D-LA2A Support Thread

[hugo]

Hi mates,
Did somebody try to make the heaters DC? If yes, how to ?

 

[ron_swanson]

Hello Silent Art.
Can you please help/direct me to "where to begin" -i wanna build my very own Dual LA2A.

My post here on top of page 95 wasn't answered and i feel like this is a very secretive project.
There's no direct instructions on where to begin and no obvious answers or solutions for beginners.
Like a "closed club".

Please help me thanks

Sorry, there isn't a step-by-step instruction for this project.  Outside of silent arts' schematic and the BOM which you indicate you have, everything else you need to complete a build is within this forum or the on the Internet. 

 

[ron_swanson]

Ok, your Audio Path is working fine on both channels, and you don't have gain reduction on both channels, right?
So both channels react the same / have the same problem?

Update... after taking some time to further wrap my head around my build and both analyzing and measuring the DC voltages within the circuits, it appears that the build was working all along - just horribly out of calibration.

Wondering though, what is GS01 and GS02 on the schematic?  Or, is my schematic out of date or am I just missing something?

 

[ron_swanson]

Ok, your Audio Path is working fine on both channels, and you don't have gain reduction on both channels, right?
So both channels react the same / have the same problem?

Build pics...

 

[ron_swanson]

Build pics...

One more...

 

[[silent:arts]]

Nice!

Wondering though, what is GS01 and GS02 on the schematic?  Or, is my schematic out of date or am I just missing something?

Those are Gridstopper resistors, added with rev02 (and not in the original LA2a).

 

[ron_swanson]

Nice!
Those are Gridstopper resistors, added with rev02 (and not in the original LA2a).

Ah, yes of course. 

I saw you had a post on another LA2A thread (first page) within this forum (sorry, I can't find that URL reference at the moment...) saying that replacing the 100k gain pots with a 22k log pot and 75 ohm resistor in series will help with the touchy / low resolution of that control.  In series would mean the 75k ohm resistor would be connected to the hot / positive leg of the pot?  Any thoughts on this mod? 

Thanks Volker!

 

[[silent:arts]]

In series would mean the 75k ohm resistor would be connected to the hot / positive leg of the pot?  Any thoughts on this mod?

Yes. I did this in my D-LA2A and it works perfect for me.

 

[ron_swanson]

Yes. I did this in my D-LA2A and it works perfect for me.

Thanks Volker and a special thanks to you for making this project possible.  Fun project!

 

[curranm]

I have a D-LA2A that I have never finished. I got stuck and frustrated with the Molex connectors. SO I have finally gotten a molex crimp tool and have tons of the little metal connectors from the original BOM order for the build. SO I need to know what gauge wire I should order for the build to work with these Molex connectors to finish this albatross around my neck! and some information on getting a GOOD insertion into the connectors so things aren't intermittent. Thanks in advance for any help you guys can give me! I really would like to get this thing done and use it in my studio!

 

[ron_swanson]

I have a D-LA2A that I have never finished. I got stuck and frustrated with the Molex connectors. SO I have finally gotten a molex crimp tool and have tons of the little metal connectors from the original BOM order for the build. SO I need to know what gauge wire I should order for the build to work with these Molex connectors to finish this albatross around my neck! and some information on getting a GOOD insertion into the connectors so things aren't intermittent. Thanks in advance for any help you guys can give me! I really would like to get this thing done and use it in my studio!

I used Belden Brilliance 8451 22 AWG 2C Mic Line Instrument Cable Beldfoil Shield wire for my build.  It's a little on the stiff side, fully shielded, easy to work with, but will stay mostly in place if you want to shape it into corners or around curves.    My build is dead quiet. 

You can see my build a few posts up from this one...

Good luck!

 

[[silent:arts]]

Shielded wire is mandatory for wiring the pots.

 

[hugo]

I used Belden Brilliance 8451 22 AWG 2C Mic Line Instrument Cable Beldfoil Shield wire for my build.  It's a little on the stiff side, fully shielded, easy to work with, but will stay mostly in place if you want to shape it into corners or around curves.    My build is dead quiet. 

You can see my build a few posts up from this one...

Good luck!

Hi, thank you for contribution.
When you say "dead quiet", did you measure this ?

 

[ron_swanson]

Hi, thank you for contribution.
When you say "dead quiet", did you measure this ?

I just finished my build this week, so the short answer is no, not using measurement tools beyond what I can see / hear within my DAW and some trace checking - which at the end of the day, is all I care about.  My unit' s'noise' is within a reasonable window with all of my other commercial manufactured hardware as well as my other DIY builds.  I'm still new to all of this, so further analyzing is definitely on the list of things to do. 

My 'dead quiet' statement was meant to suggest there's no buzzing, humming or other artifacts that are outside of what I would expect from a build  as this and in light of your wiring question.    As Volker suggest above, shielded cabling is mandatory. 

 

[hugo]

Thank you. I ask because i made several version of diy la2as and noise is really layout dependant. I had noise from -90dbfs on the opto6, about -75dbfs with my p2p utc, to -60dbfs on my dla2a...all seems quiet but 30dbfs difference is a lot for mastering purposes

 

[[silent:arts]]

The PCB layout is noise free. The wiring is not.
Tube quality is important too. Me (and others) measured up to 30dB difference with different tubes in the past.

 

[dmp]

I used Belden Brilliance 8451 22 AWG 2C Mic Line Instrument Cable Beldfoil Shield wire for my build.  It's a little on the stiff side, fully shielded, easy to work with, but will stay mostly in place if you want to shape it into corners or around curves.    My build is dead quiet. 

My build gets a high frequency oscillation at max gain (~18kHz)  -  I've been wanting to sort it out.  I'll look at your build pics and try to find how mine is different.  Yours is dead quiet even at high gain?

 

[[silent:arts]]

passing signal in both channels  but cannot  engage the compression circuit... I hear the relay switching but not engaging there circuit.

I don't think I understand this correctly. We start with the audio part and let compression circuits be compression circuits.
Put the T4Bs out.

Both channels pass unity gain signal without power?
Now power with power on, left channel only on, does it pass signal (dependent on your gain potentiometer?)
Next, right channel only, does it pass signal (dependent on your gain potentiometer?)
Cool.
Now both channels together. Do they pass signal dependent on the gain potentiometers?

 

[ron_swanson]

My build gets a high frequency oscillation at max gain (~18kHz)  -  I've been wanting to sort it out.  I'll look at your build pics and try to find how mine is different.  Yours is dead quiet even at high gain?

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. 

 

[[silent:arts]]

Sounds like it is still in bypass.
The relays must be "on" (5V) to pass signal thru the circuit.