D-LA2A Support Thread

[[silent:arts]]

feed in a +4 dBu sinus signal, 1kHz without any gain reduction
meter in VU mode should read 0 VU
change the meter to gain reduction mode, you should read 0 VU

now dial in peak reduction until your meter (still in gain reduction mode) reads -10 VU
change your meter to VU mode

should still read around -10 VU, and your output should be -6 dBu

 

[frazzman]

feed in a +4 dBu sinus signal, 1kHz without any gain reduction
meter in VU mode should read 0 VU
change the meter to gain reduction mode, you should read 0 VU

now dial in peak reduction until your meter (still in gain reduction mode) reads -10 VU
change your meter to VU mode

should still read around -10 VU, and your output should be -6 dBu

Thanks for the reply Volker!

What about gain what should that be set to? I assumed that it should be set so that the meter(s) read 0 VU with +4 dBU 1khz sine wave, is that correct??

Based on your steps, this is what I did:
- Feed in +4 dBU 1khz sine WAV - adjust signal to measure +1.228 vAC across XLR in pins 2+3
- Switch to VU mode, adjust gain until meter(s) read 0 VU (I'm not sure about this part...)
- Switch to GR mode, meter is reading 0 VU
- Dial in peak reduction using right channel PR pot (stereo mode) until reading - 10 VU
- Change meter to VU mode - meter then drops from -10 VU to -7 VU???

Confused about how to set the gain?

Thank you

 

[[silent:arts]]

yes, gain set to read 0 VU

the 3 VU offset might be because of stereo mode only using one side for PR,
or the meter is a little bit off in gain reduction mode.

I would say: all is fine with your unit  8)

 

[frazzman]

yes, gain set to read 0 VU

the 3 VU offset might be because of stereo mode only using one side for PR,
or the meter is a little bit off in gain reduction mode.

I would say: all is fine with your unit  8)

Thank you!
I will try the gr tracking adjust to see of that gets the meter more accurate in GR mode but I'm not too fussed.

I'm just surprised to see that looking at the waveforms of some drums that would appear to be getting heavily compressed, that the waveform doesn't look that way. Maybe it is that the LA2A style of compression is more subtle than say an 1176? Then I tried using some dynamic range meters to compare before and after of a drum track with heavy compression and then bypassed, it threw me off to see that the dynamic range had not been altered much with heavy compression applied.

This is my first opto comp, I have to say it sure does sound good but I wasn't sure about the gain reduction behavior

 

[[silent:arts]]

...
I'm just surprised to see that looking at the waveforms of some drums that would appear to be getting heavily compressed, that the waveform doesn't look that way. Maybe it is that the LA2A style of compression is more subtle than say an 1176?

Very different style of compression for sure.
To "hear" the D-LA2A, try it with vocals etc, sustained sounds, not with drums 

 

[frazzman]

...
I'm just surprised to see that looking at the waveforms of some drums that would appear to be getting heavily compressed, that the waveform doesn't look that way. Maybe it is that the LA2A style of compression is more subtle than say an 1176?

Very different style of compression for sure.
To "hear" the D-LA2A, try it with vocals etc, sustained sounds, not with drums 

I always hear about these shining on vocals... Well I guess I'm done now.. Thanks again for your help. Amazing project. I can't stop playing around with it

 

[frazzman]

I still have one annoying problem on my right channel. I thought I had resolve these issues but apparently not
My right channel has about a 10db worse noise floor when compared to the left channel. I'm guessing due to it being closer to the toroid. Moving the toroid doesn't seem to make much difference...

The other really annoying problem that I can't seem to resolve is when the gain on the right channel is at max or near max, it breaks into static/noise. I don't have this issue on the left channel. Swapping gain pots/wiring between the sides doesn't resolve the issue so I'm pretty confident it's not the gain pot. I'm using the 25k pot+75k resistor mod. Any ideas what could cause this issue on 1 channel only ?
Thanks!

 

[rob_gould]

Swap tubes and t4b one at a time between the channels maybe? Should be possible to isolate the issue that way...

 

[desol]

As far as reducing noise, I have wrapped toroid's in sheet mu metal and added additional shielding around them in an attempt to lessen EMI.
It did help to a noticeable degree.

To get really good performance...you would have to have a custom box made of thicker mu-metal for the transformer.

Come to think of it, there is a fellow in the white market with another solution...about 60% of the way down the page:
http://groupdiy.com/index.php?topic=38026.0

 

[frazzman]

As far as reducing noise, I have wrapped toroid's in sheet mu metal and added additional shielding around them in an attempt to lessen EMI.
It did help to a noticeable degree.

To get really good performance...you would have to have a custom box made of thicker mu-metal for the transformer.

Come to think of it, there is a fellow in the white market with another solution...about 60% of the way down the page:
http://groupdiy.com/index.php?topic=38026.0

Hi Desol,
Thanks for the reply, i've used mumetal before on past builds, on my gpultec's it made a huge difference. It's a shame its so expensive, but i've ordered some regardless.

Have you had any issues with noise/distortion sound when gain pot is maxed out? I've read a lot of posts from users who report oscillation at max gain, mine doesn't sound like oscillation but its annoying never the less. The weird thing it only happens on 1 side and it doesn't seem to be due to the pot itself, I just can't narrow down the culprit.
Cheers

 

[desol]

I don't think that I have noticed any distortion....but then again, I never turn it up that high.

