D-LA2A Support Thread

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andow

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Jan 5, 2015
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298
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Austria
amazingalf said:
I've finally got my DLA-2A put together and I am ready to turn it on. I wasn't able to find a suggested first start up procedure.

I was wondering if anyone had any recommendations for start up. Should I start the unit without the tubes first, check voltages, then start up again with tubes installed? Should I put the T4Bs in after I have measure voltages with the tubes in?

Any guidance would be appreciated.

Welcome to the forum!  8)

Since this thread is almost 100 pages long by now (edit: it is now! ;-)), most of these basic questions have been asked before. So I really advise you to use the search function before posting. This might help:
https://groupdiy.com/index.php?topic=32677.460
 

amazingalf

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May 10, 2020
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Thanks for the link andow!

I've checked the voltages on the pins, and then inserted the tubes. Voltages look good here as well.

I attempted to run some audio thru the unit and am experiencing the following strange behavior:

  • Meter: The meter very faintly lights up if I turn on the Gain Reduction Switch. Is this normal?
  • Audio: Audio passes thru the unit when in bypass. This works on both channels.
  • IN - Left: If I turn the gain knob up with the left channel set to the IN position, the Hairball LED meter will flicker at full brightness. This is accompanied by a noisy and unusual hiss, an almost robotic noise. This happens with or without audio.
  • IN - Right: If I turn the gain knob up with the right channel set to the IN position, nothing happens. The meter does not flicker and the gain switch has no impact. Is this the expected behavior, or should the gain switch work at this point?

Here are some things that may or may not be related:

I'm using stepped switches as per the AZONE BOM
I changed the neon lamp to a zener diode as seen in the compiled pdf
I did all my wiring to match what was in the compiled pdf
I have not inserted the T4Bs
 

TwentyTrees

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Sep 17, 2015
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London, UK
AmazingAlf - a shot in the dark, but have you perhaps connected the VU connection points on the PCB to the LED +/- on your VU meter rather than the audio +/-?
 

amazingalf

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May 10, 2020
Messages
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TwentyTrees said:
AmazingAlf - a shot in the dark, but have you perhaps connected the VU connection points on the PCB to the LED +/- on your VU meter rather than the audio +/-?

Thanks for the reply. I had the wires coming from the DPDT VU switch attached to the LED +/- as you had suspected. I moved these to the audio connection (the lower set) of the meters. The needle on the VU meter now moves when switched to GR (not to zero as I have not calibrated this). I just searched and found some info from Jarkko and Offthewallstudios which outlines how to power the LED lamp which I will work on now.

Any ideas on what is causing the weird robotic noise (maybe oscillation? I'm not super familiar with what that sounds like) on Channel 1 when I turn up the gain when switched to IN? I made the 25K stepped gain switch in the AZONE BOM. I have attached a 75K resistor to the input of the 25K stepped attenuator. The noise becomes very prevalent when the switch is at 40% or more.

The gain attenuation is having no effect when Channel 2 is set to IN. Channel 2 passes signal in bypass, but not when set to IN.

 

amazingalf

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May 10, 2020
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I've got the VU meter lit up and functioning properly.

I was able to figure out what the problem with the right channel was. The input transformer molex connections were bad. They were the first batch I crimped. I re crimped them all and now signal is passing thru the right channel when switched to IN.

Both channels are now behaving similarly. They each sound very tinny and robotic. Is this something that will be addressed by calibration, or is this a different problem?

I used shielded wire for this build. For the 2 wire headers I used a single wire that was surrounded by a shield. I wired these using shield as black and the wire as red. Could this be introducing problems?

Any guidance is appreciated.

Edit: It looks like I made a very simple mistake in my studio one setup when I was trying this out. I had a stereo track loaded into studio one. I had pipeline xt configured to output 3-4 and input 3-4. The track itself was set to have an input of 3-4. This appears to be the source of my issues. I set the audio track to have no input, and everything started sounding a whole lot better. Maybe that will save someone some time over the course of the next decade!
 

Manucas

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Oct 8, 2020
Messages
4
Location
France
Hello.

Thank you very much all people here, and for sure Volker !!
My unit is now working great, and has a fabulous sound.
No noise, great warm... perfect !!
I'm so happy now to have 2xLA2A for my audios projects.

May be I'll create another one for a friend ;-)
Again thank you for all the perfect informations found here.
Manu

https://imgur.com/a/RuVHJGv

Just removed the T4B for test before the photo, sorry ... ;-)
 

uptownsquash

Member
Joined
May 27, 2020
Messages
20
Location
USA, Tennessee
Manucas said:
Hello.

