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

[Unit7]

Hi!

I'm ordering the last bits for this build and I'm wondering about two items on the BOM. Btw, I've searched this thread but didn't find the answers.

- The four audio pots are no longer available from Mouser. Any tip or could these work?:
http://www.mouser.se/Search/ProductDetail.aspx?R=RV24AF-10-15R1-A100K-3LAvirtualkey14860000virtualkey31VJ501-F3

- The 14 switches. The BOM says 'SPDT, ON-ON'. Is there a difference between 'ON-ON' and 'ON-(ON)'? Otherwise perhaps these would work?:
http://www.mouser.se/Search/ProductDetail.aspx?R=A108SYZQ04virtualkey50660000virtualkey506-A108SYZQ04

Grateful for any help!

 

[Unit7]

So I got the switches above and learnt the hard way that ON-(ON) is momentary switches.. Now trying to get it right the 2nd time around I studied the schematics a bit and see none of the SPDT switcthes have the third pin connected. So why not using SPST instead? Am I missing something?

 

[zerodb]

Does anyone know if SA still have boards for this? I've emailed a few times but got no reply.

 

[Unit7]

Stone dead thread, but for potential future builders here's my little contribution.

After getting the new proper toggle switches, finally ready here. No major issues. Had the 'usual' hum on the right channel. Cranked the volume, put headphones on and started fiddling with the cables. Trying to shield the pwr xformer didn't do the slightest for my unit. Having bought too narrow shields for the power cable forced me to put them (one from the IEC inlet->power switch, the other from the power switch->power xformer) in separate shields (wrapped in shrink tube) which turned out to provide the solution. Because when I separated them the hum went down 10-20dB to barely audible. Seen on the pic at the bottom (right side of unit), the two tube wrapped leads form a square'ish pattern.

Waiting for stereo matched T4Bs from Kenetek, but tested with a single T4B from my LA2, hence the empty sockets.

I decided to trust Harpo that I'd be ok with 1/4W pots, so used these:
http://www.mouser.se/Search/ProductDetail.aspx?R=RV24AF-10-15R1-A100K-3LAvirtualkey14860000virtualkey31VJ501-F3

After the goof mentioned earlier, with the 14 switches I ordered these:
http://www.mouser.se/ProductDetail/NKK-Switches/M2012SS1W01-C/?qs=sGAEpiMZZMvudeGI7i40XOVezHpYSFdNLOdlzCspGKk%3d

Couldn't find shield for the power cables by the meter at Mouser so bought at ELFA in Stockholm:
http://www.distrelec.biz/en/shielding-braid-mm-alpha-wire-2171/p/15508676?queryFromSuggest=true

Got a cheapo Molex crimp tool at eBay:
http://www.ebay.com/itm/171762703269?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Worked fine but, as mentioned by others, that part was the least fun..

Other info I've picked up from this thread:
- Case from Collective cases
- Used nuts as spacers betwen case and PCBs (T4B fits under the hood)
- Dremeled the inside of the face plate around all holes for switches/pots
- As described in the schematics, did not connect pin 1 on the XLRs (though the shield of the wire is connected to the Molexes)
- Spaced the larger transistors from the PCB

Also, the XLR connectors I believe are not mentioned in the BOM

For wiring as in the pic from my build, these are the wire lengths I used:

L channel

Input (XLR): 8.5cm
Output (XLR): 7.5cm
Classic/mod: 28cm
30/50: 34cm
VU display: 40cm
Comp/Lim: 25cm
Bypass: 42cm
HF/Flat: 29cm
Gain Pot: 20cm
Peak red pot: 30cm
Link: 31cm
VU meter (from J11): 43cm

R channel

Input (XLR): 11cm
Output (XLR): 8.5cm
Classic/mod: 34cm
30/50: 43cm
VU display: 51cm
Comp/Lim: 34cm
Bypass: 53cm
HF/Flat: 20cm
Gain Pot: 28cm
Peak red pot: 42cm
Link: 18cm
VU meter (from J11): 53cm

As I only tested one channel at a time briefly I didn't get any impression of the sound, but of course look forward to getting the matched T4Bs, stereo trim the unit and start using it!

Edit: When ordering I missed that the component kit was stereo, so I accidentally ordered two stereo kits, which I noticed when building, two years after ordering, so...d*rn it I had to build yet another one.  It's ready tonight. Tested and calibrated. Had some time playing with it and wow I have to join the choir..these are good!!

 

[Hugo Cruz]

Hi everybody!

At first sorry for my hazardous english! 

So, I embark on this project of La-3a  stereo clone,  I want to add a "dry/wet" knob, I find this circuit (builded for the GSSL) "https://groupdiy.com/index.php?topic=61934.0" .

Do you think it's possible to adapt this one on the Sa-3a ?

Thanks!

 

[mattmartin831]

I found this schematic for another LA-3A clone in another thread. This schematic was intended for use with a powered 500 series chassis, but I am wondering if I can use a similar +/- 16VDC power supply to power the SA-3A board I plan to order. After reviewing the schematic it appears to be almost identical to the UREI schematic. Has anyone tried powering the SA-3A stereo compressor with an external DC power supply?

 

[sr1200]

As long as the voltages are correct and you meet/exceed the amperage draw, the circuit wont care where the power is coming from.

 

[soundshigh]

Resurrecting this thread to ask if anyone is building and selling those in Europe?  Or if anyone here has an unit to sell?

Cheers, K.

