All things LA2a related

[reanimatorstudio]

Hi,

I just build my LA2A with inputtrafo:  UTC  AH100X, output:  UTC  A24.

My freq. response ( no compression) is flat exept  for the bottom: 450 Hz: -1 dB;  150 Hz: -2 dB;  40 Hz: -3 dB. Increasing coupling caps has no influence.

Is that normal?

 

[reanimatorstudio]

Hi sixtyniner,
remove V3 and V4 and T4, you will have no compression now, just a preamp. Listen again and see if it sounds ok, so you now if the problem is in the audiopath or not.
If it is not ok you can remove V1, you will have no sound now, only the output stage is working, if noise has dissapeared completely, check  the input stage.
Noise can come from:  bad contacts (like tube sockets, noisy pots),power caps, coupling caps, resistors esp. in the powersupply.
If you switch the unit off it will still work for 5 sec, if noise dissapears, you have a problem at least in the powersupply.
Anyway replace the powercaps, this is more important than changing tubes.
If you have a scoop you can measure the powersupply( all tubes out first) and see if there is noise

 

[SIXTYNINER]

Hi sixtyniner,
remove V3 and V4 and T4, you will have no compression now, just a preamp. Listen again and see if it sounds ok, so you now if the problem is in the audiopath or not.
If it is not ok you can remove V1, you will have no sound now, only the output stage is working, if noise has dissapeared completely, check  the input stage.
Noise can come from:  bad contacts (like tube sockets, noisy pots),power caps, coupling caps, resistors esp. in the powersupply.
If you switch the unit off it will still work for 5 sec, if noise dissapears, you have a problem at least in the powersupply.
Anyway replace the powercaps, this is more important than changing tubes.
If you have a scoop you can measure the powersupply( all tubes out first) and see if there is noise

THANKS  ! ! !

i try tonight and let you know!
6t9r

 

[SSLtech]

Have you replaced the Neon with a Zener? also, bypass it with a smoothing capacitor. The Neons are frequently a hideous source of noise.

Keith

 

[debby]

Have you replaced the Neon with a Zener? also, bypass it with a smoothing capacitor. The Neons are frequently a hideous source of noise.

Keith

hey ssl tech 

im curious as to why a neon would cause noise, its not part of the audio path is it? i have some noise on my bloo la2a, low oscillating hum noise.

what kind of noise do bad neons produce in general?

also, does the zener have polarity when installed or any direction?

i think the only zener available are 62 volts and 2 X 33volts (parallel). is there a range that you can use in zener? like between 50-70 volts should be fine to replace the neon?

i have also read of the ua re-issue using zener for the vu meter?

thank you

 

[SIXTYNINER]

Hi sixtyniner,
remove V3 and V4 and T4, you will have no compression now, just a preamp. Listen again and see if it sounds ok, so you now if the problem is in the audiopath or not.
If it is not ok you can remove V1, you will have no sound now, only the output stage is working, if noise has dissapeared completely, check  the input stage.
Noise can come from:  bad contacts (like tube sockets, noisy pots),power caps, coupling caps, resistors esp. in the powersupply.
If you switch the unit off it will still work for 5 sec, if noise dissapears, you have a problem at least in the powersupply.
Anyway replace the powercaps, this is more important than changing tubes.
If you have a scoop you can measure the powersupply( all tubes out first) and see if there is noise

HI
" reanimator"
i replaced all tubes , some noise go away +/- 35/40% , but too noise is more present ,
then
i removed v3 -v4 -t4 , but noise don't go away
then i removed v1 , and noise go away

i checked type of noise with pro tools and Waves "paz" (spectrum analyzer plug in)
he show noise from : 0 to 16hz at -70/-80db ,
and from 1000 hz to 15000 hz floating between -70db and - 60db
this level with input and reduction knobs at 0/infinity (fully closed at left side)
(no input signal , noise generated by la2a "brains")

there is some doc for test unit , check values etc... ?

 

[SIXTYNINER]

that's not soooo bad. Maybe it's because you used carbon resistors in the first stage

hi reanimator
do you mean that noise leve is normal ?
and it is generated by carbon resistor?
:

 

[mushy]

I was wondering if anyone has a new link or something for CJ's voltage chart?  vacuumbrain.com seems to be down and CJ's box is full.

 

[basementmedia]

Hi,

i've finished soldering/connecting my Dripelectronics Opto3-Unit and did an audio pass test after having installed all the components and also the tubes (the t4 is not yet installed...but the manual says that you have to do an audio pass test first...):

Unfortunately, the test failed which means:
if i connect a microphone at the input and connect the output with my mixer i get no signal (not even hum or any other noise...).

I have recognized that the NE-2 LED doesn't illuminate, if the unit is switched on... is this a sign that something must be wrong? Or does the NE-2 only illuminate if the T4 is installed?

Also the meter doesn't move (but i think this is ok, because the t4 is not yet installed, isn't it?)

