D-LA2A Support Thread

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saxmonster said:
Cool videos Prentice,

Gonna have to go back and recheck my calibrations on this beast and see if the are up to spec.  Know a lot more now than I did before and your videos are a nice refresher, hahahah,  Might have to up grade from edcore to sowters.  Might also put on a bigger heat sink and move it to the side of the case like you did.  Also how will you compensate for heat and the meters not staying at zero once the unit warms up?  That is so annoying to me.

-Scott
Click to expand...
Thanks!  I'm about to wrap up my build with a couple more videos.  I actually got to use it on vocals this weekend.  Fantastic, so far.

As for the meter "drift" issues, replacing the neon lamp with a zener diode will help with the drifting, BUT is not a cure.  If you notice, I chose to use the neon lamp just because it was the original device used.  Also, bear in mind that the gain reduction is not accurately represented throughout the entire VU meter scale, so, gain reduction metering is only a ballpark reading anyway.  So, if the meter drifts a little from 0 (which it will), then it's no big deal, to me.  I'm more about the sound of what's going on versus what the meter reads, anyway.
 
yes I replaced the neon with zener diodes a while back but was thinking about putting them back in as they didn't really help with the drifting.  Do the neon's have  a positive or negative side to them, I can't remember if they have to go in a certain way.  I have my old ones but obviously the legs are equal and I'm not sure which way they should go back in.

How will you use it on a stereo patch if the gain reductions are not equal.  Once you put the stereo link on will both side compress the same?  I think the gain reduction on channel one work both sides.  I think thats what I read before.  I still have a lot to figure out and get set right.

-Scott

 
Mine drifts all the time. The degree to which depends on how much heat is building up in it...

 
Anybody have a recommendation for a not too expensive case for one of these? I do my own drilling etc. Just looking for a blank 3U case with good ventilation (silver perhaps?)

Hmmmm. . . .
 
hello
everybody....
3 years after i'm back for finish my la2A...

now...
my compressor work.
left channel is ok( a lot of gain ) but compression ok and vu ok.
i've a little hum around 75dB...look good.

BUT
right channel compression ok but a VERY BIG GAIN...and a hum around 60 dB (pot to zero)...
and the hum follow the pot( amplified with pot gain).

ground are ok...same as the pdf...(jumper to)
i've check my heater wiring...look good
voltage are same as the left.(ok)
shield are wired like left channel...
i've swap the tube...(one was dead...12AX7 i change it)
bypass work...with no buzz or hum ....
i've check all the wire (with wooden stick) no change...


i will try to change position ofthe inter of alimentation( because it's near the gain pot of right channel )...

i can't hear a lot of diference in comp and lim position.

and
i've "sometime" a probleme with the stolen in right channel....it's make very long time to discharge....(very very long time...)but not everytime...
i've check for a short around this but nothing....

and strange ...if i plug my rhodes (with active preamp )...but just in one end(just in the instrument not in card or other) and if the compressor is connected to my card , i can hear(in the la2A) when i touch the jack.....but there is not connection between the machine.just electric connection...

it's look like a ground porbleme but i'm lost...

i need help :)
sorry for my long post and my english.....

best
jf






 
Hi all,

My drip Opto 6 pcbs are too big for the custom cases i have (hinged, with ears).. So i have 2 questions :
- Is the D-la2a the equal of opto 6 in term of performances ?
- Can i build just one channel for a mono unit, is it easy to do ?

Thanks a lot.
 
Hi

just about to start my build of the excellent D-LA2A.

Any UK or EU builders who can recommend good source for the tubes ?    - I have pretty much everything else on the BOM sorted now except for tubes and the output caps.

I'm using DRIP slow T4s and Edcors to start with then plan to uprgrade TXs and rotar switches etc as I live with the unit for a while in my small project studio.

And....can I sub 47uf for the 12 22uf caps in the power supply etc ?  I see there is a sum of 88uF before the PS dropping resistor and another 44uF after that - so I guess its just a case of brute force capacitance to smooth the power supply and provide plenty of current for transients ?  in which case more capacitance wont hurt ?

Cheers
PeteC
 
firfe said:
hello
nobody can help me :-(
best
jf
Click to expand...