 

[WantsSweetRelease0091]

Hey everyone!

I just got my build up and running, but there seems to be an issue.  On one side of my stereo unit, physical pressure on the chassis or tightening the screws on the PCB either allows the Gain Reduction to work, and on the ohter side the same thing happens to my mic inputs.  Could it be a connection problem on the underside of the PCB, like the solder points are touching the chassis?

Any help would be appreciated!

 

[sr1200]

Theres a note about leaving a spacer under the transformers early in this thread.  I didn't do it and had the same problems at first.  Desolder pump to the rescue... pushed the trafo's up a little and perfection.

 

[WantsSweetRelease0091]

Having some issues with my meters...

I started doing the calibration and everything seemed to be working fine, until I switched to GR.  I was throwing in a 1kHz signal @ -18dB fro Pro Tools.  When I switched to GR, the meter goes to 0, but when I turn the Peak Reduction knob, the meter never moves.  I can see the gain reduction in Output mode, but in GR mode it stays at 0.  Also, what exactly does the 30/50 switch do in Classic and Mod modes?  I'm new to building my own gear so any help is appreciated!

Also, in BYPASS, the meter isn't reading anything.  Shouldn't it be showing the signal coming in without any of the compression?

Here are my notes so far about the issues I've encountered.  I'm building 2 stereo units that both have the same issues:

-Audio in:  GOOD BOTH CHANNELS
-Meter and knobs work:  GOOD BOTH CHANNELS
-Switches:  See notes below
-Outputs: WORKING


CHANNEL 1:
CLASSIC MODE meter zeros @ 1.2 on gain pot on 30dB switch.  Meter zeros on .8 on gain in 50dB switch
MOD switch drops volume. Zeros out @ 7 on Gain pot in 30dB, zeros @ 2 on 50dB switch
G/R switch, meter goes to zero, never moves even when peak reduction is maxed
OUTPUT MODE with meter @ 0, Peak Reduction Maxed brings meter to -3.5 dB.  Limit switch changes it by -.2 dB
BYPASS switch kills meter, most likely how it's supposed to function.
HF Switch barely moves, but testing with oscillator so @ 1kHz so it probably isn't affecting the signal.
*When not linked, pressing down on the opto-cell kills the signal.  Still contact errors?

CHANNEL 2:  Same issues but measurements are off by .1 or .2 dB.
CLASSIC MODE meter zeros @ 1.2 on gain knob on 30dB switch.  Meter zeros on .8 on gain know in 50dB switch
MOD switch drops volume at zeros out @ 7 in 30dB, zeros @ 2 on 50dB switch
G/R switch, meter goes to zero, never moves even when peak reduction is maxed
OUTPUT MODE with meter @ 0, Peak Reduction Maxed brings meter to -3.5 dB.  Limit switch changes it by -.2 dB
BYPASS switch kills meter, most likely how it's supposed to function.
HF Switch barely moves, but testing with oscillator so it doesn't matter right now.

Unit 1 Voltage Check:
BIAS TP1:  Channel 1:  12.5VDC Channel 2:  12.5VDC
Input Voltage:  Channel 1:  1.12VAC Channel 2:  1.12VAC
Output Voltage:  Channel 1:  1.31VAC Channel 2:  1.23VAC

Unit 2 Voltage Check:
BIAS TP1:  Channel 1:  12.5VDC Channel 2:  12.5VDC
Input Voltage:  Channel 1:  1.14VAC Channel 2:  1.13VAC
Output Voltage:  Channel 1:  1.27VAC Channel 2:  1.23VAC

LINK seems to be doing nothing.  Can't tell which channel is the master channel.
LIMIT seems to not work.

G/R switch not reading the actual gain reduction.  Meter gets to 0 and stays there.
SOLUTIONS?
-Solder points OK
-Maybe transformer tightness bending the board?  I loosened the Xformer nuts on Channel 1, but nothing changed

 

[wmarden]

Is there a mouser cart for the SA-3A BOM?

 

[Audioseb]

I'm interested 

 

[Avgatzeblouz]

Me too.

 

[Blackdawg]

yeah sucks there isn't the PCB kit anymore..

 

[andow]

I'd also be interested in a kit...

 

[theposterkid]

I just built one of these. I bought the pcb in January. Some of the other parts later in the year. I had to wait on a couple backordered parts from Mouser.

The secondary channel worked right off the bat. The primary channel with the power supply was compressing fine, but had a thin/quiet output. I spent a day removing all the transistors and testing them. Then putting in all new transistors and swapping the output transformers between the two channels. I still had the same problem. Then my finger bumped the molex of the gain connector on the problem channel, and the signal came through nice and strong. I redid that molex connector, and now it's working perfectly.

Love it! Thanks Ruckus, Hairball, and Serpent Audio!

 

[Kprellz]

Hey Guys! Just finished my build and fired it up! No explosions so thats nice, couple issues im hoping someone can help out with.

Primary channel:
Has sound but is thin, Checking all the wiring now
Meters function correctly
Limit/Compress May or may not work hard to tell the difference, 
Bypass doesnt work, If i hit the bypass it just cuts the sound,

Secondary channel:
Bypass works However sound is INCREDIBLY quiet
Buzz occurs when touching    Peak Reduction or Limit/Compress 

 

[Kprellz]

Replaced transistors and channel one works!m and sounds fucking Awesome!!! Channel two does not quite work yet. Same issue SUPER low volume

 

[Kprellz]

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!