All things LA2a related

[Guest]

Both R37 & R3 are 100% Clockwise ?

does every body just jeave these two @ clock wise ?

ive been wondering about all the final settings upon compleation.

c14(open or closed or fixed) /r37 / and r3 along with c4(open closed or fixed) .

i am wiring up another la-2 for stereo ,

does anyone have a method of calibrating two la-2 to stereo along with induvidual calibration?

any help is appreciated.[/quote]

 

[Scenaria]

change out R36 for a 1k and your values should look better

470 would be alright if you swapped the 22k and put a 10k instead

 

[cannikin]

swapped R36 to 1k

B21 - 349.2v :grin:
B20 - 260v :grin:
A1 - 60.1 :grin:
A20 - 13.37V** :sad:
A14 - 210v :grin:
A17 - 10.65V** :sad:
A19 - 68.3V** :sad:

 

[cannikin]

[quote author="Scenaria"]
oh and make sure you have the jumper strapped across A11 and A14...it wont cause the problem your having but it is something I missed in the docs[/quote]

Scenaria;

I read this earlier in the thread should I do this also?

 

[Scenaria]

yea you can put that jumper in but it wont solve that one voltage

it doesnt make sense that B20 is in the ball park but A20 isnt...

are you sure the heaters are on all the tubes?

 

[cannikin]

I traced the heater Wire and everything is correct.

Heres a little explanation of what is going into A20 and B20.
Maybe you can see the issue.

A21(260.1V) to B20 (259.9V) to B19 (259.9V)
B20 (259.9V) to R34 (22K 2W) to A20 (13.27V)
A20 to V4 Pin 5 (13.27V)

I also replaced R34 with another 22k 2W.... no change.

 

[Scenaria]

do you have the T4b in?

theres a turret that C11 ties over to coming from the octal socket... this point is coming from pin 5 of V4...just want to make sure your using a turret and not grounding it to chassis or anything?

if the T4b is in .... take it out and check the value of A20

try re-adjusting the two pots on the back... just turn them a little bit... every one I have built I have always noticed I have to turn the pots a few times and then leave them full clockwise...

 

[cannikin]

The reading for A20 has been without the T4B

 

[cannikin]

Ok the T4B is in...

I turned the R2 "peak reduction" Down all the way and I'm getting 149.9V at A20 and 280.1 at B20

 

[Scenaria]

so all of the voltages look to be within range now?

flip the rotary to GR...

is your meter sitting at or around zero?

use the front panel trimmer to set the meter to zero VU


turn the peak reduction down...

throw in some signal... switch your meter to +4

turn up the level and see if the meter is showing level


if it is then switch to GR and turn up the peak reduction to see if theres some compression..

my bet is everything is working now

 

[cannikin]

Thanks scenaria for all your help, this has been a huge learning curve. I'll give it the audio test later tonight, You mentioned to me a while back about strapping 1K resistors across the grids to prevent the unit from becoming an expensive antenna.

Can you elaborate on that for me.

Thanks again.

 

[Scenaria]

you might not even need them... so try it without first...

im assuming yout using the sowters?

if you do need them it only need to be done to the 12BH7A

drop a 1k resistor in series on pin 7

and put a 1k in series on pin 2

you already have wires going up to those two pins... so all I did was pull the wires off pins 7 and 2

solder a 1k on pin 7 and the wire to the other side


and a 1k to pin 2 and a wire to the other side

so they fall in series now... get it?

only need to be done if your getting some wierd oscillations on the output

 

[cannikin]

Ok I Still have to do the tests Scenaria recommended.

but...

The Unit is Quiet
It is passing audio! :grin:
The unit is really colored, bordering on... Dirty (although, I have to test it with other Mics and Pres). But any thoughts are welcome.
R1 is working, good gain.
If I turn R2 below 20; the unit makes this Low Freq. clicking sound (actually sounds like its farting).
Lastly, The VU isn't happening at all, I have to rewire SW3 and all the front panel pots; using better wire- making better contacts (I think the I have a short somewhere).

This is very exciting.

Talk to you soon.

 

[Scenaria]

if you havent put the grid stoppers in yet then do so... that clicking sound will go away once you put them in.. same problem I had when I put sowters in..


oh and be sure to make sure your making good ground contact with the pots etc.. scrape a little powder coating off the chassis or do what I do... I run a small piece of wire to each pot and back to the main ground...

 

[Ad0lescnts]

Hello,
I finally finished my homebrew LA-2A and it sounds and works well except for one problem. It seems the release time is verry slow. While compressing program material the gain reduction meter seems to just move very slowly and stay in the general area according to how much peak reduction is applied. THen once audio is stopped from being fed into it, the meter gets to about -2 after about a second or two and then sloooowwwly climbs to up to 0. I'm sure this isn't normal and am wondering what could be the problem?

Thanks!
Tyler

 

[Scenaria]

did you make your own T4b or buy one already made?

keep in mind that la2a's by their very nature are rather slow.. more of a leveler than a compressor.. good on things like bass guitar..

not so good on things like drums..

 

[dukasound]

Hi
Does anyone discuss about R25 (27K-100K) resistor. I used on mine 33K.
Also, anyone who use Sifam VU, I think, must use 3,6K instead R24-3,9K.
Because I will build another one what mains transformer (220V pri.) is good.
Duka

 

[SSLtech]

[quote author="Ad0lescnts"]While compressing program material the gain reduction meter seems to just move very slowly and stay in the general area according to how much peak reduction is applied. THen once audio is stopped from being fed into it, the meter gets to about -2 after about a second or two and then sloooowwwly climbs to up to 0[/quote]
...If you're compressing hard, this sounds like every LA-2a I know... the release is not simple or constant.

Sounds normal to me.

Keith

 

[sleepingtiger]

Hello All,

This is my first post. I've been checking it out for a while and I love it here... I'm building the Bloo kit and I'm pretty inexperienced and could use some help. This is confusing to me:

Posted: Thu Apr 07, 2005 7:49 pm Post subject:

--------------------------------------------------------------------------------

steve;

I'm hooking up the Allied Power Trannie and just want to confirm my connections:

Primary:

1 Black to Live on power connector (Wire to B24 then to B25)
1 Black to Neutral

Secondary:

Center Tap 6.3v (green w/yellow stripe) to ground Bus/TAG 3
Center Tap 250v (red w/yellow stripe) to ground bus/TAG 3

2 - 6.3v (green) to A24 & A25 with heater Wire.
2 - 250v (red) to A22 & A23

Ground:

Grey to Gound on the Power Connector.

It's the black wires from the primary that I'm confused about. I've ended up with something that, to me, looks much more like Ron's wiring diagram . What I don't understand is how the switch can work if B24 and B25 are linked together as suggested above. Doesn't that complete the circuit that the switch is there to control? Perhaps I'm having a hard time understanding the wording. The wiring diagram is a lot of help but it doesn't show the connections at the power connector. Can any of you guys get me on the right track?

Much appreciated,

 

[cannikin]

I got it to Compress... :grin:

I still need to go over the unit - yet again . :shock:

Now... trouble spots

1. - my gain is low
2. - I have to put 1K across the grids of the 12BH7A (because I'm getting a little high frequency tone)
3. - meter is inactive at +10 or +4 - but works for the gain reduction

thoughts?

SleepingTiger - Get Cayacosta's La2a Layout diagram its very helpful in tandem with the bloo manual.