy

 

[ron_swanson]

Hello again folks,
need some help wiring the xlr's;
from left to right with + on the left and - on the right...
do I wire it:
+ = xlr pin 2
middle = xlr pin 3
-= xlr pin 1 (shield)?

also for the VU led lights and power light indicator... is it okay to use the 6.3 heaters power supply?

I know I've read it through the many pages of notes... sorry for redundancy

Without knowing what meters you are using and the corresponding power requirements for same, I doubt you will find anyone able to answer empirically.  (Apologies if you stated the meter specs in an earlier post...)

That said, if your meter LED's and pilot are AC, maybe?  You'd have to add up the current for all of the tubes (see data sheets for current requirements) on which ever heater leg you choose to use.  If you're under 2A total including the current draw of your meters / pilot, then you should be good.  You may have to adjust the voltage also if your meters are not rated for 6.3ACV.

If you need DC to power your LEDs, (probably), you might be able to use the 5V bypass circuit.  Again, you'll need to assess your requirements and compare that against what you have available.

As for your XLR wiring question, see the attached picture...

 

[Rlucas41]

okay so Im powering up and getting a little higher voltages on 250vac and 5vdc

red green=278vac
white & blue 278vac
black each leg 3.5vac
brown each leg 3.5vac
orange each leg 6.5vac

at 5vdc post I am getting 12vdc

fortunately I didn't have relays hooked up yet

Om the mains side I have white tied together going to neutral on IEC and yellow tied together on power switch connected to main hot.

Think problem in the 5vdc area is the linear voltage regulator ... this is what I used

https://www.mouser.com/ProductDetail/STMicroelectronics/L7805CP?qs=%2fha2pyFadujE9KQ1BxQHaOTrAgdQBljfIUWjbIUFUzk%3d

I need some help figuring this out please

 

[[silent:arts]]

From your regulators data sheet:

Note: Minimum load current for regulation is 5 mA.

Or your regulator is a 7812 by mistake (Check input vs. output voltage)

 

[Rlucas41]

it says 7805 on it but...  I will order another and replace... do you have a recommendation or part number Volker?

are the voltages from the Rondo transformer I'm getting  within acceptable range?

 

[Rlucas41]

input is 13.82vdc
output is 11.88vdc

sure seems like 7812 not a 7805 like is printed on it

would this be acceptable?
https://www.mouser.com/ProductDetail/STMicroelectronics/L7805CV-DG?qs=sGAEpiMZZMtUqDgmOWBjgFjpeeKn1ONkxyyFIyAr5GI%3d

 

[[silent:arts]]

Before replacing it measure it with a load.

 

[ron_swanson]

Hey guys,

Hoping for some assistance with where to go with my silent:arts build...    I've built a number of Hairball and AML units with success, but this is my foray into sourcing and building from scratch using silent:arts D-LA2A PCB.  In other words, noob in the house!

Finally got everything together last night, fired it up with mixed results... sadly...

Using Volker's supplied Rondo XFMR, Sowter 8940 & 4383 I/O. , New KENETEK T4B's. , NE2 neon bulbs. 117VAC USA wall voltage (Variac controlled).  No modifications outside of a basic build attempted.

Measured the basic rondo transformer voltages at the PCB header connections. 
• 265VAC on both high voltage legs
• 6.3VAC on both heater legs
• 13.8VAC  at the Orange wire connections
• 5.052VDC at the relay header
• Meters light up (Hairball 8020)

Using first time power up instructions found elsewhere ( https://groupdiy.com/index.php?topic=32677.1680 ) within this thread as well as the compiled information from page one (dla2a - doc.pdf) as reference for build and checks...

• Audio passes on both channels in bypass with no tubes.
• Audio passes on both channels WITH tubes, not in bypass - gain controls working.

All tubes are lit (heaters), but outside of the XFMR measurements noted above and checking that the correct heater pins / sockets on the PCB board are correct, I've not checked any deeper on the PCB.  Double checked that all of the I/O XFMR wires in the headers are correct as noted on PCB.

Zero'd the meters while in gain reduction mode - both neon bulbs glowing.

Now, the bad news...  After adding the T4B's, there's no compression on either channel. 

• In VU mode, the meters do deflect with audio applied
• In GR mode, there's no (none) meter movement nor audible 'compression'.  (Using stereo audio track, not a test tone at this point...)
• Adjusting the peak reduction makes only the very smallest amount of audio change at near full rotation, but nothing like I would expect.
• When either gain is set about 8 or higher on the dial, the corresponding meter moves from reflecting the input audio to  deflecting full right - hard.

The link and comp / limit switches have no affect in any position.  Probably because of having no compression in the first place.  Just mentioning, in case.

Since both channels exhibit the exact same behaviour, that leads me to think that I've committed some fundamental wiring or component placement error, but being new to this, I'm a flummoxed where to start to troubleshoot? 

I've seen a number of posts within this thread with various voltage measurements, but I haven't been able to find a consolidated measurement schematic  / document.  Does that exist somewhere?

