SA-3A (LA-3A Clone) Support Thread

[Harpo]

The shunting LDR resistance between T4B-pins 5/6 is missing in your measurement and will bring your voltages down.

 

[salomonander]

The shunting LDR resistance between T4B-pins 5/6 is missing in your measurement and will bring your voltages down.

thanks a lot. so this is alright? i can just go ahead and plug it in? cheers

 

[salomonander]

may i bump this again? im very confused. everybody told me that pin5 should be connected to ground. which is not the case on my units. what am i doing wrong? any help is appreciated. all this is measured without the t4b in the socket.

 

[Harpo]

everybody told me that pin5 should be connected to ground.

These 'everybodies' relate to the LA3A. You are building a SA3A that has pin6 of the T4B connected to ground instead. The LDR inside the T4B that connects between pins 5/6 doesn't care.

all this is measured without the t4b in the socket.

so put it in circuit and your measurement will behave ...

 

[salomonander]

great! thanks a lot.
btw: i checked my (unfinished) silent arts la2a and it was the same. no ground connection on pin5. i assume its a similar issue (not an issue at all). cheers

 

[salomonander]

and thanks again. it works now and sounds great!

 

[Brotastic]

I was wondering if someone could help me out.  I have most of the SA3A boards populated.  I am using the Cinamag B11178B input transformer.  I have to use the through holes to solder the leads.  One one side there are holes for Blue, Can?, Gray, and Green.  There are only Blue, Gray, and Green leads.  The other leads go to the other side.  What do I do with the other extra hole?  Thanks.

 

[Brotastic]

bump

 

[Brotastic]

I am not that great at reading schematics, but when I look t them it looks like the can goes to the shield.....(ground?)  If anyone can help a brotha out it would be much appreciated.  Thanks.

 

[sr1200]

If the can has a shield connected to it it goes there.  Sometimes you'll see a soldered bare lead coming from the chassis of the trafo.  Would be that.

 

[Dr Gris]

The " grey" and "can" pads on the PCB have continuity.
My guess is that the gray cable might have continuity with the transformer housing ("can")??
And that's all you need, test it...
I have the PCB mount version in mine so I can't be of more help, sorry.
I wish I had all the parts to finish mine.

Best
//M

 

[Brotastic]

Thanks for the replies. 

Dr Gris, you are the winner....hahaha.  The grey through hole and the can have continuity. 

Again, thanks for the replies.

 

[owestgate]

Hello all,

This is my first post here. I was hoping to solve my problem by reading the thread in it's entirety but unfortunately i'm still having some noise issues on my build.

I have no noise issues with the PSU or any of the usual components, where i seem to be struggling is the front panel switches.
Initially I had connected pin 1 of the in and out XLRs to the shield of the in and out jumpers on the boards. My star ground was connected to the PCB power jumper, IEC ground and power switch shield.

In this configuration i was getting a significant increase in 50hz hum whenever i touched the mod/classic switch when in classic position but no issues when in mod mode. After staring at the schematic for a bit i thought there must be a grounding issue with my shields that somehow caused noise to be induced into the audio path where the mod resistor is located. So i decided to re-wire the xlr connectors (to improve the grounding of any shielded wires) routing all pin 1s to star ground and disconnected them from the shield of the in and out jumpers. This gave me a higher noise floor and now meant touching any of the shielded switches gave me even more hum!

I have since tried various configurations for the xlr pin 1s and shield connections but cannot improve this behavior, in fact i am now struggling to get the issue back to where i started; just affecting the mod/classic switch. Whatever I try just seems to exaggerate the issue.

Has anyone else noticed anything similar?

 

[Dr Gris]

I haven't even put mine together yet so I can't comment really.
Did you take away the case coating where the switches and pots go through the front panel?
Don't know if it relate to this, but I've seen it mentioned in this thread that it's a good thing to do.
I actually do it in all my cases, and also making sure all panels have continuity with star ground.

Best
//Magnus

 

[owestgate]

I haven't even put mine together yet so I can't comment really.
Did you take away the case coating where the switches and pots go through the front panel?
Don't know if it relate to this, but I've seen it mentioned in this thread that it's a good thing to do.
I actually do it in all my cases, and also making sure all panels have continuity with star ground.

Best
//Magnus

Hi Magnus,

I had considered this but as the problem only initially affected the mod/classic switch i had presumed this was not the source of the problem. Perhaps i should check the continuity before being so presumptuous!

Thanks for the suggestion I will check it out and let you know how it goes.

 

[owestgate]

This has done it. Should have checked the continuity in the first place!

Cheers magnus.

 

[Dr Gris]

As a newb, I'm glad to have been of assistance, for once  ;D

I hope you'll enjoy it.

Cheers
//M

 

[charlievela]

So i got my unit finished. and immediately noticed some more strange behavior. When I unhooked the power branch cable, the primary board seemed to operate properly. That's when I realized my critical mistake. I had failed to flip the power branch cable so that the pins lined up properly.

Primary                Secondary
Pin 1 - +35V        Pin 1 - Ground
Pin 2 - +28          Pin 2 - +V
Pin 3 - +V            Pin 3 - +28
Pin 4 - Ground    Pin 4 - +35

My question is, how bad did i mess up? after fixing the cable, channel one seems good, although I'm not sure if all the switches are working and channel 2 isn't compressing really at all.

What are some likely components that i messed up? what would be the best way to start testing and identifying the ramifications of this epic f**k up?

 

[mulletchuck]

according to what you wrote, all pins went to the right places. 

Pin 4 went to ground on both boards, etc...  Can you revise what you wrote?

 

[charlievela]

Ok sorry about that. I modified my post to reflect the fact that what should've been going to pin 4 was actually connected to pin 1 and so forth.