All things LA2a related

[keithcamilleri]

hey guys i just finished wiring the bloo one...one problem it seems that i don't have at lease a sign of any voltages coming out of the hammond transformer... i am using the 369jx... can someone guide me out on the wiring for this transformer i feel i've missed something...

my wiring is

greens = a24 and a25 = 6.3v
reds = a22 and a23 = high voltage
purple = idle

black brown = linked
blue going to the power inlet
white = b25

is this right?

thanks loads

 

[Dino]

Dear all,

A couple of days ago I finished building my LA2A and (of course) I've encountered some problems. Here's a list of things I found:

- audio output is way too high - I'm feeding it into my mixer and as soon as the gain pot is higher than about 20% I get a clipping indicator in the mixer. Is that normal?

- meter seems to work in "output+4" or "+10" mode.

- it does compress when I turn the gain-reduction pot clockwise, maybe up to 10 dB.

- I can't get the meter to 0 dB in meter-compress-mode:
the highest I can get it is to - 3dB with R4 set to 0. However, then the neon lamp is off... is that normal??? Furthermore, the neon is only glowing for R4 between 30% and 70%.... is that supposed to be like that? I've tried the "matching resistor" protocol in Jahnsen's appendix (replaced R25 with a 100K pot etc), but it doesn't help....

- I've used Jensen transformers (JT-11P-1 input) and JT-10K61-1M (output) with the corresponding changes in the schematics (as indicated by the Jensen datasheet - basically: R5=11K, R17=680 Ohm (!!), R18 and R20 are both 330 Ohm, C5=22u).

- For all other component values I sticked to the ones in the original (?) United Industries LA2A schematics (1968)... I'm beginning to wonder whether that was a mistake? Should I have used D. Jahnsen's values instead?

Some of the voltages just don't seem to be correct, but I can't find what's wrong... here's some of my measurements:

point measured: without tubes ; with tubes (should be)

- main voltage (at R29): 370V; 242V (275V)
- pin6 (6AQ5A): 146V; 48 V (100-137 V)
- pin2 (6AQ5A): n.d.; 1.9 V (7-7.5 V)
- pin5 (6AQ5A): 146V; 149 V (114-138 V)
- pins 1,6 (V3): n.d.; 80 V (107 V)


I'd be extremely grateful for any help!

Best,
Dino

 

[lanxe]

man,
i just finished my bloo kit..............BUT of course there are problems.

The voltages seem to be close, the neon glows as well as the tubes

it seems to compress fine, but i am getting very little gain out of it. even with the bloo turned all the way up, compression all the way down, i get very little signal (signal is about as loud as the noise!).

i have gone through the wiring already....but i am going to go back over it. any pointers of where to start?

Thanks,
Ryan

 

[Dino]

I'm still having trouble figuring out what's wrong with my LA2A.

Is it normal that the neon goes off when changing the setting of the R4 pot? I'm unable to get the meter to 0dB in meter compress mode.

Any ideas?
Many thanks in advance

Dino

 

[audioforge]

dino
i ve got the same issue in my diy la2a (not a bloo one). what is your vu meter? it appears that mine had not a rectifier inside so i can adjust the 0db in gr mode but neon fails light for this setting and the meter do not work in +4 and +10...
i ve had 4 diode (1n4148) and everythings now ok and the neon shine again within the same setting.
hope it help

 

[Dino]

Hey Audioforge,
Thanks for the hints. I'm using a Shurite 7801Z vu-meter. And the thing does work in both +4 and +10 mode. It's only the damn "meter compress mode" in which I'm unable to get it to 0dB.
How did you connect the 4 diodes?

Best,
Dino

 

[audioforge]

dino
unfortunately i have nothing to post a drawing... but i will try to help.
download this schematic even it s not the la2a...
http://www.montagar.com/~patj/am-864u-sch.gif
at the upper right corner you ll find the vu diodes rectifier. connect the + and - to your + and - of your vu. the 2 other leads will gone to R24(3,9k) ,the other to sw2 .
hope it help.....