Hum following the gain means HUM is BEFORE the gain pot, somewhere Inside teh sidechain, maybe. Did you check teh T4B to be sure is was ok? Other than that, maybe the heater wiring is polluting your input transformer via the chassis? Maybe your ground scheme is not right? A faulty ground connection on the ocb, in the sidechain circuit?

Other than that, do you have some oscillation trouble, when putting the peak knob at near max (ie. the vu meter needle who sit to the left in GR mod)?
 
thank you for your support :)

i will check again my heater wiring and change the T4b, and the ground scheme .

Deepdark said:
Hum following the gain means HUM is BEFORE the gain pot, somewhere Inside teh sidechain, maybe. Did you check teh T4B to be sure is was ok? Other than that, maybe the heater wiring is polluting your input transformer via the chassis? Maybe your ground scheme is not right? A faulty ground connection on the ocb, in the sidechain circuit?


Other than that, do you have some oscillation trouble, when putting the peak knob at near max (ie. the vu meter needle who sit to the left in GR mod)?
Click to expand...
yes i've a a lot of  gain and oscillation when the pot is around 12..(center)

Best
jf
 
firfe said:
thank you for your support :)

i will check again my heater wiring and change the T4b, and the ground scheme .

Deepdark said:
Hum following the gain means HUM is BEFORE the gain pot, somewhere Inside teh sidechain, maybe. Did you check teh T4B to be sure is was ok? Other than that, maybe the heater wiring is polluting your input transformer via the chassis? Maybe your ground scheme is not right? A faulty ground connection on the ocb, in the sidechain circuit?


Other than that, do you have some oscillation trouble, when putting the peak knob at near max (ie. the vu meter needle who sit to the left in GR mod)?
Click to expand...
yes i've a a lot of  gain and oscillation when the pot is around 12..(center)

Best
jf
Click to expand...

Also, check your wiring, use shielded wire everywhere, and be sure the actual shield (bare wire) is connected to ground. If not, then the shield isn't doing anything, or if it is connected to anything other than ground, it will act as an antenna. For your Oscillation, unfortunatly, LA2A has an curious behaviour with oscillation. Not always the same origins (some are related to the transformer used) but lot of time, oscillation comes from the sidechain circuit. what is important is to validate where the oscillation comes from. If coming from the sidechain, you could look around V3 (12ax7) maybe an grid stopper between pin 7 and the wiper of R2 (something around 470K would probably do it). Or, you could start by strapping an 100pf cap across R2, this will act as an LPF, and maybe will reduce and/or be enough to cut the oscillation frequency. You coudl also try teh same cap across Gain pot, and try the grid stopper at the 12BH7
 
Ok I'm almost finished 100% with building my Dual LA2A, just waiting for a few parts to come in and my question is this.

About the zeners which replace the neon lamps NE1, NE2.  What is the orientation for those zeners?  It wasn't too clear to me on the documentation.

Also, I am looking for a toroid mounting kit for the power transformer and was wondering which one would be the best fit for it?

Other than that I am totally stoked because I first bought the PCB, TB4's and Pwr transformer 8 years ago and now finally owning my own custom built LA2A has become a reality.  :D
 
Hi,
I did not receive the 2U enclosure yet, but i would like to populate the pcb. I have just this question about T4B sockets...can i skip them and solder directly t4b to pcb ?. Other sockets are already modificated to fit the case.
Hugo
 
No, you can't skip them. What if you want to change the t4bs? The sockets for the t4b don't need any modification to fit in a 2he enclosure since they are not as tall as the EL90 tube.
Bernd
 
Yes, sorry for this i thought that was like IC's..i did not have pcb's in front of me when i was thinking about this
Anyway, thank you very much for reply.
 
Just an other question...if i plan to make a stereo unit, behind one mono frontpanel, which way is the best ?

- just connect the "stereo link"
- taking stereo stepped pots ?

Maybe the same result, i do not know...My project is a little crazy,  impatient to show the result.

Hugo
 
hugo said:
Hi all,

My drip Opto 6 pcbs are too big for the custom cases i have (hinged, with ears).. So i have 2 questions :
- Is the D-la2a the equal of opto 6 in term of performances ?
- Can i build just one channel for a mono unit, is it easy to do ?

Thanks a lot.

Salut Hugo .
Tu veux le vendre ton opto 6 ?
Bien à toi
Click to expand...
 

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