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

[ron_swanson]

Turned out to be a faulty input transformer! I’ve got my mouser cart saved with the parts I used if anyone is interested! lots of things on the original BOM has been phased out. Thanks to hairball and serpent for this awesome build!

Kprellz,

I'd be interested in seeing a copy of your Mouser BOM, if you don't mind? 

Thanks in advance
Greg

 

[meltintohuman]

Turned out to be a faulty input transformer! I’ve got my mouser cart saved with the parts I used if anyone is interested! lots of things on the original BOM has been phased out. Thanks to hairball and serpent for this awesome build!

I would also be interested in your cart. Thanks!

 

[tesco_1]

I also added a switch to the 604 1/2 w output termination.  So know I can switch that in and out from the front panel as well. 

Hey guys, can anyone explain how to implement this loading/termination mod?  The old la3a units had terminals on the back, the SA-3A doesnt.  So would I just strap a 604 1/5 watt resistor on the (+) and (-) output jumper pins on the board or am I missing something.  (see pic attached)

 

[tesco_1]

bump

 

[Blackdawg]

Turned out to be a faulty input transformer! I’ve got my mouser cart saved with the parts I used if anyone is interested! lots of things on the original BOM has been phased out. Thanks to hairball and serpent for this awesome build!

also be interested in the BOM tweaks you did

 

[jameson1895]

Turned out to be a faulty input transformer! I’ve got my mouser cart saved with the parts I used if anyone is interested! lots of things on the original BOM has been phased out. Thanks to hairball and serpent for this awesome build!

I would also be super grateful for the Mouser Cart info.  Thank you!

 

[Blackdawg]

Hey guys, can anyone explain how to implement this loading/termination mod?  The old la3a units had terminals on the back, the SA-3A doesnt.  So would I just strap a 604 1/5 watt resistor on the (+) and (-) output jumper pins on the board or am I missing something.  (see pic attached)

PRetty sure the load mod AKA the clearmountain mod is what the switch on the front thats says "Mod" does.

 

[RJS]

Hey Guys,

I just finished mine and quickly made sure there was no smoke, fuse blowing etc.  I haven't calibrated yet but just plugging a mic into the inputs, to see if the unit reacted to a signal I noticed that the meters respond to Output mode only.  They do not move at all in GR mode.  This applies to both meters.  Any suggestions as to where I should look to begin troubleshooting?

Thanks,
Robert

 

[theposterkid]

Hey Guys,

I just finished mine and quickly made sure there was no smoke, fuse blowing etc.  I haven't calibrated yet but just plugging a mic into the inputs, to see if the unit reacted to a signal I noticed that the meters respond to Output mode only.  They do not move at all in GR mode.  This applies to both meters.  Any suggestions as to where I should look to begin troubleshooting?

Thanks,
Robert

When you say the meters "do not move in GR mode" are they properly "snapping" to 0db when you switch to show gain reduction, and they are simply not showing any gain reduction? Or are they sitting at -infinity (to the left) when you switch to show gain reduction?

If it's the former, I suggest you plug a line level device into the compressor, rather than a microphone. The reason for this is that it will be much easier to push the unit into gain reduction by feeding it a level for which it was designed.

 

[RJS]

Hey Posterkid, thanks for the reply.

I actually managed to get the meters to respond in GR mode, reading rainton’s instructions posted earlier in the thread; turn the stereo adjust fully clock clockwise.

I finished the project and everything worked right away adjusted TP1 to 12.5V and completed the stereo calibration successfully.  However, I had an intermittent buzz issue even though I sanded the back of the panel for the switches and grounded pin 1 of the XLR’s to the star ground.  It drove me crazy for 2 days.  I could get it to stop by pressing on parts of the case and once I put the lid on the unit and tightened the screws, the buzz went away.  So I am guessing the case had to make better contact with ground and once it was screwed together, it finally made solid contact to ground. 

Next time I am going to use the screw down terminals with shielded wire, the molex ones in these size are a pain and are not the most secure.  The trifurcation pins are a much better connection but they only come in .156 sizes.

The unit is very quiet.  Even with Classic and 50dB selected.  I used a matched pair of medium speed Kenetek TB4s, and the compression is very nice, a great compliment to my GSSL (with Turbo board) sound.