 

[Guest]

on the shurite meter , i had no luck and was not able to get the meter to
zero .

i was using the shurite 8801z rectifier type.

it would work on audio in , but when i finally bought a siafam meter
it worked perfectly.

i dunno , but i think shurite might be lame. :roll:

i thiink i was expirienceing the same problem
so before you rip your wiring apart you might try another
vu meter.

hope this helps

 

[audioforge]

oops i forget to read :"And the thing does work in both +4 and +10 mode. It's only the damn "meter compress mode" in which I'm unable to get it to 0dB. "
my " rip off vu meter did not have rectifier and after add one everythings was fine.... but if driller says that the shurite allready have a rectifier inside (and it have one if it works on +4 +10) adding diodes rect. will not help you. maybe the sensitivity is too hight (much more that 100ua) try adjust R24 (put a pot and tweak till you ll can adjust your 0db in gr mode without the neon fails lighting or as driller suggest, buy a 100ua vu as the sifam)
good luck

 

[Dino]

Thanks so much for your help fellas!
Driller, I got the same impression: the shurite is lame/weird. I'll buy a Sifam and give it a try. Thanks again!!

Dino

 

[keithcamilleri]

my volages are a bit high is there anyone that could point me in the right directon...

a20 is way too high its 240v
b20 is around 300v
and pin 5 on the t4 is aroun 52v

definetely something wrong...all other voltages seem right or within limits i think...

these voltages are wit tubes in and no t4

regards

 

[kruz]

ok dudes.. i would like to introduce you my just finished bloo series two

NOW, the problems:

1- There is something wrong around the meter.. in GR mode the meter tilt to full scale and stays there even if compression is applied (yes, seems that the compression is working). In +4 mode it reads more then in +10 mode..

2- I scoped the output, and the phases haven't got equal amplitude

3- When i open the front panel, the difference between the two phases flips (hopefully this is a simple solving problem, maybe something is shorting when closing the door)

 

[kruz]

ah, few things i'd need to add..

I did the basic voltages tests described in teh manual and they are all in the ballpark..
I'm using utc transformers

 

[kruz]

I did my homeworks today and found the solutions to all these problems.
Now the unit is 100% perfect, dead silent too.

I had miswired the wiper of R2 to A16 instead of A15
Also, the meter wasn't working cause i found that i missed to bridge 1b and 3b on SW3

but beside this, i found that the problems i had on the output phases was caused by a not correct wirings of both input and output transformes to their XLR
Bloo's wiring guide is not correct here. TAKE NOTE!
At page 10 where it talks about the ground connections, the ground path DO NOT have to be connected to the pins 1 of both xlr but JUST to the ground tags.. pins 1 of both xlr NEEDS to be tied to pins 3 (or 4, shorted) of each transformer (xlr in pin1 to pin3 of the input transformer, out xlr pin1 to pin3 of the out transformer) as in the original schematics, transformers needs that!!

I still have to test it in the studio, checked just with a cd and it's perfect but i can't yet judge its sound. I'll let you know.
I'm really proud of MY diy :green:

Now.. i want to truely thank Scenaria for his amazing kit anbd to all the peeps here that keeps helping people like me :wink:

 

[kruz]

this is how the + and - on the output looked like before the correction on both the in e out transformers and xlr's wirings

notice that the two waves weren't fully out of phase and that the top one is much lower then the other one

 

[CJ]

Good deal, Kruz Mon!

 

[kruz]

today i listened to it quite a bit..
and.. what can i say?..
it's imrpessive.. i really love this kind of compression on vocal tracks
but also noticed that i had a serious roll off on the HF..
so i sweeped the out and i confirmed my ears

Now, i set C4 fully CW, this is supposed to be the position with less roll off, am i right?
I don't know what to think now.. but i'll take a look at it tomorrow again

 

[Bluzzi]

Maybe that's why you like it!

It would be interesting to see if others are getting wider frequency responses from their LA2A.

Jim

 

[CJ]

Clockwise tightens up the plates, shunts more hf feedback to ground= less roll off.

That looks like an A-24 curve to me.

Which vintage?

Black, drk gry, lt gry or TRW blu/grn?

 

[kruz]

[quote author="CJ"]Clockwise tightens up the plates, shunts more hf feedback to ground= less roll off.[/quote]

done

That looks like an A-24 curve to me.

are you sure? have you seen the starting freq of my roll off? it seems way to much imho

Which vintage?

Light grey A24