D-LA2A Support Thread

[[silent:arts]]

You are puzzling me. How do you recognise increased gain in a channel not passing signal?

 

[Holger]

Another one: built around an old Weston 862 meter. Currently I'm using Kenetek's here. I/O TX are Carnhill 9k6:600.The meter has a sticker marked 1966 on it. The 5V PSU went crazy when connecting the meter bulbs so I used a little 5V MeanWell SMPS for relays and meter illumination. Knobs are 40mm dia. Fat looking guy...

 

[[silent:arts]]

Nice as always - only one but big meter as always - a true CLAßEN.

This will be used in the Röhren(Rein)Raum at the Krässemaschinenwerke Hamburg?

 

[Holger]

Nice as always - only one but big meter as always - a true CLAßEN.

This will be used in the Röhren(Rein)Raum at the Krässemaschinenwerke Hamburg?

;-) yes...

 

[dmp]

It's my understanding that LA2A's run very hot gain-wise by nature and running them with the gain above 7-ish or so can / will result in artifacts.  Mind you, I don't have past hands-on experience here as this is my first hardware LA2A.  I have read within this forum and on the Interwebs suggesting that this is 'normal' behaviour, so at this point I haven't worried about any of that.    If I remember correctly, some of the 'fix' included swapping the 12AX7 out for lower gain tubes.  Honestly, at a gain setting of 7 the signal is WAY too hot for anything I'd ever use or want.  The signal is very distorted at those levels and not in a pleasant way IMHO.

If others here have contrary information to add here, a little help / input would be appreciated.

Be that as it may be, I'm interested in actually testing here.  So I undertand.... when you turn the gain up above 7 or so, you get an oscillation at 18KHz with no audio signal being input?  If so, I'll give this a test when I get a few minutes and report back.

I have to go back and look into it again, but my recollection is that with peak reduction way up and the gain way up, we got this ~18kHz noise. We were running a track into it at the time .
I made mine with Jensen 1:1 line in transformers which works really well (unless you want to run mic signals into it).  The gain is needed in this configuration when compressing heavily.

 

[Eliani]

I haven't gon through the whole thread yet...  :
But the BOM to dropbox link is broken on the first post...
Is anyone willing to share his.. mutch appreciated

 

[QNote]

I haven't gon through the whole thread yet...  :
But the BOM to dropbox link is broken on the first post...
Is anyone willing to share his.. mutch appreciated

See Page 89 in this thread.  I have an updated link there, along with other resources.  New theory and troubleshooting videos in just a few weeks (I shot one of them yesterday).

BOM Link:  https://www.dropbox.com/s/2xky62b30ccsvfw/D-LA2A_BOM_QNS.xlsx?dl=0

 

[weiss]

Another one: built around an old Weston 862 meter. Currently I'm using Kenetek's here. I/O TX are Carnhill 9k6:600.The meter has a sticker marked 1966 on it. The 5V PSU went crazy when connecting the meter bulbs so I used a little 5V MeanWell SMPS for relays and meter illumination. Knobs are 40mm dia. Fat looking guy...

where do you always find them?
i only come across these way overpriced meters for several hundred bucks.. 

https://reverb.com/item/11073137-1950-s-weston-electric-model-862-vu-meters-vintage-bakelite-with-black-panel-free-shipping

 

[Holger]

I've purchased them years ago...

 

[groselicain]

Had this sitting on my shelf for over two years now and decided to finally finish it yesterday. I've gotten the left channel running perfectly, but the right channel has issues. I've checked it against the left channel with the eye test and all seems to be correct, but I really might be overlooking something. Right channel meter doesn't register audio on output, but it does zero on gain reduction. Output pot works fine, gain reduction does not introduce compression—only distortion in the last 25% of its throw. Stereo linking is switched off, the stereo adjust is wide open. I've switched all tubes and T4Bs from left to right to no avail. Here's a list of voltages at test points:

[list type=decimal]
[*]99.6
[*]1.137
[*]209.4
[*]108.9
[*]1.204
[*]227.5
[*]111.1
[*]274.3
[*]19.59
[*]52.69
[*]84.2
[*]0.846
[*]5.48
[*]167.3
[*]96.3
[*]365.4
[/list]

Any help is so appreciated.

 

[groselicain]

I didn't post pictures just because I felt certain there's no discrepancy between the two channels, but would it help if I did?

 

[scott2000]

I felt certain there's no discrepancy between the two channels,

The voltages above are for both channels?

 

[groselicain]

No sir, those are voltages for channel two only. I omitted channel one since it’s operating properly. Should I post them as well?

 

[groselicain]

Closer view of PCB

 

[groselicain]

Looks like my first picture got messed up in the upload. Sorry for the rat's nest, I had intended to wait to ziptie the wiring until I had everything sorted. It might be worth mentioning that when I pass audio through the malfunctioning side, it gets louder when I remove the T4B. Is that a clue to anything? Thanks so much.

 

[scott2000]

Any links to what the test point voltages represent?

No sir, those are voltages for channel two only. I omitted channel one since it’s operating properly. Should I post them as well?

 

[groselicain]

This is what I was working with.

 

[[silent:arts]]

I've switched all tubes and T4Bs from left to right to no avail.

Check the side chain tubes heater voltage.

 

[groselicain]

Check the side chain tubes heater voltage.

Same on both channels 1 and 2,.

 

[scott2000]

What's the voltage on the working channel at ?? TP 10 out of curiosity.... bulb??

All the tubes  in right places???