All things LA2a related

[SSLtech]

It's inside the T4... nothing you should concern yourself with. Most T4's don't even have it.

 

[college101]

SO its not required for me to connect it in between pin 4 and 3 on the t4b? 

 

[kazper]

The 68 schematic shows it inside the T4A cell assembly. So disregard it unless your building T4A clones.

 

[Sredna]

Do you get signal trough now?

 

[college101]

I haven't re-wired that much yet..I just got my hot air gun in the mail today... Im waiting on some new wire...I got the PT wired..

 

[college101]

Sredna...Having problems with my wiring...WELL actually just trying to make sure I get the right amount of signal in to the input..

For some reason, I had to cut off my input XLR and connect a different connector for another test...

SO I need to re-connect the old xlr...I connect the copper shield to ground,  red to two, and white to three

Does this seem right?

I hooked up R5 in between the Grey(grounded side) and green..Connect to ground, and put my tester probe onto the green side of R5...signal comes threw..but its quiet compared to the turret board terminals...on the primary side...

((Im gonna go out an geuss this is because R5 is hooked up that the signal is reduced? I thought maybe I hooked up the xlr wrong, and the signal is inverted?

 

[Sredna]

For now, it doesent matter if the signal is inverted.


White wire? That's the CT, what did we say about that? Dont touch it! 

The correct way would be the red wire to Pin 2 on XLR and blue wire to pin 3,
pin 1 on XLR goes to ground.

No wonder that you get weaker signal when you connct the input between red and white wire, then you use just half of the primaty winding. So: White wire=CT= Dont touch it!

It is important to realize the difference between "balanced" and "unbalanced"
XLR is balanced and the signal is applied to pin 2 and 3, pin 1 goes to the shield (ground)and doesen't really carry a signal. A guitar cable is unbalanced and the signal goes to the tip and the sleeve and the sleeve has also a function as a shield (ground).

When connecting unbalanced sources to balanced (guitar ->LA2A or CD player->LA2A) you connect the tip "+" of the guitar cable to pin 2 on the XLR and the sleeve "-" (shield) to pin 3 on the XLR. From your CD player you connect either one or both of the L/R channels (blue and red on earbud cable) to pin 2 on the XLR and the copper shield (on the earbud cable) to pin 3 on XLR.

Hope this helps....

 

[college101]

I was refrencing the XLR cable wires, not the input transformer wires....Im just worried that the XLR red and white wires are inverted...I have the Input wired correctly! That was all too easy...

I just think the signal is much lower...but I maybe wrong...

If I test the Red Primary.. the signal is full and very loud...while the green is much more quiet then the red wire on the input tranny

I just want to make sure I set the XLR up correctly, so the signal is not inverted...BUT like I said...When I do test R5, I get signal...so maybe everything is ok!

 

[Sredna]

Please be more specific of what you describe, how could one now what colours the wires of your XLR connector have?

If the signal is inverted or not does not change the level.

You did a test before with the signal source direct to the transformer and the signal on the secondary
was louder. So yes, there seems to be something wrong with your connections.

I suggest that you read up on basic wiring of connectors: http://www.rane.com/note110.html

 

[college101]

Thanks for the help Sredna...yes...I basically took my whole LA2A completely apart, and Im starting fresh...Im going to make my own cables today, and follow the RANE set up...which will make me much more confident in the signal...

I think last time, I got lucky with test's...  I am trying to get back to where I was at...Just set up correct!


I just went back through my old posts, and it doesnt seem to matter whether red and white of xlr is inverted or not, because they go through Red wire of the Primary... SO I am back to wiring again... I was so worried I had Inverted the signal, and was getting a much quieter signal

 

[college101]

OK..I re-solder'd connections for stereo guitar jack, + to 2, and - to 3, ground to 1

Then I did a brand new XLR....same config as above...Check for CONT. Passed...

Hooked guitar jack into CD player, turned on the music...Hooked the XLR into the LA2A input...Connected green tester gator clip to grey ground...connected the test probe to green...BOOM...audio

 

[college101]

OK..Just got audio all the way up to the T4b!! My wiring is coming along nicely!

Quick Question...can the capacitor across V1 pins 1 and 7 be an orange drop cap instead of a ceramic disc?

 

[Sredna]

You mean C1?

It seems that the original and the reissue have a ceramic disk there but a 400V Polyester Film Capacitor (orange drop or similar) would probably give better specs.

 

[college101]

Sweet,...Its turning out nicely...Wiring is slow, But I know for a fact everything is being set up correct the first time!!  

YES sredna...C1

 

[college101]

OK..Im about to wire up the output transformer...I want to make sure I am setting it up correctly...

In reference to Sowter 1010 output transformer

Yellow is ground of Primary which goes to tb#10 and wired to pin 3
Red is the + to the Primary which goes to tb#18 and wired to pin 2/split to 3 of sw#2

Black Elctrostatic screen goes to ground that is connected between T4b and isolated solder terminal of R20+R10

Secondary
GREY wire goes to 10uF/100 volt
WHITE goes to r20+R10 junction point

Does this look right guys?

 

[Sredna]

No, you got it wrong!

Primary is where the signal goes in (Red/Yel) and secondary is where it goes out (Grey/Wht.)

When reading the LA2A (1968) schematic, the signal goes from left to right (input to output).

Sowter 1010 red lead is same as pin 7 on the UTC A-24, yellow lead = pin 10, grey = pin 1 and white lead = pin 6 on the A-24.

So, red lead goes to C5, yellow to ground, grey to XLR on 3 and white to XLR pin2/R23.

 

[college101]

I was more then just off in that answer...

 

[Sredna]

GREY wire goes to 10uF/100 volt

Shouldn´t that be 10uF/450 Volt? C5 right?

 

[college101]

OH man..YES it is a 10uF/450 Volt cap... For some reason I put down 100 volt which is wrong...

I have a 10uF/450 volt Sprague Cap for C5

my bad

Somehow I got things backwards...It made perfect sense, just got my info backwards...

 

[college101]

Done Wiring...popped in the tubes...Fired it up...passes audio and everything!!!  I am having some sort of grounding issue...When I adjust R4...it does not go from being not lit to lit...it is just lit...has to be a grounding issue...

I also have the needle moving on +4- Im guessing the CD output is low,and wont register on +10

What do you guys think????

Im burning it in for 24 hours... Dont have the T4 in yet...