D-LA2A Support Thread

[innercityman]

maybe wrong value resistor in series with the meter ?
on the la-2a the meter is just taking the unbuffered signal from the output.
If there is healthy audio signal on the output of the compressor there is nothing else that could be wrong except the wiring to the meter, the switch, the series resistor, or the meter itself.

regarding the hum you mentioned, the AC wiring from the power transformer should be kept as far away as possible from high impedance circuitry.
It seems from the photos both the mains wiring and the lamp supply are very close to the gain pot. Any noise picked up there will be amplified in the following stages.
The wiring to the limit/comp switch is also in the input grid circuit of the first amplifier stage, I believe on the original La-2a this wire is shielded.

It would help to have the mains switch on the side of the front panel. I have seen some commercial units using a shielded microphone cable for mains wiring going to the on/off switch in the center of the front panel.

3.6k resistors on meters.

Re checked connections and made some tests this morning... Meters work on output position but really tiny gain. When sending 1Khz sine wave at 0db left channel goes to -7db maximum on meter with gain pot fully open, right channel goes to -3db. Still no compression on both channels.

 

[beatnik]

Sounds like the problem could be in the audio path.

Check audio transformers wiring is correct.

If you can post DC voltages on V1 and V2 that might reveal some issue.

An oscilloscope would be very useful in diagnosing this kind of problem as it allows tracing the audio path from input to output and see where the signal drops.
You can pick old analog scopes for bargain prices on ebay.

 

[rfused33874]

Hello I finally got my DLA2A put together but having some issues. I hope someone can give some insight or troubleshooting ideas

Both channels pass audio, the gain controls work, and the VU meters work properly when in Output mode. When switched to Gain Reduction mode, the meters go to 0 as expected

But both channels are pretty noisy with slightly different sounding humming noise and turning the Peak Reduction knob doesn't seem to do anything--the meters always stay at 0 when in Gain Reduction mode.

I've tried the stereo adjust trimmers all the way in both directions but still compression never kicks in

One thing I'm not 100% confident on is the wiring for the Cinemag transformers, here is what I did:

Sowter 4383 brown = Cinemag 2570 brown
Sowter 4383 pink = Cinemag 2570 orange AND red
Sowter 4383 green = Cinemag 2570 yellow
Sowter 4383 black = Cinemag 2570 black
Sowter 4383 grey = Cinemag 2570 green
Sowter 4383 blue = Cinemag 2570 blue
star ground = Cinemag 2570 white



The Cinemag 2840's only have 4 wires so I used this:
Sowter 8940 yellow = Cinemag 2840 red
Sowter 8940 green = Cinemag 2840 brown
Sowter 8940 grey = Cinemag 2840 yellow
Sowter 8940 pink = Cinemag 2840 orange
Sowter 8940 black = EMPTY


I'm super grateful for any suggestions or guidance!

 

[[silent:arts]]

How did you wire the PSU transformer primaries?
I can see the two white cables going to the back, and the two yellow wires to the front?

 

[rfused33874]

Yes my power is 115V so I put both primaries in parallel. I have the power switch disconnecting the yellow wires from the IEC power input jack.

Did I do something stupid?

 

[[silent:arts]]

No, if both primaries are wired in parallel all is fine.
I can't find anything about your Cinemag transformers. Is there a datasheet available?
The colors don't mean anything without it.

 

[rfused33874]

Thank you! Here's some more info on the transformers:

CM-2570 Input Transformer​

Currently I have it wired as:

• Sowter 4383 brown = Cinemag 2570 BRN
• Sowter 4383 pink = Cinemag 2570 both ORG and RED
• Sowter 4383 green = Cinemag 2570 YEL
• Sowter 4383 black = Cinemag 2570 BLK
• Sowter 4383 grey = Cinemag 2570 GRN
• Sowter 4383 blue = Cinemag 2570 BLU
• star ground = Cinemag 2570 white
• NO CONNECT = Cinemag WHI/RED stripe

CM-2840 Output Transformer​

"BRN/RED are the primary and ORG/YEL the secondary"

Currently I have it wired as:

• Sowter 8940 yellow = Cinemag 2840 RED
• Sowter 8940 green = Cinemag 2840 BRN
• Sowter 8940 grey = Cinemag 2840 YEL
• Sowter 8940 pink = Cinemag 2840 ORG
• Sowter 8940 black = EMPTY

 

[[silent:arts]]

Yes, you posted this before.
But what is the ratio of the transformers?