I would greatly appreciate any thoughts any one would care to share.  Thanks in advance.

Cheers,
Greg

 

[[silent:arts]]

Sounds good Greg. Turn Trimmer RVX03 (Stereo Adj) 25 times to the right 

 

[hugo]

Hi all,
Could somebody help me ?
Channel 1 works good.
Channel 2 does show a compression, but i have strange values on v1:
pin 1 : 100v
pin 2 : -13v
pin 3 : 0.8v
pin  6 : 200v
pin 7 : -1.7v
pin 8 : 0v

thanks all for your support.

H

 

[ron_swanson]

Sounds good Greg. Turn Trimmer RVX03 (Stereo Adj) 25 times to the right 

Thanks for the reply Volker, unfortunately still no go...

No matter where the stereo trimmers are set, both channel meters don't move from zero when set in GR mode.    Of course, I can adjust the needles plus or minus with the PCB zero trimmers, but there's no audio driven meter movement when in GR mode no matter what I do or how the switches are set while in GR mode.

After further studying, it does appear that there is a little bit of compression being applied when the peak reduction controls are set to full CW.  I can see and audibly hear this when in VU mode using both a tone and program audio.  Again, very slight - maybe 2 to 4db reduction on the meters in VU mode only.

In light of your trimmer suggestion above, is there a complied listing of settings when first starting up that I missed within this thread? I've read through all 95 pages at least two full times and pieces here and there and don't remember seeing anything like that. 

Thanks again for your assistance...

 

[ron_swanson]

Thanks for the reply Volker, unfortunately still no go...

No matter where the stereo trimmers are set, both channel meters don't move from zero when set in GR mode.    Of course, I can adjust the needles plus or minus with the PCB zero trimmers, but there's no audio driven meter movement when in GR mode no matter what I do or how the switches are set while in GR mode.

After further studying, it does appear that there is a little bit of compression being applied when the peak reduction controls are set to full CW.  I can see and audibly hear this when in VU mode using both a tone and program audio.  Again, very slight - maybe 2 to 4db reduction on the meters in VU mode only.

In light of your trimmer suggestion above, is there a complied listing of settings when first starting up that I missed within this thread? I've read through all 95 pages at least two full times and pieces here and there and don't remember seeing anything like that. 

Thanks again for your assistance...

BUMP....

Anyone?

Thanks in advance...

 

[[silent:arts]]

Ok, your Audio Path is working fine on both channels, and you don't have gain reduction on both channels, right?
So both channels react the same / have the same problem?

 

[ron_swanson]

Ok, your Audio Path is working fine on both channels, and you don't have gain reduction on both channels, right?
So both channels react the same / have the same problem?

Hi Volker,

Correct. 

My electronics work bench doesn't have a fancy audio system, so my results are always suspect on the audio side.  As such, I took the unit to my studio where I could properly interface it just to ensure I wasn't being fooled into thinking the audio was as clean as my crappy desktop speakers were indicating.  My scope traces look clean so I guess all of that is well.  Anyway...

While wired up in my studio, the audio is again clean without any noticeable distortion, humming or other obvious artifacts. 

For both channels...

• Audio is being passed when the unit is off.

• Audio is passed when the unit is on and in bypass. 

• Meters display both tone signal and program material movement in VU mode.

• Audio is passed when in 'not passed' mode.  There's no audio with the gain at full CCW which I assume is normal behavior?  The gain volume is VERY hot when applied, but if I remember correctly, there's a mod buried somewhere in this thread to help with usability of the gain volume.  If so, that's a task for another day after the unit is working.

• When the GR mod is switched on, both meters display 0 on the meter after adjusting the meter zero trimmer - both neon bulbs glowing. (I haven'y measured the voltage across these bulbs when at zero on the GR meter.  Assuming that since they are lit the voltage is within an acceptable range?)

• Peak reduction control does nothing, although... very slight audio change and meter deflection ( a few db) when near full CCW but that is also with a bit of audio distortion.

As you originally suggested, turning the stereo adjust trimmer on either channel does nothing to the audio or the meter display no matter how many turns.

As mentioned in my first post here, since both channels are exhibiting the exact same problems, I suspect I committed a fundamental component and / or wiring error that was duplicated across both channels.  If so, what that might be and how to address the issue is unclear due to my lack of troubleshooting skills.  While I'm unhappy that I'm stuck here, I'm looking to learn how to fix this as a learning challenge.

Thanks again for your input and patience.  Sorry for the lengthy posts.  Just trying to be clear and concise in hopes of reducing the amount of question volleying while trying to be respectful of this group's time and experience.

Greg

 

[MiamiBoy]

C8 won't see more than 5V.
NE2 is the neon bulb.

Hello Silent Art.
Can you please help/direct me to "where to begin" -i wanna build my very own Dual LA2A.

My post here on top of page 95 wasn't answered and i feel like this is a very secretive project.
There's no direct instructions on where to begin and no obvious answers or solutions for beginners.
Like a "closed club".

Please help me thanks