D-LA2A Support Thread

[Deepdark]

Probably ou reversed the trimmer yes. It's a linear so one way or another, it doesn't change anything, you will just have to trim one way or the other That's why I changed the kind of trimmer I planned on my la2a board. Now I use single turn trimmer with the middle pin upfront, so we always install it the same way. If you want to change the hi freq of the unit, try replacing C4. This one boost the actual high frequencies (it was implemented to compensate the loss of the UTC transformer). With modern transformer, such as Cinemag, I tried some configuration and ended up completly removing C4 without any trouble. Frequency response is flat up to 18K, or so.

Also, maybe you drive V1 too hard? The make up gain section don't like to be pushed hard with the actual 12ax7. You can swap it to a 12AY7.

 

[schrobbelbop]

Removed C4, just still a bit of boost, See attached screenshot.
Green: C4 150pf
Brown: C4 None

any other ideas how i can flatten it a bit more in the high end?
is it safe to let C4 out?

Measurment screenshot:
http://i.imgur.com/BqHhrRL.png%22%20alt=%22Palm%20Springs%20commercial%20photography%22%3E%3C/a%3E

 

[Deepdark]

maybe try a HPF. Put a cap (maybe 150pf) across gain pot, between pin 1 and 3 and check out the curve. You can try all value you need until you get a curve that match your needs

 

[schrobbelbop]

It seems to measure almost flat without C4, but with some music runnning through it sounds harsh i think its distortion in the high freq's. i ordered the EH 12ay7 and a 25k pot. could also be the cheap JJ tubes im using now.

could it also be low voltages? i noticed some voltages are a bit lower than they should be.

R29 = 247
R34 = 125
R13 = 105
R17 = 206

UPDATE: when i connect the transformer centre on the sec. side to ground it seems all good.
but i'd read somewhere that the edcors only use +/- and no centre tap's?

 

[schrobbelbop]

Anybody knows why R37 (highpass for the comp s/c) is not working correctly? it's only creating less compression in general and no diffrence in freq response of the compression. when turned extreme counter cw distorion comes in with the compression.

 

[Deepdark]

playing with R37 will affect the compression of the high frequency, not the high frequency curve. It will determine how sensitive the compression will be to high frequencies. For what I've read and experiment, it also have a great part on how much it will bit the bass.

 

[Deepdark]

It seems to measure almost flat without C4, but with some music runnning through it sounds harsh i think its distortion in the high freq's. i ordered the EH 12ay7 and a 25k pot. could also be the cheap JJ tubes im using now.

could it also be low voltages? i noticed some voltages are a bit lower than they should be.

R29 = 247
R34 = 125
R13 = 105
R17 = 206

UPDATE: when i connect the transformer centre on the sec. side to ground it seems all good.
but i'd read somewhere that the edcors only use +/- and no centre tap's?

There must be a short somewhere, a bad solder, or something like that. No need to use the Center tap.

 

[Deepdark]

Or maybe your distortion is some sort of oscillation?

 

[schrobbelbop]

No, the compression becomes less and the sound is distorting.

If i dont use the centre tap's to ground it sounds like shit.
it sounds very fine right now and is all the way linear (+/- 0,5 dBs)

 

[[silent:arts]]

Your Edcor may have a broken winding, or is wrong connected.
Both happened with Edcors before, since they don't have any quality control ...

 

[schrobbelbop]

then they both should be broken at the same point, that'll be weird.
and strange that it sounds and behaves okay now execpt the highpass in the sidechain.

 

[Deepdark]

if the link froom secondary hi is Brocken, then it will sound like shit, so when you connect it to the center tap, you basically bypass the sec. hi, but the impedance is lower

 

[schrobbelbop]

but i only connected the centre tap to ground from output trans.. seems that the sowter's also have that in the schematic. 
how do i check if my trans is okay?

 

[Deepdark]

look at the pads of the edcor. you will see a tiny little wire coming from the tranny body and twisted around each legs. If that tiny wire is broken, then you're screwed. I had that trouble with edcor once

 

[schrobbelbop]

It was my passive monitor controller... as it changes the load, when i turn it down, the HF response shifts...

when i put i directly into my soundcard or interface it with my api gear everything is fine...

so indeed no need to connect the centre tap when interfaced with the correct loads

but still the HF sidechain trimmer isnt working correct..

 

[Deepdark]

nice you have sorted out the impedance trouble.

HF freq now. As this trimmer/pot works nearly like a RC filter with the bypass cap across it, when the trimmer is set at no resistor, the signal just pass through it, you have a "flat" response, which mean you have not the most sensitive to high freq. setting, but you let the bass pass through without getting scooped, which is probably why they mean "flat". The more you increse teh resistance of the trimmer/pot, the more signal will be bypassed through the cap, which then form a HPF. You will get more high freq. sensitivity but less bass. At full resistance, the signal pass all the way through the cap and it form a HPF of about, maybe 150hz. Try but extremes of the setting and play a bass track just to see if it works or not. If one setting give you nearly no bass compression and the other one do, then I would think the trimmer works

 

[schrobbelbop]

nope it doesnt work, i know what it's suposed to do and would really like this feature on the panel!

i tried changing the 1nf cap across it... it only drops a few db of the total level.

what else to try?

 

[Deepdark]

play with the side chain tubes, try replacing them. Do a continuity test to be sure the traces really connect each one and there is no bad connection. Try playing with R3, too

 

[schrobbelbop]

Every thing is fine by traces... and values.. swopping them doesnt matter.  im using philips 6AQ5A

the thing that i noticed is that my IGX cells dont have any
caps inside, as i seem them by other brands... might that something have to do with it?

 

[Deepdark]

what is that cell?