D-LA2A Support Thread

[[silent:arts]]

I'm preparing for tonights grand unveiling... first power on. I think everything looks good, does this toroid wiring look correct?

Looking good!

One other thing I noticed, in silent-arts original picture of the toroid wiring, his picture shows a "brown" and a "brown/red" wire. On my transformer, there are only 2 pairs of brown wires. I take it these can be used interchangably?

this is fine. the "brown/red" and the "black/red" is my personal (red) heat shrink marking since I wanted the heaters to be "in phase" - but I guess this doesn't matter.

Time to power her up!

 

[frazzman]

Powered up... Worked straight away first time. I was surprised as there are so many points of failure with all these molex connectors and wiring.  First power on revealed that disconcerting kind of electrical burning smell but in absence of any smoke or concerning signs - it seems to be fine. I thought it was maybe the smell of the regulator heating up or the tubes. Anyhow, looks like I need to do the highly documented gain pot mod... Can't even crank it half way without the speakers exploding ... This is an amazing project

 

[[silent:arts]]

Great stuff!

The electrical burning smell is normal, the tubes burn away your fingerprints ...

 

[frazzman]

Great stuff!

The electrical burning smell is normal, the tubes burn away your fingerprints ...

I figured. The PCB layout is exceptionally good. I'm just so psyched that it worked first go. I'm waiting for my meters to arrive but so far everything sounds right to my ears.

 

[frazzman]

Great stuff!

The electrical burning smell is normal, the tubes burn away your fingerprints ...

Hi Volker,
Quick question for you (that I need to hopefully finish the build...!). Sorry if it's been covered, I searched the thread but couldn't find a definitive answer.... If I want to use 12v lamps in the VU meters, where is the best spot to power from ? Or is it better to find an led powered meter and borrow some power off the relay psu ? I wanted to use some of the hairball HB-8037 meters. Thanks a lot

 

[[silent:arts]]

Don't know what kind of Lamp the 8037 uses, best would be to replace it with 5V Lamps.

 

[frazzman]

Don't know what kind of Lamp the 8037 uses, best would be to replace it with 5V Lamps.

Hi Volker,
It's a hairball meter, runs on a 12v lamp:
http://www.hairballaudio.com/shop/product_info.php?products_id=40

They used to offer a 5v led version but doesn't look like they do anymore

 

[[silent:arts]]

The lamp should be replaceable. Just replace it with a 5V version.

 

[Palmito]

Hi folks
I just finished my dla2a, it passes audio, is dead quiet, so that a good start. Bypass switch seems to be working since the gain pot gets active when compression is on. The vu meter seemd to work fine also, it shows the level and stays at 0dB on gr. The problem is that it doesnt compress.

Could my problem come from the relays ? Since i read that some models dont work... Did anybody used Omron G5V-2 ?
Thanks
Alex

 

[[silent:arts]]

Since "gain" is working the relays are fine (and Omron G5V-2 are the correct relays).

 

[Palmito]

Ok thanks.
Strange thing is that both sides arent compressing... i tried swapping tubes, t4bs, same thing... So maybe this could have something to do with stereo linking ?
At first i mistakely install the t4bs sockets the wrong side around, then i changed them, do you think i could have damaged them by powering the unit ?
Another hint: when i turn the gain reduction pot at max (fully clockwise) all i hear is a slight distortion. Maybe someone had the same problem ?

 

[[silent:arts]]

Turn all trimm pots to far to the right first.
Multiple times.

 

[Palmito]

I tried this already...
I used Edcor xsm 10k/10k on input and xsm 10k/600 on output. Is that correct ?

 

[[silent:arts]]

Transformers are fine.

 

[Palmito]

I used Kenetek T4B, with R25=33k. Is that right ?

 

[Palmito]

Sorry for all the questions, im trying to find where to search...
Could i have damaged the T4Bs by connecting them in reverse ?

 

[Palmito]

Ok i sorted it out, I had the center tap connected on the input Xformers, i disconnected them and now its working !
Thanks a lot Volker

 

[frazzman]

Hi Volker, and any other D-LA2A experts who still hover over this thread..!

My first D-LA2A is about 98% complete, I just have a few questions to help get me to the finish line.

Issue 1)I completed the stereo adjustment calibration, both channels show the same amount of gain reduction in stereo mode. The meters are spot on with each other. The problem is, to my ears it just doesn't sound like there is near as much compression going on as the meters would indicate. With peak reduction dialed in at max, the meters are pretty much hovering around -20db (GR). If I dial back the peak reduction, both meters respond accordingly... Rather than describe to you what it sounds like, heres some very short drum clips to explain:
- NO LA2A: https://dl.dropboxusercontent.com/u/108741277/LA2A/la2a-BYPASS.mp3
- LA2A, max peak reduction, gain about 50% - https://dl.dropboxusercontent.com/u/108741277/LA2A/la2a-STEREO-GR.mp3

For R125/R225 I have installed 100k trimmers pretrimmed to 'default' value of 33k....
If I don't adjust these for GR tracking adjustment , will GR metering or behavior be off?
Also the OPTOs are stereo matched.

I Just don't know if it sounds right! Are my eyes or ears lying to me?

Issue 2)
I completed gain pot mod - 25k pot+75k resistor in series.
>> On the left channel I can now dial max gain without issue.
>> On the right channel when I get to about 3/4 gain, the audio on right channel breaks into noise/static sound, if I dial back, the problem disappears. I've tried testing the pot from the Left side on the right to rule out the pot... no difference
As a side issue (maybe related, maybe not) the right channel has a little bit of hum, measuring about -65db noise floor (pretty noisy?). Grounding is fine... I'm guessing some noise from the toroid as this is closer to the right channel. Don't know if this has any bearing on the gain issue...

Sorry for the long winded post... so keen to get this build finished...

Thanks all for the support

 

[frazzman]

I think I might have answered 70% of my own questions .... In short, the fender jewel bezel light is satan! I had one in the center of my front panel, with it removed the noise floor just improved by about 10db, and now I can turn up my right channel gain pot without it crapping out into noise and distortion (the right channel already had a little bit of noise which seemed to be exacerbated by high gain setting). I have to work out a way to route this cabling without adverse affect. I haven't mounted the mains toggle switch to the front panel yet but I'm worried about the impact having those leads next to the pots could be...

So now with the gain pot and noise floor addressed, my only looming concern is a perceived lack of compression, stereo calibration is completed, limiter response set to full CW as per la2a manual. With the meter showing max GR it just doesn't sound like the signal is being crushed...

Reading other users reports, it sounds like turning the limiter response trimmer CCW increases compression ? The only thing I haven't done is the Gr meter tracking, trimmers are set to 33k, I can cope with the meter being slightly off as long as know that the compression is responding as expected... Appreciate any thoughts from other builders

 

[frazzman]

Sorry for the post overload... But this thing is driving me nuts! Everything is working... I have a useable gain range, stereo adjust is complete, meters show gain reduction and respond to changes in the peak reduction pot... BUT when I look at a wave form with the unit at max peak reduction, it just doesn't look very compressed!! Any ideas ? I've tried adjusting the limiter response trimmer but it's hard to tell if it's helping or not.