 

[rfused33874]

Cinemag CM-2570 (1:4)
Cinemag CM-2840 (5:1)

 

[[silent:arts]]

5:1 for the output should be ok (the Souter is 3:1), and it should pass audio the way you wired it.
However, I would wire it BRN to YEL, RED to GRN, ORG to GRY, and YEL to PNK.

The input is difficult to say (is it 1+1:4 or 0,5+0,5:4?
If it is 0,5+0,5:4 I would wire it
BRN to BRN, RED+ORG to PNK, YEL to GRN, GRN to BLU, BLU to GRY
WHI+BLK to BLK
WHI/RED not connected

 

[rfused33874]

Thank you, your suggestion on the output transformer has fixed the noise issue!

Perhaps I was mistaken on the specs on the input. I contacted David from Cinemag and he responded:

It can be hooked up for 1:9 (primary windings in series) or 1:18 (primary windings in parallel). 150/600:48.6K

 

[beatnik]

You want the 1:9 configuration, so tie red+orange together but do not connect this to anything else

 

[rfused33874]

Thanks @[silent:arts] and @beatnik

I tried both configurations for the input transformer and it doesn't seem to make a difference whether RED+ORG is connected to "PNK Sowter 4383" or not. The volume and everything stays the same

In both configurations it passes audio and the Gain controls work, but compression won't kick in (I tried both directions on the stereo adj trimmers)

 

[[silent:arts]]

Even 1:9 is too much, you should think about another input transformer.
However, this has nothing to do with your gain reduction problem.
What T4B are you using?

 

[rfused33874]

OK thanks! I will replace the input transformers once I get this gain reduction issue fixed

It is a matched pair of Kenetek T4B's

 

[[silent:arts]]

Keneteks are fine. If all voltages are fine etc check the wiring of the peak reduction potentiometer.

 

[TwentyTrees]

A quick question about front panel layout. I'm planning a 2U build for my D-LA2A, and am looking at how to orient the channels. All the D-LA2As I've seen have the two channels side by side - version (A) in the graphic below. For reasons of ergonomics I'm considering a stacked layout - (B) below, like the Neve 33609 or Chandler TG1.



Are there any compelling reasons not to pursue a stacked (B) layout for a D-LA2A build? I know that some of the front panel control wiring needs to be shielded and kept away from AC as it's relatively high impedance - but could simply having the controls adjacent (or the channel wiring closer) lead to issues, such as stability, noise or crosstalk?

Thanks!

 

[delatsch]

Here's a live demo od the recently finished D-LA2A adopted by a local studio here in Krakow, Poland, hope you'll get a kick out of it:

 

[innercityman]

Here's some pics of my build...

Got some connections issues that have been solved once I bought the proper Molex crimping tool and redone all my wiring connections.

 

[innercityman]

Hi all,

I realised that my unit wasn't compressing too much, it works but I expected more compression so I've just watched this video from this guy showing how to make the GR meter accurate and realised that I probably have an issue. When doing this GR calibration I had to turn the peak reduction knob to almost 70 to get less 5db on meter. On the video, he turns the knob to about 30 or so. I've checked my limiter response trimmers and they are in a flat position so fully clockwise. I've tried to turn them other way but less compression as I turn trimmers opposite way. Stereo adjust trimmers fully counterclockwise, no compression when fully clockwise. Been able to calibrate for stereo operation. Same behaviour on both channels. 100K pots for gain and peak reduction. Any idea ?