Even through I read through this support thread about 10 times, I was a little nervous taking on this project because this support thread has seen little activity in recent years.  I reached out to some members who were very helpful and gave me a nice confidence boost.  Thank you again guys, I am most appreciative.


-Robert

 

[theposterkid]

Glad to hear it, Robert!

 

[RJS]

Actually.....

The buzz I mentioned came back.  So I sanded some more of the case but that did not help.

I noticed that the molex connections were not the best so I decided to replace them with screw down terminals as one poster mentioned here earlier on. That seemed to work at first but then I noticed the buzz came back sporadically.

After some troubleshooting I noticed that putting pressure/tapping on the mic input transformers would recreate the buzz/noise. I figured maybe cold solder joint.  So I took the boards out and reflowed the solder joints on the mic input transformers.

I plug it in now and have nothing, it passes a signal in bypass but when engaged--nothing.

I spent several days going thought this and I am at my wits end with this thing.  Would anybody be interested in troubleshooting/fixing this?  I will pay you of course.  I just would hate to see this collect dust and not be used.  (When it worked it sounded great)

Please PM me if you would be interested.

Thanks,
Robert

 

[RJS]

I'm wondering if I grounded the input transformers by accident after reflowing.  Is there a way I can test to see if I am shorting the transformer?  It looks like while in the PCB all pins are making continuity to ground--that cant be right.  When mounting should the transformer be flush to the PCB or should there be space in between?

Thanks,
Robert

 

[RJS]

Soo.....

I read over the instructions thread and cannot believe I missed the part of not mounting the input transformer flush with the pcb!  I only ready the part about the transistor cans not being too close to the board.

Anyway, I desoldered the transformers and unfortunately took out some component side pads in the process.  The trace side pads are all still intact.

I am going to replace the input transformers but was wondering if I should use the flying leads version over the PCB mounted one.  Any suggestions?


Thanks,
Robert

 

[kishibashi]

I just purchased pcbs. The original links to schematic, BOM everything is dead. Can someone send me schematic and updated BOM that seems to be going around to keita at 3dbsound.com Please and thank you!

 

[RJS]

Finally success!

I replaced the input transformers-gave them plenty of space between the case and PCB,  put a piece of fish paper in between as an added precaution and everything is now working.  Again, really nice sounding unit. 

Lesson learned: Read the manual several times before beginning the project!


-Robert

 

[RJS]

For those interested he is my BOM from Mouser.  If you have the 600 Ohm Switchable Mod, you will need 16 toggle switches. 

The meters, transformers and knobs were from Hairball Audio, and the case was from Collective cases.

Hope this helps.

-Robert

 

[RJS]

Kishibashi,

Attached is the schematic.


-Robert

 

[HoneyBadger Audio]

Finally success!

I replaced the input transformers-gave them plenty of space between the case and PCB,  put a piece of fish paper in between as an added precaution and everything is now working.  Again, really nice sounding unit. 

Lesson learned: Read the manual several times before beginning the project!


-Robert

Any idea where the "manual" you speak of might be located?

 

[theposterkid]

Any idea where the "manual" you speak of might be located?

To my knowledge, there is no "manual" .... it seems like what he is referring to is simply the very beginning of this thread where those instructions were posted. They may have been staggered over the course of a few threads on the first page.

I actually made the same mistake with one of my input transformers. Except in my case, I did read those instructions, and kept them in mind during the build, and DID space the input transformer off the board with plenty of room to spare, but then I used too much solder on one of the pins. That channel would cut out, and come back with the slightest pressure applied to the PCB near the input transformer. After I removed some of that excess solder, the unit worked much more reliably.

Now, the only issue that remains with that same channel is that occasionally the signal will cut out, until I send a very loud signal into the unit. For example, if I am tracking acoustic guitar and it cuts out, I can lightly scratch my mic with my fingernail, crank my mic preamp feeding the SA3A, and the signal will immediately return and continue working for a while.

I actually built a 3rd unit this month but Hairball is all out of the output transformers, currently. I ended up buying a UREI 11148A output transformer on Ebay, and put that into this new 3rd PCB, tossed that into my existing chassis from my first build, and it works and sounds great right off the bat.