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

[ruckus328]

Tsane, I'm gonna say it's a bad toroid.  First time anyone's had this issue, but I don't see any other cause at this point.  Check your PM.

 

[Tsane]

It's alive!!!

Wiring is a total disaster, but I learned to live with it. This is my first completed project, with a lot of headaches, but with very, very good support from Mike and this forum! Thanks!

Both channels are dead quiet, not the slightest hum, not even on channel 2 with the toroid placed as in the picture (so I'm not going to bother with the messy wiring). Voltages measuring almost spot on (+- 0,2V max). Just need to calibrate, mount the toroid and it can finally get from my bench into the rack.

Thanks again Mike for this great project and support.

 

[lowtone]

another finished and fully functional unit, thank you ruckus, it's a true pleasure to build this for a noob like me.

 

[sr1200]

Hey, i got my t4bs from drip, and they look nothing like pics ive seen on here... They kinda look like a mini pipe bomb (copper cap with tube pins and a black rubber grommet).

Did i not get the right thing? Theres no tell tale markings on them that even say theyre T4Bs. Hope to have the unit done before the new year.

 

[sr1200]

Sorry got one last question here, is it ok to use plastic standoffs for the boards or do they need to be in contact with the chassis?

 

[ruckus328]

I've been meaning to message Drip but from what I've seen it looks like he changed his T4B enclosures to a custom metal enclosure is all (presumably so they'll fit in a 500 module).  Reality is the off the shelf relay housing you typically see are way bigger than what is actually needed space wise, but those are the only option without rolling your own.

You could probably get away with plastic standoffs if u use metal screws and nuts, but Metal standoffs would probably be better, there's no ground connection to the circuit via the mounting locations but theres alot of weight on the boards and the xfmr bodies should be tied to chassis ground.  Whatever you do make sure you put standoffs under the xfmr locations.

 

[sr1200]

K finished her up tonight, I calibrated the one trim pot that said to have 12-13v at TP1 (i didnt see a build manual or anything on here, did i miss it?)  I cal'd the meter to 0 in GR mode with the GR adjust and followed the stereo cal adjustments.  I have one "odd" thing happening, one of the transformers (the round can like one)  it sounds like it add a bit of gain if i push a little bit when i let go it goes back to normal.  (i was noticing a odd hum on that channel and accidentally bumped the tx and noticed the hum went away when i knocked it) i resoldered the pins and no difference.  The unit works fine as long as it doesnt get hit at all.  (hopefully things wont get rough in the studio!)

 

[ruckus328]

K finished her up tonight, I calibrated the one trim pot that said to have 12-13v at TP1 (i didnt see a build manual or anything on here, did i miss it?)  I cal'd the meter to 0 in GR mode with the GR adjust and followed the stereo cal adjustments.  I have one "odd" thing happening, one of the transformers (the round can like one)  it sounds like it add a bit of gain if i push a little bit when i let go it goes back to normal.  (i was noticing a odd hum on that channel and accidentally bumped the tx and noticed the hum went away when i knocked it) i resoldered the pins and no difference.  The unit works fine as long as it doesnt get hit at all.  (hopefully things wont get rough in the studio!)

Did you miss this at the begining of the thread?:

"CRITICAL***: The input transformer (T3) and metal can transistors (Q5, Q6, Q10, Q11) MUST be spaced off of the board some.  Because it is a double sided board, if you don't space them off of the board when you solder the pins, solder is going to flow through the plated holes to the underside of the parts and short to the metal cans.  get my drift?"

 

[sr1200]

I miss a lot of things... i havent slept in days lol.  The TX's are spaced off a bit, maybe not enough though.  As I said it IS working as long as noone touches the TX (which is IN the case and rack mounted at this point) lol.  This was a challenging build (more so than the SB4000 I thought)  I probably only feel that way cause i hand crimped all 70 wires with a pair of needle nose pliers... doh.  Note to self, get crimper.

 

[Marcocet]

Okay: quick problem that's eluding me.

I just rewired the whole unit and I got the noise floor WAY down, which is nice. However one of my units won't meter gain reduction. It's reducing gain, just not metering. The output meter's fine. I tried chasing around the meter relay and touching up solder joints but that doesn't seem to be helping. The real confusing part is that the meter was working fine before the rewire....

EDIT: Further testing has allowed me to discover that the resistance from TP2 to ground is static on the working channel, while on the non-functioning side it fluctuates with the Peak Reduction knob. For the life of me I can't figure out why.

EDIT II: Got it! It was the peak reduction pot. Somehow it had shorted inside. Casing looks fine, and it doesn't look like I overheated it or anything, but I suppose I must have. Weird one. CW side of the pot was working fine, CCW was working at about a 250R, and the two outer pins were reacting to each other (I was reading a sweep of about 100R between the two of them). Anyway, it's kicking arse now.

 

[miketeachesclass]

I think I'm going to order a kit in the next week or so.  Can anyone comment on what the most appropriate Drip T4B is?  (Fast/Medium/Slow)?

Thanks,
Mike

 

[speakerface]

I think I'm going to order a kit in the next week or so.  Can anyone comment on what the most appropriate Drip T4B is?  (Fast/Medium/Slow)?

Thanks,
Mike

Just ordered all the parts for one myself...I wasn't able to find a real clear "use the slow/medium for LA-3A" reference, but if you check out the bottom of the Drip Opto-5 site it states "fast/medium-urei 1975/slow 1968 release".  My guess is earlier versions used equivalent to the slow and later versions possibly the medium. 

If you check out the Opto 4 build manual (about 15 pages in), it talks a bit about the T4Bs and discusses Drip's fast version...if you are going for an original LA-3A sound I think you can rule out the fast. 

I think you'd probably be happy with either the slow or the medium, but I'm sure drip would offer a suggestion if you emailed them; they seem like really responsive folks.  I went with the slow version myself (arrived VERY quickly and look pretty sweet).

Hope that helps.   

 

[sr1200]

I used the fast for mine.  Was recommended by drip for a more modern sound, which is more of what i'm after.  I don't believe its a tonal characteristic, just how fast the cell reacts and for me, with voiceover and heavy metal... fast was the way to go.  I was originally thinking of getting 1 fast and 1 slow just to have some variation (ill never use the unit as a stereo pair... thats what my SB4000's are for)

 

[miketeachesclass]

Thanks, guys.  I think I'll go with medium to start.

 

[miketeachesclass]

Also, can anyone recommend an equivalent meter to the Hairball HB-8037?  Hairball won't have them in stock until June, and I really don't want to wait that long to build these things.  I read that maybe the sifam AL-39 will work.  It's ridiculously expensive, in my opinion, but is that the only option?

Thanks,
Mike

-EDIT-
It's the AL29-WF.  Nevermind!

 

[monobass]

Hi,

Has anyone done a sidechain HPF mod on the SA-3A?

Thanks

 

[tom f]

Hello,
I have a friend who is building me the SA- 3A.
But there is one question:
What are the two "black boxes" on the PCB in the picture below?
Where can we order these (live in Germany) ?

Thank a lot for your help
Tom

 

[earl]

T-4's.  Drip Electronics

 

[sr1200]

The new Drips dont look like that anymore though, they look like little brass caps (like youd see on a pipe or something)  Same innards though.

 

[tom f]

Thanks for reply.
I ordered it.
Tom