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

[dtrax]

SUCCESS!!! Sounds f*cking bad ass Mike!

I made one booboo so far that I've found. Peak Reduction is wired backwards on one of the channels, so the knob works in reverse. Easy fix.

Right channel does have a bit more noise than the left, since it's closer to the prw xfrmer. Gain cranked up to 10 and w/ Mod and 50dB switches engaged I measured -75dBFS. But at that rate it's clipping the hell outta my AD/DA, so I can live with that bit of noise. Left side is dead quite (well, quiet enough that I didn't feel the need to measure it) w/ Mod engaged.

Ok, back to playing with my new toy. Thanks again guys for all the help. And Mike, kudos to you my friend for such an awesome project. I had some minor growing pains along the way, but it was well worth it. Cheers.

Davo/Mike:

Thanks so much for the help. I'm alllllmost there, just one more question regarding the power switch. Would I wire Line to the top position, blue/violet to middle, and then the ground/shield to the bottom position? Then I wire shield to Earth on power inlet as well?

Bare with me guys, I've built my share of kits but it was always more of a "solder by numbers" affair (ex: Seventh Circle Preamps).

No worries man. It's even simpler than that. Just wire the IEC jack positive to one side of the switch, and the blue and violet power transformer lines to the center. That way when the switch is in one position they will be connected, and in the other position the power transformer will be connected to nothing.

If you did what you suggested and wired the third point to ground, then when you switched it off the power transformer would go to ground. That wouldn't cause a problem, but it's certainly not necessary. If however you put the blue/violet on the top and the IEC hot in the middle, then when you switched off hot would be connected directly to ground! You'd blow a fuse every time you shut it off. Assuming you had a proper fuse in line. If not you'd blow something further up the chain (prob the circuit breaker).

Yes you want to wire the IEC ground connector to the chassis. Then make sure that all the sides of you chassis are connected to ground with a continuity tester. I had to scrape some paint off of all the screw holes holding the chassis together for the sides to make contact.



I finished the build today. Wiring was a breeze. Thanks so much for putting this together! After some fussing with the switches the only problem I'm having is that channel two is WAY hotter than channel one. The reduction is metering the same (or at least very similar) level so I've got to assume that the problem is in the output amplifier section near Test Point 1. I'll start pouring through it on Wednesday when i get a minute. It sounds great so far!

 

[Davo]

Nice! 

As far as noise goes, and Mike might've covered this already, but I was able to get my unit dead quiet doing a few things:

I put in a steel shield over the xformer, rotated it for minimal noise...
but the most important part was in adjusting the stereo link....  when I got the trimmers fully clockwise, the noise just disappeared.

The shield is probably a bit overkill, but this puppy is sensitive

cheers,
dave

 

[ruckus328]

Nice! 

As far as noise goes, and Mike might've covered this already, but I was able to get my unit dead quiet doing a few things:

I put in a steel shield over the xformer, rotated it for minimal noise...
but the most important part was in adjusting the stereo link....  when I got the trimmers fully clockwise, the noise just disappeared.

The shield is probably a bit overkill, but this puppy is sensitive

cheers,
dave

Yes Dave, shield over the toroid certainly doesn't hurt anything, it can only help.  Depending on proximity to the boards it may or may not be necessary.  On my one build it was, on the other it wasn't.

Dtrax, you should be able to get it dead quiet though like Davo indicated.  Quickest bang for your buck is to rotate the toroid until you find the sweet spot where it is quietest.  Gap in the windings will result in higher noise depending on rotation.  I got the noise floor on my right channel to drop approx 8dB just by doing this.  Also go through the stereo link process as Dave inidicated as well.

In any case, glad to here another successful build!  Seems like everyone is loving the sound, myself included.

If anyone has access to one, I would loooooove to hear how it compares to a reissue and/or original.

 

[jandoste]

In any case, glad to here another successful build!  Seems like everyone is loving the sound, myself included.

+ 100
Love it ! Great project Mike ! Thanks....

If anyone has access to one, I would loooooove to hear how it compares to a reissue and/or original.

I already heard SA and LA and love the SA Sound !
next time I'll try to upload some Audio files !
Cheers,

 

[Marcocet]

Got it working today. Problem was a bad solder joint at C5, and was easy enough to track down. I must say they sound FANTASTIC. I took a bunch of pictures but of course left my camera at the studio. I should have them for tomorrow.

 

[dandeurloo]

wow you guys are tearing through these!  I can't wait to get my hands on one.  Please do post some pics!

 

[ruckus328]

Yea post pics! 

I'm really glad everyone's so happy with them.

 

[Marcocet]

Here are a few:

Here's my sloppy wiring job. I was too impatient to wait for shielded cable but the thing's still way quieter than any LA-3A I've ever used.