I'd first try what Rob suggested above...

 

[frazzman]

I don't think that I have noticed any distortion....but then again, I never turn it up that high.

I'd first try what Rob suggested above...

Hi desol,

Thanks for the reply. I tried what rob said, and so far I can't get the problem to follow the components, so even when swapping gain pots/tubes/t4b , the problem is always on the right. I know having the gain at this setting is not practical, but I'm still trying to understand why it could affect one channel and not the other (all components are the same)...

This is what it actually sounds like, you can hear in the last 5 seconds when I turn the gain pot down a little, the problem immediately disappears ... Really weird...

https://dl.dropboxusercontent.com/u/108741277/la2a%20problem.mp3

 

[rob_gould]

Are your transformers on molex connectors? Can you move those between channels too?

 

[frazzman]

Are your transformers on molex connectors? Can you move those between channels too?

Yep they are, I'll give that a shot too. Will have to unscrew them from the chassis. Will let you know how I go.

 

[DaTastenrasta]

Hey guys,

sorry for interrupting the tech talk but I'm actually new to the DIY-forum though I've built an mnats-1176 before. The problem is that I've been searching through a lot of the posts so far and I can find posts going into depth in almost every thread but I can't seem to find some kind of beginning.

I would like to build an LA-2A in the original version, so with the turret boards and a non-PCB-style one. And to be honest I'm still at the very beginning apart from knowing what it is, what it does and a very undetailled knowledge of what a turret board is  :-[

Is there anyway you could help me get started? Would really appreciate that.

Thanks for your help!

 

[[silent:arts]]

http://groupdiy.com/index.php?topic=3278.0

 

[desol]

I don't think that I have noticed any distortion....but then again, I never turn it up that high.

I'd first try what Rob suggested above...

Hi desol,

Thanks for the reply. I tried what rob said, and so far I can't get the problem to follow the components, so even when swapping gain pots/tubes/t4b , the problem is always on the right. I know having the gain at this setting is not practical, but I'm still trying to understand why it could affect one channel and not the other (all components are the same)...

This is what it actually sounds like, you can hear in the last 5 seconds when I turn the gain pot down a little, the problem immediately disappears ... Really weird...

https://dl.dropboxusercontent.com/u/108741277/la2a%20problem.mp3

Yeah...somethings off there. If I was more well versed in theory (I more have solid Refrigeration electrical theory...with some electronics, I'm not a theory engineer) I could really help. Sorry man...

About the best I could offer is to trace the audio signal with a scope (carefully ~ 350v) and see where it starts getting messed up. Seeing as everything seems to work up until a certain level of gain it sounds like it could be a bad tube, poor connection, bad switch or wiring configuration.

 

[frazzman]

I don't think that I have noticed any distortion....but then again, I never turn it up that high.

I'd first try what Rob suggested above...

Hi desol,

Thanks for the reply. I tried what rob said, and so far I can't get the problem to follow the components, so even when swapping gain pots/tubes/t4b , the problem is always on the right. I know having the gain at this setting is not practical, but I'm still trying to understand why it could affect one channel and not the other (all components are the same)...

This is what it actually sounds like, you can hear in the last 5 seconds when I turn the gain pot down a little, the problem immediately disappears ... Really weird...

https://dl.dropboxusercontent.com/u/108741277/la2a%20problem.mp3

Yeah...somethings off there. If I was more well versed in theory (I more have solid Refrigeration electrical theory...with some electronics, I'm not a theory engineer) I could really help. Sorry man...

About the best I could offer is to trace the audio signal with a scope (carefully ~ 350v) and see where it starts getting messed up. Seeing as everything seems to work up until a certain level of gain it sounds like it could be a bad tube, poor connection, bad switch or wiring configuration.

Thanks Desol, I will see how I go. It's really weird because this issue literally occurs on the very last few millimetres of the gain pot, I can get it extremely loud,  but as soon as it's maxed out this issue occurs. My logic was that if everything works perfectly when the gain pot isn't maxed then it can't be a wiring issue etc

 

[Sammas]

Hey guys, I am in the process of ordering the transformers to complete my D-LA2A.

What are your thoughts on using Carnhill VTB2380's on the input and output? They are 15k:600ohm ungapped.

Shipping edcors to Australia is horrendously expensive. It works out the same to get 4 carnhills from Colin in the UK!


http://www.audiomaintenance.com/acatalog/CA-18-VTB2380_extended_info.html

 

[frazzman]

Hey guys, I am in the process of ordering the transformers to complete my D-LA2A.

What are your thoughts on using Carnhill VTB2380's on the input and output? They are 15k:600ohm ungapped.

Shipping edcors to Australia is horrendously expensive. It works out the same to get 4 carnhills from Colin in the UK!


http://www.audiomaintenance.com/acatalog/CA-18-VTB2380_extended_info.html

Hi Sammas,

I'm from Oz as well, I had a similar dilemma... The postage direct from Edcor in the USA is ridiculously expensive but the price of the transformers are ridiculously cheap...
The transformers for this project cost me $10usd each + $50usd shopping so $90 all up, I think that will still come in cheaper than the carnhills ...