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

[craigmorris74]

Darn it!  Reading the schematic closely and noticed I was supposed to pre-trim VR1 and VR2, but I've already got the soldered to the board.  Any tips as what to do there?

You should be fine, the Pots should come centered by default (or fairly close to centered anyways).

Also, on the schematic, it says to set the stereo adjustment fully counterclockwise, but the instructions for stereo calibration say to start with it fully clockwise.  Which should I start with when powering up?

Doesn't matter.

Fired up my SA-3A and nothing bad happened.  Adjusted the bias with VR1. 

I before I asked the questions above, I messed with VR2, and wanted to know what voltage should be going to the meter.  I'd like to adjust this before starting stereo calibration.

Thanks,
Craig

 

[ruckus328]

It will vary from unit to unit, hence the pot.  No analysis needed, just turn it until the needle sits at 0VU in gain reduction mode with no signal present.

Ohh and congrats on a smooth build

 

[craigmorris74]

Thanks for the quick reply, Mike.  Now I'm ready to take it into the studio for stereo calibration.

This has been an amazing project to build with great documentation.  This is easily the most complex thing I've built, but the instructions and schematic made it very easy. 

Thanks again,

Craig

 

[Tsane]

I finally finished mine today, but have a small issue with the wiring for the power switch. I wasn't completely sure how to wire it, so I searched on this thread and on the web. I thought I had figured it out, but when plugging in the power cord, my unit turned on.
It wasn't supposed to, the switch was in the off-position according to my thinking. So I switched it "off", and there goes the fuse. I'm not gonna try it again before I'm sure how to properly wire everything.
The SA-3A didn't catch fire, nor did I see or smell any smoke, which is already a good thing. I'd like to keep it that way ;D

I attached a diagram which shows how I have it wired now (operating at 230V). Can someone spot the (obvious) mistake?

Thanks,
Tsane

 

[Tsane]

Anyone? 

 

[tzman]

Anyone? 

I could help you, but I can't really figure out your drawing. Take a look at his though: http://sound.westhost.com/psu-wiring.htm#s2.2. Let me know if I can help you further...

 

[Tsane]

I could help you, but I can't really figure out your drawing. Take a look at his though: http://sound.westhost.com/psu-wiring.htm#s2.2. Let me know if I can help you further...

Thanks, I based my wiring on that picture, but my power switch only has 3 pins (one row).

I'l try to explain my drawing;
- Blue, Brown, Grey and Violet are primary leads on the transformer; Grey and Violet have to be tied together for 230V operation.
- I soldered the blue lead to the N (neutral) of the IEC inlet
- I soldered the brown lead to the middle pin of the power switch
- I connected the L (live) on the IEC inlet to one end of the fuseholder
- The other end of the fuseholder goes to the top pin on the power switch

Does that make sense?

Thanks!

 

[ruckus328]

- I connected the L (live) on the IEC inlet to one end of the fuseholder
- The other end of the fuseholder goes to the top pin on the power switch

Tsane, this doesn't sound right.  Can you take a pic of your IEC?  You shouldn't need to connect anything to your fuse holder, the fuse should be internally shorted to you "L" on the IEC already (on any IEC I've ever seen).

There should only be 3 tabs on your IEC: L, N, and Ground.

L should go to the power switch.  Other pin of power switch then goes to the xfmr.
N should go directly to xfmr.
Ground to star ground point.

How are your secondaries wired?

 

[Tsane]

Thanks ruckus, I didn't have an IEC with an internal fuse holder at hand, couldn't get any at the local stores I tried either. So I decided to use an IEC  and external fuse holder (as pictured here: http://sound.westhost.com/psu-wiring.htm#s2.2, picture of mine attached).

IEC L goes to the fuse holder and then to the power switch (top position), middle pin of the power switch goes to transformer
IEC N goes to transformer
Ground goes to star ground

Secondaries are as you described;
Red and Orange tied together
S1S: Black
S2F: Yellow
0V: Star ground

 

[ruckus328]

Ahh, yea then that's fine.

Next question - what size fuse are you using?  Are you sure it's a T-Lag (Slow Blow)?

Also, disconnect the secondary wiring from the board and see if she still blows.  That way you can determine if it's a primary side issue or secondary side.

 

[Tsane]

The fuse is a slow blow 200mA. Full inscription on the fuse is "T200mAL 250V".

I disconnected the secondaries and tried again, the fuse still blows...

 

[Harpo]

.., but my power switch only has 3 pins (one row).

What type/vendor of mains switch?. There are only 2 pins needed to close the connection. Your 3rd pin might be there for mechanical/optical reasons, but more likely this could be an illuminated switch and this (for usual a little smaller) 3rd pin connects to N to light up the neon inside when the switch is closed.

I'l try to explain my drawing;
- Blue, Brown, Grey and Violet are primary leads on the transformer; Grey and Violet have to be tied together for 230V operation.

maybe. Colour scheme of transformer wires is not standarized and differs between manufacturers.
What type/vendor and VA rating is your transformer?
(The transformers VA question relates to the required fuse rating for your transformer.)

 

[Tsane]

What type/vendor of mains switch?. There are only 2 pins needed to close the connection. Your 3rd pin might be there for mechanical/optical reasons, but more likely this could be an illuminated switch and this (for usual a little smaller) 3rd pin connects to N to light up the neon inside when the switch is closed.