Also the tubes don't illuminate... (is "illuminate" the correct translation...my english is not that good...)

Can anybody give me some startup tips for troubleshooting? Some points to check the voltage / amper?
A path to find the faulty component/connection step by step...

and another question: i use a LED with a pre-connected resistor as power lamp but as a LED must be connected with the correct polarity, can someone tell me, where the + and where the - connection is at the board (sorry for the stupid questions... ;-(

Best regards and a happy new year ;-)

Daniel

 

[SSLtech]

the Neon not illuminating means that you don't have the approx. 60V at the neon.

Check that the meter position trimmer isn't all the way to one end or the other.

-And no, the T4 doesn't have to be installed to light the neon.

Keith

 

[basementmedia]

Hi,

unfortunately this wasn't the fault... ;-(
I tried with the Trim Poti turned fully clockwise and fully counter-clockwise, but nothing changes - the NE-2 stays dark...

Any other suggestions?
every idea is appreciated

Is there something i can check with the multimeter?
I have the power lamp not yet installed, but i think this can not be a problem, can it?

Best regards

Daniel

 

[mushy]

You might have better luck with the drip forum.  Those intimate with the LA2A circuit here aren't necessarily up that particular layout.

http://dripelectronics.com/forum/viewforum.php?f=5&sid=ed37d211697f3a9b84c514404afc9ed6

That said, it sounds like you aren't getting any power at all.  Grab your meter and start at the AC plug and see where you stop getting voltage.  Check the stupid stuff first like the fuse. Please be careful!!!

 

[basementmedia]

Hi,

thanx for your help.
I have found the reason for the trouble:
Unfortunately the Transformator is defective (because i'm a fool! In Germany we have 230 V but the primary of the trafo needs 110 V.... please don't laugh

I'll be back when my new trafo arrives
Another 23 Dollars and 86 Dollars Freight(!!!!) because this f*** trafo seems to be only sold by allied directly...
I will buy two, so if you want one

Best regards

daniel

 

[bobine]

Hi all... My LA2A (Drip Opto v4) sounds good and is quiet as a mouse but has a weird oscillation/resonance at around 7 or 8Hz that I don't understand. If you scrape the grill of the mic with a fingernail it sounds like a motorboat for few seconds.  I attached a picture of the response: if I start a 10 second sweep above 9Hz it doesn't happen, but starting below produces this 7db bump that peaks above 10Hz and doesn't settle down until 20-30Hz. This is with zero compression.

I've swapped the preamp 12AX7 but I don't have a second 12BH7 to compare yet. The tubes don't seem microphonic (tapping them doesn't create the problem). All nominal cap and resistor values in the preamp are double checked.

My temporary fix is to put a 2uF cap in series from the #2 input pin before the transformer. Works to nicely roll off the bottom below 70Hz so that there is no problem at 8Hz. Sounds okay for vocals but I'm not sure that an inline cap is an ideal solution, fidelity wise...

Ideas? Diagnoses?

Thanks

b

 

[andre tchmil]

I finally started building my Bloo. ( was one of the first who ordered  ;D )
First question rises.
For the T4B , Is it normal that wires on pcb point 2 and 3 need to be twisted somehow  to get properly into the octal connector ?

 

[mushy]

Hi,

thanx for your help.
I have found the reason for the trouble:
Unfortunately the Transformator is defective (because i'm a fool! In Germany we have 230 V but the primary of the trafo needs 110 V.... please don't laugh

I'll be back when my new trafo arrives
Another 23 Dollars and 86 Dollars Freight(!!!!) because this f*** trafo seems to be only sold by allied directly...
I will buy two, so if you want one

Best regards

daniel

Search "grid stoppers"

 

[drpat]

...

 

[SSLtech]

Replace the neon (think of it as basically open-circuit) with either a new neon (the type WITH NO RESISTOR inside it!) or -even better- with a 60V Zener diode.

One of my LA-2a's neon started to flicker a little, and with each flicker, the needle would 'twitch' in GR display. -I replaced it with a Zener last week, and now it's rock-solid... and quieter to boot! -Oh, and one final diagnosis:

On a properly working LA-2a, if you leave the unit set at 'GR' when you power it off, the needle should sit a 0VU for a second or two, then should creep slightly UPWARD (around +1dB) before diving to the left. -If the neon is open cicruit or otherwise faulty, it will just start to fall as soon as the unit is powered off...

With a Zener, the needle stays rock-solid and then just falls off with no 'upkick' before falling.

Keith

 

[drpat]

...

 

[canidoit]

I heard you can use 2 X 33volt zeners or a combination in series or was it parallel, I think of 32 volts and something else to get you somewhere to 66 volts.

Can someone confirm if you can use the zener in series or is it parallel with non matched voltage, like 30 volts and 36 volts zeners and use it for your La2a?

I am considering doing this also, but I do not have matched voltages in my pair of zeners.