And here it is in it's new home in my effects rack which is the only place there was any space

 

[leitrim_lad]

Hey everyone this is probably the stupidest thing you are gonna see and hear with this project id say but i would really appreciate your help. I am new to the whole DIY world and when i got the kit i jumped right in and started soldering without reading the CRITICAL notice on page 1 of this thread. I ended up soldering Q5,6,10 and 11 to the board without leaving any space. All im wondering is how would i know if they are now shorting and would ye have any advice about how to go desoldering them if so?

Thanks a million

 

[ruckus328]

Was actually just writing you an email:

A multimeter will tell you if they're shorting, if any 2 pins have continuity it's shorting, however having them raised up off of the board gains additional thermal cooling of the part (especially in the case of Q5/Q6 ) as it exposes the can to air on all sides - allows it to breathe more.  I'd really recommend desoldering the parts and raising them.  If you've already trimmed the leads you might need to just order new ones, farnell/mouser should have them in stock. 

If you just use a desoldering tool from the bottom or solder wick you should be able to get them off.  Might have to work it out little by little, 1 pin at a time (ie - remove as much solder from each pin as you can, then heat one pin and simultaneously tilt the part so that pin lifts out a little bit, then do the next pin, then the third.  Just keep working your way around the 3 pins until all the pins are free.  After you get the first pin out it should be easy to get the other 2.

 

[leitrim_lad]

Thanks a million.. would this be the right part for 2N4037:  http://ie.farnell.com/jsp/search/productdetail.jsp?sku=1862536 it doesnt say its bipolar?

Cheers

 

[ruckus328]

Yup, he's fine.

 

[leitrim_lad]

Sorry about the newbie questions again but i have all the boards stuffed etc now and im about to start wiring and im just wondering what would be the best cable to use etc.. Shielded for mic in's and outs, unshielded for others etc or is it best to use shielded all round? Also would 18 gauge be perfect for everything except the ground the cable going to the switch and light?

Thanks a million

 

[dtrax]

I use belden 8451 22awg 2 con shielded for hook up. It's about $30 for 100ft.

18 gauge is a bit overkill. Although I used 16awg for the AC run... Thick stuff!

 

[ruckus328]

22 gauge shielded (what I always use) is fine everywhere except the power runs, they should be at least 18 gauge (mains & transformer wiring), anything less than that is unsafe IMHO.  For the power branch connector bringing power from the first board to the 2nd board you could probably get away with 22 gauge, but 18 would be better there as well, especially for the ground connection between the 2 boards.  For the ground connections, bigger the better.  As far as using 18 gauge shielded everywhere, I think you're going to have issues trying to fit the crimp connectors onto 18 gauge wire, that's pretty beefy for the signals, and it'll be difficult to work with in general.

As far as the signal wires, whether or not you want to use shielded everywhere is up to you.  The ones that need to be shielded (for noise purposes) are all indicated on the schematic as well as how to wire them, important to refer to the schematic so you get the toggle switch orientations all right.  The ones that don't need to be shielded - it surely won't hurt anything using shielded wire but not necessary either as they're just switching 24V On/Off, so up to you on those.


If you can spring for it, I'd get a roll of 22 gauge shielded wire and a roll of 18 gauge single strand.  That will cover you for pretty much any project on the forum.

 

[AlbertoM]

;D Hi all! mine is finished and working. GREEEAT SOUND!!!. Thanks Mike Pildis for the project and the "full monty", and thanks Mike hairball audio for your great service. I've made some photos, I´'ll post them briefly.

And now the questions, after solving some minor problems (wrong connections) it works and sounds great, but while adjusting the vu-meters I  have noticed the following:
Feeding a 600 hz tone and adjusting the gain to read 0 db, I have routed the output so I read -10 db in pro tools. Then I have adjusted the peak reduction knob so I read -15 db in pro tools. Setted this way, the vu-meters display -5 db in the SA-3A reading output and -9 db aprox. reading gain reduction.

I figure that the compressor is truly reducing 5 db, so there must be something wrong with the gain reduction readings. Any idea?, does this happen to any body else's?.

 

[ruckus328]

;D Hi all! mine is finished and working. GREEEAT SOUND!!!. Thanks Mike Pildis for the project and the "full monty", and thanks Mike hairball audio for your great service. I've made some photos, I´'ll post them briefly.

And now the questions, after solving some minor problems (wrong connections) it works and sounds great, but while adjusting the vu-meters I  have noticed the following:
Feeding a 600 hz tone and adjusting the gain to read 0 db, I have routed the output so I read -10 db in pro tools. Then I have adjusted the peak reduction knob so I read -15 db in pro tools. Setted this way, the vu-meters display -5 db in the SA-3A reading output and -9 db aprox. reading gain reduction.

