All things LA2a related

[college101]

So..at work electronic hacking...an old set of ear buds cut off for the XLR connector

Will this work?

I wanna build the tester Mark...Seems like I will be using a lot more then just a few times!

 

[Biasrocks]

That'll work for signal input.

But, you'd probably want something a little more heavy duty, like a guitar cable or mic cable for the signal tracer, especially since you'll be poking around in high voltage areas.

Mark

 

[college101]

OK..I got some mic cables at home!  I will try this crappy ear bud one for kicks

 

[college101]

Hey MARK...should I be trying to add the 1000V dc blocking capacitors to the tester?

 

[Biasrocks]

Hey MARK...should I be trying to add the 1000V dc blocking capacitors to the tester?

A film cap in the 500-600 volt range will be enough.

Mark

 

[college101]

I cut up an old Shure xlr cable...checked for continuity Before I solder'd and then hooked it to the input of the 2a, ran an output cable to a xlr/male guitar jack in to a old guitar amp...turned it all on, and hit play...no signal..So I will be building the tracer next, to test for where the signal dies!

 

[Sredna]

Now you're on good way!


Did you test your setup by connecting the both XLRs with each other? So to say directly from the CD to the guitar amp, that way you could be absolutely shure that your adapters are working correctly.

 

[college101]

Good Call...Im on my way to work on it...

 

[college101]

I crossed the new cable and the output cable to amp with the cd playing and it passes audio... pics some time tomorrow of the tracer I built

OK..I built the Trace tester! Bingo..Got some sweet music playin on my old guitar AMP!!!

BUT it seems, the audio only goes from input mic to turret board#1 and then stops there?

WIERD

I did the voltage check on when Com side of DMM was at tb#1 ground and RED was on Tb#1 input...voltage was up around .130 when the cd was on,,,then when I would turn music off, it would drop to .003- if I measured AC on the output transformer turret board..it would be around .333 ac

C7b has dropped to 317 and after the diodes at R29 is still 353v dc

I have a Mastech ms2889 multimeter...works pretty good...reliable

 

[college101]

This makes me think the Input transformer is wired wrong, or that I have it set up backwards...either way...i got two new variables to try and change and see results...

 

[college101]

OK guys...Ive been trying to signal to pass to R5 And R6...I tested the CT off the Primary..and I am getting signal when I put the tracer to it...Im starting to think my transformer's wires are mislabeled...cuz I Get signal off the CT, and nothing at the isolated terminal points..BUT if I jumper a wire from the CT to the ground of TB#1, then When I trace the R5/R6 point...I get audio!! BUT this does not seem right. and still no audio at the Ground/R5 junction point...Nothing at R6/R7...help me out guys

 

[lassoharp]

On mine...There is no ground to hook #10 up to..So I have to just tie it directly to seprate chassis ground..which then connects to the neon...

The "lo side" (the "#10") of your input xfor sec must tie to ground for (full) audio to pass.  From what you've just said it sounds like your lo side is not properly tied to ground.  I don't know what input iron you're using but if your xfor has two separate windings like an A-10, then  they have to be wired together - series in this case, as shown on the original schematic - for audio to pass.  If by CT you mean a single wire on the sec, then I'd recheck the ground connection.

The bottom of R10 and the lo side of you input xfor sec should show clean on a continuity check. 

 

[simonsez]

You should get audio here...

 

[college101]

OK..the CT which goes to #3 on TB#1 of the input...the input TB, has audio going to the CT? Is this correct?
It is in the middle of the winding...but #10 is connected to a isolated turret point, and that point is tied to the ground the connects to the NEON ground...

SO..when I have the tracer set up, No signal is going to R6..even though they are connected...

YES it is tied to a insulated turret point that is connected to the NEON ground...SO I need to remove the turret point, tie R5 bottom side to ground, and then re-solder it in place with #10 then...?

 

[Sredna]

#10 of the input transformer should be connected to the case (ground) with a screw as shown in this picture. Left side at the bottom.

http://www.recproaudio.com/diy_pro_audio/teletronix_la2a.htm

You mentioned that you use the Sowter 1009 that should be a A10 replacement, so I presume the numbers are the same...

Do like this:

Step 1. Connect the croc clip of your tracer to #5 on TB1 and poke with the tip of the tracer on #1. Now you should get audio if you remembered to turn on your CD player. If yes, go on.

Step 2. Connect the croc clip to #10 on the input transformer and poke with the probe on #7 on the transformer. Audio? If yes, go on.

Step 3. Leave the croc clip on #10 (=ground) and follow the path R6-R7-R1-C1-C2-C5 with the probe.
If you have audio all the way, finally connect the croc clip to #8 on TB2 and the probe on #10 (TB2)

You dont have to have the LA2A turned on for step 1 & 2, on step 3 you could check R6-R7-R1 unpowered but afterwards it has to be on.

Please be careful when checking powered on!


(Dont mess with the center taps, just see to that 3 and 4 on the primary are connected together and on the secondary 9&8 are soldered together.)

 

[lassoharp]

OK..the CT which goes to #3 on TB#1 of the input...the input TB, has audio going to the CT? Is this correct?
It is in the middle of the winding...but #10 is connected to a isolated turret point, and that point is tied to the ground the connects to the NEON ground...

SO..when I have the tracer set up, No signal is going to R6..even though they are connected...

YES it is tied to a insulated turret point that is connected to the NEON ground...SO I need to remove the turret point, tie R5 bottom side to ground, and then re-solder it in place with #10 then...?

As long as all the correct ground points are connected you don't need to rearrange their placement.


Follow as Sredna says.

If possible, post or list the schematic of the Sowter 1009.  They do not show it on the website and it's possible that it's been miswired.  This way we can confirm which leads on the Sowter correspond with the A-10 leads from the schematic. 

 

[college101]

1010 sowter

 

[college101]

la2a sowter 1009 input transfrmr

 

[college101]

Ok..I re wired it anyway to make the connection as close to the spec on the schematic as possible...Thing is, the CT on the primary of the input, has to be grounded in order for me to get signal at R5.R6 test point...The CT shows in the schematic, that it floats... not grounded... I re-checked my wiring on the audio path, and I still dont get audio to pass to the next couple points!

Help guys...Somethin has to be wrong or the transformer is labeled wrong...

 

[lassoharp]

Is it convenient to remove the transformer and run your CD output through it using croc clips?  i.e - pull it out and wire it as a step-up to see if it passes signal properly.