All things LA2a related

[fum]

Did wire up the T4 myself. checked pin 7 and 8 and they are good with continuity to the correct points( ground and 2.7K/pot junction).

Here's the poor mans test. It appears that the compression circuitry is working from the LDR onward, just not getting the panel to light up. I took the can off the T4B, and turned off my overhead light. Adjusted volume ( My LA2A likes Zeppelin). Switch on light, Jimmy and Co get much quieter, but are not metering quieter. So looks like two problems. No ELP light, and no metering..

Should I try my other T4B?

Checking what kind of AC voltage is coming into the T4B next.

Regards

ju

 

[Scenaria]

how about this...

im assuming you have another la2 if you have another t4b no?

pop the one you just built in the known working la2 and see if it works... if not then you know its T4 related if it does then atleast you didnt risk frying an EL in your working T4

 

[fum]

Correction. Did the last test with the panel down. The metering works just fine too. It's purely a ELP not lighting problem.

And no, I don't have another working LA2A yet(although that is a good idea =) ). This is the first of two LA2A's (actually four, but two that will look like this one)to get built. I do have the other T4B put together tho.



Regards

ju

 

[CJ]

You can put 120 vac wall current onto the el panel thru a .1 cap to see if it lights. or go series thru the existing cap tie wrapped onto the panel.
be careful.

 

[fum]

Ok. CJ says that it takes roughly 100V AC to light up the ELP, and I'm only getting like 10V AC ( if I crank the input), so looks like I need to do some hunting for why this is.

And man it's nice when you guys are online. Progress goes quick :!: Thanks :thumb:

ju

 

[fum]

Was reading back through the thread, and noticed the grounding stuff that Zee talked about. R37 and R3 loop back on themselves. If they aren't grounded to chassis.....?? Checking now.... No joy...

OK, grounding is all fixed. Still have the same problem. I'll be going over the schematic and layout, unless someone has more specific direction =). What I'm lookin for is some kind of error in the gain reduction / attenuator drive amp. It's not puttin out enough AC poop to drive the ELP. Plenty of DC poop (137 V DC), but only 0-10V of AC.

Thanks for your help guys

Regards

ju

 

[Zee1usa]

It appears that my La2a is working properly ! :guinness: :wink:


I'll have to do some more testing , but so far it seems like it is working ok , hum free and all. Gain reduction and output metering seems to be good.

Happy Camper ! :thumb:

Z

Fum,Wilebee...we should hook up and compare numbers/functionality. La2apollooza date pending! :grin:

 

[cayocosta]

Ju,

Set R3 and R37 to full clockwise.

Jahnsen's book recommends this. (That's how my La2a is set.) I believe if you set R3 midway, you're not going to get the full input signal to the 6AQ5 - so turn it up all the way and see what you get then.

Also, is your input signal hot enough? The gain control in effect only controls output and is independent of gain reduction. In other words, with the gain set to off, you will still see gain reduction on the meter (in GR mode), but have no output. Therefore, should you have a very weak input signal - and the gain set very high - the sidechain input signal will still be weak even though you have plenty of output volume.

In my experience, the gain and gain reduction controls never seem to need setting above 10:00. That is to say, with a 0dB input signal, the gain reduction control only needs to be at about 10:00 to trigger around -4dB reduction, and the gain control set to about 10:00 should pass that 0dB input back out in +4 mode at 0dB.

So, for the sake of testing, I would check that I have enough input signal to drive 0dB output in +4 mode with the gain control set to 10:00 and the gain reduction control off - this would ensure your input signal is plenty hot enough. Then set gain reduction to about 12:00 and you should be seeing some action.

 

[fum]

*Ron takes out hammer, hits it on head*

the signal I was using was not hot enough. This thing cranks out the volume goin out, so I thought I was hot enough. I busted out a powered DI, hooked it up, and bingo, we gots a little ELP party goin on. meters, compresses, appears to be damn happy.

Now to move it into the studio to give it some better listening, and then on to gettin it's twin done.

Thanks!!

ju

 

[fum]

Allrighty then, I finished my second unit, no problems, fires up like a champ.

Here's some pics I put together of the project:

http://www.shinybox.com/product_info.php?products_id=35

Thanks go out to both Ron and Steve.

Ron, your wiring diagram totally rocks, and was invaluable to putting this together.

Steve, you did an amazing job putting these kits together. I've still got a pair of Shinybox version to do, but it's nice to have these complete, and moved into the studio.

Regards

ju

 

[wilebee]

well as sone as my new son and daughter leave for college I should be able to finnish troubleshooting mine Wil

Wilebee

 

[JerryPbury]

Log or Linear Pots for LA2A? Or does it matter?

I 'm not sure that I understand or know which is correct for the 1 meg & 100k pots.

Thanks,

Jerry

 

[Scenaria]

the 100k are log

the 1meg ones can be linear

 

[JerryPbury]

Thanks Steve!

I used the good log ones for the 100k instead of the Alpha's and then I ordered some 1m Linears. Just need to get some Trannies and time to finish them up.

 

[wilebee]

does it really matter whether you use log or linear on the 2 pannel mounted controls if the only thing its changing is the resistive taper ? the reason I ask is because I have 2 really nice linear ah sealed pots ? Wil

 

[Scenaria]

nope it doesnt really matter...

wont hurt anything

 

[wilebee]

ok I'm frustrated! all of my voltages are right except for the plate voltage on the 6aq5. I've got 83vdc on the plate, 120vdc on the grid and and 8.7dvc on the cathode. There is nothing between pin 5 and a20 but a piece of wire. Help Wil

Wilebee

 

[cayocosta]

Wilebee,

What value resistors are you now using for r29, r34 and r36?

Ron

 

[wilebee]

r29= 4.7k 2 watt
r34=22k 2 watt
r36=1k
Wil

 

[wilebee]

also my ac filaments are a little hot at 6.75 vac