It's a salecom T8013-T (http://www.salecom.com/pdf/T80-T_.pdf). So just a simple SPDT switch, it was included in ruckus' kit

maybe. Colour scheme of transformer wires is not standarized and differs between manufacturers.
What type/vendor and VA rating is your transformer?
(The transformers VA question relates to the required fuse rating for your transformer.)

Transformer is a Triad VPT30-830 (datasheet attached), 25VA, also included in ruckus' kit.

 

[deadpoet]

Hi there,

I (finally) just finished work on my 2 stereo units. Building was easy (my previous experience was cables and assembling SCA preamps) and I booted my units for the first time yesterday with success (meaning no smoke, no explosions  ;D )


I still have to do some testing but I have a couple of questions:

- For now I just connected the earth to the green 0v connector (J16 pin 3) and ONLY to that. I'm getting some noise when checking with a microphone and phones but that goes away after flicking some switches. In the photos other people posted I'm seeing more connections that go to the chassis ground and then to the IEC connector (I have only one wire going from J16 to the IEC ground). What should I add? XLR grounds and chassis?

- Like I said, I still have to do some testing with tones instead of with a mic but all four units go from 0db of GR to +/-15dB when I feed it nothing and put the peak reduction knob at around 7. Is this normal behaviour, does it have anything to do with the above or have I messed something up in all four units?


(still have to fix/mount the xformer, wanted to wait for that until after testing to find the quietest spot).
(haven't put in a fuse yet and haven't connected the power switch as well - might do that sometime next week)


thanks for the excellent product and kind regards,

Herwig

 

[Tsane]

Assuming it's a primary issue (since the fuse still blows without secondaries attached), I measured continuity through all the primary connections. But it all seems fine (measuring 2 ohms max). I got roughly 85 ohms between the two primary leads (measured at between IEC L & N) when the power switch is in the on position.

Does this seem right? Being a total newbie at this, I really don't know what I should be looking for next...

Thanks

 

[ruckus328]

- For now I just connected the earth to the green 0v connector (J16 pin 3) and ONLY to that. I'm getting some noise when checking with a microphone and phones but that goes away after flicking some switches. In the photos other people posted I'm seeing more connections that go to the chassis ground and then to the IEC connector (I have only one wire going from J16 to the IEC ground). What should I add? XLR grounds and chassis?

(still have to fix/mount the xformer, wanted to wait for that until after testing to find the quietest spot).
(haven't put in a fuse yet and haven't connected the power switch as well - might do that sometime next week)

Please fix your safety & grounding isues.  You can't expect the unit to behave normally when nothing's grounded.  0V on the PCB, IEC ground, and Pin 1 on the XLR's should go to star ground on the chassis.

You need a fuse.  No fuse means there's nothing between you and the mains breaker.  Make a wiring mistake or put your hand on the wrong spot........

Seriously, you can die dude.

 

[ruckus328]

Tsane, you primary wiring seems fine.  Regarding your toggle switch, just to verify it's not faulty when the switch is "up" you'll have continuity between the center pin and the bottom pin, when switch is "down", continuity between center and top pin.  However, even if the switch was busted I'd expect it would either fail completely open or completely closed, it wouldn't start blowing fuses.  Only possible was it could is if internal connections somehow shorted to the body (connected to ground via the panel).  This is a stretch but surely anything's possible.  Multimeter should tell you quick if this is the case (with power cord disconnected of course).

So assuming the switch checks out, that means either:

A) You fuse holder is shoddy

B) You have a bad toroid

Do you have any other fused IEC connector you can use temporarily (like something on another build?) just to weed the fuse out of the equation?  Also buzz it with a meter and make sure this too is not shorting to ground or something.

If everything else checks out and you can definately narrow down the problem to the toroid I can send you a new one, but shipping just the xfmr will probably cost more than the xfmr itself, plus you'll be waiting weeks for it to clear customs, probably be better for me to just refund you the money and get one from a EU source (farnell, etc) if we have to go that route.

 

[mata_haze]

Hello everybody,
I have build 2 stereo units and I have a problem (on all of them):

it does not pass audio.

I have done the following tests (without T4B in)
- power rails measures absolutely fine
-I have signal coming through up to TP2 and up to the GAIN pot after that it disappears
-Q1A and Q1B gets farly hot but a bit too much for a transistor of that size.
-Q3 it's TOO hot infact I leave the unit on for a bit in order to follow the signal and then I switch it off before the transistor goes off.
-Q4 it's as above
- Q5 and Q6 are cool
-I cannot set the bias any lower than 16V

Any ideas on where to look at?
I don't want to keep switching the beast on and off too many times and cook something up for good...I have no spare parts for this unit at all...


Best,
Mattia.

 

[mata_haze]

solved. I had the shield connected to one pole of the COMP/LIM switch..that was shorting everything to ground.

Working now, and VERY QUIET!

Best,
Mattia.

 

[Tsane]

Mike, I measured the switch, but it all seems fine, works as it should.
Next, I installed another fuseholder, but it kept blowing fuses. Everything measured fine, nothing shorted or shorted to ground.
I didn't have any fused IEC connectors at hand, so I ordered a bunch with some other stuff I needed. I replaced my IEC and fuseholder with an integrated one, but it keeps blowing the fuse. Again I measured everything before powering up, and everything again measured just fine.

Is there anything at all I can still try to make sure it's not the toroid?