Thank you very much all people here, and for sure Volker !!
My unit is now working great, and has a fabulous sound.
No noise, great warm... perfect !!
I'm so happy now to have 2xLA2A for my audios projects.

May be I'll create another one for a friend ;-)
Again thank you for all the perfect informations found here.
Manu

https://imgur.com/a/RuVHJGv

Just removed the T4B for test before the photo, sorry ... ;-)

Hello, im currently almost finished with my current build but was wondering what switch you used for your link/dual selector?
 

BGroen

Member
Joined
May 22, 2020
Messages
9
Hi guys,

I'm preparing my part list to order everything.
I can find all parts within the EU except the following:

- Solen fast caps
http://www.banzaimusic.com/Solen-Fast-0-1uF-630V.html
https://www.tube-town.net
- VU meters (I can find them on Amazon or banggood, but not sure about the quality_)
https://www.don-audio.com/
- T4B (I know uaudio, drip, kenetek, all USD)
https://www.don-audio.com/
- Input & output transformers
https://www.sowter.co.uk

Does someone know where to find them to avoid big shipping costs? Shipping to NL.

Kind regards,
Beinte
 

andow

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Jan 5, 2015
Messages
298
Location
Austria
Ok, so I got some new meters and everything works fine now, calibration was a breeze too...

When sending some signals through the unit I noticed that when switching to stereo the left channel is compressing much more than the right, even though they're the same when used in mono.
Any idea what's going on here?  ???
 

BerndVP

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Apr 28, 2020
Messages
76
Location
Belgium
http://www.banzaimusic.com/Solen-Fast-0-1uF-630V.html

BGroen said:
Hi guys,

I'm preparing my part list to order everything.
I can find all parts within the EU except the following:

- Solen fast caps
- VU meters (I can find them on Amazon or banggood, but not sure about the quality_)
- T4B (I know uaudio, drip, kenetek, all USD)
- Input & output transformers

Does someone know where to find them to avoid big shipping costs? Shipping to NL.

Kind regards,
Beinte
 

andow

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Joined
Jan 5, 2015
Messages
298
Location
Austria
Yesterday I finally put the lid on my first D-LA2A! 😎

Thanks to Volker for the nice PCB, this is a really cool project. I used Sifam meters, Kenetek T4Bs and Sowter transformers, which took ages to arrive.
I also replaced the pots with Elma switches and opted for unity gain at 0, which makes more sense to me. The output has switchable 600R termination, which minimizes distortion when followed by a high impedance input. Pretty much all the components of the two channels are matched, so stereo tracking is really good (I didn't even have to adjust the stereo adj. trimmer) and cabling is shielded throughout.

I'll have to put it through its paces but it sounds incredible in a first test!
 

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justinheronmusic

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Jan 13, 2015
Messages
222
Location
USA
Hey guys,

I have been in LA2A heaven for the last few years but today my meter wouldn't zero out. I opened it up and NE2 is not glowing. My meter will only go as high as -1db.

Any ideas? I swapped NE2 for a new LED and no improvement.
 

justinheronmusic

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Jan 13, 2015
Messages
222
Location
USA
troubleous said:
Alrighty, after fiddling with my unit a bit more, It seems the culprit setting the meters to zero are the 6AQ5's.

As soon as they are in, I can't zero the meters - without them, no problem. I tried two batches of 6AQ5's and the same problem exists with both of them. I guess it's time to order some more of those and try to find proper ones.

When the 6AQ5's are in, the unit seems to work properly (compressing nicely, though the VU-meters are not calibrated).

Or could the problem be somewhere else than the tubes? I re-checked the heater wiring and re-flowed the joints just to be sure, but that didn't change anything.

Cheers,
Jarkko

Did you ever solve this issue?
 

justinheronmusic

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Jan 13, 2015
Messages
222
Location
USA
Just like the above issues, Gain Reduction metering unable to zero out, no luminance from DS201 (NE2). Removed 6AQ5 and meter was able to zero out.

Attached is a photograph of the meter circuit for visual reference.

I swapped out R225, R226, R227 without any results.

I opened it back up and swapped out R228 (470k) just for good measure.

My solder joints on R229 (4.7k 3W) looked a little weird, so I touched those up.

I don't know if it was R228 or if it was the bad solder joints at R229, but I am willing to bet it was solder joints at R229 due to a flex in the PCB while replacing tubes/T4B that caused the solder joints to become cold.

Everything is back up and running with no issues, and I now have an Amperex Bugle Boy 12AX7 in V201  8)
 

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