I figure that the compressor is truly reducing 5 db, so there must be something wrong with the gain reduction readings. Any idea?, does this happen to any body else's?.

Alberto, I duplicated your test with my unit using a 600hz test tone and G/R, Output, and Protools all track within .3db so it's likely a calibration issue with your unit. 

Does it do this on both channels or only 1?

Is your bias ajusted?  I set mine right in the middle at 12.5VDC.

What meters are you using?

Have you adjusted your G/R pot so it shows 0db gain reduction with no signal present?

Make sure your HF boost switch is oriented correctly and is set to flat (wiper of pot shorted to ground).

Have you performed the stereo link calibration?  It's back a page or 2 on this thread.

 

[AlbertoM]

Hi Mike!, the problem is in both channels.
I have followed this procedure:
-Bias adjusted to 12.5 both channels
-Vu-meter rest position calibrated
-G/R pot adjusted to 0db with no signal present
-Stereo link calibration done as stated in this thread

Meters are Hairball's dual led (like yours).

The only thing is that the output/g/r switch is wrongly connected, it reads Output on G/R position and G/R on output position.

About the HF boost switch, have to check it.

Can this cause the problem?

 

[ruckus328]

Hi Mike!, the problem is in both channels.
I have followed this procedure:
-Bias adjusted to 12.5 both channels
-Vu-meter rest position calibrated
-G/R pot adjusted to 0db with no signal present
-Stereo link calibration done as stated in this thread

Meters are Hairball's dual led (like yours).

The only thing is that the output/g/r switch is wrongly connected, it reads Output on G/R position and G/R on output position.

About the HF boost switch, have to check it.

Can this cause the problem?

Alberto, for the moment, I'm stumped, but will think about it tomorrow with a clear head.

As far as the G/R output toggle being backwards, easy fix, just flip the toggle around.  However did you realize this before or after your original post?  If you realized it after (ie: G/R is reporting correct amount but output level is incorrect this would make ALOT more sense)  I can't figure out how the G/R would be reporting incorrect amount, especially identically on both channels - that's what really stumps me.  The G/R metering portion is very few parts (T4B Pins 5&6, R13, R22, R36, and VR2).  Take a look on the schematic and verify correct values and solder joints on your board.

Are you in Mod & 50dB mode?

Is your seteo link enabled when doing these tests?  If so try disabling it and test each channel individually.

Another thing, verify with a multimeter that your output level is actually reading 1.23V RMS between xlr pins 2&3 when your VU meter is at 0.  I remember Mike at Hairball mentioning something about not messing with the rest adjustment, but can't remember exactly what he said.

HF Contour - don't think it could cause the problem you're seeing but who knows.

 

[AlbertoM]

Hi Mike!

Today I have been doing some more testing with my partner who has a degree on electronics. He has been building the unit.
We've done the following:

-Verify values for  R13, R22, R36, and VR2, everything ok.

-G/R toggle cables soldered as they must be to read G/R in G/R position.

-Mod & 50db Mode set. Stereo link disabled. HF boost correctly oriented and disabled.

-Bias adjusted to 12.5 on both channels.

-G/R pot adjusted to 0db with no signal present. (The meters rest position has not been touched, it was a misunderstanding with my partner)

-Verify output level (between xlr pins 2&3) when VU meter is at 0, it reads 1.25v.

-Making a hardware insert in Pro tools (in/out, to/from the SA-3A to AD-DA converter) like this:
insert a, signal generator.
insert b, AD-DA converter.
insert c, waves PAZ Meters.

On channel 1 (left) of the SA-3A
With a 1 khz tone at -10 db, SA bypassed PAZ reads -10 db. With SA on, gain set to (output)VU=0db, no gain reduction, PAZ reads -17.5 db.
Peak reduction knob adjusted so (output)VU=-5, PAZ reads -22.5db. G/R VU reads -9 aprox.
Peak reduction knob adjusted so (G/R)VU=-5, PAZ reads -19.5db. Output VU reads -2 .

On channel 2
With a 1 khz tone at -10 db, SA bypassed PAZ reads -10 db. With SA on, gain set to (output)VU=0db, no gain reduction, PAZ reads -17.8 db.
Peak reduction knob adjusted so (output)VU=-5, PAZ reads -22.7db. G/R VU reads -8 aprox.
Peak reduction knob adjusted so (G/R)VU=-5, PAZ reads -19.8db. Output VU reads -2 .

We have taken a T4B and open it so light hits the cell, and measured between pins 5&6 and 7&8, the values are nearly double.

We believe that there must be something wrong with the values pins 5&6 output.

The strangest thing is that my unit is the only one known to have this problems?...