D-LA2A Support Thread

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django

Member
Joined
Jul 13, 2011
Messages
9
Right i'm having some problems with my LA2A. I'm getting pretty much no gain reducation on either channel and I have to drive the input really hard to get any gain reducation aswell. I've checked all the component values and swapped the valves around etc. Can anyone point me in the right direction for troubleshooting here?

 

django

Member
Joined
Jul 13, 2011
Messages
9
Input transformer is working fine and providing a voltage increase, just atm i'm having to put a really hot signal into the input to get any gain reduction and the output from the la2a is far to hot aswell
 

baadc0de

Well-known member
Joined
Jul 9, 2009
Messages
797
Location
Europe
I'll be remaking my DLA2A with a new PCB (the old one has had some traces damaged with soldering/desoldering etc) and I thought to maybe install some high(er) quality filter capacitors for the PSU. Not that I thought the current cheap multicomp ones are bad as such, just wanted to see if investing a bit there pays off measurably / audibly.

I went with Russian military PIO and Styroflex for signal caps.

Banzai sells illinois capacitor 22uF/500V as "good for ripple performance" so I thought that's a good thing - I didn't check any specs since I couldn't relate them to performance anyway but I thought to ask your opinion on these or some other brand / style of capacitor that would be good in this position. The price these are going for is about right on how much I thought to spend on filter caps. I don't mind that they're axial, I would shield one leg and twist it around to the pad, I have done this dozens of times.

For reference:
http://www.banzaimusic.com/Illinois-22uF-500V.html

EDIT: also, do ceramic and/or gold plated tube sockets help any? Is it just for safety or is there actually some performance benefit?
 

mrclunk

Well-known member
Joined
Nov 29, 2006
Messages
1,128
Location
London
Finally finished mine, only took me a couple of years!

Having some metering issues at the moment. They're fine up to about -10dB and the they seem to almost reverse, showing less compression?
Possibly a calibration problem, going to have another go later. Need to tidy up the wiring a bit anyway.

Sowter 10k:10K on the input, edcor 15K:600 outs. 12ay7's for V1 and 6414 for the outputs.

4394-290112113515-711834.jpeg

4394-290112113428-681946.jpeg

4394-290112113515-701383.jpeg

4394-290112113428-651750.jpeg
 

alexc

Well-known member
Joined
Sep 21, 2004
Messages
2,571
Location
Hobart
Yeah, nice!

Love those meters

And those additional features are a great idea. Looks like you implemented them nice and neatly too.

Great job.
 

electrisizer

Well-known member
Joined
Dec 26, 2008
Messages
172
Location
germany near frankfurt
@mrclunk

very nice build!

i want to ask if you can soundwise recommend the SC + drive mod. i think its the kensington suggestion taht youve done?
ive deconstructed my unit at the moment and think about adding the mods :)
 

sirko

Member
Joined
Dec 1, 2011
Messages
14
Thank you, Volker.

Next question: Does anybody have an fpd file for an 3U front panel? All knobs and switches are parts from mouser US bom.


Regards
Sirko
 

timmygrimm

Well-known member
Joined
Dec 22, 2006
Messages
100
Location
New York, NY, US
Done and works!

6804407985_f3af9baba7.jpg


6804408301_45969f31ff.jpg


This forum is amazing. Thanks to everyone here for the knowledge and supplies to make this happen.

One channel was not working at first, but turned out to be a molex issue. Gain is out of hand, and I have the oscillation problem at high settings, but will sort that all out.

So Stoked!

Now I just need some knobs :)
 

mrclunk

Well-known member
Joined
Nov 29, 2006
Messages
1,128
Location
London
Thanks guys!
It is a 'peculiar bird' indeed!
I based the look on some old Vortexion gear we have here. The panels are Trafolyte, cut and engraved on my new CNC! I'm going a bit cnc nuts at the mo...

electrisizer,
The 'mods' are as Kingston mentioned earlier in the thread.  The SC Filter is just RVx37 on a rotary switch, i recommend this for stereo operation. My values are biased toward the low frequency range.

The 'drive' control is my my kinda experimental control. At the moment its a 470K pot in series with the 68K / Rx11 feedback resistor. Increasing the resistance reduces neg-feedback, more gain, more distortion. But its too subtile for me. I'm thinking of building a multi deck switch that simultaneously increases gain and pads the output.
Unless anyone else has a better idea for adding mojo?


Issues:-
I have to hit it pretty hard to get lots of compression, i believe this is due to my input transformer not having the 1:4 step up of the original. I can use the center tap on my input to give me 1:2 which maybe enough though i'll lose some input headroom. maybe i'll add an input sensitivity switch...

nice build Timmy
 

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