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

[ComodoComplex]

Sliding some braided shielding cable over the power link wire did it for me without having to ground it or anything. I guess it creates enough of a faraday cage to stop radiated E-fields. It actually made no difference if I grounded it or not, and I secured heatshrink over the ends to make sure it couldn't short out on either side of the cable. I also had to cable-tie the assembly against a nearby cable to make sure the shield was squished down tight against the wiring to get rid of every last bit of hum, which is why I recommend using proper 3-4 conductor shielded cabling. Gotham 85225 cable would be luxurious, but you could also probably do with Mogami W2893 since the SA3A doesn't draw much current

This is what I used for shielding FYI:
https://www.mcmaster.com/shields/sleeving/interference-shielding-expandable-sleeving/

Hopefully can post some pix soon!

 

[ComodoComplex]

I think this worked! Gotta be a small small JPG

 

[ComodoComplex]

Close-up of the shielding for power link

 

[mypantsrblue]

Hi,


While assembling a stereo unit for a friend I revisited and re-calibrated my two units (from a long time ago)


One of the channels has developed a little problem which I think I've narrowed down to a problem in the output gain.

(MOD, 50dB, Compress)
Feeding a -18dBFS signal into it I get one side to Gain +/-6 for a 0dB(VU) reading while I need the other side to be at 7. Around 6 the signal gets distorted (while reading about -2.7dB(VU)).
When I turn up the peak reduction the volume lowers (obviously) and the distortion goes away.
When I compensate for the lost volume the distortion returns at the same VU reading.


Looking at the schematic logic tells me to try and replace Q3, Q4, Q5 and/or Q6 to see if the problem goes away or am I wrong here?


Thanks in advance,
Herwig

did you ever fix this? i have a similar issue

 

[deadpoet]

did you ever fix this? i have a similar issue

I replaced all of those transistors and the problem went away for a few days but came back ... something else going on unfortunately.


Herwig

 

[JMan]

After quite a long time of this unit sitting finished with a makeshift control panel, I finally got a proper front panel made, cleaned up the wiring (it was truly a mess before!), and racked this up. I went with a 3u enclosure because it was less cramped and I thought the panel I designed looked nicer that way.

 

[morro2k]

Anybody knows where to find the SA3A front panel?

Thanks

 

[MidnightArrakis]

Anybody knows where to find the SA3A front panel?

Thanks

If you are able to provide me with the various dimensions of all of the different holes and cutouts, I can not only provide you with a 3D CAD-model of this front-panel, but also a sheet-metal fabrication drawing that you can send to a metal shop to have this made. Similar to what is shown on Pages 2 & 3 of the attached PDF file. The same goes for any PCB files as well (also shown in this PDF file).

 

[mypantsrblue]

Hey yall

I got a long built SA-3A with some weird issues that only presented themselves after me putting it in my car and driving across the country to move.


Long story short, i have identified this to be 100% coming from the unit. My left side when either IN or BYPASS is selected, is quieter than my right side. Another issue is that the meter is sitting just slightly off of 0.

I did not personally build this, although I have built GSSL, and many 1176. From what I understand, the only calibration on these units is bias and the 0 set. I am going to check those, but is that a good start?

Obviously I can easily re-set the meter 0, but is there anything else I should be looking at here? Is bias even going to be a reason for my one being quieter?

 

[mypantsrblue]

Hey yall

I got a long built SA-3A with some weird issues that only presented themselves after me putting it in my car and driving across the country to move.


Long story short, i have identified this to be 100% coming from the unit. My left side when either IN or BYPASS is selected, is quieter than my right side. Another issue is that the meter is sitting just slightly off of 0.

I did not personally build this, although I have built GSSL, and many 1176. From what I understand, the only calibration on these units is bias and the 0 set. I am going to check those, but is that a good start?

Obviously I can easily re-set the meter 0, but is there anything else I should be looking at here? Is bias even going to be a reason for my one being quieter?

I cant believe that i was able to figure out without any assistance from the group but just in case anyone ever has a problem like mine was... One unit was about 5db quieter than the other, intermittently but more often than not.

input transformer was too close to the board, and in my moves and shipping to techs it must have gotten close enough to short. I gave it a tap, and it came right back and became equal again and so I pulled it away from the board a bit and all is well again.

 

[khstudio]

Is this project still valid? I can't link to the schematics or other files on Dropbox - page one.
PCB's seem to still be available, so just checking before ordering?
Thx!

 

[JMan]

Project is still valid. Check the last few pages of this thread for docs links (I think they’ve been posted recently, but I didn’t check). AFAIK there’s only a schematic and a BOM. From there it’s a very straightforward build.

 

[khstudio]

Anybody have a Front Panel to sell or know where to get one??

Also... why do the docs say "SB-3A", when this thread and PCB's are for SA-3A??

 

[JMan]

Not sure about the "SB-3A" thing (I don't see that on the file names, but maybe you're noticing it somewhere else? It's likely just a typo). Anyway, look at my posts #413 and #414 on page 21 of this thread. Those are the correct build docs.

Regarding a front panel, you're probably going to have to either get one secondhand or lay it out yourself (it isn't too hard). If you want to go with a 3U panel, I'd be happy to share my .fpd with you, but it would require a few minor tweaks if you aren't planning to use subpanels for mounting the switches.

 

[khstudio]

Front Panel Designer "FPD" Files, for the SA-3A... If anyone has a file they can post or links to where I can find one/them, I'd appreciate it!

Also, have any of you used or compared the Original UREI B11178B "Input" (or the Auto-Trans, Output) to any of the newer versions?

Also wondering if the Original input will fit/work on the SA-3A PCB??

Thanks!!

 

[JMan]

I wish you luck in finding a panel, but I also encourage you to consider designing one yourself in the FrontDesign software. This particular build is very easy to create a panel for, especially if you're aiming for something uncomplicated like the original Serpent Audio panel (don't follow in my footsteps in that case lol). You only need to account for the following:

15 mini toggle switches (7 per channel plus "link" switch)
Power switch (this can also be a mini toggle so long as it's appropriately rated)
4 potentiometers
2 meters
Optionally, the power LED

All of these components are wired off-board, which means that the only spacing consideration when laying out the panel is making sure you literally have enough space on the backside for each component -- not difficult. As you can see, if you were to use a mini toggle for power and omit the LED, you could design this whole panel with just two different hole sizes and one rectangular cutout size. And at most, you need to consider dimensions for only five elements (plus rack and case mounting holes). Spend an evening on it and I bet you can create something even better looking than the Serpent panel.

 

[khstudio]

I'm well aware of everything you said but it would be stupid not to ask or look around first, for a panel that may already be done, that I could tweak to taste.

 

[JMan]

I'm well aware of everything you said but it would be stupid not to ask or look around first, for a panel that may already be done, that I could tweak to taste.

Sure. Just trying to be encouraging. I enjoy the "DIY" of making my panels so I don't think it's stupid to use that as a starting point, but to each his own. Good luck.

 

[1wildthing]

Hi folks, does anyone knows if this project is still active and where I can buy pcbs?

 

[bobbeloud]

Anybody have a couple pcb’s laying around that I could buy? I’ve reached out to Serpent and they just said they no longer stock them