D-LA2A Support Thread

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innercityman

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0db. I've already read a lot of posts in this thread and I know that I need to send +4 db 1khz sine wave from DAW and turn the gain until vu meter needle reaches 0db. That's what I did, but I only get the needle moving to the left until I pass 50 on PR, is that normal? Other than that, no hum or whatever, the unit is really quiet. When PR knob fully clockwise I get 12db of GR no more.

New and matched pair of T4BX from IGS.
 
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[silent:arts]

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Without a reference 0dB says nothing. Your VU Meter should read 0VU with +4 dBu at the output of the D-LA2A.
If you feed your D-LA2A with +4 dBu 1 kHz signal, and you have to set your gain (RV101) higher than a few degrees to get +4 dBu at the output, your input is probably too low.
What is your input transformers ratio?
Maybe it is wired backwards (4:1 instead of 1:4)?
 

innercityman

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Without a reference 0dB says nothing. Your VU Meter should read 0VU with +4 dBu at the output of the D-LA2A.
If you feed your D-LA2A with +4 dBu 1 kHz signal, and you have to set your gain (RV101) higher than a few degrees to get +4 dBu at the output, your input is probably too low.
What is your input transformers ratio?
Maybe it is wired backwards (4:1 instead of 1:4)?
Hey, I just realised that the line out of my daw interface was at -30dbfs, I've set it up at -18dbfs which corresponds to 0dbu right ? and now I easily get 5db of GR turning the PR knob at something between 20 and 30. So you're right, my input was too low, but now my gain pot is at about 10 no more, to get 0db on vu meter, but I guess it's normal. Alpha pots. I think I'm gonna do the 25K pot / 75k resistor mod.

I'm gonna measure my outputs and let you know.

My input transformers are wired the way they should. Sowter ones so I just followed the colour code.
 
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innercityman

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Hi,

can someone please tell me on which pin of the 25K pot goes the 75K resistor to do Volker's gain pots mod ? I've searched the thread without success.

Sorry for the dumb question.
 

innercityman

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Ok, I found out. It works like a charm ! The 25K pots mod is must have IMO. By the way, I replaced the R37 limiter response trimmers by 2 clarostat and put them on the front to have more flexibility. Also removed the 5V regulator from the PCB and put it on chassis with bigger Heatsink.
 

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andYz00m

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Hey there, did a handwired build into the Don Audio chassis and have been loving it.

Just today the meter stopped working (Sifam LA-2A replacement). The unit still works properly and compresses correctly, but the meter is stuck on its default -20dB state regardless of the meter switch positions.

My plan is to test voltage coming to the meter switch as that could be a fault point. Any other ideas of what to test? I guess it could just be the meter failed, but its less than a year old and 200$ for a replacement, which Id like to avoid if possible.

Thank you!
 

FarisElek

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Ok, I found out. It works like a charm ! The 25K pots mod is must have IMO. By the way, I replaced the R37 limiter response trimmers by 2 clarostat and put them on the front to have more flexibility. Also removed the 5V regulator from the PCB and put it on chassis with bigger Heatsink.
Is this chasis you're using a 3U? If so, where did you get it if you don't mind me asking?

Ryan
 

andYz00m

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Hey there, did a handwired build into the Don Audio chassis and have been loving it.
In GR mode with no signal present the - lead of the meter has 25VDC and the + side had about 5VDC. I can see VAC coming appropriately from the output trafo to the switch and to the + side of the meter.

Feels like the meter failed. Any ideas on if these are repairable, or what would fail? What would cause this failure?
 

andYz00m

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In GR mode with no signal present the - lead of the meter has 25VDC and the + side had about 5VDC. I can see VAC coming appropriately from the output trafo to the switch and to the + side of the meter.

Feels like the meter failed. Any ideas on if these are repairable, or what would fail? What would cause this failure?
Meter had failed... got a new one and works great. They are goddam expensive though.

BTW, a quick tip, you can test an AC meter by using the Diode function on a quality multimeter. Black to - and tap the + with the red lead, meter will jump. :)
 

tedsorvino

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Hi everyone. Just ordered the pcb and I since i have a local transformer manufacturer I trust, I would like to know please, what are the appropriate primaries for EU (has it got to be 2 x 230V ac??? Why not 1x 230V ac larger one?) and secondaries measurements (voltage -Vac- and power rating- VA) of the appropriate torroidal power transformer?
 

martthie_08

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Hi everyone. Just ordered the pcb and I since i have a local transformer manufacturer I trust, I would like to know please, what are the appropriate primaries for EU (has it got to be 2 x 230V ac??? Why not 1x 230V ac larger one?) and secondaries measurements (voltage -Vac- and power rating- VA) of the appropriate torroidal power transformer?
what are you basing this info on?

In general for tube projects you need a transformer with a primary winding rated at your mains voltage (assuming 230V in Greece) and on the secondary side both a high voltage B+ and also 6.3V for the heaters.

so your options are either a single custom wound transformer with two appropriate separate secondary windings or two individual 230V to 12V transformers wired back to back (not sure if the D-LA2A circuit board has provisions for this option).
 
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tedsorvino

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Thanks Martthie. Actually I think I saw that there is a custom torroidal with 2 primary windings and several secondaries (The D- LA2A is a double one). This one is rated at 60VA.
But what I'm looking for are appropriate values of all secondaries and appropriate power rating. Assuming that I'm using a single 230 V primary and the total power rating sums up at 60VA.
 

martthie_08

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you only really need dual primary windings if you plan to use it with 115V,
the ratings for the secondaries were posted on page 3 in this thread but have disappeared.
FWIW the original part number is TRX-R2-0060-0011 - though I'm not sure whether that is a 51X Audio part number or a Mueller-Rondo part number.
 

tedsorvino

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Thanks fot the primaries tip. Actually I've found this info regarding that 60VA custom transformer:

primaries: 2 x 115V

secondaries:
2 x 250V / 2 x 0.05A
2 x 6.3V / 2 x 2A
1 x 9V / 1 x 1A

All calculated and they do add up to 60VA. And the european primary can be 1 x 230V

What the single 9V line is for?
 
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